Soil microbial biomass carbon and soil enzymatic activity under nutrient omission plot technique in maize (Zea mays)wheat (Triticum aestivum) cropping system

A 2-year (2013 and 2014) field study was carried out at the ICAR-Indian Agricultural Research Institute, New Delhi, to access the effects of omitted nutrients on soil microbial biomass carbon (MBC), enzyme activity, the rela- tionships among these parameters in maize-wheat cropping system and to validate the soil-test-crop response (STCR)-based fertilizer application for targeted yield (5.0 t/ha) of wheat HD 2967 and maize PEHM 5 each in maize (Zea mays L.)wheat (Triticum aestivum L.) cropping system. The experiment comprising 15 treatments in- volving application of N (PKZn), NP (KZn), NPK (Zn) and NPZn (K) to both maize and wheat crops, to maize (omitted in wheat) and to wheat (omitted in maize) crop only, absolute control (no nutrient applied), recommended rate of nutrients (RDN) (150-60-40-5.5 kg/ha N-P-K-Zn) and STCR-based application of nutrients (200-75-65-4 kg/ ha N-P-K-Zn). The fixed plots experiment was carried out in a 3-time replicated randomized complete block de- sign. The dehydrogenase, alkaline phosphatase and urease enzyme activities in soil and MBC were significantly higher with STCR approach-based NPKZn application than the others for targeted yield of 5 t/ha of both maize and wheat crops. The continuous omission of N, P, K and Zn in a cropping system during both the study years reduced MBC by 51.9, 7.6, 12.7, 6.5% respectively. The recommended dose of NPKZn resulted in higher activity of dehy- drogenase, urease and alkaline phosphatase enzyme than N, NP, NPK, NPZn treatments and absolute control. The continuous omission of N, P, K and Zn in a cropping system significantly reduced the soil enzymes activity in maizewheat cropping system.