Regular applications of poultry litter to a sandy arable soil: effects on nitrate leaching and nitrogen balance

Abstract

Intensive poultry units often have insufficient land for spreading manure at agronomically and environmentally acceptable rates. This experiment measured the effects of annual applications, at several rates, on nitrate-N leaching and the soil–crop N balance on a sandy soil. Poultry litter from a broiler unit was applied each autumn 1992–1995. Total loadings on the main experiment area (instrumented with ceramic and Teflon water samplers at 1·0 and 1·5 m, and monolith lysimeters, 1·5 m deep) were 0, 60 and 150 t ha−1. Additional plots (not instrumented) received 30, 90 or 120 t ha−1. There was good agreement in the nitrate-N concentrations measured by the Teflon and ceramic water samplers and the lysimeters; all three methods gave acceptable measurements of nitrate leaching on structureless sandy soils. Autumn applications of poultry manure should be avoided: leaching was much greater than when delayed into December. At rates of broiler litter which supplied more N than the crop required (generally above 10 t ha−1 each year), nitrate-N leaching losses were large; at the largest application rate (akin to a disposal, rather than a planned fertiliser strategy), concentrations peaked at c 500 mg litre−1 N. Despite the movement of dissolved organic carbon to 1 m depth, the N concentration profiles measured by the water samplers did not provide clear evidence of subsoil denitrification. A nitrogen balance sheet, based on available N applied (as either fertiliser or manure) with some adjustment for mineralisation of the manure's organic fraction (10% annually) and for volatilisation (15%) was strongly correlated with soil mineral N each spring. © 1998 Society of Chemical Industry.