Angharad Johnston, Charles Spillane
28 October 2024
LEG4DEV Project Researcher Tamirat B. Jimma from the International Livestock Research Institute recently conducted a study examining the potential for soil moisture to enable more productive, resilient and climate smart agriculture in Ethiopia – Quantifying Residual Soil Moisture through Empirical Orthogonal Functions Analysis to Support Legume-Based Cropping Systems.
Jimma et. al. modelled the long-term soil moisture trends across the Ethiopian landscape and investigated the application of this model to improve the productivity and output of legume crops. This study extends our climactic and agroecological foresight, by mapping out the spatial and temporal trends of water availability in the soil. Such knowledge can help guide farmers on what crop to grow, but also when to grow – providing a guide for the timing of cropping regimes, ultimately shaping agricultural strategies and productivity outcomes into the future.
“The dynamics and availability of soil moisture not only influence what crop to grow, but also dictate the timing of cropping patterns, ultimately shaping agricultural strategies and productivity outcomes.”

Agriculture is of major significance for Ethiopia, providing livelihoods for the majority of the population and making significant contributions to the economy. Ethiopia is characterized by an extensive complex of mountain ranges and deep valleys, covering much of the central and northern regions. Its climate displays substantial variations due to altitude differences and its proximity to the equator. Ethiopia’s agricultural systems are varied, ranging from pastoralism of livestock such as cattle, goats, sheep, and camels in the arid and semi-arid lowlands, to the cultivation of crops such as teff, wheat, barley, maize, and pulses in the highlands. Agro-pastoralism, combining both cropping with livestock rearing is practiced in some lowland areas that have good access to water.

Ethiopia’s climate exhibits distinct wet and dry seasons, with the main wet season – locally known as Kiremt – occurring from June to September (JJAS). A second, shorter rainy season (called Belg) follows, generally occurring from March to May (MAM). The Jimma et al study focused on the drier months between Kiremt and Belg known as OND (October, November and December) when legume crops are typically sown and harvested. The research team sought to model and quantify the residual OND soil moisture levels across the complex topography and micro-climates and investigate how legume cultivation could be fine-tuned to best utilise the available soil moisture. This approach has the potential to increase productivity without additional and costly water inputs. In the paper. they argue that such spatial and temporal agroecological models can help transform the agricultural industry within Ethiopia towards more efficient, resilient and robust ‘climate-smart’ systems.
To characterise the OND soil moisture profiles, Jimma et al combined agroecological, climate and topographical data from the past 40 years (sourced from the Global Land Data Assimilation System (GLDAS) to elucidate soil moisture trends across the Ethiopia landscape. In addition to the general trends observed, the model also encompassed statistical outliers and climactic anomalies such as extended periods of drought or higher than usual soil moisture that occurred between 1981 and 2020. Based on this data, they identified 5 distinct agroecological regions within Ethiopia, each with their own characteristic soil moisture profiles.

While all 5 regions, as expected, showed a general decline in residual soil moisture following the main rainy season, each started and ended the season with significantly different soil moisture levels. In addition, the more northern Regions 4 and 5 showed a spike in soil moisture around November before following the same gradual decline. In the paper, Jimma et al argue that within each region, the production of legume crops can be tailored to these soil moisture profiles, with more robust and drought-tolerant varieties used in the drier regions and varieties needing more water in the characteristically wetter regions. However, Jimma et al also suggest that the timing of cropping regime can be fine-tuned to match the changing moisture profile of each region, potentially doubling cropping outputs with minimal addition water needed.
“The spatial heterogeneity of soil moisture underscores the need for tailored agricultural strategies that account for local moisture conditions, enabling farmers to spatially and temporally optimize their selection of crop species, crop varieties and management practices based on their specific agroecological context.”
To demonstrate how this model could be utilised in this way by farmers, Jimma et al took crop water co-efficient values, sourced from the FAO, as an indicator of the water requirements of some of the major legume crops within Ethiopia (i.e. Chickpea, Fieldpea, Alfalfa, Common Bean and Soybean). They overlayed these water co-efficient values onto their soil moisture model to identify where and when the residual soil moisture levels were adequate (or inadequate) to meet the water requirements of each crop (See Figure 11).

They demonstrate that within the central highlands of Ethiopia, renowned for intensive crop production, the initial- and late-season stage of OND exhibited a positive relationship between soil moisture levels and crop water requirements across all the major legume crops included in the study. The research team thus highlight the capacity of residual soil moisture to fulfil the water demands of selected legume crops, thereby rendering these areas conducive to post- rainy season cropping. Furthermore, in regions that possess higher soil moisture values, such as wetter pocket areas in the southeastern region, implementation of supplementary irrigation could augment existing moisture levels, thereby enhancing the potential for post-harvest cropping in the region.
“The residual moisture during the OND period can contribute to soil fertility replenishment, particularly through its use for the cultivation of legumes for nitrogen fixation.”

The availability of residual moisture presents an opportunity to incorporate legumes as secondary crops within cropping regimes, with the additional benefit of enhancing nutritional security with their high protein content. Moreover, the residual moisture during the OND period can contribute to soil fertility replenishment, particularly through its use for the cultivation of legumes for nitrogen fixation.
The findings of this LEG4DEV study highlights the potential of climate-smart agriculture to contribute to the resilience and productivity of legume crops in Ethiopia; creating positive feedback loops for soil health, water use efficiency and nutritional outcomes for its people.