Index >> Rhizobium and Legume Root Nodulation >>Mineral Nutrition

Similarly, various combinations of calcium and hydrogen ions produce no effect on the legume partner as well. Thus, the depressing effect on nodulation caused by' poor calcium status and acidity of a substrate remains to be explained. The answer probably lies in understanding the effect of these factors on the pre-and post-infection stages of Rhizobium in legume roots.

It has been established that molybdenum is indispensable for symbiotic nitrogen fixation and stimulates the nitrogen-fixing activity of the nodular tissue. Nitrogen fixation by nodulated lucerne and white clover in agar cultures is enhanced by additions of molybdenum. This has also been demonstrated in field experiments with subterranean clover in the absence of combined nitrogen. The accumulation of molybdenum is higher in the nodular tissue than in other parts of the plant.

In subterranean clover, addition of cobalt to sand cultures at the rate of 0.006 to 0.06 m resulted not onl in formation of bigger nodules, but also stimulated nitrogen fixation. Under field conditions, cobalt has been found to significantly increase the yield of dry matter and nitrogen per plot of subterranean clover inoculated with R. trifolii, although no significant increase in nitrogen per cent was noticeable.

Several independent experiments show that the application of super-phosphate to leguminous crops increases the number of nodules on roots and also improves the growth and nitrogen content of plants.

Rotation of crops with phosphatic manuring enhances the nitrogen content of soil as demonstrated at the Indian Agricultural Research Institute with berseem clover (Egyptian clover, Trifolium alexandrinum) where increase in soil nitrogen amounted to about 466 lb per acre over a 1D-year period for 6 berseem crops.