Evaluation of different analytical methods for the estimation of available N, P, K and Zn in soil

Abstract Different chemical methods were tested to measure the available nitrogen (N), phosphorous (P), potassium (K), and zinc (Zn) in rice-wheat soils. The results show that the available N extracted by alkaline KMnO4 was highest (429.24 kg ha−1) followed by 4 M KCl (233.35 kg ha−1) and aerobic incubation (with a mean value of 83.63 kg ha−1). The Mehlich-3 extracted P on an average 12% more than Olsen's P and 98.92% more than Bray-I method. The available K extracted by Mehlich-3 method was highest (86.81 kg ha−1) followed by NH4OAC (83.93 kg ha−1) and CaCl2 (76.59 kg ha−1). The results also record that the Mehlich-3 extracted on average 114.04% more Zn than 0.005 M DTPA and 31.18% more than 0.1 N HCl extraction methods. The results highlight that the 0.1 N HCl extracted on average 63.16% more Zn than 0.005 M DTPA extraction method. The highest correlation of coefficient (r) for the estimation of available N, P, K and Zn were alkaline KMnO4 vs. aerobic incubation (0.972∗∗); Mehlich-3 vs. Olsen's P (0.994∗∗); Mehlich-3 vs. NH4OAC (0.995∗∗) and Mehlich-3 vs. 0.1 N HCl (0.615∗∗).The results suggest that alkaline KMnO4 and Mehlich-3 method of extraction are superior for the estimation of mineralisable N and available P, K and Zn from soils as shown by the ‘r’ values.