WINTER LEACHING OF NITRATE FROM AUTUMN-APPLIED CALCIUM NITRATE, AMMONIUM-SULFATE, UREA AND SULFUR-COATED UREA IN BARE SOIL

In a flinty clay loam at Rothamsted [England], nitrate concentrations in 0-13 and 13-26 cm layers of plots given all N sources at 100 kgN/ha in early Oct. were very small by mid-Jan. Incorporating the fertilizer in the first 13 cm slightly accelerated this loss. S-coated urea (SCU) maintained smaller nitrate concentrations than other sources in both layers. By early March SCU plots alone had slightly larger nitrate concentrations than the controls in the 0-26 cm layer, while in the 26-52 cm layer all N plots had slightly larger concentrations than the controls. Spring barley, given no more N and harvested green at ear emergence, took more N from all N plots than from the controls, most from (NH4)2SO4 and least from urea and SCU, but differences between sources were not significant. The nitrate loss had a negligible effect on soil pH and exchangeable cations. Ca(NO3)2 leaching data were used to test the equation of Burns (1975) and other simple equations which considered the effects of successive percolations in a 2-layer system assuming that the layers either could or could not become temporarily oversaturated. All the equations underestimated leaching unless the most inaccessible soil water was left out of the calculations and gave best results when only gravitational water was taken into account.