Soybean yield and root growth as affected by lime rate and quality

Abstract

Lime quality is evaluated through its oxide content and degree of fineness. The higher the oxide contents and the finer the lime, the faster should be its reaction in soils. An experiment was conducted for two years in Botucatu, Sao Paulo, Brazil, to study the effects of lime quality on soybean yields and root growth. Lime rates were calculated to raise base saturation to 70 or 90%. Two liming materials, with reactivities of 60 and 90% were used. The maximum base saturation observed was 77%, 50 days after lime application. There were no significant differences due to lime reactivity. The 60% reactivity lime tended to give higher soybean yields at the higher rate. The higher yields were related to alleviation of Mn toxicity and a better N nutrition. There was Ca and Mg leaching down to at least 60 cm at 50 days after liming, and 80 cm in the second crop. Liming led to a concentration of soybean roots in the 0–40 cm soil layer under and between soybean rows, during vegetative growth. After flowering, the highest lime rate increased rooting in the 0–20 cm layer under the row, and decreased rooting between rows down to 40 cm. There was a positive response in root growth even when the original Ca contents in soil were about 2.0 cmol kg-1. Differences in root growth were not associated with soybean yields.