BENEFICIAL EFFECTS OF MILD WATER DEFICIENCY ON GROWTH AND YIELD IN THE SEEDLING STAGE OF SOYBEAN

This experiment was conducted at Heilongjiang Bayi Agricultural University in China, using Sui Nong 26 soybeans and negative pressure water supply equipment.The study set different water control periods (V1, R1, and R5 stages) and varying degrees of water stress (normal, mild, moderate, severe) to analyze soybean yield, nutrient uptake, growth, and physiological and biochemical responses to drought and water compensation.The aim was to establish high-quality, high-yield, water-saving cultivation techniques for dryland soybeans.Results showed that increasing water stress decreased soybean plant height and stem diameter.At the V1 and R1 stages, root length initially decreased and then increased, while drought stress at R1 and R5 stages inhibited dry matter accumulation.Severe drought stress significantly reduced dry matter compared to mild stress.Mild drought stress at the seedling stage increased dry matter accumulation, but severe stress hindered recovery after rehydration.During the V1 stage, mild drought stress increased Pn, Tr, and Gs by 7.9%, 16.4%, and 1.0%, respectively.In the R1 stage, drought stress reduced Pn, Gs, Ci, and Tr, with greater reductions under more severe stress.Post-rehydration, Pn, Gs, and Ci under mild stress were higher than CK.At the R5 stage, rehydration failed to restore photosynthetic capacity.Mild drought stress increased grain yield by 5.0% at the seedling stage but reduced it during flowering and bulging stages, also increasing grain protein content while decreasing lipid content.