Accounting for the nitrogen in solid manures incorporated immediately after application in order to reduce emissions of ammonia

Abstract

In four replicated field experiments the impacts of immediate incorporation of solid manures on ammonia (NH3) and direct nitrous oxide (N2O) emissions and apparent nitrogen recovery (ANR) of manure-N were measured. The impacts of immediate incorporation on nitrate (NO3−) leaching were modelled. 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. There was, on average, no significant effect of application technique on ANR but there were significant increases in ANR following immediate incorporation in three experiments. Recovery of N by the succeeding crop was c. 8 % for cattle FYM, c. 13 % for pig FYM and c. 20 % for the poultry manures. Only c. 30 % of the applied N could be accounted for from measurements of NH3, N2O and ANR and modelling of NO3−. While immediate incorporation by plough increased direct N2O emissions from the sandy soil and all methods of immediate incorporation in autumn increased modelled estimates of NO3− leaching, these increases were only a small proportion of the NH3–N conserved which was probably either recovered by the crop or remained in the soil. Therefore concerns over so-called ‘pollution swapping’ should not be a barrier to the immediate incorporation of solid livestock manures in order to reduce emissions of NH3 and increase crop recovery of manure-N.