Crop Root Distribution as Influenced by Grain Sorghum‐Soybean Rotation and Fertilization

Abstract

AbstractSoil physical, chemical, and biological changes resulting from crop rotations are likely to affect root development. Yet, crop rotation effects on root distribution have received little attention. The objective of this experiment was to measure the effect of soybean, Glycine max (L.) Merr. and grain sorghum, Sorghum bicolor (L.) Moench, rotation and fertilization on root distribution. Root samples were collected from an experiment with a 6‐yr history of (i) continuous soybean, (ii) continuous grain sorghum, (iii) soybean‐grain sorghum rotation, and (iv) grain sorghum‐soybean rotation. The experiment was conducted on a Sharpsburg silty clay loam (fine, mont‐morillinitic, mesic, Typic Argiudoll) near Mead, NE. Fertilizer treatments consisted of (i) control (no fertilizer), (ii) N at 45 kg ha−1 on soybean plots and 90 kg ha−1 on grain sorghum plots, and (iii) manure applied at 15.8 Mg dry weight ha−1 yr−1. Roots were sampled to a depth of 120 cm in 1986 and 150 cm in 1987. Root densities were reduced at most depths when soybean had been grown the previous year. Total root lengths per unit land area were 14, 21, 25, and 33 km m−2 and total root dry weights were 111, 136, 132, and 190 g m−2 for continuous soybean, soybean after grain sorghum, grain sorghum after soybean, and continuous grain sorghum, respectively. Fertilizer effects on root development were not consistent between years. Total soybean root length was positively correlated to grain yield, whereas grain sorghum root length in the 0‐ to 30‐cm zone was negatively correlated to shoot dry matter, kernel numbers, and grain yield.