New CIAT research on soil biodiversity in Slash-and-Mulch agroforestry systems
A new paper in Applied Soil Ecology by researchers from CIAT and the University of Western Australia reports that smallholder agroforestry systems can retain relatively abundant, diverse populations of soil invertebrates. This finding, gained from in-depth research on the ‘Quesungual Slash-and-Mulch Agroforestry System’ in the remote highlands of western Honduras, has relevance for resource-poor farmers who depend on the biological productivity of the soil for their livelihoods.
The conversion of forests to farmland often results in the loss of soil biota. Healthy soils teem with life, from microscopic bacteria, fungi and mites, through to more recognisable creatures such as ants, termites, earthworms and beetles. Soil- and litter-dwelling animals measuring at least two millimetres in length are known as ‘soil macrofauna’. Macrofauna are so important to ecosystem function that they have been called ‘ecosystem engineers’ due to their influence on soil structure and the distribution of soil organic resources.
The Quesungual agroforestry system, named after the village where it was first identified, is a smallholder production system for maize, beans and sorghum. The system represents a transition from traditional slash-and-burn cultivation to slash-and-mulch agroforestry. Today, individual fields can be cultivated for up to 12 years before being left fallow. Under slash-and-burn, fields could only be cropped continuously for two or three years.
For the study, soil macrofauna were sampled across agroforestry fields that had been converted from secondary forest from between two to ten years previously. Nearly 20,000 individual invertebrates were painstakingly collected, counted and weighed as part of the research. Scientists were expecting to find that soil macrofauna would decline in agroforestry fields, compared with secondary forest. However, the results showed that abundance and diversity of soil fauna remained relatively constant across fields of different ages, and that the biomass of soil macrofauna actually increased in agroforestry fields that had recently been converted from forest.
Land management practices in the study area, such as continuous soil cover, the presence of diverse trees and other vegetation within cropping fields, the use of mulch, and the presence of a mosaic of habitat types in the surrounding area, could be the reason for the relatively abundant soil macrofauna populations observed from the agroforestry system.
Activities are underway to adapt the key principles behind Quesungual agroforestry to other hillsides of the sub-humid tropics. These activities have met with success in Nicaragua, as discussed in New Agriculturist, and there are hopes that the principles of the system could one day be trialled in upland southeast Asia, east Africa and the Andes. The potential for practices associated with the system to maintain soil biological health is further evidence that it can aid smallholder producers to better manage soil quality and soil fertility.
The full article can be accessed by subscribers to the Journal of Applied Soil Ecology here.