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in Till and No-till Systems: Effects on Water Quality and Yield. (Under the direction of Deanna Osmond).

Non-point source pollution from agricultural systems is an ever growing concern and the reduction of nitrogen, phosphorus, and sediment losses from agriculture land is not only crucial to our water quality but to the management and value of our agricultural products. Agriculture no longer has the sole responsibility of food, fiber and forage production, but it must strive for sustainability as well. Organic agricultural management has been suggested to alleviate the environmental concerns compared to conventional agricultural production. The objective of this study was to compare nutrient and sediment losses, as well as sweet corn yield, from organic and conventional agricultural production under conventional and conservation tillage management. This research was conducted in Mills River, NC on field plots that have long-term (18 years) management under organic and conventional standards. There are four replications of five treatments: conventional tillage with conventional

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by

Joshua Lee Edgell

A thesis submitted to the Graduate Faculty of North Carolina State University

in partial fulfillment of the requirements for the degree of

Master of Science

Soil Science

Raleigh, North Carolina 2013

APPROVED BY:

_______________________________ ______________________________

Deanna Osmond Greg Hoyt

Committee Chair

________________________________ ________________________________

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BIOGRAPHY

Born and raised in the foothills of North Carolina, the author found great appreciation of the outdoors early in life. Through work and recreation, Josh knew he wanted to be involved with and learn more about the natural world. Upon graduating high school in 2004, Josh attended a local community college where he studied various subjects in order to decide which direction in life was best suited for him. He graduated with an Associate’s Degree in General Education in 2007 and subsequently decided to continue his education through the advice of family and friends. In 2010 Josh graduated from North Carolina State University with a Bachelor’s Degree in Soil Science. During his undergraduate tenure, Josh was a member of the Agronomy Club, Alpha Zeta Honors Agriculture Fraternity, and the Soil Judging Team. Among other jobs, Josh worked for the United States Geological Survey in the last year of his undergraduate career, where he traveled unsupervised through the Pacific Northwest collecting hundreds of soil samples and driving 17,000 miles in as little as four months. The exposure to the environmental and agricultural sciences throughout his

undergraduate career left Josh to decide to further his education and gain research experience by pursuing a Master’s in Science. In the fall of 2011 he began his M.S. degree in the

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ACKNOWLEDGMENTS

I would like to thank everyone responsible for the completion of this maintenance and time intensive project, specifically:

The Good Lord: For the perseverance; there was always a light at the end of the tunnel.

The Committee Members: For the guidance, expertise, and advice. Dr. Deanna Osmond

Dr. Greg Hoyt Dr. Julie Grossman

Dr. David Crouse

Field, Lab and Technical Support Staff: For the many, many hours you labored. Daniel Line

Wesley Childres Collin Suttles Sara Seehaver

Joy Smith

The entire staff of the Mountain Horticultural Crops Research Station for assisting in any research related work that was asked of you.

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TABLE OF CONTENTS

LIST OF TABLES ... viii

LIST OF FIGURES ... ix

CHAPTER 1: REVIEW OF LITERATURE ... 1

1.1INTRODUCTION... 1

1.2TILLAGE ... 1

1.2-1 Weed Control and Yield ... 2

1.2-2 Soil Physical Properties ... 4

1.2-3 Tillage Influenced Losses ... 8

1.2-3.1 Erosion, Runoff, and Leaching ... 8

1.2-3.2 Nutrient Losses ... 12

1.2-4 Tillage Conclusion ... 20

1.3MANURE APPLICATION ... 20

1.3-1 Weed Control and Yield ... 21

1.3-2 Soil Physical Properties ... 24

1.3-3 Nutrient and Soil Losses ... 29

1.3-4 Manure Application Conclusion ... 32

1.4ORGANIC AND CONVENTIONAL AGRICULTURE SYSTEMS ... 33

1.4-1 Yield and Weed Control ... 34

1.4-2 Soil Physical Properties ... 37

1.4-3 Nutrient and Soil Losses ... 38

1.4-4 Organic and Conventional Agriculture Systems Conclusion ... 43

1.5CONCLUSION ... 43

1.6REFERENCES ... 47

CHAPTER 2: COMPARISON OF ORGANIC AND CONVENTIONAL AGRICULTURE PRODUCTION IN TILL AND NO-TILL SYSTEMS: EFFECTS ON WATER QUALITY AND YIELD ... 56

2.1INTRODUCTION... 56

2.2MATERIALS AND METHODS ... 59

2.2-1 Experimental Design ... 59

Figure 2a: Plot layout ... 60

Table 2a: Soil properties at the initiation of each growing season ... 61

2.2-2 Climate... 61

2.2-3 Field Activities ... 62

2.2-3.1 Planting ... 62

Table 2b: Planting, harvest, and fertilization dates by treatment ... 63

2.2-3.2 Fertilization ... 64

Table 2c: Fertilization rates by treatment ... 65

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2.2-4.1 Surface Runoff Collection ... 66

Figure 2b: Plot Design ... 67

2.2-4.2 Acidified Runoff Samples ... 68

2.2-4.3 Non-acidified Runoff Samples ... 68

2.2-5 Water Quality: Deep Soil Samples ... 69

2.2-5.1 Deep Soil Sample Collection ... 69

2.2-5.2 Deep Soil Sample Analysis ... 70

2.2-6 Sweet Corn Yield ... 70

2.2-7 Agricultural Cropping Efficiency Coefficient ... 70

2.2-8 Irrigated Runoff Events ... 71

2.2-9 Weed Competition Assessment ... 71

2.2-10 Statistical Analysis ... 71

2.3RESULTS AND DISCUSSION ... 73

2.3-1 Water Quality: Surface Runoff ... 73

2.3-1.1 Total Suspended Solids ... 73

2.3-1.2 Total Phosphorus ... 74

2.3-1.3 Dissolved Phosphorus... 74

2.3-1.4 Total Kjeldahl Nitrogen ... 75

2.3-1.5 Ammonium-Nitrogen ... 76

2.3-1.6 Nitrate-Nitrogen... 76

2.3-1.7 Total Dissolved Nitrogen ... 77

2.3-1.8 Total Organic Carbon ... 78

Figures 2c-r: 2011 and 2012 surface runoff nutrient load results ... 79

2.3-2 Water Quality: Deep Soil Samples ... 88

2.3-2.1 Ammonium-Nitrogen Leaching ... 88

Figure 2s-t: 2011 and 2012 deep soil sample results of total ammonium-nitrogen below the root zone ... 90

2.3-2.2 Nitrate-Nitrogen Leaching ... 91

Figure 2u-v: 2011 and 2012 deep soil sample results of total nitrate-nitrogen below the root zone ... 93

2.3-3 Sweet Corn Yield and Weed Competition ... 94

Figure 2w-x: 2011 and 2012 mean sweet corn total and marketable yield ... 96

2.3-4 Agricultural Cropping Efficiency ... 97

Table 2d: ACE coefficients, normalized values, and p values ... 98

2.4CONCLUSION ... 99

2.5REFERENCES ... 101

CHAPTER 3: SURFACE RUNOFF AND NUTRIENT CONCENTRATIONS FROM ORGANIC AND CONVENTIONAL CROPPING SYSTEMS UNDER CONVENTIONAL AND CONSERVATION NO-TILL MANAGEMENT ... 106

3.1INTRODUCTION... 106

3.2MATERIALS AND METHODS ... 108

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3.2-2 Surface Runoff and Rainfall ... 108

Figure 3a: Plot Layout ... 109

3.2-3 Rainfall Erosion Index Values ... 110

3.2-4 Soil Infiltration Analysis ... 110

3.2-5 Statistical Analysis ... 111

3.3RESULTS AND DISCUSSION ... 111

3.3-1 Surface Runoff ... 111

Figure 3b-c: 2011 and 2012 total surface runoff and rainfall ... 114

3.3-2 Rainfall Erosion Index Values (EI) ... 115

3.3-3 Surface Runoff Concentrations ... 116

3.3-3.1 Total Suspended Solids ... 116

3.3-3.2 Total Phosphorus ... 116

3.3-3.3 Dissolved Phosphorus... 117

3.3-3.4 Total Kjeldahl Nitrogen ... 118

3.3-3.5 Ammonium-Nitrogen ... 119

3.3-3.6 Nitrate-Nitrogen... 119

3.3-3.7 Total Dissolved Nitrogen ... 120

3.3-3.8 Total Organic Carbon ... 121

Figures 3d-s: 2011 and 2012 nutrient and sediment concentration results ... 122

3.4CONCLUSION ... 131

3.5REFERENCES ... 133

APPENDICES ... 137

APPENDIX A:MATERIALS,METHODS, AND RESULTS ... 138

Figures ... 138

Figure A1: North Carolina State University and Mountain Horticulture Research Station locations ... 138

Figure A2: 2011 soil total ammonium-nitrogen by depth ... 139

Figure A3: 2012 soil total ammonium nitrogen by depth ... 139

Figure A4: 2011 soil total nitrate-nitrogen by treatment ... 140

Figure A5: 2012 soil total nitrate-nitrogen by treatment ... 140

Figure A6: 2011 soil total nitrate-nitrogen by season ... 141

Figure A7: 2012 soil total nitrate-nitrogen by season ... 141

Figure A8: 2011 rainfall and runoff by month... 142

Figure A9: 2012 rainfall and runoff by month... 142

Tables ... 143

Table A1: Methods for constituent analysis ... 143

Table A2: Statistical transformations and procedures used (CH2) ... 144

Table A3: 2011 surface runoff mean nutrient load summary ... 145

Table A4: 2012 surface runoff mean nutrient load summary ... 146

Table A5: 2011 and 2012 covariate analysis ... 147

Table A6: 2011 and 2012 mean marketable and total yield ... 147

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Table A8: Statistical transformations and procedures used (CH3) ... 148

Table A9: Soil infiltration rate results ... 149

Table A10: 2011 surface runoff mean nutrient concentration summary ... 150

Table A11: 2012 surface runoff mean nutrient concentration summary ... 151

APPENDIX B:RAW DATA ... 152

Tables ... 152

Table B1: 2011 summary of constituent loads and sweet corn yield ... 153

Table B2: 2012 summary of constituent loads and sweet corn yield ... 154

Table B3: 2011 covariate analysis data ... 155

Table B4: 2012 covariate analysis data ... 156

Table B5: Surface runoff by collection event ... 157

Table B6: Total suspended solid concentrations by collection event ... 160

Table B7: Total phosphorus concentrations by collection event ... 163

Table B8: Dissolved phosphorus concentrations by collection event ... 166

Table B9: Total kjeldahl nitrogen concentrations by collection event ... 169

Table B10: Ammonium-nitrogen concentrations by collection event ... 172

Table B11: Nitrate-nitrogen concentrations by collection event ... 175

Table B12: Total dissolved nitrogen concentrations by collection event ... 178

Table B13: Total organic carbon concentrations by collection event ... 181

Table B14: Deep soil sample nitrogen concentrations ... 184

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LIST OF TABLES

Table 2a: Soil properties at the initiation of each growing season ... 61

Table 2b: Planting, harvest, and fertilization dates by treatment ... 63

Table 2c: Fertilization rates by treatment ... 65

Table 2d: ACE coefficients, normalized values, and p values ... 98

Table A1: Methods for constituent analysis ... 143

Table A2: Statistical transformations and procedures used (CH2) ... 144

Table A3: 2011 surface runoff mean nutrient load summary ... 145

Table A4: 2012 surface runoff mean nutrient load summary ... 146

Table A5: 2011 and 2012 covariate analysis ... 147

Table A6: 2011 and 2012 mean marketable and total yield ... 147

Table A7: 2012 weed biomass and nitrogen results ... 148

Table A8: Statistical transformations and procedures used (CH3) ... 148

Table A9: Soil infiltration rate results ... 149

Table A10: 2011 surface runoff mean nutrient concentration summary ... 150

Table A11: 2012 surface runoff mean nutrient concentration summary ... 151

Table B1: 2011 summary of constituent loads and sweet corn yield ... 153

Table B2: 2012 summary of constituent loads and sweet corn yield ... 154

Table B3: 2011 covariate analysis data ... 155

Table B4: 2012 covariate analysis data ... 156

Table B5: Surface runoff by collection event ... 157

Table B6: Total suspended solid concentrations by collection event ... 160

Table B7: Total phosphorus concentrations by collection event ... 163

Table B8: Dissolved phosphorus concentrations by collection event ... 166

Table B9: Total kjeldahl nitrogen concentrations by collection event ... 169

Table B10: Ammonium-nitrogen concentrations by collection event ... 172

Table B11: Nitrate-nitrogen concentrations by collection event ... 175

Table B12: Total dissolved nitrogen concentrations by collection event ... 178

Table B13: Total organic carbon concentrations by collection event ... 181

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LIST OF FIGURES

Figure 2a: Plot layout ... 60

Figure 2b: Plot Design ... 67

Figures 2c-r: 2011 and 2012 surface runoff nutrient load results ... 79

Figure 2s-t: 2011 and 2012 deep soil sample results of total ammonium-nitrogen below the root zone... 90

Figure 2u-v: 2011 and 2012 deep soil sample results of total nitrate-nitrogen below the root zone ... 93

Figure 2w-x: 2011 and 2012 mean sweet corn total and marketable yield ... 96

Figure 3a: Plot Layout ... 109

Figure 3b-c: 2011 and 2012 total surface runoff and rainfall ... 114

Figures 3d-s: 2011 and 2012 nutrient and sediment concentration results ... 122

Figure A1: North Carolina State University and Mountian Horticulture Research Station locations ... 138

Figure A2: 2011 soil total ammonium-nitrogen by depth ... 139

Figure A3: 2012 soil total ammonium nitrogen by depth ... 139

Figure A4: 2011 soil total nitrate-nitrogen by treatment ... 140

Figure A5: 2012 soil total nitrate-nitrogen by treatment ... 140

Figure A6: 2011 soil total nitrate-nitrogen by season ... 141

Figure A7: 2012 soil total nitrate-nitrogen by season ... 141

Figure A8: 2011 rainfall and runoff by month... 142

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CHAPTER 1: REVIEW OF LITERATURE

1.1 INTRODUCTION

In a survey reported by Morton et al. (2013), agricultural producers have become less concerned with environmental impacts of agriculture. More specifically, it was reported that the larger the farm, the less care was given to nutrient impacts on water quality, the overreliance of chemicals and sustainability in general. Regardless of the conclusions of Morton’s survey, agriculture no longer has the sole responsibility of food, fiber and forage production, but it must also meet the increasing demand of sustainability and environmental responsibility.

It has been suggested that organic agriculture, given its goal of ecological harmony, can provide the answer to this dilemma. Certified organic production is highly regulated in the United States by the United States Department of Agriculture (USDA) and the application of synthetic inorganic materials, pesticides and fertilizers to be specific, is prohibited. Due to the inherent management requirements of organic production, tillage and fertilization type dictate differences in crop yields and effects on water quality. This literature review focuses on cropping and tillage systems that affect production, soil and nutrient loss and water quality.

1.2 TILLAGE

Cultivation has undoubtedly had an important role throughout history in agriculture. Its usefulness and practicality has been debated for many years and with the most recent green-revolution, never more so than now. The term cultivation alone provides little insight to the on-going investigation and we must examine the different levels and effects it has.

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surface (Conservation Technology Information Center, 2002). Its counterpart, conservation tillage, leaves 30% or more of crop residue of the soil surface in order to minimize soil surface disturbance to prevent wind or water erosion (Conservation Technology Information Center, 2002). No-till tillage, which can be used with conservation tillage, is the act of only disturbing the soil surface in order to plant the seed in a narrow slit created by the planter (Conservation Technology Information Center, 2002). No-till is the most extreme form of minimal-soil-disturbance and is the focus of many agricultural comparisons; however, depending on the cropping system, no-till may not meet the conservation criteria of 30% or more crop residue.

Both conventional and conservation tillage have their benefits. Conservation tillage benefits include potentially higher crop yield, reduced soil erosion, improved infiltration, and lower labor and fuel costs (Conservation Technology Information Center, 2013; Havlin et al., 2005). Conventional till production benefits include: reduced herbicide use, higher soil temperatures in spring (resulting in earlier germination and growth), and in some cases easier management of insects and diseases (Havlin et al., 2005; Triplett and Dick, 2008).

Examining the effects these tillage systems have on crop yield, soil properties, and nutrient and soil losses is critical to understanding how tillage affects our agriculture products and ecosystems.

1.2-1 Weed Control and Yield

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weight. They found that not only did weed pressures vary year to year but that it also varied crop to crop (Yau et al., 2010). Most authors agree, however, that weed control is associated not only with tillage or herbicides, but also cropping systems and rotations (Buchholtz and Doersch, 1968; Mulugeta and Stoltenberg, 1997; Schweizer, 1998; Swanton and Knezevic, 1999).

Weed control is of the highest priority in production agriculture and conventional tillage has historically been the primary method to control weed competition (Triplett and Dick, 2008). With the advancement of no-till equipment and herbicides, the positive influence of

conservation tillage on soil and crop systems, and increased profitability, many farmers have switched to conservation tillage (Osmond et al., 2012).

A long-term study in Ohio found that corn production yield in no-till systems improves every year the system is in place (Dick et al., 1991). Similarly, Ismail et al.( 1994) found that in the first 12 years of a 20 year experiment in which bluegrass sod was converted to corn

production, conventional tilled systems yielded more than no-till systems at low nitrogen (N) application rates (0 and 84 kg N/ha). However, the opposite trend was observed after the first 12 years. To strengthen the argument that no-till yields can compete with conventional till yields, a 3-year study in Pennsylvania compared corn hybrid yields under different tillage practices (no-till, shallow in-row till, deep in-row till and chisel plowing and disking) and concluded “there was no tillage x hybrid interaction for emergence, midseason height, or yield” (Duiker et al., 2006, p. 441). Yau et al. (2010), suggests the effects of tillage on yield can result in different outcomes based on crop type and other factors. Unlike barley, the authors concluded that chickpea and safflower gave similar yields in both tillage systems, crediting the differences to not only crop type and root structure, but to soil fertility and planting time” (Yau et al., 2010).

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conventional till conditions, found that while yield increased in both tillage treatments with increasing N rates, the conventional tilled systems yielded up to 16% more than no-till systems (Halvorson et al., 2006). With that evidence in place, the authors concluded that conservation tillage could replace conventional tillage in the Great Plains but suggested using a more intense form of conservation tillage such as strip-till (Halvorson et al., 2006).

Yield response to different tillage practices can be location, crop, and management specific. Besides yield, tillage affects many other aspects of the agriculture system. A tillage systems’ effect on soil properties and water quality has to be considered, especially in regard to regulation and legislation that directly affects agriculture.

1.2-2 Soil Physical Properties

The disturbance of soil changes many properties that are inherent to its formation and in agriculture systems this can be a crucial management aspect. Properties, like soil bulk density, structure and carbon content, can affect aspects such as root penetration and nutrient holding capacity. Examining the research that has been conducted relative to tillage and soil physical properties gives us insight to how tillage affects soil-plant relationships.

Soil bulk density and compaction are two of the most important soil properties when

considering tillage’s effects. A soil’s bulk density directly controls soil-water relationships as well as soil-plant interactions (Brady and Weil, 2004; Havlin et al., 2005). Soil compaction is inevitable in agriculture systems, regardless of tillage type, due to in-field traffic that is required. A four-year Wisconsin study conducted by Lowery and Schuler (1991) on two soil series, Rozzetta (Fine-silty, mixed, superactive, mesic Typic Hapludalf) and Kewaunee (Fine, mixed, active, mesic Typic Hapludalf), subjected the soils to three levels of compaction (tractor axle loads; >4.5 Mg, 8Mg and 12.5 Mg) the first year and then

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and Schuler, 1991). Other studies have reported similar results using till, finding that no-till systems have led to characteristics such as lower soil temperature, slower seed emergence and reduced plant development (Halvorson et al., 2006), higher bulk densities and higher soil penetration resistance (Duiker et al., 2006; Halvorson et al., 2002; Sidhu and Duiker, 2006). When comparing the two tillage systems it is difficult to determine which system will regularly experience compaction issues. One might be led to believe that with reduced soil disturbance and continuous traffic, no-till systems would reflect higher levels of compaction. However, a 26-year tillage study that used five different N fertilization rates (0, 34, 67 and 135 kg N ha-1) under continuous grain sorghum found that while N fertilization had no effect on soil bulk density, the soil bulk density in the no-till systems were significantly lower than conventional systems at all measured depths (Presley et al., 2012). Bulk density

measurements were taken in five cm increments up to 15cm in this study. Bulk density results for the 0-5cm depths were 1.28 Mg m-3 and 1.38 Mg m-3 in no-till and conventional till respectively. At the 5-10cm depth bulk density results were 1.44 Mg m-3 and 1.52 Mg m-3 in no-till and conventional till systems respectively. Lastly, the reported bulk density

measurements at the 10-15cm depth were 1.46 Mg m-3 and 1.53 Mg m-3 in no-till and conventional till systems respectively (Presley et al., 2012). Similar results under long-term no-till were also reported by Rhoton et at. (2002.) Regardless of the tillage type, Sidhu and Duiker (2006) suggest that yield reductions due to compaction are similar in both types of systems.

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Differing yield outcomes as a result of compaction and tillage require studies occurring over a period of time because the impacts may not be immediate. Differences in length of time that the tillage system has been utilized may be a reason for contradicting evidence.

Moreover, the timing of field activities and the equipment used can greatly affect the results and should be considered as well. Sidhu and Duiker (2006, p. 1263) concluded that “if farmers can limit their traffic to drier soil conditions, keep axle loads below 10Mg, and keep tire inflation pressures below 250kPa, compaction effects on these soils on no-tillage corn yields would be minimal.”

Tillage can not only reduce weed pressure and disrupt weed emergence but it has also been the traditional method of counteracting soil compaction. More specifically, subsoil tillage has been found to reduce compacted soil layers and could prove beneficial (Copas et al., 2009). However, not only is this technique not beneficial to those seeking to use conservation no-till due to tillage reducing residue cover but deep tillage does not guarantee to reduce the stress of compacted soils (Sidhu and Duiker, 2006).

Conservation tillage can also affect soil organic matter and thus soil carbon levels. Ismail et al. (1994, p. 198) stated that increased organic matter “is probably the most important long-term change that has occurred” when referring to the benefits of conservation tillage systems. Havlin et al. (2005) stated that of all the properties that affect soil productivity, “soil organic matter content is the most critical, because of its influence on many biological, chemical, and physical characteristics inherent in a productive soil.”

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The results of increased soil carbon inputs have been studied thoroughly and are well documented. A six-year study in South Carolina examined the effects of tillage on soil organic carbon in southeastern U.S. Coastal Plain soils (Novak et al., 2009). This study used a corn-cotton rotation in which crop residue was incorporated at least 15cm deep in the conventionally tilled plots with disking and the conservation tilled plots were deep-tilled in a manner that left maximum residue on the surface. Findings included an average increase of 0.62 Mg ha-1 of soil organic carbon in conservation tilled soils in the top 3cm. The

conventionally tilled soils saw a loss of 0.28 Mg ha-1 of soil organic carbon in the top 3cm. At a depth of 3-15cm the conservation tilled treatments saw a decrease of 2.39 Mg ha-1 in soil organic carbon and the conventionally tilled treatments saw an increase of 0.26 Mg ha-1 in soil organic carbon. This was credited to the incorporation of crop residue deeper in the soil profile in the conventionally tilled treatment. This led the authors to conclude that while conservation tillage with high surface crop residue can be used to increase soil organic carbon at shallow depths, organic carbon contents at deeper depths are likely to decrease (Novak et al., 2009). Likewise, Presley et al. (2012) examined the long term N and tillage systems effects on specific soil properties and found that no-till systems had 30% more soil organic carbon in the top 0- 5cm of soil and higher infiltration rates compared to

conventional tilled systems. This led the authors to conclude that if a system is managed to promote biomass production and to reduce soil disturbance, soil organic carbon will increase, specifically within the root zone (Presley et al., 2012).

Even with reduced tillage, some data suggests the cropping system is also critical to carbon sequestration in soils. Halvorson et al. (2002) considered the impacts of tillage, N and

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surface residue cover is highest in conservation no-till system (Duiker et al., 2006), the amount of residue produced is crucial to increasing soil organic carbon.

1.2-3 Tillage Influenced Losses

1.2-3.1 Erosion, Runoff, and Leaching

Soil surface disruption, surface residue, soil compaction and organic carbon content directly affect the amount of soil and nutrients lost in agriculture systems. Nutrient and sediment removal from agriculture systems not only increases the cost of agriculture production through the loss of applied nutrients, but it hinders the functioning of ecosystems and affects human health. Erosion on US croplands was estimated to be 1.73 billion tons in 2007. While this is a decline of 43% over the past 25 years, soil erosion is a major factor in agriculture sustainability (USDA, Natural Resource Conservation Service., 2010). Currently in many agricultural watersheds, the majority of the sediment is from stream erosion or stream banks (Osmond et al., 2012). However for continued abatement of upland erosion, decreased tillage and residue additions can limit erosion by stabilizing soil aggregates, improving infiltration and thus reducing surface water runoff and wind erosion.

A field scale study conducted in Oregon, examined the effects of conventional till (inversion tillage) and no-till on runoff and soil erosion in two neighboring water drainages. This four year study used a winter wheat-fallow rotation in the conventional tilled drainage (5.8 ha) and a winter wheat-chemical fallow-winter wheat-chickpea four-year rotation in the no-till drainage (10.7 ha). Water samples were collect by placing runoff collectors at critical backslope positions and automated storm water samplers at the mouth of the drainages. The authors found that the conventional tilled and no-till drainages lost 0.42 Mg ha-1 and 0.01 Mg ha-1 of sediment respectively. The authors concluded that compared to the conventional till, no-till systems resulted in nearly zero runoff and soil loss (Williams et al., 2009).

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semiactive, mesic Typic Kanhapludult). Nine treatments were used that included no-till; in-row subsoiling; fall chisel plow; spring chisel plow; disk; fall chisel plow plus disk; spring chisel plow plus disk; fall moldboard plow plus disk and spring moldboard plow plus disk. The study was in randomized complete block design with a 6m alley between each block. There were 4 blocks containing each treatment with each plot measuring 15.5m x 5.5m. The site was pasture in 1982 and then converted to continuous corn in 1984. In 1989, the current corn-soybean rotation was put in place with fertility practices based upon North Carolina Department of Agriculture and Consumer Services recommendations. Bulk density samples were taken before spring tillage in 2010 to estimate soil loss. In June 2010, ground-based lidar data was collected from four locations in the experiment to estimate plot elevation. At this time emerging soybeans measured 2.5-5cm tall. Since original elevations were not known, the NT treatment elevation was used as a reference because this treatment is known to result in lower soil losses than the other treatments. Moreover, the authors also had to assume no soil was deposited in NT treatments. This assumption was deemed plausible due to the site characteristics and layout. Positive elevation change was noticed in plots in four of the nine treatments (in-row subsoiling, fall chisel plow, spring chisel plow, and disk). This was credited to weed growth or residue stubble in these treatments, due to less intense tillage practices, that resulted in lidar readings to be higher than the actual soil surface. The spring chisel plow plus disk and fall chisel plow plus disk treatments resulted in the second highest soil loss with an estimated total soil loss up of to 1500 Mg ha-1. The ); fall moldboard plow plus disk and spring moldboard plow plus disk treatments resulted in the lowest relative elevation and greatest estimated soil loss which ranged up to 1891 Mg ha-1. The authors state that soil loss estimations could be improved by having more consistent crop residue and weed cover. Moreover, they state that lidar scanning before the treatments were put in place would have added to the accuracy but this was not an option. The soil loss estimates found in this study closely resemble those reported in other studies, which lead the authors to

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the notion that conservation tillage greatly reduces erosion in agriculture systems (Meijer et al., 2013).

Shipitalo et al. (2013) measured soil loss in a 16-year study from seven watersheds at the North Appalachian Experimental Watershed in Ohio. All watersheds were within one kilometer of one another. Of the watersheds, two were no-till (2-yr corn-soybean rotation), two were chisel-till (2-yr corn soybean rotation), and three were disked with reduced

fertilizer inputs (3-yr corn-soybean-wheat/clover rotation). The corn-soybean watersheds had been managed in this manner for the six years prior to this study. Two of the three disked-reduced input watersheds were previously paraplowed and converted to the current management in 1990. The third disked-reduced input watershed was previously an uncultivated meadow and was added to the study in order for there to be one phase of the rotation present each year. Each cropping/tillage treatment had a watershed that historically produced lower runoff in order to better document the range of measured losses. Chisel-tilled watersheds were cultivated just prior to planting each spring and rye was used as a winter cover crop in these watersheds after soybean harvest. Disked-reduced input watersheds were disked three to four times each spring just before planting. Additional cultivation occurred in corn and soybean years between rows as a method to control weeds. Soil losses under these management conditions were lowest when the most ground cover was provided. The lowest average soil loss occurred in the disked-reduced input system (198 kg ha-1 yr-1) when the wheat-red clover cover crop provided the most coverage. However, when considering only row crop years, the disked-reduced input rotation experienced the highest average amount of erosion (1667 kg ha-1 yr-1). This was followed by the chisel-till watershed (1073 kg ha-1 yr-1) and then the no-till watershed (807 kg ha-1 yr-1) (Shipitalo et al., 2013).

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(34yr no-till corn). Runoff and soil loss data were collected by using simulated rainfall at an intensity of 50mm h-1 for 1hr at each location. Soil samples were collected at 4 depth increments (0-1, 1-3, 3-7.6, 7.6-15cm) for organic matter and aggregate stability

measurements. At the Mississippi location (nine year) the authors found an average runoff reduction of 17% in the no-till cotton and 26% in the no-till corn compared to the

conventional tilled treatments. At the Ohio site (34yr) the authors found an average runoff reduction of 77% in the no-till corn compared to the conventional tilled treatment. The authors found soil organic matter content was significantly higher at 0-3cm depths in most cases, which in turn resulted in higher aggregate stability. Measureable soil loss from the no-till plots was almost nonexistent and was credited to the higher aggregate stability and reduced runoff associated with the no-till treatment (Rhoton et al., 2002).

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treatments reduced mean annual runoff 47.2% and rainfall infiltration was 12% greater when compared to wheel traffic stubble mulch plots. The authors concluded that controlled traffic and conservation tillage practices could be a solution to managing sustainable farming systems in, the often water limited, Australian climate (Li et al., 2007).

Other researchers have demonstrated similar results; conservation tillage reduces runoff and erosion (Benham et al., 2007; Zang et al., 2007; Tiessen et al., 2010; Araya et al., 2011). Preventing soil losses from agricultural fields not only protects critical soil mineral and organic components, but also maintains and prevents the loss of nutrients, which can degrade water resources.

1.2-3.2 Nutrient Losses

Nonpoint source pollution is defined as pollution that is not considered “point source” pollution. Point source pollution was defined by the Clean Water Act as:

“. . . Any discernible, confined and discrete conveyance including but not limited to any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, or vessel or other floating craft, from which pollutants are or may be discharged. This term does not include agricultural storm water discharges and return flows from irrigated agriculture.” (United States Environmental Protection Agency, 2012) The loss of nutrients from agriculture systems through runoff and leaching is the chief source of nutrient loading for surface and ground waters (Havlin et al., 2005). Nitrate (NO3)

concentrations are regulated in drinking water with a maximum contaminate level of 10 mg L-1 (United States Environmental Protection Agency, 2012) and consumption of high NO3 water can result in Methemoglobinemia, low blood oxygen levels. Other risks associated with N and phosphorus (P) in water includes, eutrophication, which can lead to hypoxia (low dissolved oxygen) and anoxia (lack of oxygen) in water systems that are the result of

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ecosystems are limited by P and others are limited by N. Carpenter (et al., 1998) reported that while P is an essential component to eutrophication, most estuaries and coastal waters are N deficient. Similarly, an extensive review of the Chesapeake Bay eutrophication stated that lower salinity waters are more P deficient while higher salinity and warmer waters are N deficient (Boesch et al., 2001). Management to curb agricultural additions to nonpoint source pollution is wide spread and has been in effect for some time but primarily since the early 1990’s when the full effect of point source control from the 1972 Clean Water Act had time to affect water quality. Two macro-nutrients – N and P - are of primary concern when considering agriculture’s effect on water quality.

Plant available forms of N are NO3 and ammonium (NH4) and are primarily applied through synthetic fertilizers in conventional agricultural systems. Other sources of plant available N include atmospheric deposition, N from leguminous crops, and the mineralization of organic additions. Ground water quality concerns for N primarily focus on NO3 due to soil’s

generally low anion holding capacity and the large leaching losses of NO3. Among other forms of N (organic and dissolved), both NO3 and NH4 can be lost through surface water flow. Soil N is mediated by microbial processes and has the ability to change forms readily and thus can be difficult to manage in cropping systems.

Phosphorus moves primarily with sediment through surface runoff. Inorganic P (H2PO4-, HPO4-2, and PO4-3) is adsorbed readily to soil minerals (aluminum/iron hydroxides, calcium carbonates) and is transported with erosion. Likewise, organic P, bound within soil organic matter or crop residue, will move with sediment. Dissolved P is typically the result of P escaping out of organic material on the soil surface and moving with surface water runoff. While the potential for P leaching is much lower than N, the possibly exists under two

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Halvorson et al. (2006) studied the effects of N rates and tillage on continuous irrigated corn and found soil NO3-N levels down to 180cm were comparable regardless of tillage system (conventional vs. no-till) prior to planting the first two years of a four year study. However, residual NO3-N levels were higher in conventional tilled systems after year two at the highest N application rate of 224 kg N ha-1 (Halvorson et al., 2006).

Kanwar et al. (1997) conducted a five year (1988-1992) experiment in Iowa that examined the effects of cropping and tillage systems on NO3-N leaching. The study area used 36 one acre plots on Aquic Hapludoll soils (Floyd loam, Kenyon silty-clay loam and Readlyn loam series) that had been under the same management for 14 years. Two cropping systems, continuous corn and corn-soybean rotation, and four tillage practices, moldboard plow, chisel plow, ridge-till and no-till, were replicated three times. Moldboard plow plots were cultivated six to eight inches deep in the fall and disked in the spring. Chisel plow plots were cultivated in both the spring and fall. Ridge-till plots were managed by reestablishing the ridge after planting to a height of six to eight inches. All treatments, including no-till, were cultivated with one or two passes to control weeds. Continuous corn and corn-soybean rotations received 180 and 150lb N acre-1 of anhydrous ammonia, respectively, each year and no N was applied to soybeans. Drainage tiles were installed four feet deep, 95 feet apart, and were located in the middle of each plot and along both boarders. Both the cropping systems and drainage tiles had been in place for 14 years or more. The middle drainage line of each plot was used to collect water samples for analysis approximately three times per week when tile flow was present and after any substantial rain storm. The first two years of this study (1988 and 1989) were especially dry, falling well below the 30 year average, while the following two years (1990 and 1991) were especially wet. The 1992 rainfall was average but

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management than no-till management. While peak flow from moldboard plow treatments was the lowest, yearly average NO3-N concentrations were consistently higher from

moldboard plow tillage plots under continuous corn cropping systems than no-till or ridge-till plots. This was thought to be due to moldboard plowing disrupting the soil structure,

eliminating macropores, and thus exposing more soil to water for longer periods due to micropore drainage. Furthermore, continuous corn cropping systems, having more applied N, resulted in a higher potential for N leaching. Continuous corn cropping systems experienced higher tile-water peak flow as well as significantly higher three year (1990-1992) average NO3-N concentrations than corn-soybean rotations for all tillage systems. Higher NO3-N concentrations from continuous corn should be expected due to higher rate of applied N. While not statistical significant, continuous corn systems utilizing no-till experienced the highest NO3-N loss (96 lb ac-1) in 1990. Chisel till was the highest in 1991 (68 lb ac-1). Even though moldboard plow continuous corn plots had the highest NO3-N concentrations, the higher volume of tile flow under no-till and chisel-till management resulted in higher total NO3-N losses. This illustrates the importance of considering not only concentration but volume of flow as well. Within the corn-soybean rotation there was no significant difference of NO3-N leaching losses between tillage systems (Kanwar et al., 1997).

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1970 to 1975 the conventional and no-till treatments lost 0.62 and 0.21 Mg N ha-1 from the 0-5cm zone, respectively, indicating that N mineralization was higher in the conventional treatments. Data from later in the study (1981 and 1982) showed that inorganic N

concentrations to a depth of 30cm were comparable between both tillage types (Rice et al., 1986). The results from this study indicate that N mineralization in conventional systems occurs rather quickly and no-till systems limit the extent of the changes.

Nitrogen and P losses influenced by tillage practices from Canadian Prairies were assessed by Tiessen et al. (2010). This long-term paired watershed study used two conventionally tilled watersheds (4.2 and 5.1ha) to “calibrate” the nutrient losses associated with

conventional tillage the first three years (1993-1996) of the study. In 1997, one watershed (5.1ha) was converted to conservation tillage and runoff and nutrient measurements were made for an additional 10 years (1997-2007). Runoff monitoring and sampling from

snowmelt and rainwater runoff occurred at the mouth of the watershed with the use of a weir and auto-sampler. When compared to the conventional tilled watershed, conservation tillage reduced the total export of total N, particulate N, total dissolved N and nitrate + nitrite 68, 63, 50, and 81% respectively. This study reported a reduction of 65% in total suspended solids (TSS) under conservation management, which in turn resulted in a reduction in particulate P (P bound to sediment) losses by 20%. While P losses were reduced in this form, total

dissolved P losses increased 36% due to increased soil test P near the soil surface under conservation tillage. The authors concluded by saying; “. . . Management practices such as conservation tillage that are designed to improve water quality by reducing sediment and sediment-bound nutrient export from agricultural fields and watersheds can be less effective in cool, dry regions where nutrient export is snowmelt driven and primarily in the dissolved form.” (Tiessen et al., 2010, p. 977).

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crop, were slightly larger than the 72 year average of 962 mm yr-1. No-till watersheds

experienced the highest number of runoff events; however, the runoff volume as a percentage of rainfall was similar to chisel-till watersheds and both were substantially lower than the disked-reduced input watersheds. The runoff as a percentage of rainfall was 10.4%, 9.3% and 13.5% for the no-till, chisel-till and disked-reduced input watersheds, respectively. The authors reported NH4-N losses to be relatively small (<1 kg ha-1 ya-1) for all tillage

treatments. Nitrate-nitrogen losses, on average, during corn years, were slightly lower in no-till and disked-reduced input watersheds than chisel-no-till watersheds, even though no-no-till watersheds experience a higher number of runoff events. During soybean years, NO3-N losses decreased due to no application of fertilizer N, however this decrease was not as evident in the disked-reduced input watershed due to the continuous mineralization of manure and red clover N. Average NO3-N losses for the entire cropping rotation were 3.7, 4.1, and 5.5 kg ha-1 yr-1 for no-till, disked-reduced input, and chisel-till respectively. This suggests, under these conditions, that reducing mineral N inputs reflects no benefit in NO3-N runoff losses. Organic nitrogen losses were the highest from the disked-reduced input

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that no-till crop production led to greater nutrient loss through surface runoff under these environmental and soil conditions. The disked-reduced input system experienced generally greater nutrient losses due to the continued mineralization of the manure and cover crops used to replace mineral fertilizer (Shipitalo et al., 2013).

A study conducted in Virginia in 2002 examined the effects of conventional, strip and no-till on edge-of-field losses in burley tobacco (Benham et al., 2007). Ryegrass was terminated and incorporated with a moldboard plow in the conventional treatments while it was killed with Roundup in the strip and no-till treatments. Based off of initial calculations, additions of ryegrass residue were made to bring the residue cover to 5%, 59%, and 82% in the conventional, strip and no-till treatments respectively. Fertilizer (10-6-18, N-P-K) was broadcast at a rate of 2,240 kg ha-1 in each plot before planting and was incorporated into the conventional treatment and left on the surface of the other two treatments. Boarders 30cm tall were installed after planting around each plot to guide runoff to a flume at the bottom of each treatment where a ditch was dug for sample collection. Simulated rainfall was used in June and July (three runoff events each month) of the same year to induce runoff. Rainfall time was determined by the time required for runoff to reach a steady-state. Runoff volumes were measured and samples were analyzed for NO3, NH4, total Kjeldahl N, orthophosphate, total P and TSS. After a total simulated rainfall rate of 174mm, runoff from the conventionally tilled plots was 100.8mm, whereas runoff was reduced by 33% from the strip-tilled fields and 50% from the no-till treatment. Total suspended solids results were similar in that strip and no-till treatments; TSS losses were less than the conventional treatment. Over all measured N and P constituents and across all sampling dates, the strip and no-till treatments experienced less nutrient loss than the conventional tillage. However, initial simulated rainfall nutrient measurements showed that NO3, NH4 (first and second runoff event in June) and

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1.2-4 Tillage Conclusion

While the main purpose of tillage has traditionally been weed control (Buchholtz and Doersch, 1968), advancements in pesticides, tillage equipment and genetically modified seeds have allowed producers to utilize conservation tillage for weed control, while

maintaining crop yields. Soil compaction tends to be minimized with long-term maintained conservation tillage hence high soil bulk density does not appear to be a significant issue (Rhoton et al., 2002; Sidhu and Duiker, 2006). Reducing soil surface disturbance and increasing organic inputs through returned crop residue has shown increases in soil carbon (Duiker et al., 2006; Ismail et al., 1994; Presley et al., 2012) that can result in greater aggregate stability, reduced wind erosion and improved soil-water relationships. Soil losses from fields under conservation tillage systems are virtually non-existent when compared to conventionally tilled soils (Rhoton et al., 2002). Nutrient losses tend to be constituent specific, in that particulate and sediment bound nutrients losses are limited by the

stabilization of soil particles and reduced erosion, whereas dissolved nutrient concentrations can increase in conservation tillage due to the higher concentration of nutrients at the soil surface (Tiessen et al., 2010). Tillage has also been shown to affect nitrogen leaching and water movement through the soil profile (Kanwar et al., 1997). While no-till tends to allow more water to infiltrate the soil allowing higher volumes of water flow downward,

conventional tillage has shown to result in higher concentrations of NO3-N in tile drainage

flow; load, therefore, tends to be similar between different tillage systems.

1.3 MANURE APPLICATION

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is variable, not only in its nutrient content but also its carbon content due to differences in manure type, source and animal feeds (Brady and Weil, 2004; Havlin et al., 2005). Thus it is important to examine the effect of manure inputs to cropping systems

1.3-1 Weed Control and Yield

As discussed earlier, tillage has been the primary form of weed control in agriculture and eliminating competition is crucial to maximizing crop yields. A major drawback when applying animal wastes to cropping systems is the potential of introducing weeds to the field. When ruminates graze they inevitably consume seeds from various plants. It is known that the digestive track of rumens can reduce but not fully eliminate the viability of weed seeds (Atkeson et al., 1934; Blackshaw and Rode, 1991). A 1991 study examined the viability of weed seeds at specific time intervals spent in the digestive tract of fistulated bovine. The researchers concluded that the survival rate of seeds is often species specific and that seed degradation over time was not gradual (Blackshaw and Rode, 1991).

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2000). This data suggests a more complex relationship between compost and seed resilience. Similarly, Larney and Blackshaw (2003, p. 1113) concluded that “The lack of definitive relationships between temperature and weed seed viability demonstrated that factors other than temperature may play a role in eliminating weed seeds during composting.”

Multiple studies have compared manure applications to inorganic fertilizers and/or a combination of the two.

Corn yields under different fertilizer treatments were studied in a five year experiment by Walker et al. (2009). Four treatments were utilized; unprocessed liquid swine manure, processed liquid effluent, inorganic fertilizer and a control. All treatments were fertilized to supply 200 kg N ha-1 except the control, which received zero inputs. Fertilization occurred just prior to planting for all treatments. However, the inorganic fertilizer treatment was side dress with 28% Urea Ammonium Nitrate at the third leaf crop stage. Results showed that corn grain yield was statistically similar between all treatments except for the control. This indicates that when applied at nutrient equivalent rates, animal manure is a feasible form of fertilization.

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that when only considering crop yield and labor, manure was not a viable option for producers. However, the authors noted that manure was an optimal choice for increasing nutrient capacity and supply in the soil (Gong et al., 2011).

Corn yields under different fertilization practices from 2002-2005 were studied by

Lithourgidis et al. (2007). The equivalent available N and P treatments included: 1) liquid dairy manure; 2) single application of P and N inorganic fertilizer; 3) P and spilt application of N inorganic fertilizer, and; 4) control with no fertilization. The application rates were 260 kg N and 57 kg P ha-1 yr-1. The authors found that liquid dairy manure increased corn grain and silage yields similarly to the inorganic fertilizer treatments and that all three of these treatments were significantly higher than the control treatment. Like many other studies, these findings suggest that when applied at nutrient equivalent amounts, the liquid dairy manure is a viable source of fertilization (Lithourgidis et al., 2007).

In another study demonstrating the value of manure as a viable fertilizer source, Nyiraneza et al. (2009) examined the residual effects of long term (28 year) dairy cattle manure at a rate of 20 Mg ha-1 (averaged to 440 kg total N ha-1). Following the 28 years of manure application, the manure fertilization was stopped and new treatments were initiated. The new treatments included plots that had the long term application of manure and plots that did not have long term manure application. Inside these main treatments the study used a control of no fertilizer use, inorganic fertilizer P-K, and inorganic fertilizer NPK. Phosphorus and K were applied at soil test recommended rates and 160 kg available N ha-1 was applied to the respective plots. Each treatment was plowed in the fall, disked in the spring, and all crop residues were removed from the field each year. The highest yielding treatments were those that received the long term manure applications. Due to increased available nutrients and soil properties associated with manure applications, this paper concluded that the sustainability of

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The introduction of weeds through manure applications is a potential draw back to using animal manure as a fertilizer source (Atkeson et al., 1934). Weed seed viability can be diminished through composting, however the resilience of weeds has been found to be species specific (Blackshaw and Rode, 1991). When applied at nutrient equivalent amounts, animal manure is a viable source of fertilizer (Lithourgidis et al., 2007; Nyiraneza et al., 2009) and can benefit the agriculture system due to increase soil carbon.

1.3-2 Soil Physical Properties

In addition to supplying nutrients, manure can affect soil properties by increasing organic matter and soil carbon that may or may not improve the soil and therefore the cropping system as a whole.

Manure, being a carbon based compound, can have lasting effects on an agriculture system and specifically to the soil physical properties, as discussed relative to tillage (Brady and Weil, 2004; Havlin et al., 2005). Increasing the soil organic matter, and hence carbon content through manure additions, has been widely studied but its benefits are ambiguous primarily because of the complexity of agriculture systems.

An 11-year long-term study conducted in Alberta Canada examined the effects of cattle feedlot manure on specific soil properties. Manure was applied at rates 30, 60, 90 and 60, 120, and 180 Mg ha-1 to non-irrigated and irrigated soil respectively. The manure was

incorporated immediately after application and these rates represent one, two and three times the recommended manure application rate for barley production on irrigated and

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respect to increased manure rates (60, 120, 180 Mg manure ha-1; Chang et al., 1991). Similar results were noted by Gong et al. (2011).

While the above data suggests that soil carbon content will increase with increasing manure rates, Lithourgidis et al. (2007) found that after eight years of liquid manure application, the soil carbon content was unchanged. This was thought to be due to the lower dry matter content found in liquid manure when compared to solid forms (Lithourgidis et al., 2007). With this in mind, it should be considered that composition of the manure (livestock species and the manure handling system) and the rate of application will dictate soil carbon changes. Zhong et al. (2010) suggested that fertilizer additions can affect microbial populations in soil systems. Since many microbial mediated properties contribute to plant growth, the effects of manure and or chemical fertilizer additions are important to understand. Zhong’s analysis showed that microbial populations varied among treatments. For example, bacterial, Gram-negative, and total phospholipid fatty acid (PLFAs) profiles were highest in the manure plus fertilizer treatment while Gram-positive and anaerobic PLFAs were highest in the organic manure treatment and aerobic and fungal PLFAs were highest in the NPK treatment. These data suggest that a balanced approach of manure and fertilizer applications can promote a more diverse soil microbial community.

Bulk density measurements were made after 12 years of cattle feedlot manure applications (Chang et al., 1991; Sommerfeldt and Chang, 1985). These researchers showed that bulk density was significantly lower in treatments where manure was applied, especially at the highest application rates (correlation r=-0.76; Sommerfeldt and Chang, 1985). The non-irrigated treatment that received zero manure had a bulk density of 1.22 Mg m-3 while the highest application rate (90 Mg ha-1) had a bulk density of 0.92 Mg m-3 at the 0-15cm depth. The irrigated treatment had a bulk density at 0-15cm of 1.14 and 0.74 Mg m-3 at zero and 180 Mg ha-1 (highest rate for irrigated treatment) of manure respectively. Furthermore, this trend was apparent in the 15-30cm depth but only significant in the irrigated treatment

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observed soil bulk densities were not high enough to restrict root growth (~1.5 M m-3; Brady and Weil, 2004) in any of the treatments.

Sommerfeldt and Chang’s observations of reduced bulk density measurements only occurred when manure application rates were two to three times higher than recommendations. Other researchers have shown that at lower manure application rates, insignificant changes to bulk density have occurred. The manure in Nyiraneza’s et al. (2009) study was applied at 20 Mg ha-1 for 28 years and had an average C/N ratio of 21:1 and yearly carbon inputs of

approximately 9400 kg. The initial soil C was 2.8% and at the end of the study had decreased to 2.1% in the non-manure plots and remained relatively the same in the manure plots. There were no significant changes in bulk density in this study suggesting that the manure

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Similar results reported by Eghball (2002) and Nyiraneza et al. (2009) concluded that higher rates more similar to the study used by Sommerfeldt and Chang (1985) were required to decrease bulk density. Due to environmental, health, and cost implications, application rates should never exceed agronomic needs.

In contrast, the 18-year long-term fertilization study by Gong et al. (2011) had an initial 0.4% soil organic carbon and on average the C/N ratio of the manure was 7:1 with yearly manure carbon inputs of 1,164 kg. Bulk density values were significantly higher in the control treatment, 1.4 g cm-3, when compared to the manure treatment 1.2 g cm-3. At the conclusion of the study the soil organic carbon was 0.9% and the soil C/N ratio increased to 11:1 from 9.8:1.

Initial soil characteristics will affect the soil carbon and bulk density response to which animal waste is applied. Soils with low initial carbon concentrations are more likely to respond, as in Gong et al. (2011) study, than soils with higher concentrations. Moreover, system management, such as tillage and traffic, environmental factors, such as precipitation, and the type of animal waste and the applied rate need to be taken into account to properly assess the relationship between carbon inputs and bulk density.

Manure applications can also affect soil acidity, soil salinity and trace metal accumulation in soils. These factors, while briefly discussed here, can have significant negative effects on crop growth and yields.

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in pH when inorganic ammonium fertilizer was applied. Smith et al. (1980) demonstrated that while soil pH increased, averaged over the whole soil profile down to 90cm, there was only a maximum change of just a few tenths of a pH unit. No significant difference was observed at the soil surface (0-30cm) in this study (Smith et al., 1980). This evidence suggests that the application of manure can have an effect on soil pH but there is an interaction due to soil buffering capacity, the initial soil pH, the type of animal waste, the type of feed supplied to the animal and other factors.

Increased salt content, determined through the indirect measurement of soil electrical conductivity, has been known to have adverse consequences to plant growth (Brady and Weil, 2004). Lithourgidis et al. (2007), Chang et al. (1991), and Eghball (2002) all reported increases in soil salinity with the use of manure especially at higher application rates.

Irrigation can be used to leach salts out of the rooting zone and into the subsoil (Chang et al., 1991), but this could also result in the leaching of nutrients, especially NO3-N to ground water.

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1.3-3 Nutrient and Soil Losses

As mentioned earlier, nutrient loss from agriculture systems not only hinders crop production but can potentially harm environmental systems and human health. Nutrient losses from manure applications are much like inorganic fertilizer in that they are influenced by

application type, timing, and amount. While the additions of organic matter may improve the soil/agriculture system, assessments of nutrient losses, or potential losses, are critical due to the varying forms and amounts of these nutrients within animal manure.

Nutrient concentrations in soils can vary between organic and inorganic nutrient sources. While inorganic fertilizers tend to provide nutrients that are readily available for plant use, organic fertilizers contain both available and unavailable plant nutrients. Unavailable plant nutrients bound to the organic fraction in soils can be made available once the organic

material is mineralized and this presents a unique management challenge in reducing nutrient losses.

As expected, total organic N concentrations have been found to be highest in manure applied soils compared to inorganic fertilization (Gong et al., 2011; Nyiraneza et al., 2009) however the amount of available nutrients, that could be potentially lost, appears to be a source of conflict in the literature. Lithourgidis et al. (2007) found that after 8 years of manure

application, soil NO3-N was comparable to inorganic fertilized treatments down to 90cm in the soil profile. Analysis of soil samples 0-20cm deep by Gong et al. (2011) found total inorganic-N and NO3-N significantly lower in manure applied soils. Nyiraneza (et al., 2009) found that after 28 years of manure application, pre-plant NO3-N concentrations increased significantly in dairy cattle manure applied soils. The contradictions in this data suggest the level of complexity when managing agricultural systems. Moreover, the varying nutrient contents of manures can make comparisons such as this difficult.

The impact to surface water from inorganic fertilizer has been studied thoroughly and

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losses associated with poultry manure in a corn-soybean cropping system with two types of application: incorporated and unincorporated manure. This three-year study was conducted at nine different fields from 2004-2006 in Iowa. Poultry manure was applied at rates of 0, 84, and 168 kg total N ha-1 and then simulated rainfall was used to induce runoff. This study found NO3-N losses were low in all treatments and were not affected by tillage or manure rate application. Moreover, data showed that when the poultry manure was incorporated runoff concentration and loads of total Kjeldahl N and ammonium were reduce almost 50% and 90% respectively, suggesting that when poultry manure is left on the surface it is more apt to release nutrients into surface waters (Diaz et al., 2010).

A similar study resulted in the same conclusion when examining P losses associated with liquid swine manure (Allen and Mallarino, 2008). This experiment took place in two fields; one conventionally tilled and the other had been under no-till management for 10 years. Both fields exhibited low soil test P, had no manure applied within 20 years and were under corn-soybean rotation. Liquid swine manure was applied the first year at rates 0, 0.5, 1 and 2 times the suggested grain P removal rate of 24 kg P ha-1 yr-1. In the second year, manure rates were applied at twice the first year rate. Simulated rainfall was used to induce runoff on three different occasions: 24 hours, 15 days, and 6 months after application. Runoff samples were collected then analyzed for dissolved runoff P, bioavailable P and total runoff P. Results from this study showed runoff events within 24 hours of application had P concentrations 3.3-7.6 times higher for non-incorporated treatments than incorporated across all measured

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Little et al. (2005) found that when beef cattle manure was incorporated into the soil that surface runoff total N and P loads were reduced 95% and 79% respectively. These data further demonstrate that nutrient losses from manure are reduced through incorporation. Walker et al. (2009) found that inorganic fertilizer treatments had significantly higher NO3 concentrations in shallow soil water compared to processed and unprocessed swine slurry treatments. Lysimeters were placed 1.2-1.5m deep in each treatment and samples were collected for comparison. Median values for NO3in the inorganic treatment, processed swine effluent treatment and unprocessed swine slurry were 14.2 mg L-1, 5.5 mg L-1, and 2.5 mg L -1

, respectively. Ammonium concentrations at the same depth were negligible among

treatments. While the inorganic fertilizer treatments exhibited higher NO3 concentrations at shallow depths, samples taken from wells showed that manure fertilized treatments led to higher concentrations in groundwater. The median NO3 concentrations in the groundwater were 0.20 mg L-1 in the inorganic fertilizer treatment, 0.80 mg L-1 in the processed swine effluent treatment, and 1.5 mg L-1 in the unprocessed swine slurry treatment. While elevated levels of chlorides were also found in the groundwater beneath the manure treatments, other indicators of ground water contamination, such as metals and other nutrients, were not present.

Manure applications are a valuable source of N. Unfortunately when manure is applied on an N basis, P is oversupplied as most manures have lower N:P ratios than what is required by crops. Smith et al. (1998) reported that while manure N:P ratios range from 2-6:1, the

requirement for most crops is 7-11:1. Phosphorus enrichment of soils can lead to increased P losses that directly affect eutrophication and hypoxic conditions as discussed earlier.

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applications in respect to the most abundant element within the manure complex is required to avoid the over application of nutrients.

As seen earlier, tillage and soil surface disturbance results in higher turbidity of surface runoff (Rhoton et al., 2002; Williams et al., 2009). Organic amendments have the ability to increase aggregate stability as found by Tejada and Gonzalez (2008). Their study found that incorporated organic amendments reduced soil loss under simulated rainfall when compared to a control that used no amendments. A lower rainfall rate of 60 mm h-1 and higher rate of 140 mm h-1 was used to determine losses. Results from the lower rate found that soil loss were reduced 14.5-20.8% in treatments that had incorporated poultry manure and reductions of 19-22.6% were observed with incorporated cotton gin compost (Tejada and Gonzalez, 2008). While the incorporation of manure may both reduced nutrient and sediment losses, tillage often increases erosion.

1.3-4 Manure Application Conclusion

Manure has long been used as a fertilizer source and is a partial answer in dealing with the large amounts of animal waste produced in agriculture. Introducing weeds through manure applications is a potential drawback (Atkeson et al., 1934; Blackshaw and Rode, 1991). Composting can alleviate the problem, however seed resilience is variable and species specific (Atkeson et al., 1934; Larney and Blackshaw, 2003). While fertilizing with manure has proven to be a practical management technique that results in similar yields as inorganic fertilizers, special concern must be taken to the composition of the manure (Gong et al., 2011; Lithourgidis et al., 2007; Walker et al., 2009). The benefits of increased soil carbon are plentiful and include a potential to lower soil bulk density, although this is a complex

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can be significantly reduced through the incorporation the manure (Little et al., 2005), although erosion and nutrients attached to the soil may be increased.

1.4 ORGANIC AND CONVENTIONAL AGRICULTURE SYSTEMS

Organic agriculture is often promoted for its ability to solve the dual responsibilities of today’s agricultural systems: food, fiber or forage production and environmental

sustainability. With the ever growing population, it is crucial that we maintain crop yields while we also minimize the impacts to the environment. The USDA National Organic Standards Board (NOSB) defines organic production as;

“. . . an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain and enhance ecological harmony.” (United States Department of Agriculture, July 29, 2009).

Strict criteria are set by the NOSB in which producers must adhere to in order to be certified “USDA Certified Organic.” Cover crops (green manures), animal manures and other organic compounds are used to supplement plant nutrition in place of inorganic fertilizers; all

amendments applied to the system must be certified by the USDA.

Given the requirements for organic production and the mission statement of “ecological harmony” it is essential to compare organic agriculture to conventional methods of production for both yield and environmental sustainability. Understanding how these

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1.4-1 Yield and Weed Control

As discussed throughout this review, limiting weed competition in agriculture systems is a priority. This becomes increasingly more important in low-input organic systems, where traditional chemical herbicides are not allowed. Moreover, when deploying alternative cropping systems to meet sustainable and environmental needs it is pertinent that yields are evaluated to fully understand the value of the system.

Cavigellia et al. (2008) conducted an eight year study in Maryland and examined the yield differences between organic and conventional corn, soybean and wheat. This study used five cropping systems that included two conventional and three organic crop rotations that consisted of corn (C), soybean (S), wheat (W), rye cover crop (r), wheat followed by double-cropped soybean (W/S), hairy vetch green manure (v) and hay (h). The conventional

treatments were no-till and chisel-till with C-r-S-W/S cropping rotations. The organic

production treatments were all conventionally tilled and the cropping rotations were two-year (C-r-S-v), three-year (C-r-S-W-v), or four plus-year rotations (C-r-S-W-H). Fertilization consisted of inorganic N-P-K for conventional treatments and a combination of green manure, animal manure and potassium sulfate for organic treatments. When the green

Figure

Figure 2a: Plot layout
Figure 2b: Plot Design
Table 2d: ACE coefficients, normalized values, and p values  2011
Figure 3a: Plot Layout
+7

References

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