Effect of Long-term Manuring and Rotational Cropping on Fertility Status of Alluvial Calcareous Soil

In the Pusa Permanent Manurial Experiments in north Bihar, the average crop yields for the last four decades have no doubt shown the superiority of farmyard manure under the rainfed system of cropping on the alluvial calcareous soil but a nearly comparable efficiency has been observed with NPK fertilizers. The beneficial role of phosphate on soil fertility has been clearly evidenced more so with the introduction of legumes in the rotation. The limited efficiency of green manuring has tremendously gone up with phosphate supplementation in producing the highest yields of wheat and barley.

FYM and green manuring with phosphate have resulted in the highest contents of organic matter and nitrogen in the soil. Similarly, use of NP and NPK fertilizers has also indicated noticeable increases. Phosphate manuring has markedly improved the available P status. The C.E.C. has increased with green manuring, the effect of FYM and NPK fertilizers being rather small. The exchangeable base status and soil reaction have not undergone any appreciable change due to the treatments.

The treatments and rotations have not brought about any major differences in the total P, K, Ca and Mg contents in the soil. The total manganese content has shown a small variation. Water soluble Mn is present in negligible amounts. FYM application has resulted in an increase in the exchangeable Mn status. The content of easily reducible Mn has been fairly high under green manuring and NPK treatments leading to a decrease in the total/active ratio. Significant and positive correlation has been observed between organic carbon and easily reducible Mn and between available P₂O₅ and active Mn in the soil.