Variation In Soil CO2 Flux In a Tropical Dryland Agroecosystem: Impact of Addition of Various Resource Quality Inputs

Management strategies of agroecosystems influence CO2 flux as well as its sequestration potential in soil. In tropical dryland agroecosystems use of organic resources has been advocated for conserving soil moisture and improving soil fertility, A two year study was conducted to evaluate the effect of chemical fertilizer (CF) and three organic inputs, carrying equivalent amount of N, but with differing resource quality (high quality, HQR; low quality, LQR; and mixed quality, HQR +LQR, MQR) on soil CO2 flux in a tropical dryland rice-barley-summer fallow agroecosystem.

A distinct seasonal variation in CO2 flux was recorded in all treatments, higher during warm and moist (rice) period, and much reduced during cool dry (barley) and hot dry (summer fallow) periods. During rice period the mean CO2 flux was greater in LQR and MQR treatments; however, during barley and summer fallow periods differences among treatments were small. The trend of annual cumulative CO2 flux was: LQR> MQR > HQR > CF. Resource quality of inputs (in terms of C:N, lignin:N and polyphenol+lignin:N ratios) played key role in regulating soil CO2 flux.

The ratio of CO2 flux per unit C added (CO2: C) was lowest in LQR indicating possibility of high C retention in soil despite of huge loss of C. A reverse trend was found in CF and HQR with higher CO2: C ratio inspite of lower cumulative CO2 flux indicating an overall net loss of C. In MQR, although the ratio was comparable with that of LQR yet the cumulative CO2 flux was significantly lower.

CO2: C ratio may give a better indication of C dynamics as compared to cumulative CO2 flux alone. It is suggested that use of combined input may contribute to mitigation of atmospheric CO2, along with maintenance of long term soil fertility (C sequestration) in dryland agroecosystems.