Response of canola, wheat and green beans to leonardite additions

Abstract

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 resulted in a 15% increase in yield when all nutrients were applied. In addition, uptake of S, N, P and K by canola were significantly affected by the application of leonardite. The yield response of canola was apparently due to the supply of S by leonardite with an increasing rate of leonardite supplying increasing amounts of S. This result was confirmed in a second experiment where high quantities of leonardite were applied. We concluded that leonardite increased the yield of canola by supplying S directly and by possibly facilitating the uptake of other nutrients. The lack of response of wheat and green beans to leonardite was attributed to their lack of response to S. The experiment showed beneficial effects of leonardite on canola, though high rates may be needed to exploit this benefit in field situations. Key words: Leonardite, humic acid, green house, canola, fertility