The chemical composition of the soil in a factorial experiment with citrus. II. Extractable ammonium

Abstract

Data are presented on the ammonium content of soils in a factorial field experiment with citrus, involving different cultural treatments and ammonium sulphate levels. This is an experiment under spray irrigation, located in a semiarid area with high summer temperatures. In the 0–4 in. layer of a no-tillage, bare surface treatment, extractable ammonium persisted long after the ammonium sulphate application. Below a depth of 4 in. this treatment also gave higher extractable ammonium and lower nitrate contents than the tilled treatment. Some short-term experiments indicated that the absence of mixing in the 0–4 in. layer was a contributing factor in the reduced nitrification of the bare surface treatment. It was also found, however, that the nitrifying capacity of the soil from the area between the trees of the bare surface treatment was reduced as compared with those of the rest of the experiment. It is concluded that under the experimental conditions nitrification was rapid in the soil of the tilled plots, even in those which had a soil pH as low as 4.3.