Maize plants (Sweetcorn cv. Earliking) were grown in plots where four types of soil surface coverings were used to induce soil temperature differences During the vegetative stage of growth measurements were made of total leaf area per plant on a daily basis, and relative rates of leaf area increase were found to be closely correlated with mean daily soil temperatures at 5 cm. depth. The results were consistent with evidence that the temperature of the apical meristem strongly influences rates of leaf expansion in maize seedlings.

Effects of environmental temperature on boll maturation period of cotton and the genotype response, investigated in a 3-year field experiment, showed a negative correlation between period and mean temperature and revealed genotypic differences regarding degree of temperature influence and sensibility to temperature changes. The observed genotype × temperature interactions may help cotton breeders in establishing breeding centres and in creating desirable gene combinations for wider adaptability to temperature.

Pasture experiments may be grazed using either variable (put-and-take) or fixed stocking rates. Considerations such as the risks of introducing bias, the reliability of the data, and the resources required for these methods of grazing are discussed, and criteria are described for choosing between the methods.

In fifteen field trials with Phaseolus vulgaris cv. Canadian Wonder time of planting was the most important factor affecting yield of dry beans in the Shire Highlands of Southern Malawi. Under-cropping maize with beans had no deleterious effect on the yield of maize and gave a worthwhile yield of beans. Little response was found to different plant populations when conditions for growth were good, but when conditions were poor yields were greatest from the highest population of 47,000 plants per hectare. A response in yield was obtained from 11 kg. N ha.−1 but there was no effect of source of nitrogen or response to phosphate, potash or inoculation.

The seed of American Cotton, Var. 134, was stressed at 50, 60, 70, 80 and 90°C for 24 or 48 hours before seeding. Stresses at 50 to 70°C had a stimulatory effect on seedling emergence and subsequent performance of the cotton plants, but higher temperatures caused thermal injury or killed the seed.

The variety Nigerian Synthetic-5 was sown on eight occasions, five in the first season and three in the second, at approximately 15-day intervals from 15 April to 15 June, and on 20 August, 4 September and 23 September. The method of seed bed preparation and time of planting both affected yields, effects that could be related to soil temperature and soil moisture reserve during crop development. Maize planted in August produced the highest yield; heaps and ridges gave the lowest yield at all planting dates, while planting on the flat or in furrows produced the highest yield.

The yield of cowpeas could be increased by judicious defoliation of the older leaves or by topping the growing apices at the onset of flowering. Limited defoliation at the pre-flowering stage did not reduce the yield of beans significantly but severe defoliation at any stage prior to maturity drastically reduced yield. Satisfactory yields of cowpea could be obtained by maintaining only about one-half to two-thirds of the potential leaf-area of the plants, suggesting that a reduction in the number and area of leaves, coupled with a better display of the fewer remaining leaves, could make cowpeas more productive than hitherto.

At Ukiriguru, Western Tanzania, three experiments over 4 years investigated the effects of nitrogen (up to 240 kg. N/ha.) and phosphate (up to 50 kg. P/ha.) on a Cenchrus ciliaris pasture. Dry matter yield increased with up to 160 kg. N and dry matter content also increased with nitrogen, whereas crude protein contents were initially lowered and then increased by the higher rates of nitrogen. These differences are attributed to changes in the leaf/framework ratio. The crude protein yield increased with each nitrogen level. Sulphate of ammonia markedly lowered the soil pH. The only responses to phosphate were when it was cultivated into the top soil, when there was a small increase in yield and a fall in crude protein.

Using coffee trees sprayed with cuprous oxide and captafol it has been shown that both fungicides are redistributed within the tree canopy by rain. Under conditions of light rain fungicides are removed from upper parts of trees and redeposited at lower levels within the canopy in amounts capable of providing effective protection against coffee berry disease (CBD). With heavy rainfall, however, redeposition of fungicide at effective levels is less likely to occur. The results are discussed in relation to the success of overhead boom sprayers in controlling CBD and the observations that shoots in the upper parts of coffee trees are an important source of spores of the CBD strain of Colletotrichum coffeanum.

Maize was grown for three years at three levels of nitrogen, 56, 112 and 224 kg. N ha.−1, involving altogether nine different timing and splitting treatments. Measurements were made of grain yield, plant nitrogen status and total-N-uptake, and, in one year, movement of nitrate-N in control plot soils. Where only 56 kg. N ha.−1 was applied, its time of application made very little difference to yield; at higher rates of nitrogen an unsplit application as late as seven weeks was very inefficient, but only at the highest rate did a split application give any appreciable yield increase over an unsplit application to the seed bed. Consideration of the soil nitrate-N data and the long-term pattern of rainfall distribution leads to the conclusion that leaching is unlikely to be a serious problem in the nitrogen nutrition of early-planted maize.

Effects of fertilizers on harvest time and yield of cowpeas were studied on upland soils in Sierra Leone. In a 25 confounded factorial trial, on soil which had been cropped successively with 2 years of Smooth Cayenne pineapples and 14 months of cassava, the treatments did not affect harvest time significantly, but N, P and NP Mg produced very favourable effects on grain yields. In a randomized complete block experiment on soil previously cropped with two successive cassava crops, there was a significant difference in total yield of dry pods between the control and most treatments.

Crop yield on continuously cultivated tropical forest soil was maintained at a fairly high level by the application of mineral fertilizer. Although the low rate of nitrogen applied as ammonium sulphate did not increase yield, there was a significant effect on pH of the soil resulting in a reduction of the divalent cations on the exchange complex. The effect of mulch was mainly chemical through the release of nutrients.

This paper reports the heterotic pod production of three different crosses between a Nigerian local selection (N38) and three Trinidad Introductions (CF47, CF56 and CF207). The hybrids consistently outyielded the inbreds throughout the first 19 years of pod production. N38 × CF56 hybrid produced the highest number of pods per tree, closely followed by N38 × CF47 hybrid; while N38 × CF47 hybrid showed the best heterotic response. Pod production figures of (CD207)2 and (CD302)2, both double inbreds of N38, support the hypothesis that N38 is a Trinitario × local selection hybrid which segregate for pod production.

The nitrogen content of weeds was significantly higher than that of Dular rice-straw, but with Taichung Native I rice in winter there was no significant difference between the nitrogen in weed samples and rice plants at the tillering stage. Rice straw contained a higher proportion of nitrogen where there were three hand weedings. The total dry matter of rice was much reduced by weed competition. Weed species contained much nitrogen at the vegetative, flowering and post-flowering stages, indicating severe competition for nitrogen by weeds throughout the growth of rice under dry land conditions.

Effects of moisture stress during different stages of cotton development were evaluated by using correlation and regression methods on data of six irrigation experiments from three different climatic regions. Significant negative correlations were found between the number of days in which soil moisture was below a threshold level, and several plant traits. Flower number was usually affected adversely by stress at the beginning of flowering; boll number, boll retention, boll weight, lint yield, lint length and seed index by stress at the end of flowering; earliness and lint fineness by stress during early boll development. Lint index, per cent and strength were affected by stress at different periods and effects of stress on lint yield were correlated with its effects on boll number, boll weight, lint length and early maturity.

The mass selection reservoir (MSR) is one way to take a population approach to the breeding of sugarcane. Yield data from four successive plantings of a sugarcane MSR showed consistent superiority to a commercial clone. The problem of defining satisfactory selection indices for the MSR is discussed.

Irrigation, mulch and N-fertilizers increased the yield of fresh fruit/tree by 66 per cent due to increases of 42 per cent in the number of fruiting nodes/tree, 14 per cent in number of fruits/node and 15 per cent in fresh weight/fruit; these three yield components accounted for 42, 13 and 6 per cent of the variation in yield among all treatment combinations. Bean/fruit weight ratios and times of flowering were not affected. Correlations between yield components were positive, suggesting that still more nodes could be produced per tree and per unit area before physiological limits to yield were reached.

Growth of the sunflower cultivar Peredovic was examined when exposed to periodic severe moisture stress, with and without soil drench application of CCG at the two-leaf stage. The experiment was conducted in sand culture under partly controlled environment conditions. Morphological and physiological measurements were made throughout the growing period. Amongst the responses to CCC were increased stem and petiole width, and decreased length of internodes, head diameter and photosynthetic area. Moisture stress reduced photosynthetic area and the root/shoot ratio. Both CCC and moisture stress increased the number of stomata per unit area.

Four-year-old seedlings of twenty-eight hybrid progenies were infected with the Ghanaian swollen-shoot virus strain A, but all were too severely affected to be of practical value in combating the disease. Sensitivity was assessed by comparison with uninoculated controls; reduction in crop and in growth and deterioration of canopy were correlated. The Amelonado × Amazon crosses were no more sensitive than the better inter-Amazon progenies. The rapid decline of the infected trees may have been partly due to infection coinciding with the slowing down of vegetative growth as cropping commenced.

Four methods of applying boron to the oil palm were studied and the results indicated that applications to the soil or to leaf axils were best. Tests of five sources of boron showed that alkaline borate fertilizers were superior to boric acid.