Effect of Organic and Inorganic Fertilizers on Zinc Fractions and Their Contribution to Zinc Uptake under Rice-wheat System

The long-term effect of organic and inorganic fertiliser on Zn fractions in soil and their relation with Zn uptake in the rice-wheat system was studied in calciorthents of the Dr. Rajendra Prasad Central Agricultural University, Pusa Samastipur, Bihar. Application of NPK and compost and crop residue increased the water-soluble + exchangeable, carbonate and amorphous oxide, organically bound, complexed, crystalline oxide, residual and total Zn in the soil. The decreasing order of dominance of different fractions in soil was: total Zn > residual Zn >Zn bound to crystalline oxide > complexed Zn > Zn bound carbonate and amorphous oxide > organically bound Zn > water soluble plus exchangeable Zn. All the soil Zn fractions were significantly correlated among themselves indicating the existence of dynamic equilibrium with each other. Zinc uptake by rice-wheat was improved with NPK along with crop residue plus compost. Among the different Zn fractions, Zn bound to crystalline oxide followed by Zn bound to carbonate and amorphous oxide play a key role in explaining the variation in yield and nutrient uptake by rice and wheat.