Making the Most of Moisture in Somalia

On the shimmering, cracked clay plains of Somalia, careful water management means survival. Only with indigenous water-conserving practices can crops be grown. Even with this knowledge, agricultural potential is limited.

In Somalia more than half the sorghum is produced in one small region, the southern Bay Region, an area that comprises less than seven percent of the country. Two moisture-conserving practices are used there: earthen bunds, and intercropping of sorghum with cowpeas. A study by the Bay Region Agricultural Development Project compared these two traditional methods with two nontraditional methods-the incorporation of crop residues, and the use of a clean fallow-to determine their moisture-conserving potential and their effects on subsequent crop yields.

Agriculture in the Bay Region is mostly rainfed. There is no primary tillage, and crop stubble is grazed after harvest. The use of manure is rare, and exhausted fields are left fallow. The study began in 1986 and lasted three years. The soils are Vertisols: alkaline, calcerous, cracking clays, low in available phosphorus. Rainfall is bimodal. The first rains are in April-May, and the second, less dependable rains are in October-November.

Bunding

Bunding trials consisted of two treatments, bunded and unbunded sorghum. The treatments were 20 x 20 m, with 16 bunded squares that were 5 x 5 m each. The unbunded plots were of similar dimensions. Diammonium phosphate fertilizer was broadcast (250 kg/ha) before planting. Soil samples were taken fortnightly to determine soil moisture. After harvest in August, head and seed yields from four central plots were analyzed for moisture content.

After a low rainfall season, the bunded trials produced higher yields even though the moisture content was only slightly higher than in the unbunded trial.

Intercropping

On-farm intercropping trials in 12 sites compared traditional sorghum/cowpea interplanting ratios and spacial arrangements with an increased cowpea component. Three of the four subtreatments were reported. The treatments were: sorghum monocropped, sorghum and cowpeas intercropped at the traditional density (4,000 plants/ha), and an intercrop with a high cowpea density (17,000 plants/ha). Seed yields were analyzed for moisture content.

The 12 on-farm sites showed a yield decrease in sorghum when intercropped with the higher density cowpeas. The traditional intercrop showed no significant decrease compared with monocropped sorghum. Random and row spacial arrangements showed no significant difference.

Cowpea yields were three times greater at the higher density (90 kg/ha) than at the lower (34 kg/ha). More efficient land use would be achieved by intercropping at the higher density than by monocropping.

Stubble Incorporation

A stubble incorporation trial consisted of four treatments: stubble incorporation followed by either sorghum or mungbean, or stubble removal followed by the same. About 2 1/2 weeks after the sorghum was harvested, local varieties of sorghum and mungbean were sown. After harvesting, soil moisture content was measured.

Stubble incorporation significantly enhanced sorghum and mungbean production in subsequent crops. Sorghum grain was 150 kg/ha higher, and 800 more kg/ha dry stover was produced than in fields where stubble was removed. The mungbean fields had more moisture in the top levels of the soil than did the sorghum. However, annual rainfall was below average during this trial. With average rainfall, production might be reduced because stubble incorporation reduces the amount of available nitrogen.

Clean Fallowing

Weed-free fallow trials were executed at two sites. Three treatments were done at both sites: clean fallow, and two treatments planted with cultivars of sorghum (cv. "local" and cv. "dabar"). Plots were 130 x 30 m, and were maintained with herbicide, as well as animal or tractor cultivation. After harvest soil moisture content was determined. In March, plots were planted with local cultivars of sorghum or peanuts. In July, a 3x3 m quadrant from each plot was analyzed.

Fallowed crops stored significantly more moisture than cropped plots. The sorghum showed no response to the fallowing, but peanut yields were significantly increased. This was reflected in both seed and stover yield.

Fallowing and stubble incorporation are not traditional practices in the Bay Region. In this study the value of fallowing and stubble incorporation was conceptual, not intended to be transfered to the farmer. Both methods forgo immediate gains for longer term benefits. To the farmer this means a degree of risk, risk that the subsistence farmer is wary of.

Two proposed systems to combine the benefits of clean fallowing and stubble incorporation, without the risk to the farmer are: relay cropping with a perennial legume such as the pigeon pea (Cajanus cajan), and planting pigeon peas along bund walls. Pigeon peas could conserve moisture without competing with the staple crop. Any new system must also increase the availability of crop nutrients.

Eagleton, E.G., A.A. Mohamed, A.A. Odowa, and H.A. Muse. (1991). A comparison of moisture-conserving practices for the traditional sorghum-based cropping system of the Bay Region, in Somalia. Agriculture, Ecosystems, and Environment, 36, 87-89.