Plant litter–soil enzyme interactions and biochemical index of soil fertility in Jhum Agroecosystem
Loading...
Date
2016-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
College of Post Graduate Studies in Agricultural Sciences, CAU-Imphal, Umiam
Abstract
This study assessed whether the slash-burn practice (jhum) induced disturbance on the above-ground biological inputs (plant and leaf litters) had any influence on the soil biochemical processes in terms of soil enzyme activities and thereby framing up biochemical index of soil fertility. The jhum cycles of 5 yr, 10 yr and 15 yr from Mizoram and 5 yr, 10 yr and 20 yr from Nagaland were selected. Litter (adjacent fallow stands/secondary forest) and soil samples (burnt and unburnt cropping phase) were collected from three slopes (upper, middle and lower) from each site and were analyzed for chemical and biochemical properties. Two microcosm experiments were conducted using jhum soils (before and after burnt and unburnt from 5 yr and 10 yr fallows) to investigate the effect of different forest floor litter types on stress physiology of jhum rice, soil chemical and biochemical processes, and also to compare the effects of litter amendment (LA), microbial consortium (MC), LA+MC, ash amendment (AA) and no input on physiology and growth of jhum rice and soil biochemical properties. Forest floor litter (FFL) accumulation significantly increases with the increasing fallow length and accumulation dynamics showed an increasing trend in the order of January> April> August> November. Quality of FFL (N, P, Ca, Mg and Zn contents) varied significantly among fallow lengths with maximum contents in the longer fallows (P0.05, Kruskal-Wallis H-test). Higher content of Carbohydrate, Cellulose, Hemicelulose, Pectin and Lignin in FLL was in the order of 20yr & 15yr > 10yr > 5yr and effects were significant. Soil chemical and biochemical properties varied significantly between burnt and unburnt or among fallow periods (P0.05, Kruskal - Wallis test). In microcosm experiment-I, there was significantly positive influence on reducing physiological stress and root growth of jhum rice due to burning or longer fallow lengths or types of FFL (5, 10 and 15 yr FFL). The extent of positive influence of FFL addition on rice grain was more pronounced under burning situation. The extent of grain yield enhancement decreased with the increasing complexity of the litter types. However, such influence was nullified under 10 yr burnt situation. In microcosm experiment II, the extent of physiological stress in jhum rice was the minimum in LA+MC followed by MC and AA. Application of LA+MC and MC supported better soil enzyme activities (AMY, ASA, DHA, GSA, PHA and PRO) in both 5yr and 10 yr burnt jhum soils as compared to other LA and AA alone applied pots. The extent of change of soil biochemical attributes, SOC and Avl P relative to reference site (reserve forest) were more pronounced due to burning as well as fallow lengths. Among soil enzymes, PRO, PHA and DHA were more sensitive to burning. Soil BD seems to be more sensitive to burning than fallow lengths. Higher fallow lengths reflected higher SQI. The differences in SQI among fallow lengths were significant under unburnt situation. In general, SQI values were higher in unburnt compared to their respective burnt situations. In conclusion, burning of biomass releases a higher quantum of plant available nutrients in jhum soils momentarily, which can support better crop growth under longer fallow lengths. However, burning negatively impacted the biochemical quality of jhum soils. Thus, it indicates that burning gradually decrease the inherent nutrient cycling potentials of jhum soils. Application of less complex litter materials along with native microbial consortium as biological inputs can rejuvenate the biochemical and biological activities of jhum soils. The SQI index values of different fallow lengths under burnt situation indicated that jhum soils seem to attain a new threshold limit of soil quality at approximate 10 yr fallow length, where SQI value was comparable with the SQI values of 15 yr and 20 yr fallows.
Description
Keywords
Shifting cultivation, Soil fertility