Stuart Lindsey

Nitrous oxide emissions from application of urea on New Zealand pasture

Abstract The use of nitrogen (N) fertiliser has been identified as a possible important source of nitrous oxide (N2O) from pastoral soils, and urea is the main form of N fertiliser used in New Zealand. The aim of this study was to examine the effects of urea application on N2O emissions from pastoral soil. A closed soil chamber technique was used to measure the N2O emissions from a pasture which received either 0 (control) or 50 kg N ha–1 (as urea) per application during different seasons between 2003 and 2005. Overall, urea fertiliser application generally increased N2O fluxes above control levels for up to 30 days, but the duration for which N2O levels were elevated depended on the season. These increases in the N2O fluxes were largely caused by a combination of changes in the soil mineral N level due to urea application, and moisture content of soil in different seasons. Nitrous oxide emissions were higher during the winter and spring measurement periods when the soil water‐filled pore space (WFPS) was mostly above field capacity, and the emissions were lower during the summer and autumn measurement periods when the soil WFPS was below field capacity. The estimated N2O emission factors for urea ranged between 0 and 1.56% of the urea‐N applied, with a calculated average emission factor of 0.56%. The findings of the seasonal measurements suggests that a reduction in the use of N fertilizers under wet winter or wet spring conditions in New Zealand could potentially reduce N2O emissions from pastoral soil.

Effects of irrigating dairy-grazed grassland with farm dairy effluent on nitrous oxide emissions

While irrigation of farm dairy effluent (FDE) to land is becoming popular in New Zealand, it can lead to increased emissions of the greenhouse gas nitrous oxide (N2O). This paper reports the results from trials on N2O emissions from irrigation of FDE to two dairy-grazed pastures on two poorly drained silt-loam soils located at Waikato and Manawatu, New Zealand. These pasture soils were periodically irrigated with FDE under contrasting soil moisture conditions with water-filled pore-space (WFPS) ranging between 26% and 94%. Nitrous oxide emissions were measured from the FDE irrigated and unirrigated sites using large numbers of static chambers (12–20). Irrigation of FDE generally increased N2O emissions compared to the control. N2O emissions varied with changes in climatic conditions and soil WFPS. Overall N2O emissions from effluent-derived N ranged between 0.01% and 4.93% depending on irrigation time and soil WFPS. Lower N2O emissions from FDE were attributable to very low soil WFPS conditions during the dry seasons. Higher N2O emissions were measured from application of FDE to a recently grazed pasture on wet soil. Our results suggest strategic application of FDE during dry summer and autumn seasons can reduce N2O emissions from application of FDE. Delaying effluent-irrigation after grazing events could further reduce N2O emissions by reducing the levels of surplus mineral-N.

Effect of rate and form of dicyandiamide application on nitrate leaching and pasture production from a volcanic ash soil in the Waikato

Abstract Animal urine has been identified as the main source of nitrate leaching from grazed pastures. The nitrification inhibitor dicyandiamide (DCD) can potentially reduce nitrate leaching losses and increase pasture utilisation of nitrogen (N) from urine. A mowing trial was established on a sandy loam (Typic Orthic Allophanic) soil in the Waikato region to examine the effect of liquid and granular forms of DCD, applied in May at rates of 0, 7, 14 and 28 kg ha‐1, on the fate of urea applied at 600 kg N ha‐1 in artificial urine. The DCD treatments increased pasture production over 211 days by an average of 15% (P < 0.001) and there was no significant effect of rate or form of DCD. Soil sampling 76 days after treatment application showed greater amounts of ammonium remaining in the top 450 mm of soil in the DCD treatments (average ammonium‐N for all DCD treatments of 93 kg N ha‐1 compared with 43 kg N ha‐1 for the urine‐only treatment). Total inorganic N in the top 600 mm of soil at the final (118 day) sampling showed a linear response to DCD application rate (113–190 kg ha‐1 from lowest to highest rate; P < 0.05) and the liquid DCD tended to retain more inorganic‐N than the granular DCD (179 and 131 kg ha‐1, respectively; P < 0.1). Averaged across all DCD treatments, 37% of the applied DCD was measured in the top 450 mm of soil at the day 48 sampling and most of that DCD was found below 150 mm. Leaching of N was measured using ceramic cup samplers at 600 mm depth in the 14 kg DCD ha‐1 treatments and showed that DCD reduced nitrate leaching by 24% from 275 to 208 kg ha‐1 (P < 0.01), with no significant effect of DCD form. Thus, DCD in both liquid and granular forms proved effective in reducing nitrate leaching from urine, indicating its potential for N loss mitigation in grazed pastures.

Effects of the nitrification inhibitor dicyandiamide (DCD) on pasture production, nitrous oxide emissions and nitrate leaching in Waikato, New Zealand

Mowing and grazing studies over 3 years were used to examine the effects of application of the nitrification inhibitor dicyandiamide (DCD) on pasture production, soil nitrogen (N) transformations, nitrous oxide (N2O) emissions and nitrate leaching from dairy pastures in the Waikato region (northern North Island) of New Zealand. In all cases, DCD inhibited nitrification and reduced the amount of nitrate production. Emissions of N2O from pastoral soil receiving cow urine in autumn were reduced by 18%–71% due to DCD application. Lysimeter studies showed a decrease in nitrate leaching from urine due to DCD by up to 74%, but it was dependent on timing and frequency of DCD application. DCD applications between April and June were most effective for reducing nitrate leaching, but timing of applications needs to account for the temperature profile effects on DCD longevity in soil and three applications may be necessary to achieve greatest benefits. In the mowing trial in one year there was a 4% (P < 0.05) increase in pasture growth during the winter/spring period. Otherwise, there was no significant effect of DCD applications (two to five applications per year) on seasonal or annual pasture production. This study indicates that DCD can provide valuable reductions in N emissions to the environment, making it an effective N mitigation option for use on dairy farms in northern North Island regions.

Nitrous oxide emission factors for urine and dung from sheep fed either fresh forage rape ( Brassica napus L.) or fresh perennial ryegrass ( Lolium perenne L.)

In New Zealand, agriculture is predominantly based on pastoral grazing systems and animal excreta deposited on soil during grazing have been identified as a major source of nitrous oxide (N2O) emissions. Forage brassicas (Brassica spp.) have been increasingly used to improve lamb performance. Compared with conventional forage perennial ryegrass (Lolium perenne L.), a common forage in New Zealand, forage brassicas have faster growth rates, higher dry matter production and higher nutritive value. The aim of this study was to determine the partitioning of dietary nitrogen (N) between urine and dung in the excreta from sheep fed forage brassica rape (B. napus subsp. oleifera L.) or ryegrass, and then to measure N2O emissions when the excreta from the two different feed sources were applied to a pasture soil. A sheep metabolism study was conducted to determine urine and dung-N outputs from sheep fed forage rape or ryegrass, and N partitioning between urine and dung. Urine and dung were collected and then used in a field plot experiment for measuring N2O emissions. The experimental site contained a perennial ryegrass/white clover pasture on a poorly drained silt-loam soil. The treatments included urine from sheep fed forage rape or ryegrass, dung from sheep fed forage rape or ryegrass, and a control without dung or urine applied. N2O emission measurements were carried out using a static chamber technique. For each excreta type, the total N2O emissions and emission factor (EF3; N2O-N emitted during the 3- or 8-month measurement period as a per cent of animal urine or dung-N applied, respectively) were calculated. Our results indicate that, in terms of per unit of N intake, a similar amount of N was excreted in urine from sheep fed either forage rape or ryegrass, but less dung N was excreted from sheep fed forage rape than ryegrass. The EF3 for urine from sheep fed forage rape was lower compared with urine from sheep fed ryegrass. This may have been because of plant secondary metabolites, such as glucosinolates in forage rape and their degradation products, are transferred to urine and affect soil N transformation processes. However, the difference in the EF3 for dung from sheep fed ryegrass and forage rape was not significant.

Optimizing the nitrogen application rate for maize and wheat based on yield and environment on the Northern China Plain

Optimizing the nitrogen (N) application rate can increase crop yield while reducing the environmental risks. However, the optimal N rates vary substantially when different targets such as maximum yield or maximum economic benefit are considered. Taking the wheat-maize rotation cropping system on the North China Plain as a case study, we quantified the variation of N application rates when targeting constraints on yield, economic performance, N uptake and N utilization, by conducting field experiments between 2011 and 2013. Results showed that the optimal N application rate was highest when targeting N uptake (240kgha-1 for maize, and 326kgha-1 for wheat), followed by crop yield (208kgha-1 for maize, and 277kgha-1 for wheat) and economic income (191kgha-1 for maize, and 253kgha-1 for wheat). If environmental costs were considered, the optimal N application rates were further reduced by 20-30% compared to those when targeting maximum economic income. However, the optimal N rate, with environmental cost included, may result in soil nutrient mining under maize, and an extra input of 43kgNha-1 was needed to make the soil N balanced and maintain soil fertility in the long term. To obtain a win-win situation for both yield and environment, the optimal N rate should be controlled at 179kgha-1 for maize, which could achieve above 99.5% of maximum yield and have a favorable N balance, and at 202kgha-1 for wheat to achieve 97.4% of maximum yield, which was about 20kgNha-1 higher than that when N surplus was nil. Although these optimal N rates vary on spatial and temporal scales, they are still effective for the North China Plain where 32% of Chinas total maize and 45% of Chinas total wheat are produced. More experiments are still needed to determine the optimal N application rates in other regions. Use of these different optimal N rates would contribute to improving the sustainability of agricultural development in China.

Nitrogen gaseous emissions from farm effluent application to pastures and mitigation measures to reduce the emissions: a review

Potential losses of nitrogen (N) from land application of effluents include ammonia (NH3) and nitrous oxide (N2O) emissions. In this review paper, the extent of the NH3 and N2O losses resulting from application of effluents to pastoral soils is assessed. Nitrogen losses, as NH3 and N2O, from applied effluent to pastoral soil ranged from 1%–66% and <0.1%–6% of the applied N, respectively. The potential mitigation methods include: reducing livestock numbers; lowering N content of the effluent; using N process inhibitors; optimising timing of effluent application; and applying effluent at rates that match plant uptake. It is important to remember that some of these options can result in ‘pollution swapping’ and some of them are in the early stages of development. Future research needs to focus on the overall impact of mitigation options on the whole suite of gaseous emissions and the practicality of those options.

Using alternative forage species to reduce emissions of the greenhouse gas nitrous oxide from cattle urine deposited onto soil

Grazed pastures are a major contributor to emissions of the greenhouse gas nitrous oxide (N2O), and urine deposition from grazing animals is the main source of the emissions. Incorporating alternative forages into grazing systems could be an approach for reducing N2O emissions through mechanisms such as release of biological nitrification inhibitors from roots and increased root depth. Field plot and lysimeter (intact soil column) trials were conducted in a free draining Horotiu silt loam soil to test whether two alternative forage species, plantain (Plantago lanceolate L.) and lucerne (Medicago sativa L.), could reduce N2O emissions relative to traditional pasture species, white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). The amounts of N2O emitted from the soil below each forage species, which all received the same cow urine at the same rates, was measured using an established static chamber method. Total N2O emissions from the plantain, lucerne and perennial ryegrass controls (without urine application) were generally very low, but emissions from the white clover control were significantly higher. When urine was applied in autumn or winter N2O emissions from plantain were lower compared with those from perennial ryegrass or white clover, but this difference was not found when urine was applied in summer. Lucerne had lower emissions in winter but not in other seasons. Incorporation of plantain into grazed pasture could be an approach to reduce N2O emissions. However, further work is required to understand the mechanisms for the reduced emissions and the effects of environmental conditions in different seasons.

Dung and farm dairy effluent affect urine patch nitrous oxide emissions from a pasture

Urine patches in grazed pastures have been identified as important sources of nitrous oxide (N2O) emissions. An increase in N2O emissions is possible where urine patches coincide with dung patches and farm dairy effluent (FDE) applications. The aim of the present study was to quantify the effects of dung additions and fresh FDE applications on N2O emissions from urine patches. A field experiment was conducted on a pasture site at the AgResearch’s Ruakura dairy farm in Hamilton, New Zealand. A closed soil chamber technique was used to measure the N2O emissions from a free-draining volcanic soil that received urine (492 kg N/ha, simulated urine patches), with or without dung (1146 kg N/ha) and fresh FDE (100 kg N/ha) and to compare these with controls receiving no urine. The addition of dung delayed the peak N2O fluxes from the urine patches by ~30 days. This could be due to temporary nitrogen (N) immobilisation during decomposition of carbon from the dung. However, over the whole measurement period (271 days), dung addition increased the N2O emission factor (EF, % of applied N emitted as N2O) for the urine from 1.02% to 2.09%. The application of fresh FDE increased the EF to 1.40%. The effluent- or dung-induced increases in N2O emissions from the urine patches were possibly caused both by the direct input of N from effluent or dung and through the indirect priming effect of addition of dung or effluent on the availability of N from urine patches for N2O production. We conclude that when EFs are used in calculations of N2O emissions from urine, consideration should be given to the likelihood of coincidence with dung or FDE applications.

Effect of dicyandiamide (DCD) on nitrous oxide emissions from cow urine deposited on a pasture soil, as influenced by DCD application method and rate

Animal urine deposited on pastoral soils during grazing is recognised as a dominant source of nitrous oxide (N2O) emissions. The nitrification inhibitor, dicyandiamide (DCD), is a potential mitigation technology to control N2O emissions from urine patches on grazed pastures. One delivery option is to include DCD in animal feed so that the DCD is targeted directly in the urine patch when excreted in the animal urine. The hypothesis tested in the present study was that DCD in urine, excreted by cows that were orally administered with DCD, would have the same effect as DCD added to urine after the urine is excreted. The study also aimed to determine the most effective DCD rate for reducing N2O emissions. Fresh dairy cow urine (700 kg N per ha) was applied to a free-draining silt loam pastoral soil in Waikato, New Zealand, in May (late autumn) or July (winter) of 2014, and was mixed with DCD at rates of 0, 10, 30 and 60 kg/ha. In late autumn, there was an equivalent treatment of urine (containing 60 kg DCD per ha) from DCD-treated cows. A static chamber technique was used to determine gaseous N2O emissions. An annual emission factor (EF3; the percentage of applied urine N lost as N2O-N) of 0.23% or 0.21% was found following late-autumn or winter applications of urine without DCD. Late-autumn application of urine containing DCD from oral administration to cows had the same significant reduction effect on N2O emissions as did DCD that was mixed with urine after excretion, at the equivalent DCD application rate of 60 kg/ha. Application of urine with DCD mixed with the urine after excretion at varying DCD rates showed a significant (P < 0.05) linear decrease in both N2O emissions and EF3 values.