Effects of Soil Water Content in Four Soybean Genotypes in Different Environments in the Central Area of the Argentine Pampean Region

In the Pampa Region there is limited information about the dynamics of soil water and the consumption rate of different soybean genotypes. In the Pampa Central Area, the first 15 cm of soil concentrates 80% of the soybean plant’s root weight and over 40% of root absorbent surface. Despite the importance of extracting the first centimeters of water, the water supply in deeper zones could be very important as well. Because of this fact, the evaluation of the evolution of soil moisture was proposed: in two soil types—Typic Hapludoll and Entic Hapludoll; in different climatic years; in four soybean genotypes—NA 3731RG, NA 4209RG, NA 4613RG and NA 5009RG; in their effect on crop yield. In each of these environments, soil water content measurements were made in the first 100 cm with a TDR (Total Dormain Reflectometry) drill, over varietal performance tests with three replications per genotype in each location. In all evaluated situations, a significant effect on interaction genotype x soil depth, genotype x crop emergence days and crop emergence days x soil depth was established. Also a fast development of roots was observed, having found active roots for the absorption of water within the first meter of depth 24 days after crop emergence. A difference in difference of radical elongation rate among varieties was also observed; because of the low water availability in vegetative phases with similar soil humidity distribution, the genotype NA 5009 RG had reached 20 cm more of radical activity faster than NA 4613RG. The highest crop yields were not associated to higher water content in soil during the whole cycle. Highest crop yields were associated to a combination of genotype, water availability between 50% of useful water during the whole vegetative cycle and the beginning of the flowering period, and high water availability in the first centimeters during reproductive phases. Under less water availability, the genotype with higher speed of radical deepening reached the highest yields.