Application of biochar and rhizobacteria to ameliorate the drought in maize (Zea mays L.)

Abstract

Drought is one of the major abiotic stresses among all the abiotic factors and it is recurrent climatic factor usually faced by plants in arid and semiarid areas and serious threat to food security. Biochar is a carbon rich product of pyrolysis, which have high water retention capacity due to its high surface area and highly porous nature. Plant growth promoting rhizobacteria (PGPR) are group of microorganisms in the rhizosphere, which improves plant growth through different mechanisms i.e. hormone production, ACC deaminase and exopolysaccharides production etc., under stress conditions. Simultaneous application of biochar and rhizobacteria could be an effective approach for improving growth, physiology and yield of maize under drought stress. In this study crushed corn cobs biochar was produced at 300 and 400 ̊C pyrolysis temperature. Three levels of biochar (0, 1 and 3%) were applied into the soil to find best biochar type and level for improving drought resilience in maize. Drought levels (100, 70 and 40% FC) were maintained gravimetrically. Biochar application significantly improved the growth and physiology of maize under drought stress. Overall 3% biochar produced at 400 ̊C significantly improved shoot and root length, shoot and root dry weight, relative water content and protein content in maize under drought stress. Among soil quality parameters, aggregate stability, carbon pool index (CPI), lability index (LI) and soil moisture contents were also increased significantly with 3% (400 ̊C) biochar as compared to control and increase in aggregate stability and moisture content was 80 and 132% more as compared to control at drought level 70% FC, respectively. Therefore, 3% biochar produced at 400 ̊C was selected for further evaluation in the pot trial along with PGPR under drought stress. A number of rhizobacterial strains were isolated from maize rhizosphere from arid and semi-arid areas of Punjab, Pakistan. Fast growing rhizobacterial isolates were subjected to drought tolerance assay and further screening was done under drought stress. Nine most effective isolates (LK2, LK7, LK9, LK13, LK16, LK18, LK21, LK24 and LK29) were selected to evaluate their potential for improving growth and physiology of maize under drought stress. Inoculation of LK13 and LK16 significantly improved maize seedling growth, fresh and dry weight, photosynthetic activity, transpiration rate, stomatal conductance and water use efficiency as compared to control. Isolate LK-13 and LK-16 showed maximum growth promotion and were selected for pot trial. Biochar at 3% (produced at 400 ̊C) was applied in combination with PGPR strains LK-13 and LK-16 for improving growth, physiology and yield of maize (Zea mays L.) under drought stress. Combined application of biochar and PGPR significantly improved the growth, yield and physiological parameters compared to control. Results also revealed that antioxidant enzymes (CAT, SOD, POD, APX, GPX) activity in plant leaves was reduced while soil enzymes (acid phosphatase, alkaline phosphatase & β-glucosidase) activity and microbial biomass C and N were improved significantly as compared to control. Grain yield was increased significantly upto 80% with biochar + LK-16 compared to control at 70% FC. Finally, is was concluded that biochar application @ 3% produced at 400 ̊C) along with rhizobacteria significantly improved the growth, physiology and yield of maize under drought stress. However, further evaluation should be needed for practical application under field conditions.