The problems resulting from genotype × environment interactions are discussed, giving an example where the application of statistical techniques to maize breeding makes it possible to assess the effects of such interactions. A method of maize breeding is proposed which enables a number of objectives to be achieved from a single breeding programme.

The mineral N (NH4 + NO8) in soils at a savanna site was low at the time of crop planting except after groundnuts and when dung had been used. Nitrification occurred whatever the previous crop, but the numbers of nitrifying bacteria were small and varied with the level of substrate ammonium.

Research and observations on how climate effects the growth and yield of the tea plant are reviewed. Despite differences in the types of tea grown and the cultural techniques practiced in the different tea areas, an attempt is made to define quantitatively the climatic conditions needed to maintain growth rates at a high level. The need for critical work in the future is emphasized.

The effects of nitrogen fertilization on growth, nutrient uptake and yields of upland and lowland taro were studied on the island of Kauai, applying o, 280, 560 and 1120 kg./ha. N. Nitrogen concentrations of upland and lowland taro leaves were significantly correlated with yields, although regression analysis showed that per cent N in both blades and petioles decreased with age. Higher yields were obtained from the lowland than from the upland crop, regardless of amounts of N fertilizer applied. The highest yield obtained from lowland taro was at 1120 kg./ha. N harvested at fifteen months (57·6 tons/ha.) and from upland taro the highest yield was obtained at 560 kg./ha. N harvested also at fifteen months (25·5 tons/ha.).

Taichung (Native) No. 1 rice was grown under controlled conditions with a basic temperature regime of 30°C by day and 20°C by night. Periods of 2, 4 and 12 hours at 15°C (59°F) were imposed during darkness for the first or second 40 days, or for the first 80 days after sowing. Floral initiation was delayed by cool periods of 2 hours at night or longer, and delay from this cause was always accompanied by reduced grain yields, resulting from fewer spikelets per panicle or increased tiller sterility. This effect was not overcome when the cool periods ceased after floral initiation. Cool periods longer than 4 hours had a greater effect when they were given in the first 40 days.

The growth of two varieties of white yam was analysed from planting in December to harvest in September. Four stages were recognized, viz.: dormancy, rapid growth of vine and root, rapid tuber development accompanied by leaf senescence and tuber maturity followed by reduction in tuber weight. The period of rapid growth coincident with maximum demand for nutrients was early June, suggesting that fertilizer should be applied in mid-May so that it is available in June.

High yield in the tapioca varieties studied appears to be associated with sink activity of the tubers and consequently with crop index. Growth measurements indicate that assimilation is significantly affected by sink activity as well as by the functioning of the assimilation apparatus. The form of the crop growth curve, and the effect of spacing on yield and distribution of dry matter are also considered.

The yield data obtained from fertilizer experiments conducted at 195 locations for three years were examined to study the relations between yield, response to nitrogen and phosphorus, soil test values, and number of irrigations, using multiple regression technique. Irrigation accounted for 20–36 per cent of the yield variation, whereas soil factors did not show appreciable effects. Nitrogen response was influenced by irrigation, while some soil factors affected response to phosphorus.

Results from an experiment with maize (variety NEH 1151) at three plant densities indicated that normally favourable environmental conditions promoted tillering and it was difficult to maintain the desired tiller densities. The higher densities produced more vegetative dry matter but less grain than the lower densities. In a second experiment, where tillers were removed from the plants, there was no advantage because the remaining tillers grew larger to compensate for the removal. It is concluded that it is desirable to breed or select for non-tillering varieties where other management parameters can be controlled.

Variation in the percentage of nitrogen, phosphorus and potassium content of a variety of white yam, grown without fertilizer, and the nutrients removed per acre by various portions of the plant, were determined. The time to apply fertilizers, and the most suitable portion of the plant for foliar analysis, were deduced from the changes in nutrients with age. The effect of nitrogen fertilizer on yield, and the nutrient content of the harvested tuber, were studied. The influence of a yam crop in a rotation is discussed.

The growth of improved short varieties of rice with low and high tillering capacities was compared under a wide range of nitrogen levels and spacings. A high tillering variety performed better than a low tillering one under the experimental conditions tested. Leaf area index values as high as 10 to 12 were not detrimental to grain production unless the crop lodged.

Three varieties of rice, selected for their differences in height and tillering ability, were grown side by side in 10-row plots to determine the effect of varietal competition on plot yields. Plants in border rows performed differently from those in the centres of plots, higher-tillering or taller varieties tending to depress the performance of adjacent plants. Comparisons among varieties based on plot yields, determined with and without excluding the border rows, gave different results. Excluding two rows on each side of a plot was sufficient to eliminate the effects of varietal competition on yield data.

Compost or ammonium sulphate improved and maintained cotton yield for 6 years but both, together with triple superphosphate, were needed to maintain it for 9 years, after which yield declined and lime was necessary. Compost supplied necessary but insufficient phosphorus, potassium, calcium and nitrogen. Manganese toxicity was severe when potassium chloride was used on very acid soil. At suitable soil pH and with adequate phosphorus and cations, response to nitrogen was large, but for it to be most effective, calcium seemed necessary to maintain the cation: anion ratio. Without lime, yields declined with heavy rain; with it they were largest in the wettest seasons.

Comparison of an overhead boom sprayer (Monica Mist) with a conventional air-assisted sprayer (Conomist) showed that the former gave relatively poor cover, but control of coffee berry disease (CBD) was equally good with both machines. It is suggested that the success of overhead spraying is dependent upon effective redistribution of fungicide within the tree canopy during rain.

Under controlled environment conditions rice variety IR8 was subjected to night temperatures of 15, 20 and 25°C during each of the three periods (a) sowing to floral initiation, (b) initiation to panicle emergence, and (c) panicle emergence to maturity, with day temperatures of 30°C throughout. Night temperatures of 15°C prevented floral initiation throughout the experiment, an effect partly overcome by transfer to higher temperatures after 102 days but not without yield loss. The optimum night temperature was 20–25°C, with some evidence of change of temperature effects, as distinct from the effect of actual temperature levels. As IR8 was developed under relatively stress-free conditions, its sensitivity to temperatures below 15°C may be greater than in varieties developed elsewhere.

Yield response to a range of plant densities (0·7–7·2 plants m.−2) achieved by uprooting plants at random was curvilinear, with an optimum plant density of 3·3 plants m.−2 at which fertilizer increased the yield at Makoka by over 1000 kg. ha.−1 to 2227 kg. ha.−1. There was no interaction between fertilizer and plant density. At Ngabu there was no response to fertilizer. Top dressing was effective on unfertilized cotton at Makoka, but filling in was ineffective at both sites. A method of partitioning components of yield is described which illustrates the stages of plant development which benefitted or were adversely affected by the different agronomic practices.

Eight trials, covering a wide range of conditions in Malawi, have assessed the effect of applying nitrogen (0, 45 and 90 kg. ha.−1), sulphur (0, 22, 45 kg. ha.−1), phosphorus (0, 15 kg. ha.−1) and boron (0, 0·63 kg. ha.−1) on growth and yield of cotton. A nitrogen × sulphur interaction was very highly significant at one site, and good responses to nitrogen were obtained at six sites. Phosphorus and boron gave significant increases at one site. Increased yields of seed cotton indicated that there is an overall need for a compound fertilizer to supply nitrogen, sulphur, boron and in some areas phosphorus.

Hand-pollinated pods of the Crin Elite establishment cocoa progeny C77 X C23 showed that pod maturity, based on pod age, significantly affected bean viability as well as leaf area, leaf number, plant height and plant girth of the seedlings produced. Beans extracted from immature unripe cocoa pods only 15 weeks from hand-pollination were more than 50 per cent viable and produced seedlings vigorous enough for transplanting to the field after 20 weeks in the nursery compared with beans from 25-week-old normal, mature-ripe cocoa pods. Loss by black pod disease (Phytopthora palmivora Butl) could therefore be avoided and time of waiting for pods to attain normal maturity and ripening saved, by early harvesting.

Experiments on seed rate, time of weeding and thinning confirmed that lower seed rates, weeded and thinned early, give higher yields. A reduction in yield of 400 kg.ha.−1 seed cotton caused by late weeding emphasized that farmers who spray should limit their acreage to that which can be weeded satisfactorily.

A rapid, simple method is described for estimating the area of rubber leaves from two measurements on the middle and one of the side leaflets. The relationship between the area of a leaflet (A) and its length × breadth (LB), described by the expression A = 0.654 LB, does not vary between the three leaflets or between leaves of different ages, and clonal differences are slight.