Relating smallholder management of agroecosystem biodiversity to maize (Zea mays) nutritional quality in Sarstún, Guatemala
Biodiversity in agroecosystems has been shown to contribute to soil and plant health by way of multiple environmental services. Higher crop biodiversity may also lead to improved nutritional value for human consumption. In the tropical lowland region of Sarstún, Guatemala, land dispossession, expanding indigenous population, and shorter fallow periods in a swidden agricultural cycle are contributing to severe declines in subsistence crop productivity and smallholder nutritional security. We hypothesized that agroecosystems managed to increase biodiversity, especially through use of cover crops to smother weed populations and reduce herbicide inputs, could produce higher quality maize grain in addition to improving yields per area. This study sought further understanding into the impacts of nitrogen-fixing cover crop (Mucuna pruriens) intercropping with maize, number of maize landraces cultivated, multiple- or mono-cropped growing system, and extent of insect herbivory on relative maize nutritional quality (based on kernel protein) in the Sarstún region. In addition to nutritional analyses of maize kernels, farmer surveys were conducted to determine key management factors with potential to affect agroecosystem function. One hypothesis was that current challenges to soil conservation would be exacerbated by landscape-level alterations such as export-oriented plantation agriculture and increased microclimatic variability in Sarstún.
Only smallholder use of Mucuna cover crop had a significant effect on percent protein in maize samples (p=0.008). Farmers who planted Mucuna grew maize with an average of 13% higher protein concentration than those who did not report use of the cover crop. Neither cropping system (mixed or single crop) nor the number of maize landraces cultivated by a farmer had a significant relationship to maize protein (p=0.620 and p= 0.419, respectively). Level of herbivory by the maize weevil (Sitophilus zeamais) also did not affect protein concentration (p= 0.184). Data demonstrate that intercropping with Mucuna in Guatemalan tropical maize agroecosystems has the potential to improve not only soil and plant health and augment yields per area, but also to increase relative crop nutritional quality of maize grain, a staple crop in Sarstún that provides as much as 65 percent of the daily carbohydrate and 71 percent of the daily protein in local diets. Elevated maize protein concentration could therefore create a socio-ecological incentive for farmers in Sarstún to intercrop maize with Mucuna pruriens or other nitrogen-fixing cover crop species, potentially increasing field biodiversity, conserving soil communities, and increasing agroeosystem resilience to climate shifts while improving the quality of subsistence crops.