Diversifying maize cropping systems increases drought resilience and productivity

Leah L.R. Renwick and Amélie C.M. Gaudin, Department of Plant Sciences, University of California, Davis, Davis, CA, Leah L.R. Renwick, Departamento de Ingeniería y Suelos, Universidad de Chile, Santiago, Chile, Bill Deen, Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada, Anthony A. Kimaro, ICRAF Country Programme, World Agroforestry (ICRAF), Dar es Salaam, Tanzania, United Republic of, Todd S. Rosenstock, Land Health Decisions, World Agroforestry (ICRAF), Kinshasa, Congo (The Democratic Republic of the)

Background/Question/Methods
Inspired by positive diversity-stability relationships in less managed ecosystems, agroecologists propose that crop diversification enhances agricultural system resilience. We report two drought manipulation experiments conducted to test if crop diversification in space (intercropping) or time (rotation) alters the drought resistance of maize-based systems. The first experiment tested the impact of medium-term maize-legume intercropping and agroforestry with pigeonpea and gliricidia on cropping system drought resistance in low-input tropical semi-arid systems (Dodoma, Tanzania). The second experiment tested the impact of long-term crop rotation diversification using small grains and cover crops on maize drought resistance in high-input temperate maize-soybean systems (Ontario, Canada). We imposed drought at existing experimental sites using rainout shelters and, depending on the experiment, monitored soil moisture, maize growth, water stress physiology, yield, and mechanisms thought to underlie drought resistance, namely soil physicochemical and hydraulic properties and root water uptake depth using stable isotopes.
Results/Conclusions
Results from the first experiment show that pigeonpea yield was unaffected by drought whereas maize yield was reduced by drought in some cropping systems. Intercropping systems lost similar or less whole-system grain yield to drought (≤ 3 t ha-1 loss) than the standard monoculture maize system (3.5 t ha-1 loss), despite higher planting density and potential competition for soil moisture. Maize-pigeonpea intercropping required less land than monocultures to produce the same yield (Land Equivalent Ratio 1.1-3.0), and along with maize-gliricidia achieved similar whole-system grain and nutritional yields as maize monoculture. Intercropping does not significantly protect against yield losses under drought but provides opportunity to produce the same food, particularly protein, on less land under drought and non-drought conditions.
Results from the second experiment show that that diversifying maize-soybean rotations with small grain cereals and cover crops mitigated maize water stress at the leaf and canopy scales and protected against yield losses to drought (17% less). Soil organic matter increased with rotation diversity and was associated with lower maize water stress and higher maize yield, but not with trends in soil water retention, infiltration, nor root water uptake depth. Rotation diversification constitutes an underappreciated drought management tool to adapt to climate change through building soil health. Drivers of soil organic matter benefits for maize under drought, particularly soil biology, require attention.
Overall, these findings support the idea that diversification enhances cropping system drought resilience, in that rotation diversification significantly protected against yield losses to drought and intercropping protected against or did not affect yield losses to drought.