Identifying Agro-Ecological Niches for Long-Duration Legumes: Modeling Maize-Legume Systems Under Variable Climate Scenarios in Malawi.

Participatory trials in Malawi have identified cropping systems that include the long-duration legume pigeonpea (Cajanus cajan), as showing promise for improving soil fertility. These systems include maize-pigeonpea intercrops and a 2-year rotation of pigeonpea and maize. Including a long-duration and deep-rooted legume like pigeonpea in a rotation increases water use, which could reduce maize yields and soil fertility benefits, especially in years with drought or poorly distributed rainfall. The risk of yield reduction for a given site is difficult to predict using short-term field trials, in part because risk will be substantially influenced by soil type and rainfall distribution. Therefore, it is important to identify the soil and climate conditions that are appropriate for long-duration legumes. Evaluating legume systems becomes more difficult when accounting for the effects of climate change. Many climate models project shortened rainy seasons in Southern Africa, which would increase the risk of crop failure.

We use the crop simulation model APSIM to assess appropriate agro-ecological niches for long duration legumes in Malawi under current climate and a range of future climate scenarios. Simulations include continuous maize, a maize-pigeonpea rotation and a maize-pigeonpea intercrop, using three soil types representative of the range of soils in the area. Climate change scenarios are created by modifying long-term daily weather station rainfall and temperature data to correspond to a range of future climate predictions, including shortened rainy seasons and more concentrated rainfall. Results show that yield response to legumes and risk of crop failure is influenced by rainfall distribution and soil type, while total rainfall is only significant in very dry years. Rotation systems show the greatest benefits on low fertility sandy soils, suggesting that planting legumes on lower fertility fields, which is consistent with farmer practice, is a good strategy for maximizing the effects of this practice.