Response of canola, wheat and green beans to leonardite additions.

Leonardite, an oxidized form of lignite obtained from coal mines, is readily available and high in humic acids (HA). It has potential as a soil amendment and may have positive effects on crop growth and yield. This greenhouse experiment evaluated the agronomic effect of leonardite on three crops: canola (Brassica napus), wheat (Triticum aestivum) and green beans (Phaseolus vulgare). The factorial design combined five rates of leonardite with five fertility treatments. The fertility treatments had a significant effect on the dry matter yield (DMY) of canola, wheat and green beans. There were also significant effects of fertility on the concentration and uptake of N, P and K by the three crops and S by canola. The application of leonardite had no significant effect on the DMY of wheat and green beans but that of canola was significantly increased. Application of 10 g of leonardite to 3 kg of soil caused a 27% increase in the DMY of canola when S was excluded from added nutrients, while 1 g of leonardite res...