15N-labelled Urine Research Articles

Are nitrification inhibitors effective in reducing N2O from farm-scale emission hotspots?

Livestock congregation areas are nitrous oxide (N2O) hot-spots and could be key areas to focus mitigation action. We tested whether combined cattle urine and fertiliser N2O-N emission factors (EFs) would be higher from a farm gateway area compared to a standard pasture under sub-tropical conditions, and whether the nitrification inhibitor, dimethyl pyrazole phosphate (DMPP), would lower N2O EFs from the gateway area. Treatments (n = 3) included: (i) fertiliser applied to a standard pasture (50 kg urea-N ha−1), (ii) fertiliser (50 kg urea-N ha−1) + urine (350 kg N ha−1) applied to a standard pasture, (iii) fertiliser (50 kg urea-N ha−1) + urine (350 kg N ha−1) applied to the gateway area, and (iv) fertiliser (50 kg urea-N ha−1) + urine (350 kg N ha−1) + DMPP (1.5 kg ha−1) applied to the gateway area. Emissions were monitored via an automated static chamber-based system and 15N-labelled urine treatments (n = 4) used to assess N2O + N2 emissions, N2O:N2 and 15N recovery from the pasture. No significant differences (p > 0.05) were observed for EFs between the fertiliser + urine treatment for the standard pasture (1.10 ± 0.17%) or the gateway area (1.46 ± 0.40%). DMPP did not lower the N2O-N EF from the gateway area (1.50 ± 0.22%), where wet and warm conditions may have accelerated DMPP degradation. In the 15N-labelled urine treatments, significantly (p < 0.05) greater N2O + N2 emissions occurred in the gateway compared to the standard pasture, but disaggregating EFs between the contrasting areas was not warranted.

Does sowing an oats catch crop reduce nitrate leaching from urine deposition following simulated winter forage grazing? - a growth chamber experiment

Growing winter forages, such as brassicas and fodder beets, is a common feed strategy to build body condition for non-lactating cows, prior to calving, in the temperate regions of New Zealand. However, the large quantities of feed grown, ~14-20 tonnes ha-1, and resulting high stocking rates, means large volumes of urine are deposited during grazing, over relatively small areas, on cool, bare and often wet soils. These conditions create a high potential for large N leaching losses. Sowing a catch crop might be one way to mitigate this potential but most catch crops are sown in late-summer/autumn, not late winter/spring, so this study’s objectives were to examine the potential of a cold-tolerant cereal, oats, to establish and take up soil N over this period. A study was undertaken using free-draining repacked soil cores in two climate-controlled growth chambers at 6° and 10°C, and at two lighting intensities, 5 and 10 MJ m-2, reflecting the mean soil temperature (0-100 mm) and light levels experienced in Canterbury, New Zealand, around late winter and mid spring, respectively. The cores all received an application of 15N-labelled urine (350 kg N ha-1) and two weeks later, oats were sown in half the soil cores, with the remainder left fallow. Sowing oats at 6° and 10°C both proved highly effective in reducing nitrate leaching loss by around 33% and 75%, respectively, compared to fallow treatments. Soil temperature, however, was the chief driver of oats development, growing an order of magnitude more rapidly at 10°C and reducing nitrate leaching loss quickly through a combination of increased N uptake and reduced drainage. However, ammonia oxidising bacteria (AOB) abundance in 10°C fallow treatments increased more rapidly after urine application than at 6°C, meaning soil nitrate concentrations rose quickly, leaching twice as much nitrate as the 6°C fallow treatments after 90 days. Greater plant growth (10-times more) at 10°C than at 6°C, 75 days after sowing, was offset to some degree by greater N% and N content in the plant stems and roots at 6°C (2-4 times more). Higher light intensity increased evaporative water loss in both 6° and 10°C chambers, reducing drainage and nitrate leaching, and increasing the rate of oats development at 10°C. The sowing of oats as a catch crop following simulated winter forage grazing conditions shows promise as an effective means to limit nitrate leaching. Further research, however, is needed to show that a catch crop can be sown successfully in most years at farm paddock scale across a range of soil conditions.

Isotope Ratio Mass Spectrometry Monitoring of Nitrogen Volatilization from Beef Cattle Feces and 15N-Labeled Synthetic Urine

A 15-day bench-scale manure storage experiment with a slurry mixture comprising beef cattle feces and synthetic urine with 15N-labeled urea was conducted to evaluate the source of volatilized ammonia nitrogen (NH3-N). Beef cattle feces was mixed daily in a 1:2.2 mass ratio with 15N-labeled urine and added for four consecutive days to 2-L storage containers and then left undisturbed for eleven days. Isotope ratio mass spectrometry was used to determine the origin of aerial NH3-N losses from the relative isotopic abundance of N in the 15N-labeled slurry mixture. On average 84% of total NH3-N losses originated from the urine portion and were highest during the first two to four days, when fresh material was added. After fresh material addition ceased, daily NH3-N emission from the urine decreased gradually, whereas emission from the feces remained relatively constant. Calculations showed that over 34% of aerial N was not captured, suggesting that other N gas emission is significant from slurry mixtures. Likely all uncaptured N losses were from urinary urea. The study verified the applicability of 15N-labeled synthetic urine for beef slurry mixtures. However, the results suggest further research to explain and model the NH3 and N release from fecal material is warranted and to determine the identity of the uncaptured N losses.

Bovine urine and dung deposited on Brazilian savannah pastures contribute differently to direct and indirect soil nitrous oxide emissions

Cattle ranching is one of the most important agricultural activities in Brazil. The impact of livestock on soil N2O emissions in Brazil has only been assessed using a Tier 1 approach of the IPCC guidelines, as there are no data available from field studies. Apart from the need for accumulating data for the development of proper direct N2O emission factors, we tested for possible differences between urine and dung as N2O sources and the difference in emissions between the dry and wet season. An area of Brachiaria brizantha at the Embrapa Rice and Bean Centre in the Cerrado (central savannah) region (Goiás state) was subdivided into plots where fresh cattle urine and dung were monitored for three consecutive periods (two in the rainy and one in the dry season) for N losses, principally N2O emissions and NH3 volatilization. 15N-labelled urine N was used in the first monitoring period for an N balance study which indicated that denitrification and NH3 volatilization were the most important processes for N loss. Percentages of N lost as N2O and as volatilized NH3 were greater for urine than for dung. In addition, N losses as N2O in the rainy season were much greater than during the dry season. Representing the Cerrado region and the extensive pasture systems common in this region, direct emission 0.007gN2O–Ng−1 (0.7%) excreta N, well below the EF3PRP of 0.020gNg−1 (2%) used by IPCC for cattle N in excreta. The fraction of excreta N lost as NH3 of ∼15% was in line with the IPCC guidelines. Disaggregation of emission factors for excreta type is recommended.

Mid-term tracing of 15N derived from urine and dung in soil microbial biomass

Large amounts of C and N are returned to pasture soils by grazing animals in the form of urine and dung. Therefore, a field trial was carried out to investigate the mid-term effects of 15N-labeled excrements, produced by feeding a cow with 15N-labeled grass silage, on the soil microbial biomass. Simulating the deposition of excrements, 15N-labeled urine and dung were applied to a 0.09-m² area of a sandy pasture soil in October 2000 and 2001. Applied amounts of N were 1,030 and 1,052 kg ha−1, respectively. Soil was sampled at 0–15 cm depth, three times over 7 months and analyzed for total C and N, and microbial biomass C and N. Recovery of urine and dung N in microbial biomass was determined by 15N analysis of K2SO4 extracts of pre-extracted fumigated and unfumigated soils. Under dung patches, microbial biomass C was 16% and 45% higher, and microbial biomass N was 24% and 57% higher than under the untreated soil in 2001 and 2002, respectively. Under urine patches, microbial biomass C was increased after 12 weeks and decreased after 27 weeks. Microbial biomass assimilated 7% to 17% and 10% to 21% of the 15N applied initially as urine and dung, respectively. These percentages were considerably higher than those for artificially with spiked 15N urea-created and labeled manures reported in previous experiments. An important reason may be that the naturally 15N-labeled N components behave differently in soil than urea spikes.

Nitrate leaching under grassland as affected by mineral nitrogen fertilization and cattle urine.

An experiment was performed to better understand to what extent nitrogen fertilization rate and date and amount of urine deposition, when acting in combination, influence nitrate leaching under grassland. Leaching was studied during two successive winters using 2-m2 grassed lysimeters under three levels of N fertilization (0, 150, and 300 kg N ha(-1) yr(-1), referred to as 0N, 150N, and 300N, respectively), two levels of 15N-labeled urine (105 and 165 kg N ha(-1), referred to as A2 and A3, respectively), and three dates of urine application (spring, summer, and fall). During the first winter, total N leaching losses varied between 2 and 50 kg N ha(-1). When tested in combination, N applied as urine to grassland resulted in three times the total N loss by leaching that occurred following N fertilization in the first winter (4.3, 20.8, 34.9, 14.2, 17.1, and 28.7 kg NO3- -N ha(-1) for no urine, A2, A3, ON, 150N, and 300N, respectively). Leaching of 15N urine significantly depended on the date of application: 6.6, 17.3, and 29.1 kg for spring, summer, and fall, respectively. A similar pattern was observed for the contribution of 15N urine to total N leaching with 4.3, 12.9, and 21.4%. However, urine application, both in terms of amount and date, showed very little long-term effect on these N losses in Year 2. In our conditions of low winter rainfall and drainage, grazing management (through season, urinary N amounts, and urine N concentration) resulted in a higher impact on water nitrate quality than moderate N fertilization management.

The effect of a single application of cow urine on annual N2 fixation under varying simulated grazing intensity, as measured by four 15N isotope techniques

The effects of dairy cow urine and defoliation severity on biological nitrogen fixation and pasture production of a mixed ryegrass-white clover sward were investigated over 12 months using mowing for defoliation. A single application of urine (equivalent to 746 kg N ha−1), was applied in late spring to plots immediately after light and moderately-severe defoliation (35 mm and 85 mm cutting heights, respectively) treatments were imposed. Estimates of percentage clover N derived from N2 fixation (%Ndfa) were compared by labelling the soil with 15N either by applying a low rate of 15N-labelled ammonium sulphate, immobilising 15N in soil organic matter, adding 15N to applied urine, or by utilising the small differences in natural abundance of 15N in soil. Urine application increased annual grass production by 85%, but had little effect on annual clover production. However, urine caused a marked decline in %Ndfa (using an average of all 15N methods) from 84% to a low of 22% by 108 days, with recovery to control levels taking almost a year. As a result, total N fixed (in above ground clover herbage) was reduced from 232 to 145 kg N ha−1 yr−1. Moderately–severe defoliation had no immediate effect on N2 fixation, but after 108 days the %Ndfa was consistently higher than light defoliation during summer and autumn, and increased by up to 18%, coinciding with an increase in growth of weeds and summer-grass species. Annual N2 fixation was 218 kg N ha−1 yr−1 under moderately-severe defoliation compared to 160 kg N ha−1 yr−1 under light defoliation. Estimates of %Ndfa were generally similar when 15N-labelled or immobilised 15N were used to label soil regardless of urine and defoliation severity. The natural abundance technique gave highly variable estimates of %Ndfa (−56 to 24%) during the first 23 days after urine application but, thereafter, estimates of %Ndfa were similar to those using 15N-labelling methods. In contrast, in urine treated plots the use of 15N-labelled urine gave estimates of %Ndfa that were 20–30% below values calculated using conventional 15N-labelling during the first 161 days. These differences were probably due to differences in the rooting depth between ryegrass and white clover in conjunction with treatment differences in 15N distribution with depth. This study shows that urine has a prolonged effect on reducing N2 fixation in pasture. In addition, defoliation severity is a potential pasture management tool for strategically enhancing N2 fixation.

Short-term N dynamics following application of 15N-labeled urine to a sandy soil in summer

The short-term fate of 20.5 g N m −2 of sheep urine, spiked with 99 at% 15N urea was followed for 28 d after surface application to intact cores of a deep yellow sand (0–40 cm) in dry summer conditions in Western Australia. Soil N variables and soil pH were compared in cores receiving urine, an equivalent volume of water, or kept dry. A simulated 20-mm rainfall event was imposed 14 d after the urine application. The soils dried rapidly after urine addition and after a simulated rainfall. Urine-N hydrolysed rapidly to NH 4 +, as concentrations of NH 4 + of 200 μg N g −1 were found in the 0–2.5 surface soil layer. The dry, windy conditions following urine hydrolysis favored loss of urine-N as NH 3 gas, but severely limited nitrification of NH 4 +. Using the 15N balance method, it was estimated that one-third of the urine-N applied was lost as NH 3 during the first 3 d. Soil pH (10 mM CaCl 2) increased immediately after urine addition. Emissions of N 2O and NO were similar from cores receiving urine or water, and both increased after the simulated rainfall. Nitric oxide fluxes were about 10 times higher than N 2O emissions. As a loss-pathway of urine-N, however, the magnitude of the N oxide emissions were insignificant compared to the NH 3 loss estimate. Extractable organic-N (total soluble N minus NH 4 +-N) accounted for 36% of the urine-N initially, and decreased to about 12% by 28 d. Nonextractable organic-N or immobilized urine-N increased slowly over time to make up 16% of the balance by d 28. This study showed that besides a significant early loss as NH 3, urine-N transformations proceed slowly in summer conditions in a sand. Ammonium-N that originated as urine is highly conserved in the summer and should be largely available for the following winter wheat crop.

Fate of urea nitrogen in sheep urine applied to soil at different times of the year in the pasture - wheat rotation in south Western Australia

Sheep urine labelled with 15N-urea was applied toconfined micro-plots at different times of the year to follow the fate of ureaN in urine in the grazed pasture-wheat rotation in south Western Australia.Three field experiments were conducted on the same site on a loamy sand.Applications were made either to pasture residues (Expts 1 and 2) which weresubsequently sown to wheat, orto growing pasture in winter-spring, (Expt 3).In Expt 1, urine was applied in November 1990 (9·8 gN/m2) and April 1991 (46·1 gN/m2). From both applications, losses of15N attributed to NH3volatilisation were c. 50% within 2 weeks of application. Another10% loss was attributed toNO-3 leaching during the followinggrowing season and 15% was recovered by the wheat crop. In Expt 2,urine was applied in October 1991 (4·6 gN/m2), January 1992 (15·6 gN/m2), and March 1992 (13·6 gN/m2). Attributed NH3 losseswithin 2 weeks, in terms of 15N-urea applied, were40% (October and January urine) and 30% (March urine) andNO-3 leaching losses were estimated to be 20% forthe 3 applications. Recoveries in wheat (November 1992) were 4, 7, and12% of 15N applied in the October, January, andMarch urine applications. In Expt 3, urine was applied in August 1992(12·3 g N/m2) and September 1992 (25·9g N/m2). Attributed NH3 losseswere 10% of applied 15N for the August and30% for the September application. Plant uptake of15N was rapid and by mid October was 42% from theAugust application and 47% from the September application. Recovery of15N in soil organic N was generally 17-25% whenurine was applied to pasture residues and bare soil,and 21-37% whenurine was applied to growing pasture. It is suggested thatNH3 volatilisation was the predominant N loss mechanism.The amount of NO-3 leached wasprimarily influenced by summer rainfall, the length of time urine-N was insoil before the onset of winter rainfall, and the distributionof winterrainfall. Little of the 15N-labelled urine was eitherrecovered by, or available for, subsequent wheat crops, suggesting thatcalculations for estimating the N supply from pastures to cereal cropsmustdiscount most N returned in urine by grazing animals.

Transformation in soil and turnover to wheat of nitrogen from components of grazed pasture in the south of Western Australia

Nitrogen (N) mineralisation from mature subterranean clover (Trifolium subterraneum L.) shoots and roots and from sheep urine and faeces, and N uptake by wheat from the shoots, urine, and faeces, were determined with 15 N in a field study in the Western Australian wheatbelt. Treatments were applied to the soil surface of confined micro-plots in autumn and incorporated into soil immediately before wheat was sown in winter. Mature subterranean clover shoots containing 18 kg N/ha were applied to the soil surface, and root material containing 17 kg N/ha was mixed into soil. 15N-labelled urine and faeces were obtained from housed sheep fed 15N-labelled wheat straw and grain. Urine was applied at the rates of 151 and 301 kg N/ha, and faeces was added at the rate of 47 kg N/ha. There was a loss of 14% of shoot 15N in the 2 months this residue was on the soil surface, although very little mineralisation occurred. On the assumption that wind-blow caused the initial loss of 15N, 28% of shoot N mineralised in 6 months following incorporation of shoot residues into soil, and crop recovery was 11% of the 15N applied. N mineralisation from the mature roots was 26% in 6 months. NH3 volatilisation from urine, estimated by difference, was 25% for high urine (0·517 mL/cm2) and 33% for low urine (0·258 mL/cm2) application rates, the loss occurring in the first 2 weeks. Wheat uptake was 23% of the high urine 15N and 22% of the low urine 15N. Leaching losses from unplanted micro-plots were approximately 25-30% of urine 15N. In contrast, leaching losses from planted micro-plots were estimated to be approximately 10% of urine 15N. Approximately 30% of faecal N was mineralised and recovery of faeces N by wheat was 1% of applied 15N. The relative contributions of these components to N turnover in the ley pasture wheat rotation are discussed. It is concluded that assessments of the potential turnover of N in pastures to cropping phases need to consider the low rates of N mineralisation of above-ground herbage, the potential for supply of N from the total root system, the effect of grazing on NH3volatilisation, and consequent loss of N fixed by legumes.