Impact of slash-burning and plant species on soil microbial community and processes in Jhum agro-ecosystem
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Date
2020-07
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College of Post Graduate Studies in Agricultural Sciences, CAU-Imphal, Umiam
Abstract
Terrestrial ecosystem supports the above- and below-ground biota communities that interact to influence ecosystem-level processes and functions. Soil acts as the most important medium for linking the above- and below-ground communities which are very sensitive to any external disturbances. To study the effect of above- and below-ground linkages on soil microbial community composition and soil processes, the short jhum cycle can be considered as important experimental plot in farmers’ field. Because the above ground plant biomass generated during fallow phase of the jhum cycle gradually rejuvenate the degraded soil system and upon burning of such biomass suddenly breakdown the linkages between above-ground and below-ground community linkages. In this study, a jhum field (approximate 1.5 ha) during fallow phase of 5 year cycle was considered from Muallungthu village, Aizawl, Mizoram and the one half part of the field was slashed and burned and the other half part of the field was kept unburnt. The bulk quantity (800 kg) of soil (0-10 cm depth) from 4 random spots (1 sqm per spot) was collected immediately next morning of burning night from the burnt field and similar way 800 kg soil from unburnt field were collected and carried to the CPGS Farm Field for setting up of mesocosm (pot) experiments under 4 conditions viz. burnt and unburnt soils in presence of rice crop and without rice crop. Under each of 4 conditions, 6 microbial inoculation (MI) treatments were imposed maintaining 6 replicated pots. Each pot contained 4 kg soil. Altogether 144 pots were maintained (4 conditions x 6 MI treatments x 6 replications = 144). The MI treatments were: (T1) PSB+Fungi, (T2) N2-Fixer+Fungi, (T3) CDB+Fungi, (T4) PSB+N2-Fixer+CDB+ Fungi, (T5) No bacteria + Fungi and (T6) No inoculation. The rice crop used was a jhum rice landrace Khawlian Buh. The crop was maintained till harvest within a plastic shade house.
The study reveals that the soil bacterial community composition altered significantly due to burning of slashed biomass on soil surface. The introduction of rice crop also altered the bacterial community composition in burnt/unburnt which shows a distinct cluster within the soil type. The Alpha proteobacterial communities of burnt and unburnt without rice crop clustered together and distinctly separated from the clusters of burnt and unburnt soil with rice crop at 45 days of rice growth and at 90 days of rice growth the impact of rice crop on composition of Alpha and beta proteobacterial community was more consicious in burnt soil then in unburnt soil. The beta proteobacterial community of burnt and unburnt soil cluster together in absence of rice crop and there cluster was distinctly separated from the cluster due to cultivation. With the progress of time (90 days of rice growth) the effect of rice crop on beta proteobacterial community was more prominent than compared to burnt unburnt factor.
Burning had significant negative effect on the activity of DHA, GSA, PHA, SOC, pMN, POM, and MBC except ASA indicating higher activity in burnt soil. Introduction of rice crop had significant positive influence on the activity of soil enzymes and soil process indicators. There was significant positive interaction on burning and cropping on soil enzymes activities soil process indicators. There was a significant difference in the activity of soil enzymes and soil
process indicators among the microbial inoculants treatment soil process indicators. There was significant positive interaction between burnt and microbial inoculants or cropping and microbial inoculants.
The change in bacterial community composition due to burning and cropping factor significantly influence soil process indicator such as ASA, DHA, pMN, POM, and MBC as evident from analysis result of Multi dimensional Scale (MDS) 1 and 2. The change in alpha and beta proteobacterial community composition due to burning and cropping factor
significantly influence soil process indicator like PHA, ASA, DHA, pMN, POM, SOC and MBC as evident from their significant correlation with MDS 1 and 2. Burning had significant positive influence on rice growth yield. This study indicated that introduction of crop in burn soil along with microbial inoculation may positively influenced soil processes as well as crop growth.
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Keywords
Soil microorganisms, Shifting Cultivation