Nutrient Cycling

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A

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LIVESTOCKIVESTOCK S SYSTEMSYSTEMS G GUIDEUIDE

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 

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

By

ByBarbara BellowsBarbara Bellows

NCAT Agriculture Specialist

December 2001

Abstract:

Abstract: Good Good pasture pasture managementmanagement

pr

pracactiticeces s fofostster er efeffefectctivive e ususe e anandd

recycling of

recycling of nutrients. nutrients. Nutrient cyclNutrient cycleses

important in pasture systems are the

water, carbon, nitrogen, and phosphorus

cycles.

cycles. This publicatiThis publication provides on provides basicbasic

descriptions of these cycles, and presents

guid

guidelineelines s for for manamanaging ging pastpastures ures toto

enhance nutrient cycling efficiency —

with the goal of optimizing forage and

livestock growth, soil health, and water

quality.

quality. Includes Includes 19 Tabl19 Tables and es and 1414

Figures.

Table of Conte Table of Contentnts s Introduction and Summary

Introduction and Summary...22

Publication

Publication OverviewOverview...55

Chapter 1. Nutrient Cycle

Chapter 1. Nutrient Cycle Components, Interactions, Components, Interactions, andand...

Transformations

Transformations ...66

Water

Water CycleCycle...66

Carbon

Carbon CycleCycle...1010

Nitrogen

Nitrogen CycleCycle ...1313

Phosphorus Cycle

Phosphorus Cycle...1818

Secondary

Secondary NutrientsNutrients ...2121

Chapter 2.

Chapter 2. Nutrient Availability Nutrient Availability in Pasturesin Pastures...2323

Soil Parent Material

Soil Parent Material...2323

Soil Chemistry

Soil Chemistry...2323

Prior Management Practices

Prior Management Practices...2424

Soil Compaction

Soil Compaction...2424

Organic M

Organic Matteratter...2525

Soil pH

Soil pH...2727

Timing

Timing of Nutrient of Nutrient AdditionsAdditions...2727

Chapt

Chapter 3. Nutrient Distrer 3. Nutrient Distributioibution and Movement in Pasturen and Movement in Pasturess ...3030

Pasture Nutrient

Pasture Nutrient Inputs and Inputs and OutputsOutputs...3030

Manure Nutrient A

Manure Nutrient Availabilityvailability...3232

Pasture

Pasture FertilizationFertilization ...3333

Grazing Intensity

Grazing Intensity...3434

Diversity and

Diversity and Density of Density of Pasture Pasture PlantsPlants ...3636

Chapt

Chapter 4. The Soil Food Web and Paster 4. The Soil Food Web and Pasture Soil Qualiture Soil Qualityy ...4040

Diversity of the Soil

Diversity of the Soil Food WebFood Web...4040

Organic Matter Decomposition...

Organic Matter Decomposition...4040

Primary

Primary DecomposersDecomposers ...4141

Secondary Decomposers

Secondary Decomposers...4343

Soil Organisms

Soil Organisms and and Soil HealthSoil Health ...4444

Chapter

Chapter 5. 5. Pasture Pasture Management Management and and Water Water QualityQuality ...4747

Risk Factors for

Risk Factors for Nutrient LossesNutrient Losses...4747

Pathogens

Pathogens...4848

Nitrate

Nitrate ContaminationContamination...4949

Phosphorus Contam

Phosphorus Contaminationination...4949

Subsurface

Subsurface DrainageDrainage...5151

Riparian Buf

Riparian Buffersfers...5252

Riparian

Riparian GrazingGrazing...5353

References

References...5555

Resource

Resource ListList ...6161

Agencies

Agencies and and OrganizationsOrganizations ...6161

Publications

Publications in in PrintPrint ...6161

Web Resources

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As a pasture manager, what factors do you look at as indicators of high production and maximum

profitability?

profitability? You probably look You probably look at the at the population of population of animals stocked within animals stocked within the pasture. the pasture. You probablyYou probably

look at the vigor of plant regrowth.

look at the vigor of plant regrowth. You probably also look at the diversity of plant You probably also look at the diversity of plant species growing in thespecies growing in the

pasture and whether the plants

pasture and whether the plants are being grazed uniformly. are being grazed uniformly. But do you But do you know how much know how much water seepswater seeps

into your soil or how much runs off the land into

into your soil or how much runs off the land into gullies or streams? gullies or streams? Do you monitor how efficiently yourDo you monitor how efficiently your

plants are taking in carbon

plants are taking in carbon and forming new leaves, stems, and roots and forming new leaves, stems, and roots through photosynthesis? through photosynthesis? Do youDo you

know how effectively nitrogen and phosphorus are being used, cycled, and conserved on y

know how effectively nitrogen and phosphorus are being used, cycled, and conserved on your farm? our farm? AreAre

most of these nutrients being used for plant and

most of these nutrients being used for plant and animal growth? animal growth? Or are they being leached into theOr are they being leached into the

groundwater or transported through runoff or erosion

groundwater or transported through runoff or erosion into lakes, rivers, and streams? into lakes, rivers, and streams? Do you know hoDo you know howw

to change your pasture management practices to decrease these losses and increase the availability of

nutrien

nutrients to your forages and animats to your forages and animals?ls?

Effective use and cycling of nutrients

Effective use and cycling of nutrients isis

critical for pasture product

critical for pasture productivity. ivity. As indicated inAs indicated in

Figure 1

Figure 1 above, nutrient cycles are above, nutrient cycles are complex andcomplex and

interrelated.

interrelated. This document This document is designeis designed to helpd to help

you understand the unique components of

wa-ter, carbon, nitrogen, and phosphorus cycles and

ter, carbon, nitrogen, and phosphorus cycles and

how these cycles inte

how these cycles interact with one anotheract with one another. r. ThisThis

information will help you to monitor your

pas-tures for breakdowns in nutrient cycling

tures for breakdowns in nutrient cycling

pro-cesses, and identify and implement pasture ma

cesses, and identify and implement pasture man-

n-agement practices to optimize the efficiency of

agement practices to optimize the efficiency of

nutrient cycling.

W

ATERATER Water

Wateris necessais necessary for plant gry for plant growth, forowth, for dis-r

dis-solving and transporting plant nutrients, and for

solving and transporting plant nutrients, and for

the survival of soil organisms.

the survival of soil organisms. Water can also be aWater can also be a

destructive force, causing soil compaction,

nutri-ent

ent leaching, leaching, runoff, runoff, and and erosion. erosion. ManagManagemeementnt

practices that facilitate water movement into the

soil and build the soil’s water holding capacity

will conserve water for plant

will conserve water for plant growth and ground-growth and

ground-water recharge, while minimizing ground-water's

water recharge, while minimizing water's

poten-tial to

tial to cause nutriecause nutrient lossnt losses. es. Water-conserviWater-conservingng

pasture management practices include:

•

• MinMinimizimizing ing soisoil col compacmpactiotion bn by noy not ovt overgrergraz-

az-ing pastures or usaz-ing paddocks that have wet

ing pastures or using paddocks that have wet

or saturated soils

•

• MaMaintintainainining a cog a complmplete cete coveover of for of foragrages anes andd

residues over all paddocks by

residues over all paddocks by not overgraz-not

overgraz-ing pastures and by

ing pastures and by implementinimplementing practicesg practices

that encourage animal movement across each

paddock

•

• EnsEnsuriuring tng that hat forforage page planlants its inclnclude a ude a divdiver-

er-sity of grass and legume species with a

sity of grass and legume species with a vari-

vari-ety of root systems capable of obtaining

ety of root systems capable of obtaining

wa-ter and nutrients throughout the soil profile

ter and nutrients throughout the soil profile

Healthy

Healthy plant growplant growth provides th provides plant cover plant cover over the over the entire paentire pasture. sture. Cover froCover from growing m growing plants and plants and plant resiplant residues protectsdues protects

the soil against erosion while returning organic matter to the soil.

the soil against erosion while returning organic matter to the soil. Organic matter provides food for soil organisms thatOrganic matter provides food for soil organisms that

mineralize nutrients from these materials and produce gels

mineralize nutrients from these materials and produce gels and other substances that enhance and other substances that enhance water infiltration and thewater infiltration and the

capacity of soil to hold water and

capacity of soil to hold water and nutrients.nutrients.

Animal Production

Animal Production Manure ProductionManure Production

Water Availability Water Availability Water Infiltration Water Infiltration





 

 



Minimal Soil Minimal Soil Erosion Erosion Soil Organisms Soil Organisms Plant Vigor Plant Vigor Nutrient Availability Nutrient Availability

Soil Organic Matter Soil Organic Matter

Plant Cover Plant Cover Soil Porosity/ Soil Porosity/ Minimal Compaction Minimal Compaction Nutrient Nutrient Mineralization Mineralization Legumes Legumes                                      __  __                     

  

(3)

As a pasture manager, what factors do you look at as indicators of high production and maximum

profitability?

profitability? You probably look You probably look at the at the population of population of animals stocked within animals stocked within the pasture. the pasture. You probablyYou probably

look at the vigor of plant regrowth.

look at the vigor of plant regrowth. You probably also look at the diversity of plant You probably also look at the diversity of plant species growing in thespecies growing in the

pasture and whether the plants

pasture and whether the plants are being grazed uniformly. are being grazed uniformly. But do you But do you know how much know how much water seepswater seeps

into your soil or how much runs off the land into

into your soil or how much runs off the land into gullies or streams? gullies or streams? Do you monitor how efficiently yourDo you monitor how efficiently your

plants are taking in carbon

plants are taking in carbon and forming new leaves, stems, and roots and forming new leaves, stems, and roots through photosynthesis? through photosynthesis? Do youDo you

know how effectively nitrogen and phosphorus are being used, cycled, and conserved on y

know how effectively nitrogen and phosphorus are being used, cycled, and conserved on your farm? our farm? AreAre

most of these nutrients being used for plant and

most of these nutrients being used for plant and animal growth? animal growth? Or are they being leached into theOr are they being leached into the

groundwater or transported through runoff or erosion

groundwater or transported through runoff or erosion into lakes, rivers, and streams? into lakes, rivers, and streams? Do you know hoDo you know howw

to change your pasture management practices to decrease these losses and increase the availability of

nutrien

nutrients to your forages and animats to your forages and animals?ls?

Effective use and cycling of nutrients

Effective use and cycling of nutrients isis

critical for pasture product

critical for pasture productivity. ivity. As indicated inAs indicated in

Figure 1

Figure 1 above, nutrient cycles are above, nutrient cycles are complex andcomplex and

interrelated.

interrelated. This document This document is designeis designed to helpd to help

you understand the unique components of

wa-ter, carbon, nitrogen, and phosphorus cycles and

ter, carbon, nitrogen, and phosphorus cycles and

how these cycles inte

how these cycles interact with one anotheract with one another. r. ThisThis

information will help you to monitor your

pas-tures for breakdowns in nutrient cycling

tures for breakdowns in nutrient cycling

pro-cesses, and identify and implement pasture ma

cesses, and identify and implement pasture man-

n-agement practices to optimize the efficiency of

agement practices to optimize the efficiency of

nutrient cycling.

W

ATERATER Water

Wateris necessais necessary for plant gry for plant growth, forowth, for dis-r

dis-solving and transporting plant nutrients, and for

solving and transporting plant nutrients, and for

the survival of soil organisms.

the survival of soil organisms. Water can also be aWater can also be a

destructive force, causing soil compaction,

nutri-ent

ent leaching, leaching, runoff, runoff, and and erosion. erosion. ManagManagemeementnt

practices that facilitate water movement into the

soil and build the soil’s water holding capacity

will conserve water for plant

will conserve water for plant growth and ground-growth and

ground-water recharge, while minimizing ground-water's

water recharge, while minimizing water's

poten-tial to

tial to cause nutriecause nutrient lossnt losses. es. Water-conserviWater-conservingng

pasture management practices include:

•

• MinMinimizimizing ing soisoil col compacmpactiotion bn by noy not ovt overgrergraz-

az-ing pastures or usaz-ing paddocks that have wet

ing pastures or using paddocks that have wet

or saturated soils

•

• MaMaintintainainining a cog a complmplete cete coveover of for of foragrages anes andd

residues over all paddocks by

residues over all paddocks by not overgraz-not

overgraz-ing pastures and by

ing pastures and by implementinimplementing practicesg practices

that encourage animal movement across each

paddock

•

• EnsEnsuriuring tng that hat forforage page planlants its inclnclude a ude a divdiver-

er-sity of grass and legume species with a

sity of grass and legume species with a vari-

vari-ety of root systems capable of obtaining

ety of root systems capable of obtaining

wa-ter and nutrients throughout the soil profile

ter and nutrients throughout the soil profile

Healthy

Healthy plant growplant growth provides th provides plant cover plant cover over the over the entire paentire pasture. sture. Cover froCover from growing m growing plants and plants and plant resiplant residues protectsdues protects

the soil against erosion while returning organic matter to the soil.

the soil against erosion while returning organic matter to the soil. Organic matter provides food for soil organisms thatOrganic matter provides food for soil organisms that

mineralize nutrients from these materials and produce gels

mineralize nutrients from these materials and produce gels and other substances that enhance and other substances that enhance water infiltration and thewater infiltration and the

capacity of soil to hold water and

capacity of soil to hold water and nutrients.nutrients.

Animal Production

Animal Production Manure ProductionManure Production

Water Availability Water Availability Water Infiltration Water Infiltration





 

 



Minimal Soil Minimal Soil Erosion Erosion Soil Organisms Soil Organisms Plant Vigor Plant Vigor Nutrient Availability Nutrient Availability

Soil Organic Matter Soil Organic Matter

Plant Cover Plant Cover Soil Porosity/ Soil Porosity/ Minimal Compaction Minimal Compaction Nutrient Nutrient Mineralization Mineralization Legumes Legumes                                      __  __                     

  

(4)

C

ARBONARBON

Carbon is transformed from carbon dioxide

into plant cell material through photosynthesis.

It is the basic structural material for all cell life,

and following the death and decomposition of

cells it provides humus and other organic

com-ponents th

ponents that enhance at enhance soil qualitysoil quality. . Plant nutPlant nutri-

ri-ents such as nitrogen and phosphorus are

ents such as nitrogen and phosphorus are chemi-

chemi-cally bound to

cally bound to carbon in orgacarbon in organic materials. nic materials. ForFor

these nutrients to become available for plant use,

soil organisms need to break down the

chemi-cal bonds in a process chemi-called

cal bonds in a process called mineralizationmineralization. . If If

the amount of carbon compared to other

nutri-ents is very high, more bonds will need to be

ents is very high, more bonds will need to be

broken and nutrien

broken and nutrient release will be slow. t release will be slow. If theIf the

amount of carbon compared to other nutrients

is low, fewer bonds will need to be broken and

nutrient release will proceed relatively rapidly.

Rapid nutrient release is preferred when

Rapid nutrient release is preferred when plantsplants

are growing and are able to use the nutrients

released.

released. Slower Slower nutrient nutrient release release is is preferredpreferred

when plants are not actively growing (as in the

fall or winter) or if the amount of nutrients in

the soil is already in excess of what plants can

use.

use. Pasture Pasture management management practices thpractices that favorat favor

effective carbon use and cycling include:

•

• MaiMaintantainiining a ng a divdiversiersity oty of fof foragrage ple plantants wis withth

a variety of leaf shapes and orientations (to

enhance photosynthesis) and a variety of

root growth habits (to enhance nutrient

up-take).

take). A diversity A diversity of forages of forages will provide will provide aa

balanced diet for grazing ani

balanced diet for grazing animals and a va-mals and a

va-riety of food sources for

riety of food sources for soil organismssoil organisms

•

• ProPromotmoting ing heahealthlthy rey regrogrowth wth of foof foragrages bes byy

including a combination of grasses with both

low and elevated growing points, and by

moving grazing animals frequently enough

to minimize the removal of growing points

•

• MaMainintatainiining a cong a complmplete cete coveover of for of foragrages anes andd

residues over all paddocks to hold soil

nu-trients against runoff and leaching losses and

trients against runoff and leaching losses and

ensure a continuous turnover of organic

resi-dues

dues

N

ITROGENITROGEN

Nitrogen is a central component of cell

pro-teins and

teins and is used fois used for seed productir seed production. on. It existsIt exists

in several chemical forms and various

microor-ganisms are involved in its transformations.

ganisms are involved in its transformations.

Le-gumes, in

gumes, in associatioassociation with n with specialized bacteriaspecialized bacteria

called rhizobia, are able to transform atmospheric

nitrogen in

nitrogen into a form avaito a form available for plant lable for plant use. use. Ni-

Ni-trogen in dead organic

trogen in dead organic materials becomes avail-materials becomes

avail-able to plants thro

able to plants through mineralizatiugh mineralization. on. NitrogenNitrogen

can be lost from the

can be lost from the pasture system through thepasture system through the

physical processes of leaching, runoff, and

ero-sion; the chemical process of volatilization; the

sion; the chemical process of volatilization; the

biologic

biological al process process of of denitrificadenitrification; tion; and and throughthrough

burning of plant residues.

burning of plant residues. Since it is Since it is needed inneeded in

high concentration for forage production and can

be lost throu

be lost through a number of gh a number of pathways, nipathways, nitrogentrogen

is often the limiting factor in forage and crop p

is often the limiting factor in forage and crop pro-

ro-duction.

duction. Productive pasProductive pasture managementure management prac-t

prac-tices enhance the fixation and conser

tices enhance the fixation and conservation of ni-vation of

ni-trogen while minimizing the potential for

trogen while minimizing the potential for

nitro-gen loss

gen losses. es. Practices thPractices that favor effectat favor effective nitro-ive

nitro-gen use and cycling in

gen use and cycling in pastures include:pastures include:

•

• MaMainintaitainining stng stablable or incre or increaseasining percg percenentagtageses

of legumes by

of legumes by not overgrazing pastures andnot overgrazing pastures and

by

by minimizing nitrogen minimizing nitrogen applications, espe-applications,

espe-cially in the spring

cially in the spring

•

• ProProtectectinting micg microbrobial cial commommuniunitieties invs involvolveded

in organic matter mineralization by

in organic matter mineralization by minimiz-

minimiz-ing practices that promote soil compaction

ing practices that promote soil compaction

and soil disturbance, such as grazing of wet

soils and tillage

•

• InIncorcorporporatiating mang manurnure and ne and nitritrogeogen fertn fertiliiliz-

z-ers into the soil, and never applying these

ers into the soil, and never applying these

ma-terials to saturated, snow-covered, or frozen

terials to saturated, snow-covered, or frozen

soils

•

• AvoAvoidiiding ng paspasturture be burnurnining. g. If If burburninning ig is rs re-

e-quired, it should be done very infrequently

quired, it should be done very infrequently

and by using a slow fire under controlled

con-ditions

ditions

•

• AppApplyilying fng fertertiliilizerzers ans and mand manure aure accoccordirdingng

to a comprehensive nutrient management

plan

P

HOSPHORUSHOSPHORUS

Phosphorus is used for energy

transforma-tions within cells and is essential for plant

tions within cells and is essential for plant

growth.

growth. It is often It is often the second-most-limiting min-the second-most-limiting

min-eral nutrient to plant production, not only

eral nutrient to plant production, not only

cause it is critical for plant growth, but also

be-cause chemical bonds on soil particles hold the

cause chemical bonds on soil particles hold the

majority of phosphorus in forms not available

for plant upt

for plant uptake. ake. PhosphoPhosphorus is also rus is also the majorthe major

nutrient needed to stimulate the growth of algae

in lakes

in lakes and streaand streams. ms. ConsequentlyConsequently, the in, the inad-

ad-vertent fertilization of these waterways with

vertent fertilization of these waterways with

run-off water from fields and

(5)

degradation of water quality for drinking, recre-ational, or wildlife habitat uses. Regulations on the use of phosphorus-containing materials are becoming more widespread as society becomes increasingly aware of the impacts agricultural practices can have on water quality. Pasture management practices must balance the need to ensure sufficient availability of phosphorus for plant growth with the need to minimize move-ment of phosphorus from fields to streams. Pas-ture management practices that protect this bal-ance include:

• Minimizing the potential for compaction while providing organic inputs to enhance activities of soil organisms and phosphorus mineralization

• Incorporating manure and phosphorus fer-tilizers into the soil and never applying these materials to saturated, snow-covered, or fro-zen soils

• Relying on soil tests, phosphorus index guidelines, and other nutrient management practices when applying fertilizers and ma-nure to pastures

S

OIL

L

IFE

Soil is a matrix of pore spaces filled with wa-ter and air, minerals, and organic matwa-ter. Al-though comprising only 1 to 6% of the soil, liv-ing and decomposed organisms are certainly of the essence. They provide plant nutrients, cre-ate soil structure, hold wcre-ater, and medicre-ate nutri-ent transformations. Soil organic matter is com-posed of three components: stable humus, readily decomposable materials, and living or-ganisms — also described as the very dead, the dead, and the living components of soil (1).

Living organisms in soil include larger fauna such as moles and prairie dogs, macroorganisms such as insects and earthworms, and microor-ganisms including fungi, bacteria, yeasts, algae, protozoa, and nematodes. These living organ-isms break down the readily decomposable plant and animal material into nutrients, which are then available for plant uptake. Organic matter residues from this decomposition process are subsequently broken down by other organisms until all that remains are complex compounds resistant to decomposition. These complex end products of decomposition are known as humus.

Humus, along with fungal threads, bacterial gels, and earthworm feces, forms glues that hold soil particles together in aggregates. These con-stitute soil structure, enhance soil porosity, and allow water, air, and nutrients to flow through the soil. These residues of soil organisms also en-hance the soil's nutrient and water holding ca-pacity. Lichens, algae, fungi, and bacteria form biological crusts over the soil surface. These crusts are important, especially in arid range-lands, for enhancing water infiltration and pro-viding nitrogen fixation (2). Maintaining a sub-stantial population of legumes in the pasture also ensures biological nitrogen fixation by bacteria associated with legume roots.

Effective nutrient cycling in the soil is highly dependent on an active and diverse community of soil organisms. Management practices that maintain the pasture soil as a habitat favorable for soil organisms include:

• Maintaining a diversity of forages, which promotes a diverse population of soil organ-isms by providing them with a varied diet • Adding organic matter, such as forage

resi-dues and manure, to the soil to provide food for soil organisms and facilitate the forma-tion of aggregates

• Preventing soil compaction and soil satura-tion, and avoiding the addition of amend-ments that might kill certain populations of soil organisms

Soil contains 1-6% organic matter. Organic matter contains 3-9% active microorganisms. These organisms include plant life, bacteria and actinomycetes, fungi, yeasts, algae, protozoa, and nematodes.

   

  

Soil Organic Matter Soil Microbial Biomass Soil Readily decomposable 7-21% Fauna 10% Fungi 50% Yeast, algae, protozoa, nematodes 10% Bacteria & Actinomycetes 30% Mineral

particles Stable Humus70-90%

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(6)

This publication is divided into five chapters:

1. Nutrient cycle components, interactions, and transformations 2. Nutrient availability in pastures

3. Nutrient distribution and movement in pastures 4. The soil food web and pasture soil quality

5. Pasture management and water quality

The first chapter provides an overview of nutrient cycles critical to plant production and water-quality protection: the water, carbon, nitrogen, phosphorus, and secondary-nutrient cycles. The components of each cycle are explained, with emphasis on how these components are affected by pasture management practices. The description of each cycle concludes with a summary of pasture management practices to enhance efficient cycling of that nutrient.

The second chapter focuses on the effects of soil chemistry, mineralogy, and land-management practices on nutrient cycle transformations and nutrient availability. Management impacts discussed include soil compaction, organic matter additions and losses, effects on soil pH, and consequences of the method and timing of nutrient additions. The chapter concludes with a summary of pasture management practices for enhancing nutrient availability in pastures.

The third chapter discusses nutrient balances in grazed pastures and the availability of manure, residue, and fertilizer nutrients to forage growth. Factors affecting nutrient availability include nutri-ent contnutri-ent and consistency of manure; manure distribution as affected by paddock location and layout; and forage diversity. These factors, in turn, affect grazing intensity and pasture regrowth. A graph at the end of the chapter illustrates the interactions among these factors.

The fourth chapter describes the diversity of organisms involved in decomposing plant residues and manure in pastures, and discusses the impact of soil biological activity on nutrient cycles and forage production. The impacts of pasture management on the activity of soil organisms are ex-plained. A soil health card developed for pastures provides a tool for qualitatively assessing the soil’s ability to support healthy populations of soil organisms.

The publication concludes with a discussion of pasture management practices and their effects on water quality, soil erosion, water runoff, and water infiltration. Several topical water concerns are discussed: phosphorus runoff and eutrophication, nutrient and pathogen transport through subsur-face drains, buffer management, and riparian grazing practices. A guide for assessing potential wa-ter-quality impacts from pasture-management practices concludes this final chapter.

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I

NFILTRATION AND WATER HOLDING CAPACITY

Water soaks into soils that have a plant or residue cover over the soil surface. This cover cushions the fall of raindrops and allows them to slowly soak into the soil. Roots create pores that increase the rate at which water can enter the soil. Long-lived perennial bunch-grass forms deep roots that facilitate water infiltration by con-ducting water into the soil (3). Other plant char-acteristics that enhance water infiltration are sig-nificant litter production and large basal cover-age (4). In northern climates where snow pro-vides a substantial portion of the annual water budget, maintaining taller grasses and shrubs that can trap and hold snow will enhance water infiltration.

The water, carbon, nitrogen, phosphorus, and sulfur cycles are the most important nutrient cycles operating in pasture systems. Each cycle has its complex set of interactions and transformations as well as interactions with the other cycles. The water cycle is essential for photosynthesis and the transport of nutrients to plant roots and through plant stems. It also facilitates nutrient loss through leaching, runoff, and erosion. The carbon cycle forms the basis for cell formation and soil quality. It begins with photosynthesis and includes respiration, mineralization, immobilization, and humus formation. Atmospheric nitrogen is fixed into plant-available nitrate by one type of bacteria, con-verted from ammonia to nitrate by another set of bacteria, and released back to the atmosphere by yet another group. A variety of soil organisms are involved in decomposition processes that release or mineralize nitrogen, phosphorus, sulfur, and other nutrients from plant residues and manure. Bal-ances in the amount of these nutrients within organic materials, along with temperature and mois-ture conditions, determine which organisms are involved in the decomposition process and the rate at which it proceeds.

Pasture management practices influence the interactions and transformations occurring within nutrient cycles. The efficiency of these cycles, in turn, influences the productivity of forage growth and the productivity of animals feeding on the forage. This chapter examines each of these cycles in detail and provides management guidelines for enhancing their efficiency.

 

  

  

 

Water is critical for pasture productivity. It dissolves soil nutrients and moves them to plant roots. Inside plants, water and the dissolved nu-trients support cell growth and photosynthesis. In the soil, water supports the growth and re-production of insects and microorganisms that decompose organic matter. Water also can de-grade pastures through runoff, erosion, and leaching, which cause nutrient loss and water pollution.

Pro-ductive pastures are able to absorb and use water ef-fectively for plant growth. Good pasture

manage-ment practices promote water absorption by maintaining forage cover over the entire soil sur-face and by minimizing soil compaction by ani-mals or equipment.

Geology, soil type, and landscape orientation affect water absorption by soils and water move-ment through soils. Sloping land encourages water runoff and erosion; depressions and footslopes are often wet since water from upslope collects in these areas. Clay soils absorb water and nutrients, but since clay particles are very

A forage cover over the entire paddock pro-motes water infiltration and minimizes soil compaction.

small, these soils can easily become compacted. Sandy soils are porous and allow water to enter easily, but do not hold water and nutrients against leaching. Organic matter in soil absorbs water and nutrients, reduces soil compaction, and increases soil porosity. A relatively small increase in the amount of organic matter in soil can cause a large increase in the ability of soils to use water effectively to support plant produc-tion.

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layer or high water table. Soils prone to satura-tion are usually located at the base of slopes, near waterways, or next to seeps.

Impact on crop production. Soil saturation affects plant production by exacerbating soil com-paction, limiting air movement to roots, and ponding water and soil-borne disease organisms around plant roots and stems. When soil pores are filled with water, roots and beneficial soil or-ganisms lose access to air, which is necessary for their healthy growth. Soil compaction decreases the ability of air, water, nutrients, and roots to move through soils even after soils have dried. Plants suffering from lack of air and nutrients are susceptible to disease attack since they are under stress, and wet conditions help disease or-ganisms move from contaminated soil particles and plant residues to formerly healthy plant roots and stems.

Runoff and erosion potential. Soil satura-tion enhances the potential for runoff and ero-sion by preventing entry of additional water into the soil profile. Instead, excess water will run off the soil surface, often carrying soil and nutri-ents with it. Water can also flow horizontally under the surface of the soil until it reaches the banks of streams or lakes. This subsurface wa-ter flow carries nutrients away from roots, where they could be used for plant growth, and into streams or lakes where they promote the growth of algae and eutrophication.

The W at er Cy cle. Rain falling on soil can either be absorbed into the soil or be lost as it flows over the soil surface. Absorbed rain is used for the growth of plants and soil organisms, to transport nutrients to plant roots, or to recharge ground water. It can also leach nutrients through the soil profile, out of the reach of plant roots. Water flowing off the soil surface can transport dissolved nutrients as runoff, or nutrients and other contaminants associated with sediments as erosion.

Soils with a high water holding capacity ab-sorb large amounts of water, minimizing the po-tential for runoff and erosion and storing water for use during droughts. Soils are able to absorb and hold water when they have a thick soil pro-file; contain a relatively high percentage of or-ganic matter; and do not have a rocky or com-pacted soil layer, such as a hardpan or plowpan, close to the soil surface. An active population of soil organisms enhances the formation of aggre-gates and of burrowing channels that provide pathways for water to flow into and through the soil. Management practices that enhance water infiltration and water holding capacity include: • a complete coverage of forages and residues

over the soil surface

• an accumulation of organic matter in and on the soil

• an active community of soil organisms in-volved in organic matter decomposition and aggregate formation

• water runoff and soil erosion prevention • protection against soil compaction

S

OIL SATURATION

Soils become saturated when the amount of wa-ter enwa-tering exceeds the rate of absorption or drainage. A rocky or compacted lower soil layer will not allow water to drain or pass through, while a high water table prevents water from draining through the profile. Water soaking into these soils is trapped or perched above the hard

Rainfall

   

Runoff & erosion Subsurface flow Leached nutrients    



_ Dissolvednutrients   Groundwater flows       Transpiration Infiltration   Dissolved nutrients Evaporation  Crop harvest  Water vapor Soil water  Plant uptake Photosynthesis to Soil Uptake by wells

(9)

Artificial drainage

Artificial drainage practices are often used practices are often used

on soils with a hardpan or a high water table to

decrease the duration of soil saturation

follow-ing rainfall

ing rainfalls or snowmelts or snowmelts. s. This practice can This practice can in-

in-crease water infiltration and dein-crease the

crease water infiltration and decrease the

poten-tial for water runoff

tial for water runoff(5)(5). . Unfortunately, moUnfortunately, most sub-st

sub-surface drains were installed before water

surface drains were installed before water

pollu-tion from agriculture became a concern and thus

tion from agriculture became a concern and thus

empty di

empty directly intrectly into drainago drainage ways. e ways. Nutrients,Nutrients,

pathogens, and other contaminants on the soil

surface can move through large cracks or

chan-nels in the soil to drainage pipes where they are

nels in the soil to drainage pipes where they are

carried to surface water bodies

carried to surface water bodies(6)(6)..

S

OIL COMPACTIONOIL COMPACTION

Soil compaction occurs when animals or

equipment move across soils that are wet or

satu-rated, with moist soils being more easily

rated, with moist soils being more easily

com-pacted than saturated soils

pacted than saturated soils(7)(7). Compaction can. Compaction can

also occur when animals or

also occur when animals or equipment continu-equipment

continu-ally move across a laneway or stand around

ally move across a laneway or stand around

wa-tering tanks and

tering tanks and headlands or under shade. headlands or under shade. Ani-

Ani-mals trampling over the ground press down on

mals trampling over the ground press down on

soils,

soils, squeezing soil squeezing soil pore spaces pore spaces together. together. Tram-

Tram-pling also increases the potential for

pling also increases the potential for compactioncompaction

by

by disturbing disturbing and and killing killing vegetation.vegetation.

Soils not covered by forages or residues are

easily compacted by the impact of raindrops.

When raindrops fall on bare soil, their force cau

When raindrops fall on bare soil, their force causesses

fine soil

fine soil particles to particles to splash or splash or disperse. disperse. TheseThese

splash particles land on the soil surface, clog

splash particles land on the soil surface, clog sur-

sur-face soil pores,

face soil pores,

and form a crust

over the soil.

Clayey soils are

more easily

com-pacted than sandy

pacted than sandy

soils because clay

particles are very

small and sticky.

C o m p a c t i o n

limits root growth

and the movement of air, water, and dissolved

nutrients through

nutrients through the the soil. soil. Compressing andCompressing and

clogging soil surface pores also decreases water

infiltration and increases the potential for runoff.

The formation of hardpans, plowpans, traffic

pans, or other compacted layers decreases

down-ward movement of water through the soil,

ward movement of water through the soil,

caus-ing rapid soil saturation and the

ing rapid soil saturation and the inability of soilsinability of soils

to absorb addi

to absorb additional water. tional water. Compaction in Compaction in pas-

pas-tures is remediated by root growth, aggregate

tures is remediated by root growth, aggregate

formation, and activities of bur

formation, and activities of burrowing soil organ-rowing soil

organ-isms.

isms. In colder climaIn colder climates, frost heates, frost heaving is an ving is an im-

im-portant recovery process for

portant recovery process for compacted soilscompacted soils(8)(8)..

R

UNOFF AND EROSIONUNOFF AND EROSION

Runoff water dissolves nutrients and removes

them from the pasture as it flows over the soil

surface.

surface. Soil erosion transSoil erosion transports nutrients and ports nutrients and anyany

contaminants, such as pesticides and pathogens,

attached to

attached to soil particlesoil particles. s. Because nutrienBecause nutrient-richt-rich

clay and organic matter particles are small and

lightweight, they are more readily picked up and

moved by water than the nutrient-poor, but

heavier, sand particles. Besides depleting

pas-tures of nutrients that could be used for forage

tures of nutrients that could be used for forage

production, runoff water and erosion carry

nu-trients and sediments that contaminate lakes,

trients and sediments that contaminate lakes,

streams, and rivers.

Landscape

condi-tions and

tions and

manage-ment practices that

ment practices that

favor runoff and

ero-sion include sloping

sion include sloping

areas, minimal soil

protection by forage or

protection by forage or residues, intense rainfall,residues, intense rainfall,

and

and saturated soils. saturated soils. While While pasture managerspasture managers

should strive to maintain a complete forage cover

over the soil surface, this is not feasible in

prac-tice because

tice because of of plant groplant growth habitwth habits and s and land-

land-scape chara

scape characteristics. cteristics. Plant resPlant residues from idues from die-

die- back

back and and animaanimal l wastawastage ge during during grazigrazing ng providprovidee

a critical source of soil cover

a critical source of soil cover and organic matter.and organic matter.

As mentioned above, forage type affects water

infiltration

infiltration and runoff. and runoff. Forages witForages with deep rootsh deep roots

enhance water infiltration while plants with a wide

vegetative coverage area or prostrate growth

pro-vide good protection against raindrop impact.

vide good protection against raindrop impact.

Sod grasses that are short-lived and

shallow-rooted inhibit water infiltration and encourage

rooted inhibit water infiltration and encourage

runoff.

runoff. Grazing Grazing practices thpractices that produce at produce clumpsclumps

of forages separated by bare ground enhance

run-off potential by producing pathways for water

off potential by producing pathways for water

flow.

Runoff water and

ero-sion carry nutrients

sion carry nutrients

and sediments that

contaminate lakes,

streams, and rivers.

E

VAPORATION AND TRANSPIRATIONVAPORATION AND TRANSPIRATION Water in the soil profile can be lost through

Water in the soil profile can be lost through

evaporation, which is favored by high

tempera-tures and ba

tures and bare soils. re soils. Pasture soilPasture soils with a s with a thickthick

cover of grass or

cover of grass or other vegetation lose little wa-other vegetation lose little

wa-ter to evaporation since the soil is shaded and

ter to evaporation since the soil is shaded and

soil tem

soil temperatures are peratures are decreased. decreased. While While evapo-

evapo-Animals trampling over

Animals trampling over

the ground press down

on soils, squeezing soil

pores together, which

limits root growth and

the movement of air,

water, and dissolved

nutrients.

(10)

ration affects only the top few inches of

ration affects only the top few inches of pasturepasture

soils, transpiration can drain water from the

soils, transpiration can drain water from the en-

en-tire soil pro

tire soil profile. file. Transpiration Transpiration is the loss is the loss of wa-of

wa-ter from plants through stomata in their leaves.

ter from plants through stomata in their leaves.

Especially on sunny and breezy days, significant

amounts of water can be absorbed from the

amounts of water can be absorbed from the soilsoil

by plant roots, taken

by plant roots, taken up through the plant, up through the plant, andand

lost to

lost to the atmosphere the atmosphere through transpiration. through transpiration. AA

diversity of forage plants will decrease

transpi-ration losses and increase water-use efficiency.

ration losses and increase water-use efficiency.

This is because forage species differ in their

abil-ity to extract water from the soil and conserve it

ity to extract water from the soil and conserve it

against transpiration

against transpiration (9)(9). . Some Some invasive invasive plantplant

species, however, can deplete water stores

through their high water use

through their high water use(4)(4). Water not used. Water not used

for immediate plant uptake is held within the soil

profile or is transported to groundwater reserves,

which supply wells with water and decrease the

impacts of drought.















If you answer

If you answer no to all no to all the questions, you have the questions, you have soils with high water-use efficiencysoils with high water-use efficiency. . IfIf

you answer yes to some of the questions, water cycle efficiency of your soil will likely

respond to

respond to improved pasture improved pasture management practices. management practices. SeeSee Table 2Table 2, next page., next page.

Water infiltration / Water runoff

1.

1. Do patDo patches ches of baof bare grore ground sund separateparate fore forage coage coveragverage?e?

2.

2. Are shaAre shallow-llow-rooted rooted sod grasod grasses tsses the predohe predominanminant forat forage covege cover?r?

3.

3. Can you seCan you see small we small waterwaterways durays during heaving heavy rainfay rainfalls or sulls or sudden snodden snowmeltwmelts?s?

4.

4. Are riAre rivulvulets aets and gulnd gullielies press present on tent on the lanhe land?d?

Soil saturation

5.

5. FollowFollowing a raining a rainfall, fall, is soil is soil muddy omuddy or are you ar are you able to sble to squeeze wqueeze waterater

out of a handful of soil?

6.

6. FollowFollowing a raining a rainfall or sfall or snowmenowmelt, doelt, does it taks it take severe several days bal days before tefore thehe

soil is no longer wet and muddy?

7.

7. Do fDo forages orages turn turn yelloyellow or w or die ddie during uring wet wet weathweather?er?

Soil compaction

8.

8. Do yoDo you grau graze anze animaimals on wls on wet paet pastusturesres??

9.

9. Are soAre some some soils iils in the n the pastpasture baure bare, hare, hard, ard, and crund crusty?sty?

10.

10.Do you have difficulty drivDo you have difficulty driving a post into (non-rocky) soils?ing a post into (non-rocky) soils?

Water retention /Water evaporation and transpiration

1

11.1. Do you have a monoculture of forages or are invasDo you have a monoculture of forages or are invasive species prominentive species prominent

components of the pasture?

12.

12.Do soils dry out Do soils dry out quickly following a quickly following a rainstorm?rainstorm?

13.

13.During a drought, During a drought, do plants dry do plants dry up quickly?up quickly?

_____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ _____________________ ________________________________________________________________________________________________________________________________ ___________ YES NO YES NO

(11)

Ensure forage and residue coverage across the entire pasture

•

• Use pUse practiractices tces that enhat encouracourage anige animal mmal movemeovement thrnt throughououghout the t the pastupasture and re and discodiscourage curage con-

on-gregation in feeding and lounging areas

gregation in feeding and lounging areas

•

• Use Use practpractices ices that that encouencourage rage regrowregrowth oth of fof forage rage plantplants and s and discodiscourage urage overgovergrazinrazingg

•

• Use a Use a varietvariety of y of forageforages wits with a divh a diversitersity of y of root sroot systeystems anms and growd growth chth charactaracteristeristicsics

Pasture management during wet weather

•

• Use wUse well-drell-drained pained pasturastures or es or a “saca “sacrificrificial paial pasturesture” that ” that is fais far from r from waterwaterways ways or wator water bodier bodieses

•

• AvAvoid doid drivriving ming machachineinery on pry on pastastureures thas that are wt are wet or set or satuaturatrateded

•

• AvAvoid oid sprspreadeading ing manmanure ure or or appapplyilying ng ferfertiltilizeizersrs

Artificial drainage practices

•

• AvoiAvoid grd grazing azing animaanimals ols on artn artificiificially ally drainedrained fid fields elds when when draindrains are s are flowiflowingng

•

• AvAvoid soid sprepreadiading mang manurnure or appe or applyilying ferng fertiltilizeizers whrs when draen drains arins are floe flowinwingg

•

• EnsurEnsure that e that drains drains emptempty inty into a fio a filter lter area oarea or wetr wetland rland rather ather than than directdirectly inly into a sto a stream tream oror

drainage way drainage way









 

 

  

  



Effective carbon cycling in pastures depends on a diversity of plants and healthy populations of

soil organisms.

soil organisms. Plants form Plants form carbon and carbon and water into water into carbohydracarbohydrates through tes through photosynthesis. photosynthesis. Plants arePlants are

most able to conduct photosynthesis when they can efficiently capture solar energy while also having

adequate access to wate

adequate access to water, nutrients, and air. r, nutrients, and air. Animals obtain caAnimals obtain carbohydrates formed by plrbohydrates formed by plants whenants when

they graze on pas

they graze on pastures or eat hay ortures or eat hay orgrains harvesgrains harvested from fields. ted from fields. Some of the carbon and enSome of the carbon and energy inergy in

plant carbohydrates is incorporated into animal cells. Some of the carbon

plant carbohydrates is incorporated into animal cells. Some of the carbon is lost to the is lost to the atmosphere asatmosphere as

carbon dioxide, and some energy is lost as heat,

carbon dioxide, and some energy is lost as heat, during digestion and as the animal grows and breathes.during digestion and as the animal grows and breathes.

Carbohydrates and other nutrients not used by animals are

re-turned to the so

turned to the soil in the form of urinil in the form of urine and manure. e and manure. These organiThese organicc

materials provide soil organisms

materials provide soil organisms with nutrients and with nutrients and energy. energy. As soilAs soil

organisms use and decompose organic materials, they release

nutri-ents from these

ents from these materials into the soil. materials into the soil. Plants then use Plants then use the released,the released,

inorganic form

inorganic forms of nutrients for ths of nutrients for their growth and reproeir growth and reproduction. duction. SoilSoil

organisms also use nutrients from organic materials to

organisms also use nutrients from organic materials to produce sub-produce

sub-stances that bind soil parti

stances that bind soil particles into aggregatescles into aggregates. . Residues of organic matter thaResidues of organic matter that resist further decom-t resist further

decom-position by soil organisms form

position by soil organisms formsoil humussoil humus. . This stable organThis stable organic material is critical for maintainic material is critical for maintaining soiling soil

tilth and enhancing the ability of soils to

tilth and enhancing the ability of soils to absorb and hold water absorb and hold water and nutrients.and nutrients.



  

Humus maintains soil

tilth and enhances water

and nutrient absorption.

C

ARBOHYDRATE FORMATIONARBOHYDRATE FORMATION

For productive growth, plants need to

effec-tively capture solar energy, absorb carbon

tively capture solar energy, absorb carbon

diox-ide, and take up water from the soil to produce

ide, and take up water from the soil to produce

carbohydrat

carbohydrates es through through photosynthesis. photosynthesis. In In pas-

pas-tures, a combination of broadleaf plants and

tures, a combination of broadleaf plants and

grasses allows for efficient capture of solar

en-ergy by a diversity of leaf shapes and leaf

ergy by a diversity of leaf shapes and leaf angles.angles.

Taller plants with more erect leaves capture light

even at the extreme angles of

even at the extreme angles of sunrise and sunset.sunrise and sunset.

Horizontal leaves capture the sun at midday or

when it is more

when it is more overhead.overhead.

Two methods for transforming carbon into

carbohydrates are represented in diversified

(12)

pas-tures. Broadleaf plants and cool-season grasses have a photosynthetic pathway that is efficient in the production of carbohydrates but is sensi-tive to dry conditions. Warm-season grasses have a pathway that is more effective in produc-ing carbohydrates durproduc-ing hot summer condi-tions. A combination of plants representing these two pathways ensures effective forage growth throughout the growing season. A diversity of root structures also promotes photosynthesis by giving plants access to water and nutrients throughout the soil profile.

O

RGANIC MATTER DECOMPOSITION Pasture soils gain organic matter from growth and die-back of pasture plants, from forage wast-age during grazing, and from manure deposition. In addition to the recycling of aboveground plant parts, every year 20 to 50% of plant root mass dies and is returned to the soil system. Some pasture management practices also involve the regular addition of manure

from grazing animals housed during the winter or from poul-try, hog, or other associated livestock facilities.

A healthy and diverse population of soil organisms is necessary for organic matter decomposition, nutrient

miner-alization, and the formation of soil aggregates. Species representing almost every type of soil organism have roles in the breakdown of manure, plant residues, and dead organisms. As they use these substances for food and energy sources,

they break down complex carbohydrates and pro-teins into simpler chemical forms. For example, soil organisms break down proteins into carbon dioxide, water, ammonium, phosphate, and sul-fate. Plants require nutrients to be in this sim-pler, decomposed form before they can use them for their growth.

To effectively decompose organic matter, soil organisms require access to air, water, and nu-trients. Soil compaction and saturation limit the growth of beneficial organisms and promote the growth of anaerobic organisms, which are inef-ficient in the decomposition of organic matter. These organisms also transform some nutrients into forms that are less available or unavailable to plants. Nutrient availability and nutrient bal-ances in the soil solution also affect the growth and diversity of soil organisms. To decompose organic matter that contains a high amount of carbon and insufficient amounts of other nutri-ents, soil organisms must mix soil- solution nu-trients with this material to achieve a balanced diet.

Balances between the amount of carbon and nitro-gen (C:N ratio) and the amount of carbon and sulfur (C:S ratio) determine whether soil organisms will release or immobilize nutri-ents when they decompose organic matter. Im-mobilizationrefers to soil microorganisms taking nutrients from the soil solution to use in the de-composition process of nutrient-poor materials. Since these nutrients are within the bodies of soil

   

Loss via erosion  Decomposition in microbes Humus and aggregate formulation  _     Photosynthesis



CO₂ in atmosphere Mineralization   Consumption   Respiration



Carbon in soil organic matter



Crop and animal residues  

The Carbon Cy cle begins with plants taking up carbon dioxide from the atmosphere in the process of photosynthesis. Some plants are eaten by grazing animals, which return organic carbon to the soil as manure, and carbon dioxide to the atmosphere. Easily broken-down forms of carbon in manure and plant cells are released as carbon dioxide when decomposing soil organisms respire. Forms of carbon that are difficult to break down become stabilized in the soil as humus.

A healthy and diverse popu-lation of soil organisms is necessary for organic matter decomposition, nutrient min-eralization, and the formation of soil aggregates.