Patterns of Water Uptake and Root Distribution of Soybeans (<i>Glycine max</i>.) in the Presence of a Water Table¹

Abstract

Abstract The increasing importance of water use in crop production has demonstrated the need for integrated studies of water transport phenomena in the soil‐plant‐atmosphere system. A better understanding of the basic principles involved can lead to better management techniques for efficient water use. The purpose of this work was to measure water uptake patterns of soybeans ( Glycine max. ) and relate these to root distribution and water uptake per unit root length. Water uptake in soil columns was analyzed using the flow equations for water movement in the soil, treating the root system as a macroscopic sink. The sink term represents the volume of water removed by the roots from a known volume of soil per unit time. Two soil columns were analyzed periodically for water content, root weight, and root length. Graphical evaluation of the water content and soil water flux distributions as a function of depth and time permitted determination of the sink term. The results indicated that in the presence of a water table, water uptake was not necessarily related to root distribution and that a small amount of roots near the capillary fringe absorbed most of the water. The results also showed the combined importance and interaction of the hydraulic conductivity and the root distribution in determining the magnitude and the distribution of the sink term. Both of these factors limited the rate of uptake. As the plants grew, both increased water uptake per unit root length and increase in the length of roots contributed to meeting the rising daily rate of water use.