The fertiliser nitrogen requirement of cereals grown on sandy soils

The responses to fertiliser-N of winter wheat and winter barley grown on sa ndy soils were measured in 72 experiments in England from 1990 to 1994. Yie ld without fertiliser-N (Y-0) was c 1.1 tha(-1) greater following root crop s than following cereals. Following potato crops given organic manures, Y-0 was c 1.2tha(-1) greater than following unmanured potato crops, but Y-0 wa s no greater following sugarbeet to which organic manures had been applied. Only after the two driest winters was there sufficient variation in soil N supply in spring (SNSs) for this to show a relationship with Y-0. However, Y-0 increased with increasing N mineralisation during the growing season ( AM) in the three years it was measured. There was no consistent effect of s owing date on Y-0. Following potatoes, yield at optimum fertiliser-N (Y-opt ) decreased as sowing date was delayed, but this was not so after cereals, sugarbeet or overall. There was no increase in Y-opt with SNSS or AM, but Y -opt decreased with increasing moisture stress (S) in June. The mean yield response to N-opt (Delta(Y)) was c 0.4 and 0.8 tha(-1) smaller following po tatoes and sugarbeet respectively than following cereals, but not consisten tly so as there were large interactions between site, year and previous cro p. Following root crops, Delta(Y) was c 0.6 and 1.4 tha(-1) less after suga rbeet and potatoes respectively that had been given organic manures. Withou t the addition of organic manures, Delta(Y) following potatoes was similar to that following cereals. Regression on SNSs and AM accounted for 28 and 1 5% respectively of the variance in dy. The optimum economic fertiliser-N ap plication (N-opt) was similar, at c 140kgha(-1), following cereals and pota toes. Following sugarbeet, cereal N-opt was only c 110kgha(-1). The differe nces according to previous crop reported here are consistent with mineralis ation of crop residues on sandy soils being more rapid than on other soils; the potato residues were rapidly mineralised in autumn and lost by leachin g over winter. Residues from later-harvested sugarbeet were mineralised dur ing the growing season of the subsequent cereal crop. Fertiliser-N requirem ents were, at c 110-140kgha(-1), smaller than has been found on other soil types, and less than current recommendations for wheat. Requirements were s ignificantly reduced in years of drought stress. No differences were found in N-opt between wheat and barley. These data do not justify the current ad vice to invariably reduce fertiliser-N to cereals following potatoes by 20- 25kgha(-1) on these sandy soils. On average a reduction of c 20kgha(-1) cou ld be made following sugarbeet, with a further reduction of c 40kgha(-1) N if manures had been applied to the previous sugarbeet crop. A reduction of 40kgha(-1) N could also be made where cereals followed a potato crop to whi ch manures had been applied. Further refinements on the basis of measuremen ts of soil mineral N could not be justified. Seasonal variation in N respon se due to drought stress makes recommendations difficult on these soils. Ad opting the fertiliser-N recommendations proposed here would produce N surpl uses to the soil of c 37, 10 and 27kgha(-1) respectively following cereals, sugarbeet and potatoes when cereal grain is removed but straw incorporated . On farms where straw is removed, N surplus would be largely eliminated. Our recommendation that no reduction in fertiliser-N application to cereal crops grown on sandy soils should be made following potatoes will not incre ase fertiliser-N use and is not expected to increase nitrate leaching. Some reduction in nitrate leaching may be achieved if recommendations following cereal crops and sugarbeet are made in accordance with the results reporte d here. (C) 2000 Society of Chemical Industry.