Nitrous Oxide and Ammonia Emissions from Cattle Excreta on Shortgrass Steppe

Co-application of biochar and compost with decreased N fertilizer reduced annual ammonia emissions in wetland rice

Ammonia (NH3) emission from rice fields is a dominant nitrogen (N) loss pathway causing negative impacts on farm profitability and the environment. Reducing N fertilizer application to compensate for N inputs in organic amendments was evaluated for effects on N loss via volatilization, rice yields and post-harvest soil properties in an annual irrigated rice (Boro) – pre-monsoon rice (Aus) – monsoon (Aman) rice sequence. That experiment was conducted using the integrated plant nutrition system (IPNS; nutrient contents in organic amendments were subtracted from the full recommended fertilizer dose i.e., RD of chemical fertilizers) where six treatments with four replications were applied in each season: (T1) no fertilizer (control), (T2) RD, (T3) poultry manure biochar (3 t ha−1; pyrolyzed at 450°C) + decreased dose of recommended fertilizer (DRD), (T4) rice husk ash (3 t ha−1) + DRD, (T5) compost (3 t ha−1) + DRD, and (T6) compost (1.5 t ha−1)+ biochar (1.5 t ha−1) + DRD. The N loss via volatilization varied twofold among seasons being 16% in irrigated rice and 29% in the pre-monsoon rice crop. In irrigated rice, T6 had significantly lower NH3 emissions than all other treatments, except the control while in pre-monsoon and monsoon seasons, T6 and T3 were alike. Pooling the three seasons together, biochar (T3) or biochar plus compost (T6) reduced NH3 loss via volatilization by 36-37% while compost alone (T5) reduced NH3 loss by 23% relative to RD. Biochar (T3) and biochar plus compost mixture (T6) reduced yield-scaled NH3 emissions by 40 and 47% relative to the RD of chemical fertilizer (T2). The organic amendments with IPNS reduced the quantity of N fertilizer application by 65, 7, 24, and 45% in T3, T4, T5, and T6 treatments, respectively, while rice yields and soil chemical properties in all seasons were similar to the RD. This study suggests that incorporation of biochar alone or co-applied with compost and decrease of N fertilizer on an IPNS basis in rice-based cropping systems can reduce N application rates and NH3 emissions without harming yield or soil quality.

Effects of rumen undegradable protein sources on nitrous oxide, methane and ammonia emission from the manure of feedlot-finished cattle

The effects of sources of rumen undegradable protein (RUP) in diets on methane (CH₄), nitrous oxide (N₂O) and ammonia (NH₃) emissions from the manure of feedlot-finished cattle were evaluated. We hypothesized that the use of different RUP sources in diets would reduce N loss via urine and contribute to reduced N₂O, CH₄ and NH₃ emissions to the environment. Nellore cattle received different diets (18 animals/treatment), including soybean meal (SM, RDP source), by-pass soybean meal (BSM, RUP source) and corn gluten meal (CGM, RUP source). The protein source did not affect the N and C concentration in urine, C concentration in feces, and N balance (P > 0.05). The RUP sources resulted in a higher N₂O emission than the RDP source (P = 0.030), while BSM resulted in a higher N₂O emission than CGM (P = 0.038) (SM = 633, BSM = 2521, and CGM = 1153 g ha⁻² N–N₂O); however, there were no differences in CH₄ and NH₃ emission (P > 0.05). In conclusion, the use of RUP in diets did not affect N excretion of beef cattle or CH₄ and NH₃ emission from manure, but increased N₂O emission from the manure.

Interactive effects of dung deposited onto urine patches on greenhouse gas fluxes from tropical pastures in Kenya

Dung and urine patches on grasslands are hotspots of greenhouse gas (GHG) emissions in temperate regions, while its importance remains controversial for tropical regions as emissions seem to be lower. Here we investigated N₂O, CH₄ and CO₂ emissions from urine and dung patches on tropical pastures in Kenya, thereby disentangling interactive and pure water, dung or urine effects. GHG fluxes were monitored with automated chambers for 42-59 days covering three seasons (short rainy season, long rainy season, dry season) for six treatments (Control; +1 L water; +1 kg dung; 1 L urine; 1 L water +1 kg dung; 1 L urine +1 kg dung). Cumulative CO₂ emissions did not differ among treatments in any of the seasons. Water or urine addition alone did not affect CH₄ fluxes, but these were elevated in all dung-related treatments. Scaled up on the total area covered, dung patches halve the CH₄ sink strength of tropical pastures during the dry season, while during the rainy season they may turn tropical pastures into a small CH₄ source. For N₂O, both dung and urine alone and in combination stimulated emissions. While the N₂O emission factor (EF_N2O) from dung being constant across seasons, the EF_N2O for urine was greater during the short rainy season than during the dry season. Combined application of urine + dung was additive on EF_N2O. While the mean dung EF_N2O in our study (0.06%) was similar to the IPCC Guidelines for National GHG Inventories EF_N2O for dry climate (0.07%), the urine EF_N2O we measured (0.03-0.25%) was lower than the IPCC value (0.32%). In addition, the IPCC Guidelines assume a urine-N: dung-N ratio of 0.66:0.34, which is higher than found for SSA (<0.50:0.50). Consequently, IPCC Guidelines still overestimate N₂O emissions from excreta patches in SSA.

Nitrogen supply and rainfall affect ammonia emissions from dairy cattle excreta and urea applied on warm-climate pastures

Cattle excreta and nitrogen (N) fertilizer deposited on tropical grasslands are important sources of ammonia (NH₃ ) emission. We conducted three field trials (wet, intermediate, and dry conditions) to quantify NH₃ emissions from urea fertilizer and simulated excretions of heifer urine and dung on warm-climate grasslands in Brazil. Heifer excreta were derived from pastures of palisadegrass [Urochloa brizantha (Hochst. ex A. Rich.) R. D. Webster 'Marandu'] under three forms of N supply (without or with N fertilization [0 or 150 kg N ha^-1  yr^-1 ] or mixed with forage peanut [Arachis pintoi 'Amarillo']). Cumulative NH₃ -N emissions across rainfall conditions were 7.6-16.6% (mean, 11.7%) for urine, 1.4-2.9% (mean, 2.0%) for dung, and 11.2-20.5% (mean, 14.8%) for urea. Ammonia loss from urine was significantly greater than from dung under all rainfall conditions. Emission from urine and dung differed from those when urea was applied on palisadegrass. There were greater NH₃ emissions from urine in the wetter times of the year. Heifer excreta from N-fertilized pasture had greater NH₃ emission than excreta from the grass-legume mixture and unfertilized palisadegrass. Urea applied on palisadegrass presented greater NH₃ emissions in wet rainfall conditions compared with dry conditions but did not differ from intermediate conditions. Our study showed that N-fertilized systems increase N losses as NH₃ emission from excreta, and emissions from urea fertilizer must be included in this system. Heifer excreta and urea fertilizer deposited on warm-climate grasslands increased the NH₃ emissions mainly under wet conditions.