Influence of the Irrigation Regime on the Soybeans (Glycine Max) Root System

Abstract

The efficiency of crop irrigation depends largely on the extent of the root system and the corresponding depth at which the soil is moistened by irrigation. The incorrect determination of irrigation rates can cause water stress or unnecessary irrigation costs, and in both cases the efficiency of irrigation decreases. The aim of this work is to study the root system of soybean plants irrigated with full and reduced irrigation rates. The research work was been carried out on alluvial meadow soil from Bulgaria. The variety “Biser” is used. Treatments of the experiment: 1) without irrigation; 2) full irrigation (100%m), 3) irrigation with 70% of the full irrigation application rate (70%m), 4) 50%m, 5) 30%m. Water applications in treatment 2 were realized at 80% of FC (field capacity) pre-irrigation soil moisture in the 0-60 cm soil layer. Irrigation water was applied in short closed furrows. The weight of the roots and their distribution in soil layers were established. For this purpose, soil monoliths with dimensions of 10x35x10 cm at a depth of up to 100 cm have been cut. The irrigation regime had a significant impact on the soybean root weight. The small irrigation rates can increase their dry weight by almost a quarter. The higher irrigation rates can increase the root weight between 64 and 73%. The main part of the soybean roots (37-44%), regardless of the irrigation regime, is located in the surface soil layer 0-20 cm. Most of it is in the 10-20 cm soil layer. In the critical soil layer (20-40 cm), 23% of the roots of non-irrigated plants and 27% of the roots of those irrigated with low irrigation rates (30%) are formed. When applying irrigation rates in the range of 50-100%, the relative share is the same (30-31%). If irrigation rate is calculated to moisten the layer 0-40 cm, it can provide water to 67-70% of the entire root system. If it is calculated for 0-60 cm, it covers 86-89% of the root system. The conclusion is that the criterion for irrigation should be provides the optimal soil moisture in the layer 0-40 cm, and irrigation rates should be moisten the soil layer up to 0-60 cm.