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

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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.