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.

In a study of soil and water conservation systems for high-altitude Kenya farming, control of accelerated erosion in two arable crops per year for six years was achieved by contour-ploughing and tied-ridging. The Kikuyu red loam latosol lay on 10 per cent and 12 per cent slopes under rainfall of intensities often exceeding 2 inches per hour. Soil structure measurements showed progressive reduction in the acceptance rate of rainfall, but gulley erosion occurred only in the absence of ties. Six years of intensive arable cultivations were compared with rotations having two, three or four years of perennial grass ley, with and without protection by Nichols terraces. Runoff, measured through Parshall flumes, was heaviest from well-established grass immediately after intensive grazing. Productivity was highest under grass. With a basal dressing of one hundred weight of double supers, 10 acres of Cynodon dactylon carried 20 Zebu steers for seven months without supplementation and showed a liveweight gain of 1·1 lb per steer per day. Grazing was reduced by failures in establishment of short legs. The grass depleted soil moisture to wilting point to a depth of ten feet within six months of planting and annually thereafter. Water use was approximately the same as total rainfall. Results, applicable locally, indicate a limit of four years duration for arable and a minimum of five years duration for pastures. Terraces can only be replaced by a high standard of management and skilled cultivation.

Field trials in Northern Nigeria have shown that the yield of introduced varieties of maize can be economically improved with combinations of nitrogen and phosphorus fertilizer. Three response areas have been defined. In the south, where most of the maize is grown, the initial response is to nitrogen. Further north, with the exception of one small area in which the response is almost entirely to phosphorus, phosphorus and nitrogen and equal limiting factors. Estimates of the most profitable combinations of nitrogen and phosphorus to use in each area have been obtained from quadratic response surfaces fitted to the yield data of the experiments.

Latex flow can be stimulated by bark scraping and by the application of vegetable oils, auxins and some other substances to the bark, either above or below the tapping cut. Auxin preparations are now widely used in commercial rubber production, 2,4–D and 2,4–5–T being the most common. The response obtained depends upon the formulation, on the method of application, and on other factors such as the age and condition of the tree and the tapping system employed. The effect of stimulation is considered to be due to a dilution of the latex and an increased rate of flow. A larger area of bark is drained, and the duration of flow is prolonged, because plugging of the latex vessels is delayed. In young trees, the conflict between increased latex production and active tree growth requires the development of different and less intensive techniques.

Sorghum is the principal foodcrop grown in Northern Nigeria. A survey of local varieties grown during the rains was carried out in 1958 and the 821 samples collected were assigned to seven morphologically distinct races, of which four are important. Varieties belonging to the Guinea race, with loose, open panicles, are mainly cultivated in high rainfall areas south of latitude 11°30′N. Further north, three races, Kaura, Farafara and Chad are grown in the dry Sudan Savanna zone. Varieties of these races have compact panicles and bulging grains. Estimates of the contribution made by each of the four major races indicate that the Guinea race accounts for nearly 50 per cent of the total sorghum production in Northern Nigeria.

Since the profitability of the geranium crop depends to a great extent on the total yield of oil per acre, methods of increasing this yield are of prime importance. Two trials were laid down to determine the responses to nitrogen, phosphate and cutting at various times during the year. Phosphate increased total weight of green material, nitrogen had little effect, and neither significantly affected the yield of oil per ton cut. Time of cutting influenced both oil and green material yields. Climatic factors producing higher yields of green material had the opposite effect on yields of oil per ton of material cut, and vice versa. Fertilizers had no discernable effect on oil quality, but there was an appreciable difference between oil produced after wet and dry periods.

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.

Mature lucerne on shallow granite sand was irrigated at different intervals, determined by four factors, 0·4, 0·6, 0·8 and 1·0, applied to daily evaporation (E0) as measured by a USWB Class A pan. Moisture balances were calculated for each treatment, and when the accumulated sum of daily evaporation, multiplied by the appropriate factor, reached 1·2 inches, which was about 50 per cent of the available moisture in the top 2 feet of soil, this amount of water was applied to the plots of the treatment concerned. Irrigation on the basis of 0·8 E0 gave the but overall results, although the highest yield from a single cut was obtained with the irrigation frequency defined by 1·0 E0. During the rainy season yields from all treatments declined markedly, those from the most frequently irrigated treatment showing the greatest drop. The lucerne under the irrigation regimes defined by 0·4 and 0·6 E0, although subjected to considerable moisture stress in the dry weather, suffered no lasting ill effects and yielded well during the rains. The experimental area was almost certainly subject to advective energy but the results are considered valid for local conditions.

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 importance of carotene supplements in the feeding of White Fulani Zebu cattle has been studied in three experiments. The live weight gains of heifers, with and without carotene on two planes of nutrition, showed 0·2 lb/head/day gain on the ‘high’ plane, but the ‘low’ plane group did not respond to carotene supplement. The association between cottonseed feeding and vitamin A deficiency, studied by comparing the rates of depletion of heifer calves on cottonseed supplements and on a sorghum/groundnut mixture, indicated that cottonseed can enhance the rate of carotene/vitamin A depletion in the liver. Carotene supplements equivalent to 2 oz red palm oil, to cows before and after calving failed to improve the vitamin A potency of milk. The total daily secretion of carotene and vitamin A in the milk was insufficient to maintain adequate liver stores in a suckled calf.

An experiment in which irrigation intervals for lucerne were dictated by four factors applied to daily evaporation from a Class A pan has been reported by Landsberg (1966). This paper discusses data from a number of subsidiary measurements made during that experiment. An extensive soil sampling programme yielded data on the effects of treatments on soil moisture content, and plant height and per cent ground cover measurements enabled detailed evaluations to be made of crop responses. Both height and ground cover were decreased by soil moisture stress. Relative turgidity was closely related to soil moisture content in the early morning, dry treatments showing more rapid recovery of turgor than those where water was kept at more adequate levels. Radiation utilization by the crop was affected by soil moisture conditions, and also apparently by temperature.

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.

As part of a programme to improve production of the main food crops of Northern Nigeria, trials were carried out to investigate the effect of nitrogen and phosphate fertilizer on the grain yield of sorghum. Five fertilizer response areas have been defined and estimates have been made of the most profitable combinations and levels of phosphorus and nitrogen to use in each area. Fertilizers produced the greatest increase in yield in the two response areas which cover the north of the country.

Most oil palm pollen is produced by male inflorescences 2–3 days after anthesis, and this pollen is the most viable. When protected, pollen viability on female inflorescences is good up to 6 days, after which it declines. The majority of the pollen remains below the canopy, especially at bunch level. Results of quantitative evaluation of pollen dispersal showed that atmospheric pollen density is very variable and is governed by numerous factors. There is a marked diurnal variation, with highest pollen density during the afternoon and a negligible amount during the night and early morning. Rain causes an immediate drop in concentration, but pollen densities were influenced more by the number of days on which rain was recorded than by total rainfall. A relationship exists between pollen density, the number of male inflorescences in the vicinity, and rainfall, but the effects of relative humidity, sunshine and wind are obscure. Whilst pollen density drops rapidly within a short distance from the inflorescence, there is a significant dispersal over greater distances than previously thought.

An investigation was undertaken on the relative tolerance to salinity of the olive varieties Manzanillo, Souri and Sigoise in the arid zone of Israel (Negev), in an experimental grove of the Jewish National Fund, using 11-year-old trees that were grown on saline and non-saline soils under irrigation with sewage water. Manzanillo was the most sensitive to salinity, yields and development of trunk, crown and root system all being adversely affected. Sigoise was the most tolerant to salinity and vegetative development was not impaired at all. Souri was intermediate in sensitivity to salinity. In spite of the susceptibility of Manzanillo it is preferred because of its high yield, which was greater even on a saline soil than yields of the other two varieties on non-saline soil.

Two groups of mature Marwari wethers were raced at 5 and to miles/hr respectively, for 30 minutes. Rectal temperature, respiratory frequency and pulse rate were measured initially, again immediately after the exercise, and subsequently four times at 20 minute interval. The rise in rectal temperature, respiratory rate and pulse rate in the animals raced at 10 miles/hr was 2·1°F, 86 and 22 counts/min. respectively. The corresponding values in the animals raced at 5 miles/hr were 0·9°F, 72 and 19 counts/min. The rise in rectal temperature due to stress was proportional to the degree of exercise. The magnitude of increase in the respiratory rate tended to be the same under both the treatments, and the trend in pulse rate was similar to that of respiratory rate.

An early upright-bunch variety of groundnut, Barberton, and a medium-late spreading-bunch variety, Ashford, were compared at 7·5, 15·0 and 30·0 cm. intra-row spacings planted at one and two kernels per hill on 60 cm. ridges in the irrigated heavy clay soil of the Sudan Gezira in 1963 and 1964. Barberton was harvested on days 95, 110 and 125, and Ashford on days 125, 140 and 155 after planting in July–August. Ashford outyielded Barberton at the lower densities, and the best pod yields were obtained on day 125 harvest at a population of 55,000–60,000 plants per acre. A higher plant population depressed the yield of Ashford while the increased pod yield of Barberton was not significant. Field germination of kernels increased more in Barberton with delay in harvest and with decrease in plant population than in Ashford. Mean pod and kernel weights and shelling out-turn of Barberton increased with delay in harvest. Barberton gave higher oil content and shelling out-turn, and lower proportion of pods with single kernels than Ashford. The highest population of Barberton gave the best oil content in early harvests. In general, the arrangement of plants within rows at similar populations had only small effects except on the quality of nuts, which was improved by planting single kernels at close spacing (7·5 cm.) with the variety Barberton and two kernels at wide spacing (15·0 cm.) with Ashford, at optimum plant populations.

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.