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Litterfall and Soil Nutrient Dynamics in Three Coffee-based Agroforestry Cropping Systems
Dissertation Abstract:
Litterfall and leaf litter decomposition were assessed and effects of certain surface activities (i.e., weeding and litter removal) on soil nutrients in three coffee-based agroforestry cropping systems were determined. The cropping systems were CS1 (coffee+ kakawate + dapdap+black pepper), CS2 (coffee + banana+ guyabano), and CS3 (coffee+banana + black pepper). The surface activities were SA1 (no weeding and litter removal), SA2 (weeding with all litter left to decompose in the site), and SA3 (weeding with all litter removed from the site).
Results showed that litterfall varied greatly according to cropping system. CS1 showed highest litterfall at an annual total of 4,386.2 kg/ha, CS1 with 4,188.0 kg/ha. CS2 had an annual output of only 1,376.0 kg/ha. Leaves composed the bulk of litterfall in a ll cropping systems. There was leaf litterfall throughout the study period while non-leaf litterfall was largely seasonal.
Litterfall also varied among species. Kakawate in CS3 had the highest leaf and total Iitterfall, while black pepper, also in CS3, had the highest non-leaf litterfall. Generally, the proportion of nutrients returned to the soil followed the order nitrogen (N) > potassium (K) > calcium (Ca) > magnesium (Mg) > phosphorus (P).
The rates of litter decay were different among cropping systems. After 24 weeks of decomposition, CS1 lost only 75.73 percent of its original weight as against 88.63 percent in CS1. On the other hand, decomposition in CS2 was almost complete (94.67%) after 24 weeks. The general pattern from the most released to the most retained nutrient in this study was K > Mg > Ca > P > N.
Generally, theN. P, and K contents of the topsoil and the subsoil were similarly affected by cropping system and surface activities. For both soil horizons after the experiment. the trends were CS2 > CS3 > CS1 and SA2 > SA1 > SA3. On the other hand, the Ca content of the subsoil was not significantly affected by either cropping system or surface activities but the interaction between these two factors significantly affected subsoil Ca content. For Mg and cation exchange capacity (CEC) of the topsoil, the trends were CS1 > CS3 > CS2 and SA2 > SA1 > SA3. Magnesium and CEC did not affect subsoil Mg content but the cropping system worked in place ofCEC. The subsoil trend was CS1 > CS2 > CS3.
Topsoil pH was statistically the same for all cropping systems and surface activities, but the interaction of these two factors significantly affected subsoil pH.