Regenerating degraded soils and increasing water use efficiency on vegetable farms in Uruguay through ecological intensification

Abstract

This thesis investigated alternative soil management strategies for vegetable crop systems and their hypothesized effects on increasing systems resilience by sequestering soil carbon, increasing the efficiency of water use, and reducing erosion. The goal was to contribute knowledge on and tools for the integrated assessment of soil management strategies for the ecological intensification and small-scale production systems sustainability in South Uruguay. We performed a baseline assessment of key soil properties on cropped fields, and evaluated the impact of implementing different soil management strategies after re-design of systems in a co-innovation project. We showed evidence that even under smallholder conditions, it was possible to reverse the soil degradation. However, it was not possible to reduce erosion in cases that a pasture could not be included in the rotation. We evaluated reduced tillage and cover crop management in an experiment. In-situ grown mulching increased water capture by 9.5% and reduced runoff by 37% on average, leading to less erosion risk and greater plant available water. We also collected enough data to develop a simple, generally applicable, locally parameterizable mathematical model that accounts for the effect of soil cover on soil water dynamics. Exploration with 10 years of weather data showed that reduced tillage and mulching (RTmulch) would decrease water requirements for irrigation by 37% on average. Finally, we scaled up the results to study the impact of RTmulch on two small horticultural family farms with different resource availabilities. By combining process-based simulation models with empirical data and expert knowledge, we quantified inputs and outputs of production activities. Adoption of RTmulch was associated with improvements of the economic and/or environmental performances. It was possible to design production activities with erosion rates below the tolerable level without sacrificing the family income too much. Average water savings of 775 m3 ha-1 yr-1 (fully irrigated rotations) to 452 (irrigating only the most profitable vegetable crops) were obtained under RTmulch compared with conventional tillage. Reduced tillage and mulching have potential for increasing water infiltration, reducing runoff and erosion, and achieving greater efficiency of water use for vegetable crops grown in raised bed systems. These aspects are especially relevant under conditions of high rainfall variability, limited access to irrigation and high soil erosion risk. For future research, we suggest combining long-term experiments with on- farm research to capture the benefits of improving soil quality on soil productivity, while adjusting the technology to solve limitations that arise in the process. This study provides ground for testing the proposed changes on pilot farms, using a co-innovation approach combining scientific insights with farmers’ knowledge of their farms.