Short-term effects of nutrient management regimes on biochemical and microbial properties in soils under rainfed ginger (Zingiber officinale Rosc.)

The aim of the study was to determine the short-term effects of contrasting nutrient management regimes on sensitive soil biochemical and microbial parameters under an annual rainfed crop (ginger, Zingiber officinale Rosc.) grown in raised beds. The nutrient management regimes employed in the study were organic nutrient management (ONM), chemical nutrient management (CNM) and integrated nutrient management (INM). ONM involved organic manures (farmyard manure (FYM), vermicompost, neem cake, ash) and biofertilizers (Azospirillum lipoferum and Bacillus phosphaticum var megaterium), CNM involved exclusive use of chemical sources of NPK and INM involved a combination of chemical sources of NPK+FYM. The study also included a control where no fertilizers, whatsoever, were applied. The variables studied were soil organic carbon (SOC), dissolved organic-C (DOC) and -N (DON), microbial biomass-C (CMIC), -N (NMIC) and -P (PMIC), net N mineralized (NMIN), soil respiration (SR) and activities of dehydrogenase (DHA), acid phosphatase (Ac-P), β-glucosidase (βG), urease (UR) and arylsulphatase (AS). Various ratios of these biochemical/microbial indices viz., DOC:DON, CMIC:SOC (QMIC), CMIC:NMIC, SR:CMIC (metabolic quotient, qCO2) were also examined. The influence of nutrient management regimes was most evident on SOC, DOC, DON, soil microbial and biochemical properties. The levels of SOC and DOC were significantly greater in ONM and INM compared to CNM and control. Conversely, DON level was markedly higher under CNM compared to ONM and INM. CNM also positively influenced NMIC but decreased CMIC, PMIC and SR levels. NMIN followed an identical trend as microbial biomass and SR; being greatest in INM and ONM. Likewise, the DOC:DON, CMIC:SOC (QMIC) and CMIC:NMIC ratios were greatest in ONM and least in CNM. Contrarily, higher qCO2 in CNM and control suggested microbial communities which are energetically less efficient with high maintenance C requirement. Results on enzyme activities revealed that not all the treatments affected the enzyme activities to the same degree. The activities of DH, Ac-P and βG were in the order ONM>INM>CNM, while the activities of UR and AS were in the order CNM>INM>ONM. The strong effects of nutrient management regimes implied that soil biochemical/microbial parameters are sensitive enough to detect changes in soil quality even in the short-term. ► Short-term organic manuring positively influenced soil microbial activities. ► Soil microbial biomass