Abstract
Data for five major soils on soil-water properties, including water content, periodically through the growing season, and rooting depth and distribution were assessed in relation to rainfall, wheat yields and calculated estimates of water use by the wheat crop, in 1987, water was retained within rooting depth at pressures above -1500 kPa throughout the growing season in three of the five soils. In the Vertisol, however, the topsoil was dry at seeding and germination was poor. Early-seeded wheat did not respond to irrigation at the one site tested- a deep Cumulic Haplustoll. In 1988, a drier year, water within the rooting zone was depleted below -1500kPa in four of the five soils. Irrigation improved yields on the Cumulic Haplustoll. Yields were low in relation to estimated water used by the wheat crop in both years. In average years with more than 600mm of rainfall, achieved yields should be approximately double the current average of 1.6 t ha-1. Factors other than lack of water that may limit wheat yields in the northern highlands of Tanzania are discussed.
