Chemical Pools of Zinc and their Availability to Wheat in a Typic Haplustept as Influenced by Phosphorus and Manganese Fertilization

Pot experiment was conducted on a P-deficient sandy loam soil to study the interactive effects of P (0, 25, 50, 100, 200 and 400 mg P kg⁻¹ soil as KH2PO4) and Mn (0, 12.5, 25 and 50 mg Mn kg⁻¹ soil as MnSO4.H2O) fertilization on chemical pools of native Zn in soil and their availability to 90-days-old wheat (PBW 343) crop. Application of P transformed Zn in soil from exchangeable and Fe oxides-occluded pools to Mn-oxides occluded, organic matter bound and specifically adsorbed Zn fractions. A steep fall in DTPA-Zn was observed when P:Mn ratio in soil was 6.0. At a level of 16.47 mg Olsen-P kg⁻¹ soil and a P:Mn ratio of 3.28 in soil to produce 80% of the maximum dry matter yield of shoot, the DTPA-Zn and DTPA-Mn in soil under test was observed to be 0.98 and 5.02 mg kg⁻¹ soil, respectively. Both these values of DTPA-Zn and DTPA-Mn were higher than their established critical deficiency levels of 0.60 and 3.50 mg kg⁻¹ soil, respectively, thereby indicating the need for their supplemental additions in soils having a build up of available P in the plough layer of soils. Total Zn uptake by root plus shoot decreased steeply when Olsen P at harvest was >15 mg P kg⁻¹ soil and P:Mn ratio was >3. Path coefficient analysis using different pools of Zn revealed the importance of exchangeable, specifically adsorbed, Mn oxides bound and organically bound Zn fractions either directly or indirectly through each other in influencing the dry matter yield, concentration and uptake of Zn by wheat.