Abstract
High application rates of dairy effluent and manure are often associated with nitrogen (N) leaching, which can affect groundwater quality. Here, we used a lysimeter to examine N leaching losses and biomass yield following application of dairy effluent and manure under wheat-maize cropping. The field experiment included seven treatments: no N fertilizer (Control); 200/300 kg N ha(-1) synthetic N fertilizer only (wheat/maize) (CN); 100/150 kg N ha(-1) synthetic N fertilizer plus 100/150 (DE1), 150/200 (DE2) and 250/350 (DE3) kg N ha(-1) dairy effluent; 100/150 kg N ha(-1) synthetic fertilizer plus 100/150 kg N ha(-1) dairy manure (SM1); and 150/225 kg N ha(-1) synthetic fertilizer plus 50/75 kg N ha(-1) dairy manure (SM2). Compared with CN, DE1 treatment increased maize yield by 10.0 %, wheat N use efficiency (NUE) by 26.5 %, and wheat and maize N uptake by 7.7-16.3 %, while reduced N leaching by 22.4 % in wheat season and by 40.4 % in the maize season. In contrast, DE2 and DE3 treatment increased N leaching by 27.2-241 % and reduced NUE by 26.2-55.2 %. SM2 treatment increased yield and NUE by 8.8 % and 7.8 %, respectively, and reduced N leaching by 42.9 % during the wheat but not the maize season. Annual N leaching losses were 37.6 kg N ha(-1) under CN treatment, but decreased to 27.4 kg N ha(-1) under DE1. In contrast, N leaching increased to 52.8 and 84.1 kg N ha(-1) under DE2 and DE3 treatment, respectively (P < 0.05). Meanwhile, under SM1 and SM2 treatment, N leaching decreased by 71.2 % and 32.0 %, respectively, compared with CN. These results suggest that replacing 50 % and 25 % synthetic N fertilizer with dairy farm effluent and manure could reduce N leaching losses but had varied effects on crop productivity under wheat-maize cropping.