Forms of Soil Potassium as Influenced by Long Term Application of Chemical Fertilizers and Organics in Rainfed Maize-Wheat Cropping System

A study on potassium dynamics under long term use of variable doses of imbalanced chemical fertilizers and organics in rainfed maize-wheat system was carried out in Typic Ustipsamments of low hill zone of Himachal Pradesh between rabi (2007–08) and kharif (2008) seasons in the ongoing long-term fertilizer experiment at the research farm of CSKHPKV, HAREC, Dhaulakuan. Surface soil (0-15cm) after sixteen cropping cycles was analyzed for different forms of potassium. All the fractions of potassium viz. water soluble-K, exchangeable-K and non exchangeable-K decreased from its initial status in most of the treatments. Treatments receiving K fertilizer (100% NPK) showed increase in water soluble-K and exchangeable-K fraction over the initial status. Application of FYM (Farmyard manure) in both the seasons also increased the content of water soluble-K and exchangeable-K over the initial value. In general application of FYM with chemical fertilizers showed higher content of all the fractions compared to treatments where imbalanced inorganic fertilizers were applied (100% N and 100% NP). Maximum decrease in all the fractions of K was recorded in treatment 100 per cent N followed by 100 per cent NP. Use of FYM to both crops has resulted in higher yield in case of wheat crop. Water soluble-K was the important fraction of potassium contributing towards crop yields and total K uptake.