Preliminary evidence is presented in this study for the existence of (1) intraspecific physiological variants of Striga hermonthica, with Gabob population as the most responsive strain to a range of Sorghum bicolor cultivars, and (2) a local Sudanese sorghum cultivar called Tetron with broad-spectrum resistance to striga. Thus Tetron may be recommended as another standard resistant cultivar with reference to Framida of East Africa.

Considerable variation in seedling vigour was observed among 36 maize populations; genotypic variances were generally high for emergence percentage (E%), emergence index (EI), dry-matter accumulation and relative growth rate (RGR). Broadsense heritability values and environmental variances indicated that E% and EI would be more reliable indices for seedling vigour than emergence rate index (ERI). The expression of growth rate (GR) was influenced more by the environment than the genetic constitution of seedlings; GR was not therefore an effective indicator for seedling vigour, and RGR would be preferred because it was more heritable and less influenced by the environment.

Changes in growth rate of tea shoots cause yield fluctuations between seasons, but the size of the basal shoot population remains constant throughout the year. The proportion of shoots with dormant apical buds does not influence the mean weight of shoots harvested. Models of shoot extension are discussed.

Total fresh leaf yield of cassava (Manihot esculenta Crantz) variety Isunikankiyan was not significantly affected by harvesting frequency, unlike variety TMS 30211. Compared with plants whose leaves were not harvested, there was a decrease in total fresh tuberous root yields of 56–76%, 34–62% and 15–32% when leaves were harvested at 1-, 2- and 3-month intervals respectively. The two cassava varieties reacted differently to leaf harvests in terms of tuber yields. Harvesting the top leaves of cassava at 2- or 3-month intervals is recommended to ensure reasonable yields of both leaves and tuberous roots.

Nitrogen-atrazine combinations were significantly more effective in stimulating higher yield components of sorghum and depressing yield components of striga than sole treatments of either nitrogen or atrazine. Over all treatments nitrophoska at 129 kg N/ha in combination with atrazine at 1.75 kg/ha gave 224, 180, 155 and 151% increases in yield components over the control for head, straw, 1000 grain weights and plant height of sorghum, and a decrease in 83, 88 and 90% of striga density at 8, 12, and 16 weeks from sowing the sorghum. The synergistic effect of nitrogen-atrazine is demonstrated.

An experiment on wheat (variety Mexipak) was undertaken for two years at the Experimental Farm to study the effects of soil and foliar application of urea. The results indicated appreciable increases in grain yields due to foliar sprays of urea during both years of the experiment; the spray helped to increase yield-contributing factors such as thousand-grain weight, weight of grains per plant, plant height and dry weight.

Seven plant populations, ranging from 24,000 to 73,000 plants/ha of the maize variety White Composite, were established in four growing seasons between 1976 and 1978 by varying row width and number of plants per hill. Soil water profiles, leaf and soil water potentials, and leaf resistances were monitored. The results indicated a close link between these parameters, number of plants per hill and overall plant populations. Grain yield increased with increasing plant populations during the early growing season but dropped beyond 54,000 plant/ha (spaced two plants per hill at 60x60 cm) during the late season, due to adverse plant water status.

Results from field experiments showed that number of mature grains per plant was related to the plant growth rate during the pre-flowering period. This relation was further improved when growth rate was expressed relative to the rate of plant development. This evidence supports the theory that grain abortion is linked with assimilate production.

In a 3-year field study with mustard (Brassica juncea L.) on deep well-drained sandy loam and loamy sand soils, 11 post-sowing irrigation schedules based on pan evaporation and growth stages were compared. One irrigation three weeks after sowing gave maximum grain yield and water use efficiency, increasing yield 40% in 1973–74 and 30% in 1976–77 compared with no irrigation. The total water use in this treatment averaged 31·2 cm, of which 15·8 cm was extracted from the 0–180 cm soil profile. Use of soil water by the crop decreased with the amount of post-sowing irrigation. More than one post-sowing irrigation tended to decrease yield and water use efficiency.

Changing the geometry of planting under irrigated conditions from the traditional pattern of regular rows (with plants equidistant from each other) into double rows (with plants arranged in row pairs) promoted plant competition. This resulted in a significant reduction in overall yield components of sorghum but a marked increase in shoot yields of striga. A better yield of sorghum was obtained in ridged plots than in flat plots, associated with less striga infestation and a slightly higher soil moisture content under the ridged plots.

Mesquite (Prosopis spp) is a nitrogen-fixing and drought-resistant leguminous tree which exists in many of the semi-arid regions of the world but little has been done to develop its potential for wood, nitrogen fixation or pod yield. We report field and greenhouse cultural practices for mesquite and the results of a field screening trial for biomass production of 32 accessions, representing North and South American and African germplasm. Non-destructive biomass estimates, derived from height and stem diameter measurements, had a 180-fold range; the preponderance of slow-growing accessions were from the rangelands of southwestern USA.