Benefits and tradeoffs of diversifying rice-based cropping systems: Impacts on soil health, productivity, and agroecosystem multifunctionality

Abstract

Diversified crop rotations have been shown to increase soil health and yields while providing broader ecosystem services (ES), such as increasing biodiversity, water regulation and greenhouse gas mitigation. Little research has investigated the benefits and tradeoffs of diversification in what traditionally have been continuous rice (Oryza sativa L.) systems. Likewise, impacts on agroecosystem multifunctionality, relating to the combined supply of Regulating, Provisioning, Supporting, and Conserving ES, remain uncertain. Our objective was to evaluate the integrated performance of diversified crop rotations compared to continuous rice on 46 fields in terms of soil health, rice grain-yield, weed abundance, and herbicide inputs in California. Results were then organized into different ES categories to assess potential tradeoffs and systems-level multifunctionality. Under conventional management, diversified rotations led to 13 % higher rice yields and lower weed abundance than continuous rice fields. Diversification reduced soil organic carbon (SOC) concentrations, permanganate oxidizable carbon (POXC), and autoclave citrate extractable (ACE) protein, but increased soil minor element availability (Mg, Mn, Fe, and Zn). While soil microbial biomass was similar among cropping systems, microbial communities under diversified rotations trended towards higher bacterial abundance associated with mineralization processes. When translated into ES categories, under conventional management, diversified rotations in flooded rice systems presented notable tradeoffs for several Regulating and Conserving ecosystem services (lower SOC concentrations and microbial energy source retention, lower nitrogen (N) retention, and reduced bird habitat), whereas diversified rotations under organic management presented more balanced Regulating and Supporting services (N retention, microbial energy source retention, mineralization and nutrient availability). As a result of ES tradeoffs within each system, no differences in agroecosystem multifunctionality were observed. Results suggest multiple benefits for diversified crop rotations in flooded rice systems, which may directly or indirectly support farmer goals such as nutrient availability, weed control and yields, but more research is needed to understand the identified tradeoffs at the landscape scale and maximize benefits across all ES categories.