Optimizing the application of dairy farm effluent and manure to mitigate gas emission

The impact of dairy farm effluent and manure applications upon gas emissions from soil is of concern for agronomic, ecological, and environmental reasons. Yet it remains unclear how the optimized manure and effluent additions may affect gas (nitrous oxide (N2O), nitric oxide (NO), and ammonia (NH3)) emissions during wheat cultivation. We conducted a field experiment in Zhuzhen (Jiangsu), China, from November 2018 to May 2019 to examine the effects of effluent and manure on gas emissions from the wheat fields that had seven treatments (4 replicates, 28 plots): no fertilizer (control); inorganic fertilizer at a conventional application rate of 200 kg N ha−1 (NPK); 100 kg N ha−1 inorganic fertilizer plus 100 (DE1), 150 (DE2), and 250 (DE3) kg N ha−1 farm dairy effluent; 100 kg N ha−1 inorganic fertilizer plus 100 kg N ha−1 farm dairy manure (SM1); and 150 kg N ha−1 inorganic fertilizer plus 50 kg N ha−1 farm dairy manure (SM2). Applying dairy effluent during the wheat season significantly (P < 0.05) increased NH3 emissions from 1.83 (NPK) to 3.81 kg N ha−1 (DE1) and 11.4 kg N ha−1 (DE3), probably due to elevated levels of soil NH4+ and pH, with no discernable impact on N2O emissions compared with NPK. The greater application of effluent in the DE3 treatment increased NO emissions significantly by 33.3% relative to NPK. The combined application of manure and urea significantly reduced N2O and NO emissions by 25.2–27.6% and 8.3–45.8%, respectively, but increased NH3 emissions in the SM1 treatment by 73.8%, when compared with NPK. Overall, our results suggest that replacing 25% of the current conventional chemical N application rate with dairy manure could considerably mitigate gas emissions in the wheat season.