The Quesungual slash-and-mulch agroforestry system of western Honduras has been put forth as a sustainable alternative to traditional slash-and-burn agriculture for the tropical dry forest zones across Central America. This system forgoes burning and utilizes native tree species interspersed with annual crops to stabilize hillsides, promote soil fertility, and conserve vital soil moisture. Although this system has been readily adopted among farmers in the region, the mechanisms behind the Quesungual system’s success remain poorly understood. The research presented here aims to better elucidate soil organic matter dynamics and earthworm communities in the Quesungual system via comparisons with slash-and-burn agriculture and secondary forest in a replicated field trial. The Quesungual and slash-and-burn treatments were further subdivided into plots receiving standard fertilizer applications (N-P-K) or no inorganic nutrient additions. Earthworms were hand-sorted for each of the experimental plots in July of 2007 and returned to the lab for weighing and identification. Soils were collected in both 2006 and 2007 and fractionated into macroaggregates (>250 μm), microaggregates (53-250 μm), and the silt and clay fraction (<53 μm) by wet-sieving. Macroaggregates were further separated into coarse particulate organic matter (> 250 μm), microaggregates within macroaggregates (53-250 μm), and macroaggregate-occluded silt and clay (<53 μm). All fractions and bulk soils were analyzed for total C and N, while bulk soil was additionally analyzed for available P (Olsen P).
Results/Conclusions
Results indicate that earthworm numbers and biomass are considerably lower under slash-and-burn agriculture than under the Quesungual system or secondary forest (P = 0.02 and P = 0.03; respectively), with the largest populations found under the fertilized Quesungual plots. For the 2006 sampling, P availability was highest in the Quesungual plots receiving inorganic fertilizer additions (P < 0.01), despite equivalent additions of mineral P in the fertilized slash-and-burn treatment. The influence of management on soil structure, as well as C and N distribution, appears to be less pronounced than for P and earthworm populations. Our findings thus indicate that Quesungual system receiving fertilizer additions seems to be the most advantageous for the management of soil fertility and fauna.
