Effects of depth of fertilizer placement on wheat grown under three water regimes

Abstract

Wheat was grown in reconstructed profiles of a sandy red-brown earth in pots 120 cm deep. Ammonium sulphate (40 mg nitrogen per pot) and/or monocalcium phosphate (75 mg phosphorus per pot) were placed either in the topsoil at 5 cm depth or in the subsoil at 25 cm. When the wheat reached ear emergence, water treatments were introduced to provide (a) dry topsoil and water shortage; (b) dry topsoil but ample water supply in the subsoil; or (c) an ample water supply with both topsoil and subsoil wet. The yield and concentrations of nitrogen and phosphorus in the wheat and the distribution of roots in the soil were measured at maturity. Water use by the plants was calculated. Drying of the topsoil decreased grain yield and uptake of nitrogen and phosphorus by the wheat, but the effects were small compared with those of water shortage per se. Placement of nitrogen and phosphorus at 25 cm produced higher grain yields than placement at 5 cm. There was no interaction between placement depth and the water treatments: this indicated that reduced availability of nutrients because of dry topsoil after ear emergence was not a major factor limiting yield. The fertilizer treatments affected the distribution of roots more than total root length. Root growth increased at the site of placement where nitrogen and phosphorus, and to a lesser extent nitrogen alone, were applied in the subsoil; there was little effect in other parts of the profile. Efficiency of water use was increased by the application of nitrogen.