Experiments measuring the residual effects of nitrogen fertilizers

Abstract

The experiment testing N residues (made on a clay-loam soil) clearly showed that N applied for potatoes benefited the following wheat crop, but that N applied for wheat benefited the following potato crop little. There were no worth-while 1. An experiment on a clay-loam soil measured responses to three amounts of nitrogen on alternate crops of wheat and potatoes; these dressings were tested in all combinations with three rates of N applied 1 and 2 years previously. Nitrogen applied for potatoes consistently increased yields of following wheat. The residue from applying 1·5 cwt. N/acre for potatoes was equivalent to topdressing the wheat with 0·55 cwt. N/acre; the value of the residue was decreased by applying N to the wheat. Potato yields were increased little by applying N to the preceding wheat crop and the residues were of little significance when compared with the responses to new N. There was no gain from N applied 2 years previously for either crop.