Long term effect of fertilizers and manure on K-fractions in inceptisol under pearl millet-mustard cropping system

The present study conducted under ongoing long term fertilizers experiment was aimed on the effect of inorganic fertilizers with or without organic manure on yield, potassium uptake and distribution of potassium fractions after ten years of pearl millet-mustard cropping sequence during 2012-13 in an Inceptisol. The investigations revealed that the maximum yield of pearl millet (4.13 t ha-1) and mustard (2.43 t ha-1) and K-uptake by them was obtained with the treatment 100% NPK + FYM + Azo. + PSB, followed by the treatment receiving 100% NPK +FYM and 150% NPK. Available –K was found to be maximum with 100% NPK + FYM+Azo.+PSB (213 kg ha-1), followed by 100% NPK + FYM (212 kg ha-1). Moreover K-fractions Water soluble and exchangeable forms of K were found to be decreased with increasing soil depths whereas, non-exchangeable, lattice and total-K showed reverse trend in all the treatments under study. The contribution of different K fractions at various soil depths studied was in order of lattice> non-exchangeable> exchangeable > water soluble. All the K-fraction at 0-30 cm soil depth exhibited significant and positive correlation with yield. Minimum depletion of K rate was recorded in 100% NPK + FYM+ Azo.+ PSB (-3.7 kg ha-1 yr-1) to that of other treatments, while control showed maximum K depletion rate (-10.1 kg ha-1 yr-1) apparent K-balance in soil was lowest -100.4 kg ha-1yr-1 in control plot followed by -104.8 kg ha-1yr-1in treatment 50% NPK+FYM. Hence, much attention is required for potassic fertilizers to maintain K status of soil and to prevent K mining. Thus, results of the experiment indicate that the depleting K reserves even at its optimal application rates points towards taking a fresh look at the existing recommendation for pearl millet and mustard crops.