two to four fertilizer prills). Thirty-two PVC tubes, each with one of the fertilizers identified above, were randomly established, plus 32 tubes with no added fertilizer. The tubes were covered with loose-fitting aluminum caps to prevent rainfall-induced N leach- ing from the soil within the tubes. The closed-top, solid cylinder is a recommended method for estimating in situ net N mineraliza- tion (Hart et al., 1994; Robertson et al., 1999). We adopted this method because measurement of the net release of NO 3 + NO 2 and NH 4 from soil organic matter (i.e., net N mineralization) is analogous to measuring the net release of NO 3 + NO 2 and NH 4 from fertilizer prills. At eight times (at approximate 10-d intervals) throughout the growth season, four replicate tubes of each fertil- izer treatment + four check tubes were removed from the field. After the tubes were collected from the field, any identifiable fertil- izer prills within the tubes were removed. The tubes were then placed in plastic bags, returned to the laboratory, and frozen until NO 3 and NH 4 analyses could be performed. Nitrate and NH 4 analyses were performed by thawing the soil in the tubes, sieving the soil (0.5-cm mesh), and extracting 100 g of soil with 0.4 L of 2 mol L –1 KCl by shaking for 1 h. The KCl extracts were filtered and
cropping has long since been replaced by growing multiple crops in rotation, where the crop species from season to season—typically in a 2- to 4-year rotation cycle. Evidence from temperate studies suggests that breaking continuous monoculture systems can produce ecosystem services benefits such as i) improving crop yields by ca. 14% in cereal experiments (Kirkegaard et al. 2008); ii) positively influencing disease pressure by breaking the life cycle of crop-specific pathogens with less susceptible plants—taking advantage of the natural mortality and antagonistic effects in root- zone microorganisms (Ghorbani et al. 2008); iii) improving yield stability (Berzsenyi et al. 2000); iv) enhancing below-ground community structure and activity (Tiemann et al. 2015); and v) increasing crop nutrient use efficiency (Tilman et al. 2002). Growing crops in rotation also has a strong effect on crop residue decomposition dynamics. Indeed, breaking continuous monoculture patterns has been linked with microbial change in below-ground communities; e.g., different above-ground crop residues may change the composition of below-ground microbial communities by suppling a range of plant input quality, quantity and chemical complexity of decomposable material—positively impacting biodiversity-function relationships and soil aggregation (Tiemann et al. 2015). Under conditions with abundant labile organic matter resources and microbial biomass, crop residue decomposition—even low-quality residue inputs—can be enhanced, which is beneficial for soil nutrient cycling and may result in soil organic matter accrual over time via soil C and N stabilization (McDaniel et al. 2016).
Daily nitrousoxide flux rates can be highly variable under rainfed conditions due to continuously changing soil moisture and temperature conditions. Nitrousoxideemissions are largely controlled by soil water filled pore space (WFPS) (Smith et al., 2003), as it influences many soil microbial processes including nitrification and denitrification (Bateman and Baggs, 2005). Rainfall or irrigation after a dry period generally causes a pulse of N2O emission (Davidson, 1992; Aguilera et al., 2013) because the wetting and drying stimulates activity of nitrifying and denitrifying soil microbial communities (Mikha et al., 2005; Hu et al., 2015). In irrigated corn systems in Colorado where WFPS is more consistent, Halvorson et al. (2010a; b, 2014) showed that EENFs generally decreased N2O emissions. In contrast, it is possible that the EENFs were inconsistent in our rainfed study because of repeated soil wetting and drying events causing microbial stimulation and peak N2O emission events, which may have overridden any potential effects of EENFs on suppressing N2O emissions caused by microbial activity occurring during non-peak emission events. Moreover, the unseasonably high rainfall in May through July in 2015 may have hindered the effectiveness of EENFs in this season, and it is worth
managed with carefull apporoach. The mineral and organic fertilizers can overcome the disadvantages of applying single source of fertilizers however; well-managed combination has to be applied. These kinds of well-managed practices allows then sustainably achieve higher crop yields through the improvement of soil fertility, alleviation of soil acidification, and increase in nutrient efficiency usage in comparison with utilisation of chemical fertilizers only. In addition it can be pointed out that the temporal diversity using crop rotation strategies can result in increased crop yield in comparison with continuous cropping. Moreover,
Similar to DM yield, the total N offtake by the grass increased linearly with N fertiliser rate (see NUE results below and Table 4) between 0 to 400 kg N of AN application at rates of 0.58, 0.47, 0.68, 0.75, 0.68 kg N offtake per additional kg of N applied (R 2 =0.99 for all except Hillsborough with R 2 =0.98) for Crichton, Drayton, North Wyke, Hillsborough and Pwllpeiran respectively (resulting average is 0.63 kg N offtake per additional kg of N applied). When no N was applied, N offtake by the grass ranged between 50 and 89 kg N ha -1 (at Crichton and North Wyke, respectively), whereas for the AN400 treatment the offtake varied from 241 kg N ha -1 (Drayton) to 363 kg N ha -1 (Hillsborough). At the 320 kg N ha -1 rate, adding DCD, applying N in 6 splits or replacing AN by U (with or without DCD) caused a change in yield of less than 10% and the effect on N offtake was variable. Split application increased N offtake at Crichton, but not at the other sites. Urea application decreased N offtake compared to AN at Crichton, North Wyke and Pwllpeiran, but not at Drayton and Hillsborough. However, using DCD did not reduce N offtake with either AN or U fertilizers.
Previously, in Chapter 6, the complete incorporation of litter species dominant in New Zealand pastures was investigated. The N 2 O emissions increased with lower C: N ratios and
labile biochemical components. However, the experiment was performed under controlled conditions and the litter was ground and thoroughly incorporated into soil. Litter, in field conditions is not incorporated to this extent and certainly not ground. Also, temperature and soil water contents fluctuate under field conditions. Studies investigating pasture litter decomposition in pastoral conditions are also scarce (Kuzyakov et al. 1999; Vinten et al. 2002). Brunetto et al. (2011) investigated the fate of common New Zealand pasture species (clover, Trifolium repens L. and ryegrass, Lolium perenne L.) by placing litterbags on the soil surface, and used a 15 N technique to show that the grasses decomposed relatively rapidly, however, N 2 O emissions were not measured in their study and this study was performed in
Rice (Oryza sativa L.) is a common crop grown in Arkansas under flooded-soil
conditions. The saturated to nearly saturated soil makes rice production an ideal environment for the production of potent greenhouse gases, such as nitrousoxide (N 2 O). The objectives of this study were to i) evaluate the impact of water management practice (full-season-flood and intermittent-flood) and cultivar (pure-line and hybrid) on N 2 O fluxes, season-long N 2 O emissions, and global warming potential (GWP; 2016) and ii) evaluate the impact of tillage practice [conventional tillage and no-tillage (NT)] and type of urea fertilizer [ N-(n-butyl) thiosphosphoric triamide (NBPT)-coated and non-coated urea] on N 2 O fluxes, season-long N 2 O emissions and GWP (2017). For both objectives, rice was grown in a direct-seeded, delayed- flood production system. Gas samples were collected from enclosed chambers at 20-min intervals for 1 hr approximately weekly between flood establishment and 4 to 7 days after end- of-season flood release. In 2016, both N 2 O fluxes and season-long N 2 O emissions were unaffected (P > 0.1) by water management or cultivar. However, season-long N 2 O emissions ranged from 0.38 to 0.84 kg N 2 O-N ha -1 season -1 from the full-season-flood/hybrid and
DCD is used as a nitrification inhibitor because it can be broken down by microbes into C and N and thus does not prolong in the environment. However, in soils where microbial activity is high, DCD can be degraded too quickly for it to work effectively. In the tropics, high soil temperatures increase microbial activity which reduces DCD’s half-life, meaning that DCD has to be used in high concentrations (Puttanna et al. 1999a). Amberger (1989) found that at 12˚C DCD decomposed completely by 12 weeks, in contrast at 4˚C concentrations were still relatively high at 17 weeks. Puttanna et al. (1999a) found that DCD had less inhibition effect at 30˚C compared to other nitrification inhibitors. Di and Cameron (2004) found in their incubation trial that the half-life of DCD increased 5-fold when the temperature increased from 8⁰C to 20⁰C. From this, they concluded that applying DCD during later autumn-winter- early spring period in New Zealand when the soil temperature is less than 10⁰C would extend the time period DCD remained effective in the soil.
Further intensification of dairy production runs counter to our finding that, by sourcing calves from the dairy industry, emissions from beef production can be greatly decreased, while maintaining current production. This would require breeding dual-purpose cattle for the dairy herd producing less milk. While there are no breeds that currently match the productivity of pure Holsteins (Hanks and Kossaibati, 2013) which, with related Frisians, comprise ~90% of UK dairy cows, high-yielding animals produce large quantities of milk due, in part, to high-energy diets (McDonald et al., 2011). Fuller (2001) argued that when crossed with native breeds, Freisians were long-lived and highly fertile and did well on low-cost feeding regimes, producing well-conformed beef offspring. Crossbred cows have more than a year's advantage in longevity and 30% greater lifetime productivity compared with purebred animals (Hocking et al., 1988).
would aid in the reduction of these emissions and mitigate their negative effects on the atmosphere, climate and other elements of the ecosystem. This is of particular impor- tance in rural and urban-rural communes, but should also be considered in municipalities, where a significant share of the land is agricultural land or is home to a high degree of biological activity. When formulating an action plan, it is necessary to pay particular attention to exploring the potential of agricultural and rural areas (including agricul- tural soils) in order to reduce GHG emissions. For example, Syp et al. (2015), when assessing the impact of manage- ment practices on gas emissions and N losses calculated using the DNDC model, state that the N losses and GHG emissions could be minimized by controlling N application through the implementation of a nutrient management plan in which N doses are defined based on the crop needs and soil quality. However, as emphasized by Bennetzen et al. (2016), agricultural GHG emissions can only be reduced to a certain level and a simultaneous focus on other parts of the food-system is necessary in order to increase food security whilst reducing emissions.
However, other recent research found significant and longer lasting BNI effects from plantain growing in the soil (Carlton 2017; Luo et al. 2018), which may provide a continual source of aucubin, via root exudation. These studies did not determine the mechanism behind this reduction, but it likely could be due to the inhibitory effects of aucubin on nitrification. While this effect was not observed in our research (Chapter 4, Objective 2), plantain root exudation of aucubin, the derivatives of aucubin (namely aucubigenin), or other BNI chemicals, is key topic for future research, as this would provide a continual source of active BNI chemicals in soils, rather than a single application in urine. Furthermore, it is possible that the combined effects of urinary aucubin excretion and continual plantain pasture aucubin root exudation could increase the degree of nitrification
The diet of African ruminants tends to be based on grasses and crop residues that are more fibrous than their counterparts from temperate regions, with lower digestibility and protein content (Schlecht et al., 2006). Dietary protein content, feed digestibility, and sugar content are known to influence the amounts and types of N and C voided in cattle excreta (Dijkstra et al., 2011; Merry et al., 2006; Rotz, 2004). Therefore, the lower-quality feeds likely result in excreta with reduced N concentrations and higher C/N ratios. To compensate for the low-protein diet, many agencies across eastern Africa promote the use of the legume fodder tree calliandra (Calliandra calothyrsus Meissner) as a feed supplement (Dawson et al., 2014). However, calliandra has high condensed tannin concentrations that cause higher recalcitrant N concen- trations in cattle excreta (Delve et al., 2001). The increased C/N ratio and higher concentrations of recalcitrant N could result in lower N 2 O emissions from the feces (Chantigny et al., 2013)
A large quantity of the existing models have emphasized on long-term analysis, ne- glecting the smaller scales of variability of soil moisture, temperature, nitrogen content or plant uptake. However, a fraction of soil moisture and nitrate variance is at scales of a few days or weeks (Dodorico et al., 2003). Given the highly non-linear properties of the carbon and nitrogen dynamics, the common use of average monthly climatic conditions neglects the effects of high-frequency fluctuations, leading to estimates of SOM stocks and fluxes different from what is found with analysis at higher resolution (e.g., Moorhead et al.; Bolker et al., 1998). These results indicates the need for an accurate study of the soil nutrient cycle at shorter time scales (e.g., Porporato et al., 2003). Studies in the lit- erature (e.g., Aber and Driscoll, 1997; Gusman and Marino, 1999; Birkinshaw and Ewen, 2000; Butterbach-Bahl et al., 2000) have investigated the effect of climate and hydrologic conditions on nutrient and carbon budgets. Moorhead et al. highlights how models that with capacity to operate at high resolutions are needed to provide an adequate repre- sentation of the coupling between soil moisture and nutrient dynamics. To this end, a daily version of the CENTURY model (Parton and Rasmussen, 1994), named DAYCENT (Parton et al., 1998) was developed. In this model, soil moisture dynamics are calculated dividing the soil into a number of layers and performing a soil water balance for each of them. The fluxes are modeled through a simplified and discretized version of Richards’ equation. The objective of this chapter is include the oxygen dynamics in a simplified decomposition-nitro-denitro model, which account for effect of water dynamics on nitrousoxideemissions. To the knowledge of the authors, this approach has not been done before.
For many years it has been hypothesized that plants release compounds from their root systems that are capable of inhibiting the nitrification process. A bioassay experiment with exudates from a tropical pasture grass Brachiaria humidicola showed a strong inhibitory effect on Nitrosomonas europaea (a nitrifying bacteria) function and were shown to inhibit nitrification in air-dried and then rewetted soil. Results showed that the release of biological nitrification inhibition (BNI) compounds had no negative effect on soil microbial populations or plant growth promoting microorganisms, though effectiveness of BNI varied with soil type (Gopalakrishnan et al., 2009). Sorghum (Sorghum bicolor) has been shown to have significant BNI capacity, the active constituent was identified as methyl 3-(4-hydroxyphenyl) propionate. BNI compound release from roots is a physiologically active process, stimulated by the presence of ammonium. This may be a useful tool for decreasing the emission of nitrogenous greenhouse gases such as N 2 O from soil and reducing off-farm impacts
minimal disruption to existing practices. In New Zealand, fluxes, over and above the amounts of C applied, with legislation prevents the direct discharge of DFE to sur- the release of native soil C indicative of a priming effect face waters and current farming practice consists of ap- (Clough et al., 2003). The interaction of DFE and urine plying the DFE to pasture soils. Dairy farm effluent is patches, with respect to N
Gas samples were collected twice a week between 9:00 a.m. and 11:00 a.m. within an 18-min-period. Duplicate gas sample was taken from each treat- ment at 0, 6, 12 and 18 min with a 100 ml syringe, respectively. The ambient air pressure, air temper- ature, water depth in the ﬁeld and 5 cm subsoil temperature were concurrently measured. Daily temperature and rainfall were also recorded during the entire rice growth to probe into the seasonal variations of greenhouse gas emissions. The gas samples were analyzed by gas chromatography (GC, HP-5890II, The Hewlett-Packard Company, Palo Alto, California, USA) with separate electron capture and ﬂame ionization detectors (ECD at 330°C and FID at 200°C) for N 2 O and CH 4 measurement, respectively. The detection limits of ECD-GC and FID-GC were 0.08 pg C/s and 5 pg C/s, respectively.
Greenhouse gas fluxes were generally monitored two to three days per week during the 2010 growing season in each N treatment. Gas samples were collected from two sampling sites within each N treatment replicate for a total of six gas samples for each treatment on each sampling day. A vented chamber technique was used to collect the gases in the field and a gas chromatograph used to analyze gas concentration as described by Mosier et al. (2006). A randomized complete block ANOVA was used to determine differences in N 2 O emissions and
The research aimed at the assessment of N 2 O emission from agricultural soils subject to different fertilization conditions. It was carried out on a long-term experiment field in Skierniewice in Central Poland maintained with no alterations since 1923 under rye monoculture. The treatments included mineral (CaNPK), mineral-organic (CaNPK + M) and organic (Ca + M) fertilization. Measurements were conducted during the growing periods of 2012 and 2013. N 2 O emissions from the soil were measured in situ by the means of infrared spectroscopy using a portable FTIR spectrometer Alpha. N 2 O fluxes over the measurement periods showed high variability with range 0.13–11.20 g N 2 O-N/ha/day (median 2.87, mean 3.16) from mineral treated soil, 0.23–11.06 g N 2 O-N/ha/day (me- dian 3.64, mean 3.33) from mineral-organic treated soil and 0.25–12.28 g N 2 O-N/ha/day (median 3.14, mean 3.55) from organic treated soil. N 2 O fluxes from manure-treated soils were slightly higher than those from soils treated exclusively with mineral fertilizers. N 2 O fluxes were positively correlated with soil temperature, air temperature, and content of both, NO 3 – and NH 4 + , in the soil (0–25 cm) and, to a lesser degree, negatively correlated with soil moisture. Based on the measured N 2 O flux and its relationship with environmental factors it can be concluded that both, nitrification and denitrification the are important sources of N 2 O in mineral soils of Central Poland, where the average soil water-filled pore space during the growing period range from 22–35%. Under the climate, soil and fertilization conditions in Central Poland, the N 2 O emission from cultivated soils during the growing period is ap- proximately estimated as 0.64–0.73 kg N/ha.
Kingdom) using a syringe fitted with a 3-way stop cock. Gas samples were analyzed with an automated gas chromatograph equipped with an electron capture detector (SRI 8610c GC, SRI Instruments, Torrance, California, USA), as previously described (Clough et al. 1996). The detection limit of the gas chromatograph was 0.01 µL L-1 and the furnace temperature was 310°C. Nitrousoxide concentrations were converted to mass per volume concentration using the ideal gas law and air temperature at the time of sampling. Flux calculations used the change in N 2 O