Soybeans benefit from root channels created by the previous crop, but soil compaction erases that advantage.

Researchers at Sao Paulo State University in Brazil studied the effects of seven crops on root growth in soybeans. Those crops were: black oats, pigeon peas, pearl millet, mucuna, soybeans, grain sorghum and lupins. The crops were grown in pots for 37-39 days, then were cut at soil level and left on the surface for 40 days until soybeans were planted.

Soybean plant size was increased by all the previous crops compared with beans grown in pots without a prior crop. The greatest soybean root growth was in pots where black oats or pigeon peas had been grown.

A middle layer of soil in some pots was subjected to one of three compaction levels before the experiment began. Soybean root volume and length decreased as soil strength increased. The roots were unable to penetrate severely compacted soil, regardless of the previous crop.

(Rosemeire da Silva and Ciro Rosolem, Sao Paulo State University, Brazil)