Root Distribution and Shoot Development in No‐Till Full‐Season and Double‐Crop Soybean

Abstract

AbstractDry matter accumulation by soybean [Glycine max (L.) Merr.] has been studied extensively, but few data are available on the relationship between shoot development and root distribution of no‐till full‐season and double‐crop soybean. Row spacing and K availability effects on shoot growth are also well understood, but have not been thoroughly integrated with measures of root growth. The objectives of this research were to characterize soybean root length density and distribution as well as shoot dry matter accumulation under no‐tillage soil management for: (i) full‐season and double‐crop planting dates, (ii) high and low soil K fertility levels, and (iii) narrow and conventional row spacings. Potassium fertility did not alter total shoot weight at R1, R5, or R7, but did alter shoot dry matter partitioning at R7. Later planting dates reduced shoot growth at R1, R5, and R7. Seed yield was increased by greater K availability, earlier planting and a narrower row width. Dry soil conditions during vegetative growth reduced root length density (RLD). As water became more available during reproduction, RLD increased. With adequate soil moisture, full‐season soybean RLD was greater than double‐crop soybean RLD. Surface soil RLD was greater when soil K fertility was low. Leaf abscission was delayed by K stress. In crop development periods when root growth was most active, the root length/shoot dry weight ratio was greater in double‐crop than in full‐season soybean. Double‐crop soybean produced relatively more root length in support of shoot growth than did full‐season soybean. Root growth was more affected by soil K availability and less affected by plant spacial arrangement and density than was shoot growth.