A continuous daily rainfall record provides much information for agriculturalists but initial questions are imprecise and are modified in the light of experience. In order to match this uncertainty the program ‘Rainfall Statistics’ is designed as a simple interactive procedure for studying quantity probabilities, dry spell frequencies and a simple soil-moisture budget. The program has various functions depending upon user requirements. Use of the program is illustrated with rainfall records from northern Thailand.

A random sample of 13 uniformity trials was examined in terms of sensitivity to choice of block size and orientation. Five trials were classified as insensitive and eight as sensitive. Trials insensitive to blocking choices showed little variation in experimental error for various sizes, shapes and orientations of blocks, but those sensitive to blocking choices showed considerable, sometimes drastic, effects of such choices. There was often an objectionable degree of inflation of experimental error due to large or improperly oriented blocks. It is proposed that the routine analysis of field experiments based on block designs be modified to reveal cases in which ineffective blocks have been used on sensitive sites.

The effects of date of planting and soil mulching on cowpea growth and yield were investigated for three years during the middle part of the minor season in Sierra Leone. Mulching at 8 tons/ha conserved more soil moisture than other mulch rates, with greatest difference in the top 15 cm of soil, especially during drier periods. Plant height, pod number and seed yield of cowpea planted in September were significantly greater than from other planting dates whether mulch was applied or not. The beneficial effects of mulching at 8 tons/ha on cowpea growth and yield were more dramatic when the crop received an average weekly rainfall of 100 mm before 50% flowering.

Tea yields of 1 to 4 t ha−1y−1 of dry shoot tips are much less than those of other vegetative crops like grasslands or forests growing in similar conditions, partly because plucking restricts tea biomass production, but mainly because the harvest index of tea is small. In Kenya, plucked tea produced 36% less biomass per hectare per year than unplucked tea, and 64% less wood. Only 8·3% of the total annual biomass increment was harvested. This proportion might be increased by plucking older leaves, increasing the shoot:root ratio, and by lowering the plucking table so that less wood was produced.

The unit for separating juice from which 5 to 10 kg of leaf protein could be made in a day has been modified so as to make it more efficient and more convenient to use.

A field experiment was conducted on a Zn-deficient highly-deteriorated sodic soil of the Ghabdan series to determine the effect of three rates of gypsum (G0, G25, G50% of the gypsum requirement of soil) and three rates of Zn (Zn0, Zn11, Zn22 kg Zn/ha) on rice variety PR 106. Gypsum application significantly increased yield and Zn uptake in rice because of a significant decrease in soil pH and increase in Ca and Zn supply. Zinc application alone significantly increased soil and plant Zn but yields were poorer than with gypsum application alone because of Ca deficiency/Na toxicity. The same rates of Zn applied together with gypsum markedly increased yield and Zn uptake, revealing a deficiency of both Ca and Zn. The best grain yield was recorded either at G50Zn11 or G25Zn22, indicating an economy in gypsum at higher rates of Zn or of Zn at higher rates of gypsum application.

Results are described of an experiment conducted for 2 years in North-West India where grain legumes increased the N and P status of the soil compared with cereal or fallow. Maize following legumes recorded increases in growth, yield attributes, yield and N uptake. Various winter grain legumes such as chickpea, lentil, pea and Lathyrus sativus reduced the need for fertilizer N in maize to the extent of 18–68 kg/ha compared with cereal (wheat) or fallow. Application of nitrogen to the maize promoted plant growth and increased both yield and N uptake.

An intercropping experiment is described, using a parallel-row systematic design, to examine four plant populations of chickpea in all combinations with 15 systematically arranged populations of safflower in 1:1 and 2:1 row arrangements; four populations of the sole crops were included. Safflower was usually dominant and increasing the total population (i.e. both crops combined) made it more so. Safflower yield was little affected by changes in its own population and was independent of changes in the chickpea population. Chickpea yield increased with increase in its own population and it was the dominant crop at high chickpea/low safflower populations. An initial increase in safflower population caused an increase in chickpea yield at the 1:1 row arrangement; otherwise increasing safflower population decreased chickpea yield. LERs at 2:1 indicated no real evidence of yield advantages for intercropping. At 1:1 advantages ranged up to 19%, with a maximum where the highest chickpea population was combined with a low safflower one. This optimum combination could not have been identified with earlier designs.

A hydraulic press (the J-14) was compared with a Scholander pressure chamber to measure leaf water potential in Theobroma cacao, Gliricidia maculata, Cajanus cajan and Elaeis guineensis. Although the press satisfactorily estimated water status in soft, unhardened leaves of T. cacao, G. maculata and C. cajan at high water potential, it underestimated water status in hardened leaves of T. cacao. Satisfactory estimates were obtained at low water potential for hardened leaves of T. cacao but not for the others. There was a poor relation between readings of the two instruments for E. guineensis over a wide range of water potentials because press readings appeared to be influenced by leaf structure.

Using the sugar cane cultivar Co 421, competition from weeds for the whole growing season was compared at three row spacings with competition for periods ranging from 15–120 days at the start of the season or later, and weed-free conditions all through the season. The critical period for weed competition was the first three months, since weeding during the remaining 11 months did not improve yields, which were similar at row spacings of 1, 1·25 or 1·5 m. There were no interactions between the weeding and spacing treatments.

Total fresh leaf yield of cassava (Manihot esculenta Crantz) variety Isunikankiyan was not significantly affected by harvesting frequency, unlike variety TMS 30211. Compared with plants whose leaves were not harvested, there was a decrease in total fresh tuberous root yields of 56–76%, 34–62% and 15–32% when leaves were harvested at 1-, 2- and 3-month intervals respectively. The two cassava varieties reacted differently to leaf harvests in terms of tuber yields. Harvesting the top leaves of cassava at 2- or 3-month intervals is recommended to ensure reasonable yields of both leaves and tuberous roots.

Seven plant populations, ranging from 24,000 to 73,000 plants/ha of the maize variety White Composite, were established in four growing seasons between 1976 and 1978 by varying row width and number of plants per hill. Soil water profiles, leaf and soil water potentials, and leaf resistances were monitored. The results indicated a close link between these parameters, number of plants per hill and overall plant populations. Grain yield increased with increasing plant populations during the early growing season but dropped beyond 54,000 plant/ha (spaced two plants per hill at 60x60 cm) during the late season, due to adverse plant water status.

In a 3-year field study with mustard (Brassica juncea L.) on deep well-drained sandy loam and loamy sand soils, 11 post-sowing irrigation schedules based on pan evaporation and growth stages were compared. One irrigation three weeks after sowing gave maximum grain yield and water use efficiency, increasing yield 40% in 1973–74 and 30% in 1976–77 compared with no irrigation. The total water use in this treatment averaged 31·2 cm, of which 15·8 cm was extracted from the 0–180 cm soil profile. Use of soil water by the crop decreased with the amount of post-sowing irrigation. More than one post-sowing irrigation tended to decrease yield and water use efficiency.