Assessing Social, Ecological, and Nutritional Outcomes of Crop Diversification: Transitions to Agroecological Management in Southern Brazil

Abstract

Global industrial agriculture drives worsening environmental and public health crises, prompting a search for transformative agricultural approaches that can maintain productivity while increasing social and environmental sustainability. One paradigm gaining traction is agroecology, a science, set of management practices, and social movement. Agroecological management applies ecological knowledge to manage crop diversity on farms (i.e., agroecosystems) and increase multiple functions, including soil nutrient cycling and crop productivity. However, due to the vast heterogeneity of farm management systems and environmental conditions, we lack a mechanistic understanding of transitions to agroecological management, or “agroecological transitions,” and their outcomes. This dissertation develops and applies an interdisciplinary approach to analyze the processes and outcomes of agroecological transitions on family farms in southern Brazil. Chapter 1 provides a conceptual framework for assessing social, ecological, and nutritional functions of agroecosystems across stages of the transition process and introduces the remaining chapters. Chapter 2 focuses on social outcomes of agroecological transitions. I analyzed qualitative and quantitative management and socioeconomic data from 14 farms along an agroecological transition gradient to understand how changing management practices relate to farm income and working conditions. I found that agroecological farms (>5 years certified) achieved income parity and improved working conditions compared to conventional farms in the region. Farms in transition (0-5 years certified), however, struggled to manage ecological processes on their newly diversified farms, which increased work difficulty and reduced profits relative to both agroecological and conventional farms. Chapter 3 examines the cascading relationships between farm management history, background soil fertility, crop diversification practices, and nitrogen cycling during agroecological transitions. I conducted a two-year experiment to test the performance of two legume-based diversification practices, cover cropping and intercropping, across the farm gradient from Chapter 2. Structural equation modeling revealed that after accounting for variation in background fertility across sites, cover crop mixtures explained a further 67% of the variation in soil nitrogen availability at vegetable planting. Consequently, benefits of diversification practices for soil nitrogen cycling were ecologically relevant across farms within the short span of our experiment, with the greatest nitrogen availability overall on agroecological farms. Intercropped cucumber and snow pea had a yield advantage relative to monocrops across the farm gradient, contributing to a mean land equivalent ratio of 1.19 overall, and 1.27 in the second year of the experiment. Chapter 4 evaluates how diversification practices affect two nutritional functions of vegetable agroecosystems. In a factorial field experiment, I studied the individual and combined effects of cover cropping and intercropping on cucumber and snow pea nutrient content and nutrient yield, including protein and six minerals. Total nutrient yield per area increased in the combined diversification treatment, driven by 5.3 times greater cucumber nutrient yield per plant compared to the control. The highest nutrient yield overall was in the cover cropped pea treatment, reflecting 11% higher protein yield per plant compared to the control. These findings provide initial evidence that diversified cropping systems can lead to agronomic biofortification of vegetable crops, particularly in low-input systems. Chapter 5 synthesizes findings from the three studies and proposes an agenda for future research on crop diversification and agroecological transitions. This integrative dissertation illustrates that agroecological transitions, and the crop diversity they employ, offer a pathway toward agriculture that upholds farms’ socioeconomic viability, bolsters key ecosystem functions including soil nutrient cycling, and produces more nutrient-rich crops.