EFFECTS OF DEPTH OF FERTILIZER PLACEMENT ON WHEAT GROWN UNDER 3 WATER REGIMES

Wheat was grown in reconstructed profiles of a sandy red-brown earth in pots 120 cm deep. Ammonium sulfate (40 mg N/pot) and/or monocalcium phosphate (75 mg P/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 dry topsoil and water shortage, dry topsoil but ample water supply in the subsoil, or an ample water supply with both topsoil and subsoil wet. The yield and concentrations of N and P 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 N and P by the wheat, but the effects were small compared with those of water shortage per se. Placement of N and P 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 N and P, and to a lesser extent N 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 N.