Root Growth and Distribution are Affected by Corn‐Soybean Cropping Sequence

Abstract

AbstractCorn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield better when grown in rotation than when grown in monoculture, even under high inputs. The explanation for this yield increase due to rotation is not yet known. The objective of this study was to evaluate the effect of cropping sequence on seasonal root development of corn and soybean. We hypothesized that there would be more roots on rotated crops than on crops held in a continuous monoculture. The research was conducted in 1991 and 1992 at the Univ. of Minnesota Southwest Experiment Station on a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll). Destructive root sampling via soil cores was performed at the seedling and flowering stages of both crops. Nondestructive root monitoring was performed weekly and recorded on video cassette tapes via an agricultural research video camera inserted into minirhizotron tubes that had been placed into the soil beneath crop rows. Our hypothesis that there would be more roots on first‐year corn than continuous corn was generally supported. Minirhizotron monitoring suggested that corn grown in rotation had greater root length density than continuous corn, with the exception of the top 12.5 cm, where continuous corn had greater root length density early in the season. Soil cores confirmed 22% more seedling roots in the top 12.5 cm on continuous corn. Our hypothesis that there would be more roots on first‐year soybean than continuous soybean was generally not supported. Minirhizotron monitoring indicated that when there were differences, continuous soybean had more roots than rotated soybean, with the single exception of depths of 37.5 to 50 cm, where rotated soybean had more than twice as many roots at flowering in 1992. Root length density data obtained from soil cores also indicated that rotated soybean had approximately twice as many roots at depths of 36 and 48 cm at flowering. Growth and distribution of both corn and soybean roots were thus affected by cropping sequence. Fewer roots in continuous corn may have been the result of autotoxins from decomposing roots of the previous corn crop. We do not have an explanation for increased soybean roots under monoculture.