The growth and grain production of four rice varieties were compared under controlled environment conditions at two minimum night temperatures (15 and 23°C) and at two daylengths (11½ and 13 hours) where the period of daylight for active photosynthesis was kept constant at 8 hours. The lower night temperature prevented flowering but at the higher one grain yields were associated with panicle weights rather than panicle numbers, and production of so-called photoperiod-insensitive varieties was affected by photoperiod. Although the periods of natural light were constant, and photoperiods were extended by low intensity incandescent light, in-creased total plant weights, not due to effects on tillering, were observed under longer days.

Large soil monoliths, extracted undisturbed in 44-gallon oil drums, have been used to assess the available-water capacity, and the relation between the growth of sugarcane and soil water deficit for agricultural soils in Barbados. Constancy of field capacity was studied and the effect of cultivation on the storage of available soil water. Deep montmorillonite clays and oceanic soils had storage capacities greater than 20 cm. of water in an 80 cm. profile, whereas sandy or stony montmorillonite clays and most soils developed from kaolinite clays had capacities less than 11 cm. Cultivation significantly increased the water holding capacity of soils but this was rarely as great as for fabricated composts and the water was never so freely available. The data have been used in decisions about cultivation and irrigation, and as the basis for an ecological grouping of sugar estates according to their probable water balance.

Sorghum hybrids and varieties show similar responses to changing environment, with constant relative yield increases from the hybrids over a wide range of conditions due almost entirely to more florets and grains per plant and per hectare. Carbohydrate production of the leaves of good varieties is probably not much in excess of requirements for filling the grain. The extra spikelet number of the hybrid, increases in photosynthetic area and probably increased photosynthetic efficiency together enable the extra grains be filled. There is also an advantage in size and activity of the root system. The yield increase is strongly buffered against environmental fluctuations. The fact that hybrids can increase over a wide range of farming conditions should result in big increases in production simply by changing from varieties to hybrids, as is already happening in several countries.

In sixteen factorial field trials with N, P, K, Mg, trace element and farmyard manure treatments, yields declined during the first four years of cropping following a resting period under grass, responses to K and farmyard manure increased, and other treatments showed no significant changes. After a few years of continuous cropping potassium deficiency may seriously limit yields, especially of sweet potatoes. N, P and K fertilizers maintained yields as well as the farmyard manure treatment.

Uptake of the major nutrients by maize was determined throughout the growing season. Little phosphorus was accumulated, as reflected in its distribution within the plants, but uptake of labelled phosphorus showed two distinct peaks associated with root development. One fifth of the applied phosphorus was recovered by the plants.

Sisal showing symptoms of parallel streak developed more slowly than symptomless plants, both leaf length and number of leaves unfurled being reduced. In streaked areas of the leaf, ground tissues surrounding the peripheral and internal fibre bundles collapsed; decortication of streaked leaves was difficult and fibre quality was adversely affected by reduction in length and discoloration. Parallel streak was seen only in vegetatively propagated Agave sisalana, in leaves lacking marginal spines. The condition was observed only where the mean minimum temperature fell below 16°C; symptoms appeared five months after the onset of a period of low temperature. Apparently every A. sisalana plant in Kenya is affected, but the condition is masked in coastal regions due to high mean minimum temperature. The disease seems not to be due to bacterial or fungal pathogens, or to nutritional factors, but may be caused by a virus, or a genetic ‘disease’ similar to June Yellows of strawberries.

In many instances measures developed for the control of coffee berry disease in East Africa have become less effective since 1961. Changes in the flowering and fruiting patterns of the coffee tree have recently become evident, ascribed in part to the onset of a wetter and cooler climatic cycle in 1961–62, and in part to the effect of the disease itself which, by removing crop, stimulates out-of-season flowering. Consequently, instead of a single main crop in which susceptible and highly infective ripe berries are present for a short time only, a series of over-lapping crops results in ripe berries being on the trees for most of the year. This has changed the disease epidemiology: formerly the main source of infection was conidia from the maturing wood, but now conidia from the berries are often predominant. This has greatly affected the efficiency of control measures, and means are suggested for restoring the previous situation.

The shoots of high, medium and low yielding clones of tapioca were examined to see whether yield was associated with morphological characteristics of the foliage and/or with leaf area development. The lowest yielding variety had the highest leaf area per stem, and vice versa, differences in leaf area being mainly due to differences in leaf size. Leaves of the highest yielding variety possessed attenuated lobes, which tended to have a more vertical mid-day orientation, whereas the lowest yielding variety possessed large broad-lobed leaves with more horizontal orientation. The intermediate variety had acutely attenuated lobes and showed a much more vertical day-time orientation. The relationship between the leaf properties and canopy efficiency is discussed.

Experiments were made in glasshouses, growth cabinets and growth rooms to study the differential responses of the broad bean to water stress during the vegetative and flowering phases of growth. Plants in the flowering phase proved to be more sensitive to drought than in the vegetative period, and there were different responses (Relative Growth Rate) to temperature at different stages of plant growth. Day length and temperature influenced the position of the earliest flower initials on the stem, and intensity of flower shedding was aggravated by high temperature.

During the wet summer season of northern tropical Australia higher yields were attained by introduced weakly photoperiod-sensitive short-duration rice varieties than by locally-bred strongly photoperiod-sensitive varieties resembling traditional tropical indicas. There was no clear relationship between growth durations and yields. Dry season yields were lower, associated with shortened durations (especially of the reproductive phase) and lower cumulative radiation totals in the late phases of growth. Dawn, a variety of U.S. origin imported from the Philippines, outyielded all other varieties. In both wet and dry seasons yields depended largely on panicle weights, which in turn depended on high seed numbers per panicle. Individual seed weights were of less importance. The results tended to confirm a prior interpretation of climatic data, i.e. that there is no environmental factor limiting wet season yields in the region to levels below those obtained elsewhere in the tropics, provided the crop receives a high standard of care and attention.

Sisal was grown in double rows with broad-interrow covers of Pueraria phaseoloides, controlled volunteer vegetation or clean weeding. Clean weeding gave the best yield over one cycle, but Pueraria cover was best in the second cycle. Pueraria was better than volunteer vegetation in all trials, with the greatest margin on soils low in nitrogen, or where there were pernicious weeds. On an exhausted soil, sisal with a Pueraria cover responded to fertilizer nitrogen applied in the early or late part of the cycle. Manuring sisal growing with a volunteer vegetation cover with 50 tons sisal waste/ha. improved growth to the same extent as replacing the cover with one of Pueraria. In the absence of manures, yields declined from cycle to cycle with all the covers. At the level of manuring which maintained yields with a volunteer vegetation cover, yields declined slightly with clean cultivation, and improved considerably with a Pueraria cover.

Results from five years trials showed that irrigation was frequently needed to ensure early and adequate germination of cotton, that the use of a water balance to determine time and amount of irrigation was practical and economic, that there was no appreciable effect of fertilizer on yield of seed cotton on these soils, and that there was no significant change in the fertility of the soil after four crops of cotton.

Effects of rainfall on yield of cocoa from a large-scale experiment has been investigated at 10 and 12 sites, over seven years, in the Eastern and Ashanti regions of Ghana. There was a positive association between yield and rainfall at certain times of year, but a negative association at other times. Variation due to the regression of yield on monthly rainfall varied up to 23 per cent, while a maximum variation of 31 per cent accounted for the regression of yield on the total rainfall of February to April in the Eastern region.

A method is described for estimating leaf area of the oil palm. Significant correlations were found between leaf area and yield in a number of progenies of palms growing in West Malaysia.

Application of S, alone or in combination with P, significantly increased the number, yield and nitrogen content of root nodules on pigeon pea and guar. Sulphur, applied at different levels with NPK, increased the methionine content and yield of plants significantly but had no significant effect on the N content. Sulphur at 20 p.p.m., alone or in combination with P, increased the methionine content of pigeon pea significantly but the effect decreased at higher levels of S. In general, higher values of methionine were obtained in the presence of S than when it was absent.

The range, mean, genotypic and phenotypic coefficients of variation, heritability and genetic advance for various characters, of forty-seven varieties of ragi (Eleusine coracana) showed a wide range of variation and highly significant varietal differences. The genetic advance was highest for yield of straw and genotypic coefficients were higher than phenotypic coefficients for most characters. Path coefficient analysis indicated that the number of productive tillers and grain weight of main ears were the major components for seed yield.

To evaluate the potential efficacy of fungicides for the control of birds' eye spot in rubber nurseries, 49 formulations were tested in the laboratory by the paper disc diffusion and liquid culture methods. After discarding phytotoxic fungicides, only certain of the carbamate compounds, especially thiram, and those containing manganese and difolatan showed mazked activity in both series of tests. The results were compazed with field experience, and for the most part good correlations were found between laboratory and field results, a marked exception being the poor in vitro inhibition shown by zineb. A bimodal growth response was shown by the fungus to some of the carbamate formulations.

At Ukiriguru, in Western Tanzania, three levels of sulphate of ammonia were compared on natural pastures on hardpan soils. Yields of dry matter were substantially increased by nitrogen fertilizer and at high stocking rates the growth of cattle on different treatments followed fairly closely the amounts of dry matter available.

Analyses of total N and P in coffee leaves from different geographic areas have been compared. The levels of these nutrients are correlated with each other and the quadratic regression equation for leaf N on leaf P has been derived. The value of N/P ratio in the coffee leaf for diagnosing nutritional status is assessed. No correlations were observed between Mg and either N or P. Irrigation of coffee in Kenya on latosolic soils raises leaf P but not N levels, in the absence of organic mulch and fertilizers. Effects of organic mulch, N and P fertilizers on leaf levels of N or P are discussed.