GROWTH DYNAMICS OF WINTER-WHEAT IN THE FIELD WITH DAILY FERTILIZATIONAND IRRIGATION

In a field experiment with fertilized and irrigated winter wheat the a bove-ground crop was sampled once a week. Phenological development, pl ant density and canopy height were recorded and the green surface area s of leaves, stems and ears were measured. Soil mineral nitrogen was s ampled and the field climate monitored. There were four treatments. Th e daily irrigated/fertilized (IF) and daily irrigated (I) treatments w ere both irrigated by a drip-tube system. Liquid fertilizer was applie d to IF following a logistic function according to calculated plant up take. A total of 200 kg N ha(-1) was applied. Treatment I, control (C) and drought (D) were all fertilized once in spring with 200 kg N ha(- 1). In treatment D transparent screens were used to divert rainwater. Dry matter production ranged between 1400 in D and 2352 g m(-2) in IF. The corresponding amount of nitrogen uptake ranged between 15.8 and 2 4.6 g m(-2). After harvest, soil mineral nitrogen was lowest in IF. An increase in the availability of nitrogen and water enhanced total bio mass production as well as grain yield and leaf area. The daily supply of nitrogen according to crop demand delayed nitrogen uptake and incr eased total uptake. The results suggest that when the nitrogen is supp lied in accordance with crop demand, the efficiency with which the app lied fertilizer is utilized increases and the risk for nitrogen leachi ng decreases.