KLAUS-PETER GÖTZ, HELMUT HERZOG
Humboldt-Universität zu Berlin, Department of Crop Science in the Tropics and Subtropics, Germany
The soybean (Glycine max L. MERR.) was introduced to North America in the mid 1800s and was initially promoted as a forage crop. By the late 1940s, the focus had shifted almost entirely from forage to soybean grain production. However, the seeds as well as the entire plant is employed as feed stuff in animal production. The nutritive value of forage crops is a function of the composition of the individual plant components, their relative contribution to total plant dry weight and the content of nutrients. Soybeans are grown in many areas where rainfall is marginal or where drought stress is intermittent. Effects of drought on yield are known, but unknown is the impact of soil moisture deficits and the nutritive value of soybean plant organs. The influence of a 8-10 day water deficit (wd), on yield parameters was examined in 2 pot experiments in growth chambers (experiment A: wd at flowering, genotype Gieso; experiment B: wd at seed filling phase, genotype PI 416937 and Hutcheson). The dry matter (DM) and nitrogen (N) degradability of leaves, pod walls and crude seeds were estimated using the nylon bag technique (experiment A), and the in vitro gas production of crude seeds (experiment B). All yield parameters were significantly lowered by water deficit, whereas the N digestibility of pod walls and seeds, and the DM digestibility of seeds was increased. The in vitro measurements showed that seeds growth of PI 416937 which was decreased by water deficit led to a reduction of gas production, energy content and digestibility of organic matter. Such effects of water deficit were not detected in seeds of Hutcheson. This should be taken into consideration in calculating the ratio of optimum energy to nutrient utilisation, if such interactions between water deficit and genotypes prove to be generally true.
Keywords: Soybeans, water deficit, yield quality