Emission factors for ammonia and nitrous oxide emissions following immediate manure incorporation on two contrasting soil types

Abstract

We carried out four replicated field experiments to measure the impacts of immediate incorporation of solid manures on emissions of ammonia (NH3) and nitrous oxide (N2O). Four manures: cattle farmyard manure (FYM); pig FYM; layer manure and broiler manure were applied to the soil surface or immediately incorporated by mouldboard plough, disc or tine. Two of the experiments were carried out on a clay soil and two on a sandy soil to find out whether soil type interacted with incorporation technique to influence emissions of NH3 or N2O. Ammonia emissions were measured for 1 or 2 weeks while N2O emissions were measured for 60 days in one experiment and for a complete year in the other three experiments. Immediate incorporation by plough reduced NH3 emissions by c. 90% and by c. 60% by disc and tine (P < 0.001). There was no effect of soil type on NH3 abatement efficiency by plough or tine but the disc was less effective on the coarse sandy soil. Cross-site analysis indicated no effect of incorporation by disc or tine on emissions of N2OeN after 60 days but incorporation by plough increased direct emissions of N2OeN compared with surface application of manure (P < 0.001). Direct emissions of N2OeN, at c. 0.67% of total N applied, were substantially greater at the coarse-textured site than at the heavy clay site (0.04% of total N applied; P < 0.001). The impact of incorporation on total annual direct emissions of N2OeN differed in the three experiments where emissions were measured for a full year. There was no effect of incorporation on N2OeN emissions in the first experiment on the clay soil, and in the second experiment at this site incorporation by plough or disc, but not tine, reduced direct emissions of N2O (P ¼ 0.006). However on the sandy soil direct emissions of N2OeN were increased when manures were incorporated by plough (P ¼ 0.002) but not when incorporated by disc or tine. These results confirm that immediate incorporation of solid manures by plough is the most effective means of reducing NH3 emissions following the application of solid manures. The results also indicate that immediate incorporation of solid manures to reduce NH3 emissions does not necessarily increase emissions of N2O. However, the impacts of immediate incorporation on emissions of N2O may be related to soil type with a greater possibility of emission increases on coarse sandy soils.