Maize plants (Sweetcorn cv. Earliking) were grown in plots where four types of soil surface coverings were used to induce soil temperature differences During the vegetative stage of growth measurements were made of total leaf area per plant on a daily basis, and relative rates of leaf area increase were found to be closely correlated with mean daily soil temperatures at 5 cm. depth. The results were consistent with evidence that the temperature of the apical meristem strongly influences rates of leaf expansion in maize seedlings.

The seed of American Cotton, Var. 134, was stressed at 50, 60, 70, 80 and 90°C for 24 or 48 hours before seeding. Stresses at 50 to 70°C had a stimulatory effect on seedling emergence and subsequent performance of the cotton plants, but higher temperatures caused thermal injury or killed the seed.

Crop yield on continuously cultivated tropical forest soil was maintained at a fairly high level by the application of mineral fertilizer. Although the low rate of nitrogen applied as ammonium sulphate did not increase yield, there was a significant effect on pH of the soil resulting in a reduction of the divalent cations on the exchange complex. The effect of mulch was mainly chemical through the release of nutrients.

This paper reports the heterotic pod production of three different crosses between a Nigerian local selection (N38) and three Trinidad Introductions (CF47, CF56 and CF207). The hybrids consistently outyielded the inbreds throughout the first 19 years of pod production. N38 × CF56 hybrid produced the highest number of pods per tree, closely followed by N38 × CF47 hybrid; while N38 × CF47 hybrid showed the best heterotic response. Pod production figures of (CD207)2 and (CD302)2, both double inbreds of N38, support the hypothesis that N38 is a Trinitario × local selection hybrid which segregate for pod production.

Four-year-old seedlings of twenty-eight hybrid progenies were infected with the Ghanaian swollen-shoot virus strain A, but all were too severely affected to be of practical value in combating the disease. Sensitivity was assessed by comparison with uninoculated controls; reduction in crop and in growth and deterioration of canopy were correlated. The Amelonado × Amazon crosses were no more sensitive than the better inter-Amazon progenies. The rapid decline of the infected trees may have been partly due to infection coinciding with the slowing down of vegetative growth as cropping commenced.

The effects of irrigation on the yields of wheat and cotton were studied on a sandy clay loam soil, with a water-table at 7 ft below ground, under the arid conditions of Lyallpur. The conventional practice of providing 19-acre in. of water to Mexican wheat and 25-acre in. to American cotton proved to be a wasteful and unproductive practice on such soils. High yields of both these crops could be obtained without any subsequent watering after an initial 4-in. irrigation applied for seedbed preparation and sowing, while one 3-in. irrigation after sowing was needed to obtain maximum yields.

Comparison of up to ten carrot cultivars at various sites in a three-year period did not show that any cultivar consistently outyielded the others. Investigations at Samaru between 1969 and 1971 indicated that application of 100 kg. of N was beneficial, response to P was not consistent and there was no response to K or trace elements. Economics of production by peasant farmers is discussed and conclusions drawn that irrigated carrots, grown in the dry season, could be very profitable. No successful control was found for blight (Alternaria dauci) which severely inhibits the production of a wet season crop.

The uptake of S followed a similar pattern to dry-matter production by groundnuts given enough fertilizer-S to prevent S-deficiency. The fastest rate at which dry matter was produced was 140 kg./ha./day. Of the 6857 kg./ha. at harvest, 3401 were in haulm, 967 in shells and 2489 in kernels. S was taken up fastest during the eighth week, when the daily average was 0·22 kg./ha.; at harvest, of the 11·6 kg./ha. in the plants, 5·4 was in the haulm, 0·8 in shells and 5·4 in the kernels. Of the 157 kg. N/ha. in the harvested crop 62 per cent was in shells and kernels and of the 13·5 kg. P/ha., 64 per cent was in shells and kernels.

The efficiency of fertilizer N uptake by wheat, as affected by time and rate of application, was studied in the field using N15 labelled ammonium nitrate. Splitting the application was only beneficial at the maximum rate but two top dressings at tillering and boot stage were better for grain production than a basal dressing or single top dressing at stem extension stage, but uptake of fertilizer N was maximal from a single top dressing. The calculated effective rate of application (E.R.A.) was useful in evaluating the effect of time and rate of application and N availability to plants.

Data from uniformity trials on healthy and diseased wheat and oat crops showed that the coefficient of variation for yield decreased as plot size increased and became nearer to square in shape. Infection with Septoria leaf blotch of oats and powdery mildew of wheat did not appear to affect yield variability. Plots larger than rod row size (where 16 ft of the centre row of 3 rows is harvested) are recommended to detect differences of 10 per cent in yield between two treatments.

Sugarcane yields and smut incidence levels were observed in three successive crops. The effect of pathogen upon host was primarily one of stress, as smut infection was shown to increase sucrose content of cane whilst depressing yields in tonnes of cane per ha. Where infection levels were high, roguing was shown to increase disease incidence. However, smut whip removal was confirmed as the best roguing treatment for commercial fields. Disease control and yield responses related to roguing effort were much better in NCo 376 than NCo 310; and, therefore, continued cultivation of NCo 310 fields with high smut incidence was concluded to be a major hazard to the industry.

Intercropping maize or sorghum with pigeon peas, cowpeas or beans led to a reduction in leaf area indices, fresh weight yield at time of anthesis, straw yield at harvest and grain yield of the cereal crops. In sorghum, pigeon peas and cowpeas had a greater adverse effect on grain yield than beans, but with maize, beans and cowpeas had a more adverse effect on grain yield than pigeon peas. While intercropping maize with either beans or cowpeas decreased total yield of grain (cereal and legume) per hectare, intercropping sorghum with pigeon peas increased total grain yield per hectare.