Pre-emergence application of the herbicides fluometuron, oxadiazon, oxadiazon + diuron and norflurazon gave satisfactory weed control, particularly during the early stages of cotton growth, but supplementary hand-weeding 6 weeks after sowing was necessary for control of resistant weed species. The number of man-hours required for supplementary weeding was considerably less than on the untreated control (6–52%). The economic implications of supportive hand-weeding is briefly discussed. No herbicides had any adverse effect on cotton except fluometuron at 0.95 kg/ha and norflurazon at 1.59 kg/ha.

In NPK experiments over three seasons additional N gave highly significant increases in total yield, average bulb size and doubles, and decreased bolting. P application gave similar results but responses to K were negligible. The increases in onion yield due to N and P fertilization were accompanied by significant increases in the N and P contents of the leaves.

In trials with Helianthus annuus in the highlands of Kenya it appeared that the major constraints for successful utilization of sunflower for forage were: high lodging susceptibility; low DM percentage of the forage; low D-value of the forage when high yielding ( = tall) cultivars are used; and poor silage making characteristics. The proportion and quality of the stem largely governed the nutritive value of the whole plant. A reduced proportion of stem would improve all four constraints, but DM yield would also be reduced. Protein yields were highest at the beginning of flowering, but DOM yields were highest about 9 days later, towards the end of flowering. DM yields were highest towards physiological maturity of the seeds.

Black polyethylene tunnels were used to subject Armore and Missionary strawberry cultivars to 21 short-day inductive cycles at either full bloom (7–28 May) or fruit swelling (1–21 June) stages. Regardless of application date, treatments induced a second bloom 8–10 weeks after treatment in both cultivars. The second crop of Armore was as large as the first, but Missionary produced only a small second crop that would not be worth commercial harvesting. Covering plants with black polyethylene reduced the vitamin C content of the first-crop fruits of Armore without affecting yield, while Missionary responded in an opposite way. Treating plants at full bloom hastened the ripening of the first crop of both cultivars by about 1 week and resulted in a larger second crop than was obtained by the later treatment.

Dark-firc-cured tobacco varieties produced acceptable tobacco when cured with the wood of the fast-growing tropical tree Gmelina arborea, with an aroma as good as from the best traditional curing timber in Malawi. The addition to the fire of slow-burning, wet banana stalks or Kingelia pinnata fruit to increase the smoke did not change the desirability of the aroma. Factors which increase the stickiness of the leaf increase the desirability of the aroma of cured leaf.

Irrespective of the size of seed yam used, removal of mother tubers (‘milking’) from yam stands after 4 weeks of growth drastically reduced final yield, but removal after 7 weeks or more did not affect yields of individual plants of Dioscorea rotundata. If yam stands are milked after 4 weeks and the milked tuber replanted, the cumulative yield from both milked and replanted stands was significantly lower than from the control plants. However, milking and replanting mother tubers after 7 weeks or more gave cumulative yields which did not differ from the control.

Field and plant tissue tests under Sudan Kenana conditions revealed that rice does not respond to K but response to P was very clear, both from visual symptoms, tissue analyses and in yields. As early as the seedling stage, a concentration of leaf blade-P of about 1300 ppm is considered optimum. Yield, and level of soil application, corresponding to this value were 5000 kg/ha paddy rice and 42·8 kg/ha P2O5 respectively. A low yield (2400 kg/ha) was obtained from plants receiving no P2O5. Phosphate application reduced the grain protein.

Single-leaf net photosynthesis versus light response curves of four Hevea brasiliensis clonal seedlings showed that it was possible to divide photosynthetic rates into high and low classes.

An experiment designed to study differences in water requirements between some clones of tea suggests that clones which showed visual symptoms of being more susceptible to drought had a greater demand for water. Supplementary irrigation applied during the dry seasons prevented plants from dying and stimulated better early growth of clones tested. As a result of better early growth, the irrigated tea gave persistently and significantly larger yields than non-irrigated tea in the first 2 years of recording.

Daily measurements of moisture by neutron probe showed an erratic pattern of ET in the Sudan Gezira, attributed to the redistribution of water and development of cracks in a drying profile. However, dividing an irrigation cycle into periods of 3–5 days revealed a unique trend of ET that was consistently low in the early period, increased to a maximum in the middle, and fell off at the end. Roots suffer from anaerobic conditions for about 5 days after flooding but subsequent drying and cracking improves soil aeration that leads to final depletion of profile moisture and depression of ET.

Estimates of variety × environment interactions for grain yield were obtained from a study involving 16 sorghum varieties grown at the same three locations over a 3-year period. Whereas the variety × year interaction was small and not significant, the variety × location and the variety × location × year interactions were highly significant. Evidence was presented suggesting that the years of testing could be reduced by increasing the number of test locations. T.F.M.7 and Karkatib 4/1/1 were identified as desirable varieties, combining high yield and stability of performance, thereby deserving a place both in commercial production and future breeding programmes.

Two field experiments on the effects of watering at 40–50 (M1), 60–70 (M2), 80–90 (M3) and 90–100% (M4) of available soil-moisture depletion on sugarcane were conducted at Guneid during 1974–77. Intensive cane growth was observed from April to August. Irrigation treatments significantly affected yields of cane and sugar, and the percentage of sucrose, with treatment M2 giving the most economic yields of cane and sugar.

Effects of plant population on mean yield and yield components of 2-year sole cassava crops were studied on Njala upland soils of Sierra Leone in two experiments. Increasing plant population of multi-shoot Cocoa cassava over 7000/ha decreased all the parameters studied except top/root weight ratio, which increased. The observed effects were attributed to competition for environmental resources, since area of land/plant unit decreased as plant population increased. The relations between plant populations and yields of fresh root and cortex dry matter were asymptotic, indicating that the respective yields were products of the vegetative phase of cropping.

A field experiment studied the effects of BOH as a floral inductant on pineapple cv Mauritius grown on Malaysian peat. Spray concentrations of 0·1, 0·2 and 0·3% greatly increased fruit set and yield but reduced average fruit size, with no advantage from concentrations higher than 0·1%. Spraying the ratoon crops at different times (6, 8 and 10 months) did not affect percentage fruit set but optimum fruit yield and big fruit were only obtained at 8 months or more after planting.

The nutrient composition of leaves and petioles of three yam species were studied at fortnightly intervals, and in the tubers when harvested at maturity. Highest concentrations of plant nutrients were recorded in D. alata, while D. cayenensis had the lowest. The lamina was more appropriate for determination of N and P contents, while the petiole was more satisfactory for K. Peak nutrient concentration occurred between late June and early July, suggesting that that was the period of maximum demand for nutrients. The dependence of yields on nutrients was demonstrated.

Assessment of the relative advantages or otherwise of inter-cropping compared with sole cropping needs to be done over a wide range of plant populations. Systematic spacing designs lend themselves to this, and the paper discusses the interpretation of the yield/plant population curves which can be so derived.

The production of maize in every second inter-row of first and second ratoon sugar cane was studied in four locations in Mauritius in 1974, in trials based on combinations of three maize densities and three fertilizer levels. Analysis of the data showed that intercropping sugar cane with maize had no adverse effects on cane and sugar yields, and suggested that planting an early-maturing maize amongst the cane at a density of 19,000 plants, with 76 kg N, 38 kg P2O5, 62 kg K2O/ha, was the most profitable method under Mauritian conditions.

Three experiments testing the effects of nitrogen on melon showed significant varietal differences. Nitrogen increased yields by increasing fruits/plant, seeds/fruit and seed weight, had no effect on fruit weight, size and husk, and increased leaf area through leaf number and leaf size. Fruit growth coincided with a rapid decline in leaf area, indicating that the mottled green fruits contributed appreciable assimilates towards their own growth. The implications of the findings, and the inefficiency of the crop in seed formation, are discussed.

The experiment, designed to investigate the production of alfalfa in Saudi Arabia, was a factorial involving three irrigation rates and three cutting heights. The irrigation rates were sub-optimum, optimum and super-optimum, supplying 2730, 3850, and 5040 mm of water over the duration of the experiment respectively; cutting heights were low (2 cm), high (8 cm) and alternate (2 cm and 8 cm). The experiment ran for a year, with 14 harvests. Sub-optimum, optimum and super-optimum irrigation treatments produced 27·5, 31·4 and 31·9 tonnes of DM per hectare respectively. Proximate analysis of crude fibre, crude protein, and ash percentage were determined, and plant density and weed infestation recorded.

The effects of delayed hand weed control at 30-, 45-, 60-, 90-day intervals, and no weeding, on sole-crop cassava, was studied in two experiments on the upland soils of Sierra Leone. Timing and frequency of weeding were important in influencing root number and root yield, and delayed weed control depressed both attributes. The critical period of competition was in the 45-day weeding interval, with six weedings in a 14-month growing period. Rottboellia exaltata was the predominant species amongst the permanent grasses on the no-weeding plots.