SOME EFFECTS OF NITRATE ON SOYBEAN ROOT DEVELOPMENT

Abstract

The objective of this study was to determine the effect of nitrate on some morphological aspects of soybean (Glycine max (L.) Merr.) root growth and to determine the role of drainage in the response. Two indeterminate soybean cultivars were grown on 0, 10 and 40% mixtures of perlite and Brookston clay loam, supplied with Bradyrhizobium japonicum strain USDA 110, and watered with nutrient solutions containing 0 or 6 mM nitrate. Plants were grown in acrylic tubes until 21 and 53 d after emergence in corresponding field and growth room experiments, respectively. Response variables measured were the rate of taproot extension, root counts at the acrylic-soil interface, and top, root, and nodule dry weight. Nitrate suppressed nodule development and increased top dry weight but had no effect on the rate of taproot extension. Nitrate increased root counts and root dry weights in the field test, but decreased root counts in the growth room test. Top:root ratio was increased in the growth room but not in the field test. Increasing the proportion of perlite generally increased rates of root extension, root counts, and top dry weights in the field and growth room experiments. However, the soil mixture had no effect on nodule dry weight at either location, or on root dry weight in the growth room.Key words: Root extension, Glycine max, indeterminate, drainage