Established plants of bermudagrass (Cynodon dactylon (L.) Pers.), johnsongrass (Sorghum halepense (L.) Pers.) and purple nutsedge (Cyperus rotundus L.), grown in containers, were repeatedly clipped to the ground from spring to winter, at monthly and bi-weekly intervals. Regrowth of bermudagrass was markedly reduced after monthly clippings, but all plants regrew in the following March; there was no regeneration in March of bi-weekly clipped plants. Severe decrease of regrowth of clipped johnsongrass occurred after bi-weekly or monthly clippings, but a quarter of the clipped plants regenerated in the following March. Nutsedge was more resistant to clipping than the other two species and all clipped plants regrew vigorously in the following March. Repeated clipping reduced the rhizome length or tuber number and the dry matter content in the regrown plants in proportion to the frequency of clipping.

The decline in fertility of red ferrallitic soils in Uganda under arable cropping, and its restoration under permanent vegetation, is shown to be associated with losses and gains of major nutrients by the top-soil. A fertilizer mixture formulated to correct the losses and imitate the gains of nutrients consistently increased crop yields and maintained soil fertility over 4 years. Reasons for the success of the fertilizer mixture and its potential use in other tropical areas are discussed.

The persistence of residues of gamma BHC and malathion on bhindi fruits was estimated by bioassay using 1-day-old male Drosophila flies. Although the initial deposits were heavy, they dissipated quickly, with half-lives of approximately 4 and 2 days for gamma BHC and malathion respectively.

The extent of natural cross-fertilization in sesame was studied in two varieties, with contrasting flower colour, planted at two locations; in alternate rows or alternate holes; in adjacent or non-contiguous plots; and at 6 different spacings. The average out-crossing for the different treatments ranged between 3.1 and 6.7 per cent. The non-contiguous plots showed a higher degree of out-crossing than adjacent plots, in which there was a decrease in the extent of cross-pollination with increase in the distance between the dominant and the recessive parents. Alternate holes gave a higher percentage than alternate rows.

Ten wheat crosses between tall local varieties C228 and C591, a short local variety C271, and short Mexican varieties Penjamo, Nainari 60, Pitic 62 and Sonora 64, were field-tested under irrigation for heterosis for plant height, grain yield, spikes per plant and kernels per spike. Heterosis occurred to a greater degree for the last three attributes in some of the crosses, with the greatest heterotic expression in crosses involving Penjamo and Pitic 62 and the local variety C591.

A three-year study on the development of oil, protein and dry matter in sesame seeds showed that oil percentage increased rapidly 11–17 days after fertilization, reaching a maximum in 20–23 days. There was no change in the iodine value of the oil after 18 days from fertilization. Accumulation of protein was more gradual, but there was no appreciable increase after the ‘seeds’ were 27 days old. Dry matter increased more slowly than either oil or protein and there was little increase after the ‘seeds’ were 34 days old. The implications of these findings on problems of harvesting the crop are discussed.

Controlling weeds until 6 weeks after crop emergence gave a yield of soyabeans only 85 per cent that of the clean-weeded control treatment. Delaying weeding until 3 or 6 weeks after emergence gave yields 89 per cent and 69 per cent respectively of the control. Narrow crop rows (30.5 cm.) gave higher yields than wide rows (61 cm.). Defoliation of soyabeans reduced pod number, seed size and yields more with late and severe defoliation, and with lower plant populations. Delayed harvesting during the dry season led to seed shedding and yield was at the maximum for only about one week.

Aflatoxin was found in forty-one out of seventy-four samples of various pulses, whereas Aspergillus flavus occurred in all samples, and there was an apparent correlation between the occurrence of the fungus and the level of the toxin in haricot beans. There was evidence that the toxin was produced in haricot beans after harvest, and drying the pods immediately after harvest is therefore suggested as a method of controlling mould growth and the formation of aflatoxin.

Complete nutrient ± boron treatments were imposed on seedling and young oil palms growing in sand and water culture. A number of symptoms were observed on the boron-deficient palms, including the development of high endogenous auxin levels. The relation of morphological symptoms with IAA concentration is discussed. Comparisons were made of dry matter production, leaf area and leaf boron concentration.

At Samaru (11° 10′N, 7° 39′E) the growing season for rain-fed annual crops is 180 to 200days. Sole cropping, relay cropping and intercropping of long season sorghum, early millet or maize and late planted cowpeas were evaluated for most effective use of this period, all crops being cultivated mechanically. Relay cropping and intercropping gave 59 and 80 per cent more return per acre respectively than a sole crop of sorghum, the increases coming mainly from higher cereal yields. Some criteria applicable to intercropping are recognized.

A pot experiment was carried out to study various aspects of growing peanuts in highly calcareous soil, with special reference to iron chlorosis. There was good agreement among the criteria used to evaluate the need for iron and the effectiveness of different chelates or methods of application (i.e. visual symptoms, chemical diagnosis and yield response). Of the iron chelates tested, Sequestrene 138 proved the most effective. Promising results were also obtained by coating seeds with chelate as an iron starter, followed by an additional top dressing. The results indicate the possibility of growing peanut economically in the highly calcareous soil tested using iron chelate —Fe EDDHA (Sequestrene 138).

The effect on cross pollination of four directions and six distances from the marker variety in Egyptian cotton was investigated. The percentage of cross pollination did not differ appreciably in the different directions but there were significant differences in cross fertilization among the six distances. A linear relation was observed between cross pollination per cent and distance up to 8.8 m. from the marker variety. Implications of these findings on various aspects of cotton breeding methodology are discussed.

Mechanized crop production schemes continue to be the main source of grain sorghum in the Sudan, where fertilizer experiments have shown that applications of NP and NPK significantly increase the grain yield of continuous sorghum, though economic increases could be obtained by the application of nitrogen.

Potassium application appeared to increase dry matter production and yield of oil palms, primarily by increasing leaf area, while nitrogen increased both leaf area and net assimilation rate. Responses to phosphorus and magnesium were harder to interpret. Production of vegetative dry matter attained a fairly constant level at the higher rates of fertilizer application, while the ratio of bunch yield to total dry matter production was little affected by fertilizer treatments. The importance of these results for oil palm breeding, and their possible value in diagnosing fertilizer requirements, are briefly discussed.

Effects of Gamma BHC in controlling capsids on cocoa in a large-scale experiment have been assessed at 10 and 12 sites, over seven seasons, in the Eastern and Ashanti regions of Ghana. The treatments effect was not significant for the whole Eastern region, whereas it was for the Ashanti region except in the first season. For the Ashanti region the overall treatment and seasons effects were very highly significant, whereas their interaction was not. There was an increase in response with time, though the rate of response was decreasing with time.

Weekly measurements in a maize silage crop grown at three populations, each at three levels of nitrogen, showed that leaf area index, crop growth rate and total whole plant yield were greatest at the highest plant population (430,000/ha.) and lowest at the low population (47,000/ha.). At the former maximum yields of dry matter and crude protein occurred approximately seventy-five days from sowing, when the cob contribution was small. With wider spacing maximum yields occurred later. At the intermediate population (107,000/ha.), and with adequate nitrogen, sowing on the square was superior to sowing in wide rows. Nitrogen did not preferentially affect the relative dry matter yield of any growth component; plant population had a greater influence on total whole plant yield than nitrogen.

A previously undescribed mosaic disease was observed on groundnut plants in several districts of West Malaysia. The virus was transmissible through sap, grafting and the aphids Aphis craccivora, A. gossypi, Myzus persicae, Rhopalosiphum maidis and Toxoptera citricidus. A. craccivora, the principal vector, shows dual transmission. The host range of the virus included mostly leguminous plants such as Glycine max, Cassia occidentalis, Crotalaria anagyroides, Indigofera hirsuta, Stylosanthes gracilis and Phaseolus vulgaris, and a non-leguminous host Chenopodium amaranticolor. The longevity in vitro of the virus was between 40–48 hours, its thermal end-point between 63° and 65°C and the dilution end-point 10−4.

The total N uptake, crude protein content, and recovery of N in rice grains varied with varieties. Increased levels of N application gave increases in total N uptake and crude protein content in the grains, though recovery of N in the grains decreased with increased levels of nitrogen application. Irrespective of varieties and levels of application, three split dressings of nitrogenous fertilizer gave greater total N uptake, crude protein content, and recovery of N in the rice grains than where all the N was applied at the time of transplanting of seedlings.

The effect of fungicides on the development of powdery mildews on cucumber and okra was studied. Most of the chemicals tested controlled the disease and significantly increased yields, though a dimethirimol-resistant Oidium sp. appeared on okra. Seed dressing with the systemic fungicides thiophanate and benomyl conferred resistance to the disease for a few days whereas soil application gave protection for more than eleven weeks.

Artificial defoliation was used to simulate grazing by cutting-grass or cane-rat (Thryonomys swinderianus), on three rices with durations of 110–115, 130–135 and 140–145 days respectively, defoliated before, during and soon after tillering by removing leaves to half, two-thirds and the total height of the plants. All varieties showed marked compensatory growth, resulting in increased tillering and yield, especially when defoliated during tillering, but yield fell when foliage was removed after tillering, especially with shorter duration rice. Defoliation to half the height of the plant during tillering had the most beneficial effect, whereas removal of all leaves to soil level after the tillering stage had the most adverse effect.