The influence of watering regimen on soil pH and zince nutrition of soyabean cv. Wills grown in soil pot culture

Abstract

The changes over time in soil pH, plant growth and zinc uptake by soybean (Glycine max (L.) Merr.) cv. Wills grown in a zinc-deficient black earth under two watering regimens, viz. watering to weight (WTW) and constant water table (CWT), were determined in a pot experiment. In the absence of applied zinc, CWT plants achieved twice the dry matter yield of WTW plants. Interveinal chlorosis was observed on CWT plants at 20 days after sowing, but not on WTW plants at any time during the experiment. Leaf lamina zinc concentrations at a number of nodes were less than 10 ¦g g-1 in plants grown for 25 days under both watering regimens. Fertilization with zinc at 30 kg zinc ha-1 significantly increased the dry matter yield of CWT plants and, particularly, the size of laminae at node 5 and above. Plants grown in the absence of applied zinc recovered from zinc deficiency over the period from 25 to 35 days after sowing. Rates of dry matter and zinc accumulation over this period increased, while zinc concentrations in the plant and particularly in the younger leaves increased markedly. This recovery coincided with a substantial decline in soil pH. The recovery from zinc stress is attributed to the greatly increased availability of zinc to the plant roots which may have resulted from the drop in soil pH.