Responses in yield of dry bean genotypes of different growth habits [determinate (Type I), indeterminate small vine (Type II), indeterminate large vine (Type III), and indeterminate climbing (Type IV)] were evaluated over two growing seasons. Types II and III gave higher yields than Type I, with Type II the highest. Narrow between-row spacings (50 cm) tended to give higher yields than 75 cm spacings for all habits, though Type I seemed less responsive than the indeterminate habits, Types II and III. Close within-row spacing (5 versus 10 cm) was not beneficial for beans of any growth habit. Yields of beans with climbing habit grown on different support systems and at different spacings are also reported.

Two experiments to investigate the micronutrient requirements of cassava (cv Black Twig) on Malaysian peat soil are described. Cu was found to be the only essential micronutrient and Mn, Zn, Fe, Mo and B were not needed. Fertilizing with 20 kg/ha of copper sulphate approximately tripled tuber dry matter, and starch and Cu uptake, but applying 10 kg/ha of copper sulphate gave the same results. Each crop of cassava absorbed only about 2% of the applied Cu, giving a leaf Cu content of about 14 ppm compared with about 7 ppm in Cu-deficient plants. Cu deficiency symptoms were invariably observed in Cu-deficient plots and these are also described.

Water use efficiency of maize (Zea mays) and cowpea (Vigna unguiculata) was investigated, with and without tillage, under four irrigation frequencies in which 12 mm of water was applied at 2, 4, 8 and 12 day intervals, using a sprinkler system. Both maize and cowpea under no-tillage yielded more than with conventional ploughing. Water use efficiency of maize without tillage was 18·3, 17·5, 57·8 and 100% greater than with tillage at irrigation frequencies of 2, 4, 8 and 12 days respectively. Whereas the leaf water potential of cowpea was not affected by tillage, that of maize was generally higher for no-tillage compared with conventional ploughing.

Effects of Alar on growth, flowering and yield parameters of standard-planted and closely-planted late-bearing okra were studied. Lower concentrations of Alar, applied once 6 weeks after sowing on standard-planted okra, significantly advanced days to first flowering and depressed height at first flowering and final height. Higher Alar concentrations, particularly 2000 ppm applied twice after 3 and 6 weeks on closely-planted okra, produced more, longer and heavier pods, and therefore higher total pod yield in unstopped than in stopped okra, in addition to advancing days to first flowering and depressing height at first flowering and final height. The agronomic practice of stopping okra at 6 weeks reduced pod number, pod weight/plant and total pod yield/ha in unsprayed plants.

Clearing cotton stalks after picking is enforced by law in the Sudan to stop the spread of black-arm and leaf curl diseases. The magnitude of pull and lift requirements to uproot a single plant are important parameters in designing an efficient stalk-pulling machine. With the help of a specially built apparatus, 186 plants selected at random were uprooted and measurements of the magnitude of pull and plant lift were recorded. A magnitude of 121 kg pull, accompanied by a short lift of 4·9 cm, were found necessary to loosen all plants completely. Investigations have also included the percentage of plants pulled and their root dimensions in relation to the yield point.

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.

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.

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.

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 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.

Tubers of Dioscorea alata L. cv White Lisbon, affected by Internal Brown Spot (IBS) disease, and stored under ambient conditions on wooden or wire racks, did not show significant increases in IBS incidence and mean lesions over storage periods of up to 18 weeks. Storage under different conditions of temperature (13, 20 and 28 ± 3°C) did not have any significant effect on IBS incidence; but tubers stored under conditions of high relative humidity (95 ± 2%) showed less IBS and greater mean lesion diameters. Although a significant reduction in disease incidence occurred during storage under the latter conditions, the effects of increased lesion size resulted in some deterioration of tuber quality.

Differences in the net photosynthetic rates of two classes of Hevea clonal seedlings are explained in terms of resistances to carbon dioxide diffusion from the outside air into the carboxylation sites. The residual resistance, the sum of the mesophyll and the carboxylation resistances, is apparently related to photosynthetic rates.