Pruning management effects on soil carbon and nitrogen in contour-hedgerow cropping with Leucaena leucocephala (Lam.) De Wit on sloping land in Haiti

Application of hedgerow prunings to the soil in alley cropping is practiced to sustain crop yield but information is lacking on effects of hedgerow management on soil C and N dynamics under continuous cropping. Cumulative effects of 3.5 years of leucaena [Leucaena leucocephala (Lam.) De Wit] hedgerow management on soil organic C and N and potential C and N mineralization were determined in an alley cropping experiment in Haiti. Treatments were combinations of pruning uses and pruning regimes in a 3 X 3 factorial with a no-tree control (rock walls) in a randomized complete block design with 3 replicates. A hedgerow + fertilizer treatment in an adjacent trial was included for comparison. Soil samples collected at 0-5, 5-10 and 10-20 cm depths were sealed in mason jars and incubated at 25degreesC for 30 days. Organic C and N and inorganic N were measured before the incubation. Inorganic N and respired CO2-C were measured after the incubation. After 3.5 years, surface soil samples with prunings applied as mulch or incorporated at planting had, respectively, 20 and 16% higher organic C, 34 and 18% higher organic N concentrations, higher potential C and N mineralization and higher relative N mineralization than with prunings removed. Soil C and N dynamics were similar between pruning application methods. The two-cut regime with a longer regrowth period after cutting (0-40 DAP) had highest organic C in the 0-20 cm soil layer whereas two-cut with a shorter regrowth period (0-30 DAP) had highest C turnover. Within soil layers, pruning application had higher organic C and N and potential C and N mineralization than the no-tree control and alley plots with prunings removed in the 0-5 cm layer whereas the latter treatments had similar C and N dynamics at all depths. Addition of N-P-K fertilizer in presence of fresh prunings did not increase soil organic C and N but enhanced N dynamics in the surface soil.