Long Term Effects of Continuous Rotational Cropping and Fertilization on Crop Yields and Soil Properties-III. Changes in the Fractions of N, P and K of the Soil

Analysis of surface and subsurface soil samples collectedfrom a long term fertilizer experiment indicated that continuous cropping without fertilization decreased the N, P and K fractions of soil to a considerable extent. Well fertilized plots showed an increase in the fractions of these nutrients in soil. The non-distillable acid soluble nitrogen fraction constitute the highest percentage of soil nitrogen. Ca-P and Fe-P forms were more important than Al-Pinricebased cropping system. The tendencies of shift from Ca-P to Fe-P and Al-P and from total K to plant available K were noticed.