Low levels of zinc are reported in flooded rice grown on alkaline clay soils in the Lake Chad basin, north-east Nigeria. Zinc was added at 0, 5, 10 and 20 kg/ha to sample plots. For the untreated plots, the mean levels of zinc in young rice leaf and ‘available’ zinc in the supporting soil, using the alkaline extractant method of Trierweiler and Lindsay (1969), were 18·2 and 0·33 ppm respectively; corresponding mean levels for plots with 20 kg/ha added zinc were 36·5 and 1·54 ppm. There is a correlation between the two variables of r=+0·61 (P<0·01). Levels of nitrogen, phosphorus, potassium, magnesium and calcium in the rice leaf are also reported.

Insects cause serious problems during the storage of cassava chips, when quality may be reduced and significant quantities of the product consumed. The major species naturally infesting chips were Rhizopertha dominica, Lasioderma serricorne and Araecerus fasciculatus. Infestation occurs during the sun-drying process, and up to 16% reduction in chip weight due to insect feeding was recorded after 2 months storage. Chips that had not received any pre-drying storage, but contained salt as a preservative, were infested by fewer insects than chips without salt. The poorest quality chips had significantly more insects than better quality ones.

Sweet potato (Ipomoea batatas L.) virus disease (SPVD) causes severe disease symptoms of various combinations of leaf strapping, vein-clearing, puckering and stunting. The disease is widespread, especially in Africa, and yield is adversely affected, though there are no figures to quantify this effect nor is it known how yield is affected. Loss of tuberous root yield due to SPVD was studied in sweet potato showing symptoms of the disease. Slips were obtained from plants with and without symptoms and two yield trials in 2 years were conducted by planting them alternately in rows. Yield of fresh tubers was reduced by 78% in plants showing SPVD symptoms but the reduced chlorophyll level of diseased leaves did not appear to affect yield.

In contrast to earlier results, a clear advantage from mixed cropping of maize and beans (Phaseolus vulgaris) was found in the long-rain seasons (March to September) of 1976 and 1977. Pure stand yields were low due to drought in 1976 and excessive rainfall in 1977. These and other results for long-rain seasons in Kenya suggest that mixtures are more efficient where pure stand yield levels are low, but there is little difference between cropping systems where levels are high. Light interception by maize leaves was quite small until late in the life of the bean crop.

An investigation for 2 years at Kano and 1 year at Samaru evaluated the effects of plant density on vegetative growth, development and dry matter production and distribution of five varieties of groundnut. Growth and branching of individual plants were reduced at high populations but more dry matter was produced per unit area. Dense plants, particularly Spanish 205, developed a larger leaf area earlier in the season and were presumably able to make better use of light. Varieties F439.4 and 439.2 suffered the least reduction in the number of vegetative branches but the extra branches contributed few useful reproductive nodes.

Five fire-cured tobacco varieties were grown under different fertilizer levels and environments, to investigate their effects upon quality of the cured leaf. Environment exerted the greatest effect, and the best quality of leaf was produced from virgin soils. Fertilizer responses were greatest in environments where traditional agricultural methods operated, but even heavy applications of fertilizer under these conditions did not compensate for lack of good initial soil conditions. Although variety affected the style of tobacco produced, varietal differences were small compared with the effects of environment and fertilizer.

In a long-term fertility study it was observed that judicious use of chemical fertilizers maintained the levels of soil pH, total N, organic C, CEC and exchangeable Ca. Highest accumulation of exchangeable Ca and Mg was found in the 40–60 cm layer. Absence of Mg and K from the fertilizer schedule resulted in a decrease in the amounts of those elements in the soil. Profile CEC and exchangeable Ca were not affected much by the application of K or trace elements. Compared with adjacent grass fallow or virgin bush land, only the values of C/N ratio, CEC and exchangeable Mg decreased on cultivation. All the crops responded well to fertility levels but not to K; trace element response was confined to cotton and groundnut.

The effect of soil salinity on growth and yield of broad bean was investigated, using correlation analysis. The salinity level at which 50% reduction in bean yield occurred was 9 mmho/cm. The negative correlation between dry matter production and yield and ECe, together with the field observations, indicated that soil salinity may be responsible for the different growth and yield of broad bean fields in the salt-affected areas of northern Sudan.

No natural population of Rhizobium japonicum specific for soyabeans (Glycine max L.) could be found in any soil type in Israel. A crop of 5450 kg seed/ha was obtained in a field of sandy soil, inoculated with commercial granular inoculant, by maintaining soil at a moisture level near to field capacity during the growing season. In another field, on heavy soil inoculated with different strains of R. japonicum, the highest yield was obtained with strain 31-SM, a mutant derived from strain 61A75. Nitrogen fixation, as measured by the acetylene reduction method, was highest with strain 31-SM. Under local conditions soyabean plants snowed 100% nodulation when inoculated by the slurry method, by granular inoculant or by spraying bacteria into the furrow.

The yield data from a series of fire-cured variety × fertilizer trials in Malawi are presented. Variety was not important in determining total yields though it was in influencing the distribution of grades. Fertilizer had a large effect upon yields, particularly upon the Cutter and Leaf grades, but environment had by far the greatest influence. High levels of applied fertilizer could not be relied upon to replenish a depleted soil so that it produced yields comparable to those from a soil with well-maintained fertility. Application of fertilizer produced a beneficial change in the grade distribution within the crop.

Oil content (percentage) was determined by pulsed nuclear magnetic spectrometry to study its variability in rai (Brassica juncea) and yellow sarson (B. campestris). Wide inter-varietal and intra-varietal variability was observed in both crops. Genetic aspects of oil content were also worked out, and single-plant and bulk selection methods used for 3 years to exploit the intra-varietal variability. A positive trend in the improvement of oil percentage was observed in 27 out of 30 varieties, some of which showed significant improvements over their respective unselected stocks. A maximum increment of 7% was observed in variety BR 40 of rai and 6% in variety YSM of yellow sarson.

Irrigated and unirrigated crops of pearl millet were grown in Hyderabad, India, during the post-monsoon season of 1977. Irrigation increased both the dry weight of roots and the number of root axes, but because the additional axes were thick and unbranched the total length of roots was unaffected. However, irrigation did cause more of the root length to be in the top 20 cm of soil. Yield of the irrigated crop was higher than that of the dry crop, mainly because more tillers survived to produce grain. Grain growth of the dry crop occurred when the net growth of the crop was zero, probably because of movement of assimilate from stems to panicles. Possible strategies for improving yields are examined in the light of the growth data.

Growth characteristics of dry bean genotypes of determinate (Type I), indeterminate small vine (Type II), and indeterminate large vine (Type III) types were evaluated over three spacings and two growing seasons. Important observations include: (1) Type I did not give increased yields in response to planting rows closer together in Trial II because there was a large decrease in harvest index, which did not occur for Types II and III; (2) accumulation of reproductive nodes prior to anthesis is important for high yields, as are biological yield, harvest index and leaf area; and (3) within-habit spacing combinations, factors such as flowering duration, branch-, leaf- and raceme-numbers, and stem length could not be used to predict yield.

Yields of pearl millet were significantly increased when grown after legume crops such as groundnut (22·6%), cowpea (24·2%) or pigeonpea (12·1%) instead of after pearl millet. A previous crop of short-duration mung did not affect the yield of pearl millet. Benefits from previous crops of groundnut and cowpea were equivalent to about 60 kg N/ha applied to a pearl millet crop following a previous crop of pearl millet.

Maize was grown from three batches of seed, with mean 1000-grain weights of 225, 432 and 649 g. Initial plant size was larger when grown from large seed, but development rates were similar for all three sizes and relative growth rates were similar during the early stages. Relative differences in plant size became smaller as the crop matured. Crop growth rates during the linear phase of dry matter production were the same, and there were no significant yield differences. Comparisons of leaf and spikelet initiation, and individual leaf size are also reported.

Monthly partitioning of dry matter (DM) and nutrient contents of polybag oil palm nursery seedlings, planted at three spacings, showed that leaves and petioles accounted for about half of the DM up to 11 months. There was no spacing effect on the nutrient contents of seedlings, K being always higher than other nutrients followed by N, Ca, Mg and P in that order. Most of the nutrients were in the leaves and petioles, with a dramatic increase in the amount of nutrient taken up by the seedlings in November. Fertilizer rates and frequencies were deduced for an oil palm nursery based on the nutrient contents of seedlings.

Ten tomato varieties, tested at three locations for 3 years in Western Nigeria, gave variety × environment interactions, indicating that some were only suitable for specific areas and none possessed wide adaptation. It is suggested that Western Nigeria could usefully be divided into sub-zones in which specific varieties could be developed.

Banana packing systems rely on floating the fruit in water in order to remove latex produced at the cut surfaces of the crown. At some periods of the year up to 5% of the fruit sinks and rolls along the bottom of the tanks, resulting in heavy scarring of the peel. Potassium content of buoyant fruit exceeded 1·3% dry weight in the pulp and 6·0% in the peel, but in one investigation the sinker fruit had 36 and 20% less than these levels respectively. Application of potassium fertilizer in the field greatly reduced the amount of sinker fruit.

The adaptability of rice varieties to crop seasons in Taiwan was evaluated for 106 varieties. Average grain yield was higher in the first than second crop seasons. Indica varieties yielded better than Japonicas, particularly in the second crop season, when temperatures are higher. In both the Indica and Japonica groups, varieties developed in Taiwan outyielded those from overseas. Japonica varieties from Japan were lowest yielders in both seasons. Some IRRI varieties were outstanding in the first, while several Ponlais and Taiwan Indicas appeared promising in the second crop seasons.

Seed dormancy was found in the Mexican sesame cultivar Cola de Borrego but it disappeared about 6 months after harvest. Dormancy was completely broken by soaking the seeds in GA3 solutions of 100 and 500 ppm for 48 h; soaking in 1000 ppm GA3 concentration was helpful but not as good as the 100 and 500 ppm treatments. GA3 treatments also hastened emergence.