Carbon and nitrogen dynamics under simulated management systems
1998
Mtambanengwe, F.
The influence of four land-use systems on soil organic matter (SOM) dynamics was investigated during a five-year experiment. Changes in total soil organic C, total N and soil microbial biomass (SMB) C and N were monitored under conditions simulating a disturbed savanna ecosystem. This was through a) removal of grass inputs to soil (simulating grazing), b) by removal of tree litter inputs to soil (clearing for pasture), c) by removal of both (clearing for agriculture and settlement), and d) by removal of both plus intensive soil disturbance via tillage. The results indicated that conversion of miombo woodland into other land-uses resulted in a remarkable decline in SOM. Both soil C and N contents were controlled by plot treatment (p 0.01) and by the third year maximum C declines of about 30% were observed in the top 10 cm of soil in some of the treatments. SMB C and N responded to surface organic matter manipulations almost immediately. In treatments where organic matter was physically removed, the SMB size continued to decrease during the experimental period. There was a general positive increase in SOM content in the natural miombo woodland and the simulated grazing treatments compared to the other three treatments although the rate appeared to have slowed during low rainfall years. The declines in soil organic C and N and SMB pools depended upon a) land use management, b) quality of organic input, and c) disruptions in C cycling and magnitude of soil disturbance. These findings suggest that a close monitoring of the active and labile SOM pools may provide an early warning sign to try to minimize SOM declines.
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