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.
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.
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 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.
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.