Methods of determining the causes of year-to-year variation in yield are discussed. The types of data required for valid analysis, the need to build up a logical argument, and the use of direct experimentation to verify conclusions drawn from regression analyses, are considered.

Leaves of Coffea arabica L. were sampled from an artificial shade trial to examine the effects of two levels of shade, compared with full exposure, on size, structure and chlorophyll content. A grid was designed for the rapid measurement of leaf areas in the field, and individual leaf areas were found to increase progressively with shading. Since dry weight per leaf was not affected, an increase in specific leaf area was entailed. Leaf size varied greatly with season of formation, a wider range occurring in selection N39 than KP162, but the reasons for the variation were not clear. Neither lamina thickness nor proportion of palisade tissue varied with shade treatment. Chlorophyll per unit weight increased with shade in KP162 but with N39 was only greater under dense shade. Chlorophyll per unit area did not alter with shade, but N39 had significantly more chlorophyll than KP162 on both a weight and an area basis.

Three experiments and five small trials on robusta coffee and four small trials on arabica coffee have confirmed that nitrogen is the main nutrient requirement in Uganda. Magnesium and sulphur were not deficient and mulching had no effect on responses to nitrogen fertilizers. Leaf and soil analyses confirm the yield results and indicate that the optimum time to apply nitrogen is in February and September. There was little difference between ammonium sulphate and urea, but the former tended to have greater effects on yields.

The results are presented of a trial with coconuts, testing progeny of 104 unselected seed parents. The progenies of the best 5 per cent of the parents, selected on their phenotypic values, gave yields 14 per cent above the progeny population mean, indicating that mass selection is effective. There was considerable variation in breeding values between the palms tested, and a higher frequency of desirable genotypes could be isolated when the parents were selected on yield of copra rather than when they were taken at random. Prepotency in coconut palms is discussed. Leaf production of the young palms within a family, during the first 40 months of their growth, was correlated with the breeding value of the parent.

Premature wilting and death of groundnut plants in Northern Nigeria was caused mainly by termites excavating the xylem tissue of the root. Lepidopterous larvae which damaged the crown of the plant were a less common cause. Occasional wilted plants had discoloured vascular systems from which Pythium myriotylum was consistently isolated. Wilting was also caused by mechanical damage inflicted during weeding operations. Complete severance or blockage of the water-conducting tissue of the primary root did not result in immediate death of plants, because the pods and pegs were able to absorb sufficient moisture to maintain the leaves above permanent wilting point until the onset of the dry season.

Soil, water and leaf analyses were carried out on samples from irrigated orchards in the Jordan Valley. Analysis of the soil for available phosphorus and potassium gave meaningful results. Analysis of the irrigation water showed that a high sodium and chloride content caused an increase of these ions in the soil, which led to undesirable effects such as chlorosis. Irrigation water class C3–S1 should only be used if there is an annual precipitation of about 300 mm. Leaf analysis showed changes in the composition of leaves with age, but only potassium varied significantly between varieties. Standards of leaf, soil and water composition are suggested for the growing of citrus.

Supplementary irrigation experiments were conducted on a Clansthal sand and a Windermere clay. Irrigation treatments were based on the application of 1 inch of water when the soil moisture deficit reached 2·5, 3·5, 4·5 and 5·5 in. in 7 ft of soil on the sand, and 1·00, 1·75, 2·50 and 3·25 in. in 2 ft of soil on the clay. Each experiment included a dryland control and soil moisture was estimated weekly in each plot with a neutron probe. The results showed that there were significant linear increases in yield with increasing quantities of water applied. The crops exploited soil moisture to a depth of 6 ft in the sand and 3 ft in the clay, even with the maximum water treatments. Under dryland conditions, on the sand the crop exploited soil moisture to the wilting point only in the surface foot of soil, but on the clay the crop extracted moisture held at tensions greater than 15 bars in the top 3 ft of soil. The conclusions are that, where available water for supplementary irrigation is limited, heavy soils should be irrigated in preference to sandy soils, and that the most efficient use of both rainfall and irrigation water is achieved when 1 cusec is used to irrigate about 200 acres.

Experiments were conducted during three crop seasons to determine the effects of lindane and carbary1, applied to the irrigation water or incorporated in the soil, on the control of insects, on the nitrogen status of the soil and plant, and on grain yield of lowland rice. In two crop seasons the highest grain yield was obtained from three applications of lindane to the irrigation water and carbaryl sprays at 7- to 10-day intervals, and in the third season from 20 kg/ha. carbaryl incorporated in the soil without any lindane treatment or carbaryl spray. In two seasons, soil-incorporated carbaryl at 20 kg/ha. active ingredient gave a significantly higher yield than the no-insecticide control, and in one season the increase in grain yield was just below the significant level. Most of the grain yield increase with 20 kg/ha. carbaryl incorporated into the soil was caused by better control of stem borer and leafhopper and a significant reduction in virus infection.

Dormancy of six varieties of paddy, of three maturity groups, was studied under six seed-treatments. One type showed no dormancy but others showed dormancy in varying degrees 15 days after harvest. Dormancy was completely broken either by removing the kernels from the glumes, or by puncturing the glumes, or by putting acid-treated seeds in an atmosphere saturated with oxygen. The germination percentages were also significantly increased when seeds were treated with N/10 sulphuric acid solution for four hours, or when seeds were put in atmospheres saturated with oxygen. Speed of germination did not improve, as in the case of seeds germinated after four months of harvest, except in cases where the kernels were removed from the glumes or the glumes were punctured. The causes of dormancy of rice seeds were assumed to reside in the flowing glumes (lemma and palea), and different seed-treatments improved the germination of rice seeds by increasing the permeability of the glumes to oxygen and/or reducing the resistance of the tough glume covers over the germinating embryos. The magnitude of the treatment effects differed with variety. These studies suggest methods of improving germination.

There are now too many research papers on every subject for anybody to read. Authors should aim to ‘sell’ their papers to readers. Accessibility and readability are selling points. To get a paper read, pay special attention to the title and summary. Have an informative title which does not distract the reader with useless words and phrases; start it with the most significant phrase. Put a summary or abstract at the beginning, confine it to research results, and make it easily readable.