In trials over 2 years at five locations in Northern Nigeria single inputs were removed from a package of maize practices. The improved variety was most important and increased the yield of the otherwise complete package by 86%. Early sowing and high plant population were not important in all trials. The high fertilizer treatment (125–50–50 kg NPK/ha) consistently exceeded the half rate, with a mean increase of 31%. It was suggested that, with clean weeding, priority should be given to the improved variety, high fertilizer and early sowing. High populations, involving changes to traditional techniques, may be introduced gradually.

The unit is a greatly simplified screw expeller, modified so that the crop is thoroughly rubbed to liberate juice before the charge moves into the part of the unit in which pressure is applied. The throughput of the model described here is 2 kg of crop per minute; power consumption is about 400 W. The unit weighs 40 kg, but larger ones, operating on the same principles, could be made.

The productivity of seven multiple rice-cropping systems, utilizing a short-duration cultivar under irrigation, were assessed over 5 years. Systems of one, two and three crops a year were compared. Multiple cropping reduced grain yield, panicles m-2, total dry matter and nitrogen uptake per crop. However, the unfertilized three-crop-per-year system averaged 9·1 t grain, 17·1 t DM and 126 kg N ha-1 per annum, without showing a long term decline in productivity. Recovery and utilization of nitrogen fertilizer were generally low compared to other experiments, and were highest for the early dry season cropping period.

Trials to determine the optimal rate and time of nitrogen application to cotton were conducted at three sites for three seasons. The results indicate that nitrogen is used most efficiently when applied at relatively low rates, with at least half the application delayed until flowering. Early application leads to the incorporation of a greater proportion of the nitrogen into the vegetative structures which, at lower rates, may leave insufficient for fruit development. With late application a greater proportion of the nitrogen is utilized in reproductive growth, although full utilization may not be achieved at higher rates.

The development of two simple techniques, box storage and field clamps, which allow curing and storage of fresh cassava roots for 1 and 2 month periods, is described. Consistent and acceptable results have been obtained following storage of roots in boxes packed in moist but not wet sawdust and kept at ambient temperatures. The design of field clamps that maintain internal temperature below 40°C, to allow successful curing and storage, varies in different seasons. Storage life of roots is enhanced by the selection of roots in good condition, and any delay in placing the roots in storage results in poorer out-turns.

There were significant differences in dry matter yield among five forage oat varieties tested at ten environments during 1970–75. The correlation coefficients between annual rainfall and DM yield varied with variety from 0·69 to 0·88, late varieties tending to give higher yields. Lateness, and high varietal response to annual rainfall and improved environmental conditions, can be used as selection criteria in semi-arid regions. Late varieties had higher DM and lower crude protein contents, and forage produced under lower rainfall conditions tended to have more DM and crude protein.

The discrepancy between farmers' performances and research-based recommendations in the control of cotton pests in Southern Malawi is discussed. Analysis of the former in two seasons revealed that the farmers' low levels of insecticide application approached the economic optimum, whereas several factors of economic importance were omitted from the research-based justification of high spraying levels. Recommendations for improving the applicability of research recommendations to smallholder farming are made, with particular reference to the farming risks that arise from uncertain rainfall, the wide range of farming ability encountered in practice, and the dangers of atypically high levels of management in research experiments.

During a period of dry weather, seedling tea bushes were generally less stressed than the clones which had been derived from those plants by vegetative propagation. There were interesting differences between the clones in their responses to dry conditions, but these could not have been predicted from similar observations made on the heterogeneous seedlings. However, it should be possible to use tests, based on measurements of the xylem water potential and stomatal resistance, to identify potentially drought-resistant clones at a later stage in the selection programme.

Effectively nodulated cowpea plants, grown in pots without applied nitrogen, were vegetatively equal to non-nodulated plants supplied with 60 ppm N throughout growth (88 days) and produced significantly greater seed yields. Supplying non-nodulated plants with 120 or 240 ppm N improved seed yields (but not significantly) compared with plants completely dependent on symbiotic fixation. Nodulation promoted branching, and improved pod set and/or retention compared with plants relying on applied N.

The influence of leaf area and inter-plant competition on the growth and yield of a crop of high-yielding dry beans (Phaseolus vulgaris L.) in central Mexico was studied, using density and thinning treatments. The highest seed yield (4210 kg/ha at 14% moisture) was obtained with the highest density (28·8 plants/m2). Thinning showed that pods/plant was sensitive to inter-plant competition between 36 and 78 days after seeding (first flower at 50 days), but seeds/pod, and especially seed weight, were not sensitive. It is suggested that the close positive relation between yield and leaf area duration derives from the influence of photosynthate supply upon pod number.

Agronomic techniques to even out the intra-seasonal fluctuations in yields of tea in Malawi are described, and evidence presented of their effects on the level and distribution of yield. Such treatments reduce yields per acre, but by overcoming constraints on capacity they may lead to increased yields for the estate as a whole. The full benefit of some of these practices requires the prediction of yield patterns based on current and expected weather. Several techniques can be combined to form a flexible approach adapted to each particular year, but more work is required to quantify the parameters and functional relations involved before alternative strategies can be properly compared.

In experiments conducted with three rice varieties at different plant populations and N levels, the non-lodging varieties responded to 150 kg N/ha. The highest yield in non-lodging varieties were at the highest transplanted density, but at the lowest density in the lodging variety. The percentage of total milled rice of all varieties was not significantly affected by N application, which improved head-rice recovery in chalky IR-8, but had no significant effect on non-chalky varieties. Competition for nutrients could be a major factor limiting head rice return at high densities.

Seed yield in two soyabean varieties—one tall (Improved Pelican) and one short (V/1)—was mainly determined by the total number of main stem and branch pods produced when plant population density varied from 5·4 to 16·2 plants/m2. An increasing percentage of the pods was found on the main stems of Improved Pelican as the crop stand became denser.

This paper attempts to determine the relations between weather and cotton yields in the Gezira Scheme in the Sudan, and to establish a prediction function with climatic factors as variables. The precision of the function established to forecast the final yield in April will as yet be low, when based on the information available at the end of October, November or December. A significantly better yield forecast can be made at the end of January. Variables of the prediction function are temperature, humidity, radiation and evapotranspiration. A strategy is proposed to improve early forecasts step by step, by making further forecasts at later stages.

The efficiency of fertilizer P uptake by irrigated wheat, as affected by method and time of application, was studied in the field by using P32 labelled superphosphate. Fertilizer P was applied at planting in a sideband, with the seed, or broadcast, and broadcast at tillering. Phosphorus applied at tillering was most productive for grain and straw yield, and its utilization was significantly higher than from P applied at planting. Phosphorus broadcast at planting was least efficiently utilized. A high correlation was found between the ratio of fertilizer P to soil P in grain and straw, and with their respective yields.

The efficiency of the Latin square design relative to the completely randomized and the randomized complete block designs is expressed in the form (A+BF) where F is a variance ratio (or the sum of two ratios). The constants A and B are evaluated, and lines showing relative efficiencies for given F values are drawn for the 5 × 5, 6 × 6, 7 × 7 and 8 × 8 Latin squares.

Plant water potential and leaf diffusive conductance, key features of plant responses to water stress in field experiments, can be estimated, respectively, by xylem pressure potential measured with the pressure chamber apparatus, and leaf permeability measured with the air flow porometer. This paper describes modifications to these two techniques in order to increase the rapidity of measurements in wheat to 60/h with the pressure chamber, and 200/h with the porometer. Rapid measurements are needed because of the large within-and between-plot errors encountered with daytime measurements in typical field experiments, examples of which are presented.

Concentration of tea yields in Malawi into regular successive peaks within the main growing season is the cause of severe economic problems. A model of the causes of these peaks has been developed and its explanatory power is confirmed in the light of empirical tests of its component parts and predictions. A computer version of the model is presented and its predictive power demonstrated. Use of the model to explore relations between weather and yields is discussed, with indications of its limitations for this purpose.

This paper reports results of a study to investigate the problem of introducing an improved technological package into the farming system in one area of northern Nigeria. It examines the economic and technical feasibility, as well as the social acceptability to the farmer, of growing sole cowpea given his environment and constraints. Studies of this nature are important as they provide insight into the problems farmers experience with improved technologies and thus represent one way of determining how to narrow the gap between yields farmers obtain and those obtainable at the research station level.

Average seed yields of effectively nodulated cowpea plants were 38% greater than those of non-nodulated plants when both received applied nitrogen at concentrations ranging from 60 to 240 ppm during one of three periods: emergence to first flower, first flower to mid pod-fill, or mid pod-fill to maturity. Nodulation increased seed yields by 45% when plants received a ‘basal’ level of 30 ppm N throughout growth. None of the combined nitrogen treatments could compensate non-nodulated plants for the loss of symbiotic nitrogen fixation. Non-nodulated plants relying on applied N branched less, produced fewer peduncles and set fewer pods on each peduncle than nodulated plants.