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Measuring potassium fractions is not sufficient to assess the long-term impact of fertilization and manuring on soil’s potassium supplying capacity

Das, Debarup, Nayak, AmareshKumar, Thilagam, V.K., Chatterjee, Dibyendu, Shahid, M., Tripathi, Rahul, Mohanty, S., Kumar, Anjani, Lal, B., Gautam, Priyanka, Panda, B.B., Biswas, S.S.
Journal of soils and sediments 2018 v.18 no.5 pp. 1806-1820
Endoaquepts, NPK fertilizers, animal manures, calcium chloride, clay minerals, equations, fertilizer application, grain yield, long term effects, nitrogen fertilizers, nutrient management, phosphorus fertilizers, potassium, potassium fertilizers, research institutions, rice, soil sampling, India
PURPOSE: Potassium (K)-fractions, thresholds of K release and fixation, quantity-intensity (Q/I) parameters of K, K-release kinetics, and K-fixation capacity were compared for their effectiveness in differentiating the effect of various nutrient management practices on K supplying capacity of an Aeric Endoaquept soil after 45 years of puddled rice cultivation. MATERIALS AND METHODS: Soil samples (0–15 cm) were collected after the completion of 45 rice-rice cycles from an on-going long-term fertilizer experiment located in ICAR-National Rice Research Institute, Cuttack, India. The treatments involved control (unfertilized), N (nitrogen fertilizer), NP (N+ phosphorus fertilizer), NK (N+ potassium fertilizer), NPK (N + P + K fertilizer), FYM (farmyard manure), N + FYM, NP + FYM, NK + FYM, and NPK + FYM. RESULTS AND DISCUSSION: Rice cultivation without K fertilizer application resulted in lower values of soil K parameters than the K-fertilized treatments. Treatment effects were most prominent on release threshold concentration (RTC), followed by cumulative K release, K-release rate constants, and K-fixation capacity. Parameters of K-release kinetics and Q/I relationships showed better correlation with rice grain yields than soil-K fractions. Soil K thresholds were closely related with exchangeable (Kₑₓ) and non-exchangeable K (Kₙₓ), but not clay minerals. CONCLUSIONS: Among the soil K parameters, RTC, cumulative K release (Kf) with 0.01 M CaCl₂, release rate constants (b R and b S) of parabolic diffusion equation, and K-fixation capacity were most effective in revealing the nutrient management induced variations in soil K fertility. In the studied soil, K-thresholds were significantly related to Kₑₓ and Kₙₓ.