Zinc Availability to Maize and Wheat in Relation to P and K Status of the Soil in a Long-Term Fertilizer Experiment

The availability of Zn to maize and wheat was studied at different levels af applied P and K in a soil after two cycles of fixed crop rotation in a long-term fertilizer experiment at Punjab Agricultural University farm, Ludhiana.

The soil tested low in available P before the start of the experiment. After two cycles of the crop rotation, the available P content increased to medium or high levels depending on the rate of fertilizer P application. The initial low level of available K did not change even after addition of K during the two cycles of rotation. The available Zn content of the experimental soil declined with continuous cropping. The activities of Zn⁺² and PO₄⁻³ were measured in the equilibrium soil solution after treating the soil of different treated plots with graded levels of Zn in the form of ZnSO₄. Calculation of the activity product, (Zn⁺²)³ (PO₄⁻³)², in the equilibrium soil solution indicated the absence of the solid phase, Zn₃(PO₄)₂. ₄H₂O in the soils from different treatments.

The high level of available P of soils from the experimental plots reduced the uptake of Zn and yield of maize. The effect was not evident with wheat crop in the rotation. There seems to be an indication that the interaction of P and Zn occurs within the roots. The application of K enhanced the uptake of Zn and yield of maize and wheat crops. The application of phosphate without added K appears to lower the translocation of Zn from roots to shoots. The applied K may overcome the retarding effect of applied P on the translocation of Zn from roots to shoots.