Variation in Soil Microbial Population and Soil Enzymatic Activities Under Zincated Nanoclay Polymer Composites (ZNCPCs), Nano-ZnO and Zn Solubilizers in Rice Rhizosphere

Zinc deficiency is a major problem in production of rice crop, resulting in low grain Zn content. Use efficiency of conventional Zn sources (ZnSO4 center dot 7H(2)O) is very low. Therefore, technological interventions for increasing Zn use efficiency need to be explored. Nanoformulations of Zn, i.e. zincated nanoclay polymer composites (ZNCPCs), nano-ZnO (foliar application) and zinc solubilizer (Azospirillum brasilense), were compared with ZnSO4 center dot 7H(2)O (soil and foliar application) in rice (Oryza sativa var. Rajendra Mahsuri) rhizosphere at various phenological growth stages (maximum tillering, panicle initiation and harvesting). Effect of various Zn carriers on soil microbial population, enzymatic activities, DTPA-Zn content and Zn uptake was documented in pot experiment in Zn-deficient soil (DTPA-extractable Zn 0.48 mg kg(-1)). DTPA-extractable Zn content in soil at harvesting stage was found to be maximum in T-6 (3.50 mg kg(-1)) followed by T-4 (3.46 mg kg(-1)). Microbial population (bacteria, actinomycetes, fungi and zinc-solubilizing bacteria) was recorded to be highest in T-4 (RDF + Azospirillum brasilense) followed by T-6 (ZNCPC) at panicle initiation, maximum tillering and harvesting stages. Dehydrogenase activity was higher at maximum tillering stage in T-6 (ZNCPC) followed by that in T-4. Acid and alkaline phosphatase activities were found to be maximum at panicle initiation stage in T-6 followed by T-4 treatment. ZNCPC and zinc solubilizers stimulated soil microbial population consequently increasing the soil enzymatic activities and resulted in release of DTPA-extractable Zn in the rice rhizosphere. Maximum zinc uptake was recorded in treatment T-6 (ZNCPC) Zn (303.42 mg kg(-1)). ZNCPC proved to be a promising fertilizer in increasing Zn use efficiency in rice rhizosphere. Findings of the present investigation need to be further evaluated in long-term field experiment to identify its cost/benefit ratio.