Results are presented from a 3 year investigation into nitrate leaching from isolated 0.4 ha grassland plots fertilized with 250, 500 and 900 kg N ha-a-l . Cumulative nitrate leaching over the 3 years was equivalent to 1.5%, 5.4% and 16.7% ofthe fertilizer applied at 250,500 and 900 kg N ha-rates respectively. Over a whole drainage season, mean nitrate leachate concentrations at 250 kg N ha-did not exceed 4 mgl-', although maximum values of 13.3 mg1-l were observed. In contrast, at 900 kg N ha-the mean nitrate leachate concentration in two of the years exceeded 90 mg I-'. Mineral nitrogen balances constructed for the 1979 growing season indicated that leaching at 250 kg N ha-* was low because net mineralization of soil organic nitrogen was small, and crop nitrogen uptake almost balanced fertilizer application. Although the pattern of nitrate leaching suggested that by-passing occurred in the movement of water down the soil profile, it was not possible to confirm this using simulation models of leaching. Possible reasons for this, including the occurrence of rapid water flow down gravitationally drained macropores, are discussed.
Forage conservation has been a subject of research at Jealott's Hill for almost 50 years. In the last 8 years conservation of grass as silage has been of particular interest. Although silage is nutritionally more satisfactory than hay, ruminant livestock production from silage is much poorer than from grazed grass. This is because poor ensiling techniques often result in material of low nutritional quality that gives poor silage intakes by the ruminant.In the last 5 years in the UK, the quantity of grass conserved as silage has more than doubled. This is a result of increased farmer-awareness, improved machinery and techniques, and the use of chemical additives that help control the silage fermentation.A formalin/sulphuric acid additive ("SYLADE ') has been developed at Jealott's Hill following extensive microbiological, chemical and nutritional testing. It can be used either to provide a controlled, conventional lactic acid fermentation, or to restrict fermentation, producing a material nearer in composition to the original grass.This improvement in silage nutritive value is translated into better animal performance. In 12 independent trials with beef animals, daily liveweight gains have been enhanced from 0.57 kg/head on untreated silages to 0.8 1 kg/head on "SYLADE"-treated silages, an improvement of 42 %.Where silage dry-matter intakes have been measured, the average intake of "SYLADE"-treated silages was approximately 10% higher than the untreated silages. High Nitrogen Applications on Grassland : Lysimeter StudiesSixteen lysimeters as designed by Low and Armitage1 (soil monoliths 91 x 30 x 30 cm) were used in a s t~d y~-~ of the quantities of nitrogen, phosphorus, potassium, calcium, magnesium, sodium, sulphur and chlorine leaching through grass-cropped soil to which 0, 250, 500 and 750 kg N/ha had been applied-mainly as ammonium nitrate. Over the years 1971/2 to 1975/6 [which included two very dry, one very wet and two average rainfall years and making no allowance for soil nitrogen mineralised in presence of added fertiliser nitrogen, because of earlier work5 using 15N], from 31 to 84% of the nitrogen applied was accounted for in the herbage and drainage water. In general, a greater percentage was accounted for, the lower the rate of nitrogen applied. On average at 250 kg N/ha, 75 % was accounted for, at 500 kg N/ha 60% and at 750 kg N/ha 52 % per year. The nitrogen (expressed as a percentage of N applied) accounted for in the drainage water ranged in any one year from 0.25 % when 250 kg N/ha was applied to as high as 23 % when 750 kg N/ha was applied; the average percentage over 5 years being 5.1, 9.0 and 10.6 for 250, 500 and 750 kg N/ha. The nitrogen leached was 98% as N03-N. 317
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