Effect of long-term manuring and fertilization on depth wise distribution of potassium fractions under sorghum-wheat cropping sequence in vertisol

The effect of long-term manuring and fertilization on depth-wise distribution of potassium (K) fractions under sorghum-wheat cropping sequence in Vertisols was studied under the long-term fertilizer experiment (AICRP's) at Akola, Maharashtra. The treatments comprised of 50% NPK, 100% NPK (P applied through SSP), 150% NPK, 100% NPK(−S), 100% NPK + Zn @ 2.5 kg ha⁻¹, 100% NP, 100% N, 100% NPK + FYM @ 5 t ha⁻¹, 100% NPKS, FYM @ 10 t ha⁻¹ to sorghum and wheat, 75% NPK + 25% N through FYM and Control laid out in randomized block design. The results of the present study revealed that, application of 100% NPK + FYM @ 5 t ha⁻¹ significantly increased the fractions of K viz., available K (210 mg kg⁻¹), water soluble K (8.75 mg kg⁻¹), exchangeable K (201 mg kg⁻¹), non-exchangeable K (945 mg kg⁻¹) and lattice K (17078 mg kg⁻¹) in 0–15 cm depth. Similar trends in K fractions were also noted in 15–30 and 3045 cm depths. The sequential order of dominance of different fractions of K were: lattice K > nonexchangeable K > exchangeable K > available K > water soluble K. The highest negative balance of K was recorded with the application of 100% NP (−3513 kg ha⁻¹) followed by 100% NPK + FYM @ 5 t ha⁻¹ (−3110 kg ha⁻¹) and 150% NPK (−2838 kg ha⁻¹). The application of NPK + FYM (470 kg ha⁻¹), 150% NPK (432 kg ha⁻¹) and 100% NPK (378 kg ha⁻¹) resulted in improving the status of available K over its initial (358 kg ha⁻¹) status. The grain yield of sorghum and wheat was influenced significantly with the application of NPK + FYM (5.27 and 3.39 t ha⁻¹) followed by 150% NPK (4.87 and 3.21 t ha⁻¹). The SYI of the system was improved with NPK + FYM as compared to control for sorghum (−0.008) and wheat (0.004). The contribution of non-exchangeable K to total uptake was higher in NP (3316 kg ha⁻¹) followed by NPK + FYM (3060 kg ha⁻¹). All the K forms showed significant and positive correlation with yield and uptake of K. There exists a significant and positive correlation indicating dynamic equilibrium among all forms of K.