Transformation, leaching and uptake of fertiliser‐N applied to winter and to spring wheat grown on a light soil

Winter and spring wheat were grown on a light soil without fertiliser‐N or with 100 lb. of N/acre applied as ammonium sulphate or ‚calcium nitrate’︁; dressings were applied in autumn or in spring. The same treatments were also applied to uncropped soil. Most of the nitrate‐N in unfertilised soil and that from ‚calcium nitrate’︁ applied in the autumn had been leached below 36 in. by the following March. Ammonium sulphate nitrified slowly on one plot, where the soil was acid, and the dressing applied in autumn was partly retained as ammonium‐N, but on other plots most of the nitrogen was nitrified and had been leached below 36 in. by the following March. With no crops, the mineral‐N content of unfertilised plots and of those receiving fertiliser‐N in the autumn, increased from March to August. Fertiliser‐N applied in the spring remained in the surface layers and would have been available to a crop throughout the growing season. Wheat removed both soil mineral‐N and fertiliser‐N from March onwards; by the end of May most of the fertiliser‐N applied in spring had been taken up from the soil by the crop. At harvest, the soil of all plots under wheat contained similar, small amounts of mineral‐N. Both unfertilised wheat and wheat receiving fertiliser‐N in autumn had maximum dry matter and N content at harvest. Dry matter produced by wheat with fertiliser‐N in spring also increased to harvest, but most fertiliser‐N was recovered in the crop in late May. Winter wheat had a similar total‐N content at harvest as in late May, but spring wheat contained less at harvest. For both spring‐ and autumn‐sown wheats, the apparent recovery of fertiliser‐N decreased between May and harvest.