Martyn Silgram

THE EFFECTS OF CULTIVATION ON SOIL NITROGEN MINERALIZATION

Publisher Summary This chapter discusses the effects of cultivation on soil-nitrogen mineralization. The chapter provides extensive information on methods of mineralization measurement, cultivation effects on soil physical conditions and nitrogen mineralization, and management implications. The chapter summarizes the available methods of measuring mineralization, assess the effects of cultivation on soil physical properties (which will influence biochemical processes), and review evidence for the effects of cultivation on nitrogen mineralization. Within the review, one aims to quantify the size (or reported ranges) of cultivation effects on the mineral nitrogen pool, including the effects on the overall magnitude and temporal dynamics of nitrogen release; to examine the reasons for cultivation apparently increasing mineralization; and to provide information on areas where further research is required.

Mitigation options for sediment and phosphorus loss from winter-sown arable crops.

Sediment and P inputs to freshwaters from agriculture are a major problem in the United Kingdom (UK). This study investigated mitigation options for diffuse pollution losses from arable land. Field trials were undertaken at the hillslope scale over three winters at three UK sites with silt (Oxyaquic Hapludalf), sand (Udic Haplustept), and clay (Typic Haplaquept) soils. None of the mitigation treatments was effective in every year trialled, but each showed overall average reductions in losses. Over five site years, breaking up the compaction in tramlines (tractor wheel tracks) using a tine reduced losses of sediment and P to losses similar to those observed from areas without tramlines, with an average reduction in P loss of 1.06 kg TP ha(-1). Compared to traditional plowing, TP losses under minimum tillage were reduced by 0.30 kg TP ha(-1) over five site years, TP losses under contour cultivation were reduced by 0.30 kg TP ha(-1) over two site years, and TP losses using in-field barriers were reduced by 0.24 kg TP ha(-1) over two site years. In one site year, reductions in losses due to crop residue incorporation were not significant. Each of the mitigation options trialled is associated with a small cost at the farm-scale of up to pound5 ha(-1), or with cost savings. The results indicate that each of the treatments has the potential to be a cost-effective mitigation option, but that tramline management is the most promising treatment, because tramlines dominate sediment and P transfer in surface runoff from arable hillslopes.

Effects of long-term straw management and fertilizer nitrogen additions on soil nitrogen supply and crop yields at two sites in eastern England

The effects of straw incorporation (early and late cultivation) and straw burning were contrasted in a split-plot study examining the impact of long-term straw residue management, and six fertilizer nitrogen (N) rates on soil mineral nitrogen, crop fertilizer N requirements and nitrate leaching losses. The experiments ran from 1984 to 1997 on light-textured soils at ADAS Gleadthorpe (Nottinghamshire, UK) and Morley Research Centre (Norfolk, UK). Soil incorporation of the straw residues returned an estimated 633 kg N/ha at Gleadthorpe and 429 kg N/ha at Morley on the treatment receiving 150 kg/ha per year fertilizer N since 1984. Straw disposal method had no consistent effect on grain and straw yields, crop N uptake, or optimal fertilizer N rates. In every year there was a positive response (P early incorporate>late plough. The incorporation of straw residues induced temporary N immobilization compared with the treatment where straw was burnt, while the earlier timing of tillage on the incorporate treatment resulted in slightly more mineral N compared with the later ploughed treatment. Fertilizer N rate increased (P<0.001) soil mineral nitrogen at both sites. At Morley, there was more organic carbon in the plough layer where straw had been incorporated (mean 1.09 g/100 g) rather than burnt (mean 0.89 g/100 g), and a strong positive relationship between organic carbon and fertilizer N rate (r 2 =93.2%, P<0.01). There was a detectable effect of fertilizer N on readily mineralizable N in the plough layer at both Gleadthorpe (P<0.001) and Morley (P<0.05). At Morley, there was a consistent trend (P=0.06) for readily mineralizable N to be higher where straw had been incorporated rather than burnt, indicating that ploughing-in residues may contribute to soil nitrogen supply over the longer term.

Modelling nitrate river water quality for policy support

Abstract In response to the need for nitrate policy support in the UK, ADAS UK Ltd. has developed the EveNFlow modelling tool. EveNFlow is conceptually based and allows for surface and subsurface pathways and multiple diffuse sources, associated with different soil‐crop‐livestock combinations. Sources of nitrate losses from agricultural and non‐agricultural land, urban areas and point sources are all represented. The output provides information in the form of daily time‐series at any point along the catchment river network, losses from the base of the soil profile and exported nitrate loads associated with key vectors, e.g. livestock and arable land. In order to model N losses, UK wide GIS datasets for agricultural activity, climate and soil type are used. EveNFlow builds on existing models, either through their coupling or in the form of metamodels. These component models include: SLIMMER; a simple functional N loss model; a crop water use/drainage model based on elements of the MORECS and IRRIGUIDE models, and a series of export coefficients for N potentially available for leaching at the beginning of the drainage season for a range of livestock and crop types from the NEAP‐N model. The final model is capable of simulating a long daily time‐series of flow and nitrate‐N concentrations. As an example, EveNFlow is applied to the Yorkshire Ouse (3315 km2) catchment, UK, and two of its subcatchments, which have contrasting land use and climatic regimes. The results compare favourably with hydrological and chemical data collected over the period 1990–2000 at monitoring sites on these rivers.