In southern Brazil, conventional vegetable production on marginal agricultural lands has contributed to soil deterioration that diminishes crop yield and nutrient content over time. In response, farmers are diversifying crop production and adopting ecological management techniques, such as cover cropping and intercropping, to increase soil cover and rebuild soil fertility. Facilitation and niche partitioning between diversified crop species can be significantly greater in resource-poor environments. Farms transitioning from conventional to ecological nutrient management may therefore encounter differential results of agroecological practices based on their baseline soil conditions and prior management. Yet, little is known about how ecological management practices interact with baseline soil fertility to alter farms’ production capacity. In a participatory study across a gradient of farms transitioning to ecological management (n=15 farms), we planted grass-legume cover crops and legume-cucurbit intercrops in a factorial replacement design. We addressed the question: do soil fertility and management variables (% soil organic matter, macro- and micro-nutrient content, texture, pH, prior use of cover crops) predict the effects of functional diversity through cover cropping and intercropping across a farm gradient? We hypothesized that effects of increased functional diversity on vegetable production would be maximized in moderately resource-limited environments, or on mid-transition farms.
Results/Conclusions
Following one year of intercropping (n=15) and cover cropping (n=7), pea (Pisum sativum) and cucumber (Cucumis sativa) yields were significantly different across farms (p=0.002) and ranged from 11.6-3126.3 kg/ha and 0-436.8 kg/ha, respectively. Using a mixed effects model with treatments (cover crop, intercrop) as main effects and farm as a random effect, we found significant positive effects of phosphorus (p<8.8*10-8), % clay (p<0.0005), and years of cover cropping (p<0.004) and negative effects of potassium (p<0.005) and soil moisture (p=0.022) on yields across crop types (R2=0.385). With the same model parameters, we were able to predict 37% of cover crop effects and 18% of intercrop effects on vegetable yields; however, mean effect sizes for treatments across farms were not significantly different from zero. Initial findings support our hypothesis that plant functional diversity has a stronger effect on crop yield on resource-limited farms beginning the transition to agroecological management. As farms with variable management histories transition to agroecological management, there is a critical need to advance scientific understanding of the ecological processes and mechanisms that govern ecological practices’ effectiveness. Our study provides early evidence of how prior ecological management and baseline soil fertility can interact to improve productivity as farms diversify.