Stomatal conductances (g) and photosynthetic rates (A) were monitored in six tea clones planted in a clone X irrigation experiment in the Southern Highlands of Tanzania. Measurements were made during the warm dry seasons of 1989 and 1990. There was no genotype X treatment interaction in the response in A or g of the various clones to irrigation. Irrigation increased A more than it increased g. Irrigation also increased the temperature optimum for photosynthesis and decreased photo-inhibition at high illuminance. Clones differed in g and A, and in the relationship between leaf temperature and A. The implications of these findings for clone selection are discussed.

Six genotypes of cowpea (Vigna unguiculata) of diverse origin were sown on various dates at five locations in Australia in order to provide a range of photothermal environments. Times from sowing to first flowering (f) ranged between 36 d and 145 d; pre-flowering temperature and photoperiod means varied from 15.7° to 29.2°C and from 11.6 to 15.5 h d−1. In five genotypes there was no effect of photoperiod on rate of progress towards flowering (1/f), but the relation between 1/f and mean temperature was always positive. The base temperatures (at which 1/f = 0) varied between 8.1° and 10.4°C. The rankings of parameter estimates among four photoperiod-insensitive genotypes common to this study and earlier research in controlled environments were almost identical, and there was generally good agreement between field observations and predictions from controlled environments once hourly temperatures were used to describe the natural environment. When cowpea plants were exposed to temperatures below 3°C, flowering was delayed beyond expected values, presumably as a result of chilling damage. In one genotype, rate of progress towards flowering was affected by both temperature and photoperiod, and relations between 1/f and the photothermal environment were described by a two-plane linear model of similar form to that determined in an earlier controlled environment study. These latest findings support the utility of such linear models for the prediction of crop phenology in the field and for the genetic characterization of photothermal flowering response in annual crops.

Eight genotypes of cultivated mung bean, black gram and rice bean (Vigna mungo, Vigna radiata ssp. radiata and Vigna umbellata, respectively) were sown at six sites in Australia on various dates in order to provide a range of photothermal environments. In addition, four accessions of the related wild species Vigna radiata ssp. sublobata were sown on five occasions. Times from sowing to first flowering (f) varied between environments from 34 to 317 d; pre-flowering temperature and photoperiod means ranged from 12.7° to 29.1°C and from 11.8 to 15.5 h d−1. No effect of photoperiod was detected on rate of progress towards first flowering (1/f) in four genotypes, but in each case a significant positive relation was detected between 1/f and mean temperature. These simple thermal time relations did not differ significantly among these four genotypes; the common base temperature was 7.9°C. In two genotypes observations were well described by a thermal response plane when the mean photoperiod was less than 13 h d−1 (p < 0.01) but photoperiods greater than 14 h d−1 delayed flowering. In each of the remaining genotypes the observations were best described by photothermal planes, that is, 1/f was modulated by temperature and photoperiod. Predictions from the models based on our data were in good agreement with the times to first flowering observed in three genotypes in an earlier controlled environment study.

Farmer surveys have consistently shown maize storage losses to be of primary concern to farmers in the western highlands of Cameroon. Past attempts at evaluating these losses, however, have proved to be unsatisfactory, mainly because of failure to consider qualitative, as well as quantitative, losses or to take account of consumption patterns (that is, timing and end use). A simulation model is presented that overcomes these deficiencies while providing a reliable estimate of the economic value of storage losses to the farmer, albeit at the cost of requiring fairly exacting data. The model is used to estimate the value of storage losses to farmers in the North West Province of Cameroon.

Tillage trials on sandy soils in Zimbabwe have shown that sheet erosion from arable fields under a no-till tied ridging treatment is negligible but that the system generates environmental conditions that have an adverse effect on crop potential. Tied ridging improves crop production by preventing waterlogging in high rainfall years and improving rooting depth when adequate water supply prevents soils from setting hard, but it causes high temperatures in the ridges and rapid drying during dry weather, resulting in poor or delayed emergence and thus in low and uneven crop stands. New strategies need to be developed to minimize these effects.

Twenty one accessions of yam bean (Pachyrhizus Rich. ex DC.) were tested in yield trials under short day conditions in Tonga, South Pacific. Fresh weight tuber yields ranged from 5.3 to 72.0 t ha−1, dry matter content from 8.0 to 20.8% and dry matter yields from 1.20 to 8.57 t ha−1. Crude protein content of peeled tubers varied between 5.1 and 9.8% of dry matter, yielding 71–540 kg ha−1 of crude protein. Varietal variation in leaf defoliation by the rose beetle, Adoretus versutus Har., was noted.

Pearl millet is a staple cereal cultivated mainly by subsistence farmers on 14 million ha of the West African semi-arid tropics. Increasing pressure on the land has reduced the length of the fallow periods, which are necessary to restore soil fertility, resulting in declining yields. To investigate ways of reversing this decline, three systems combining phosphorus fertilizer application, improved varieties of millet and cowpea, and improved agronomic practices were compared with the traditional millet–cowpea intercrop system in a three year experiment. The most productive system involved the rotation of fertilized millet and cowpea. Pre-sowing tillage increased hay and fodder yields in all the improved systems. The application of fertilizer increased the amount of available phosphorus in the soil. Soil pH declined somewhat in all treatments, although the initially low soil organic matter did not change.

The after effects of three years' continuous cropping with sole millet, sole cowpea or a traditional millet/cowpea intercrop were compared using five levels of nitrogen fertilizer. The continuous sole cowpea system had reduced the carbon to nitrogen ratio more than the continuous sole millet or the traditional intercrop. The test crop millet yielded much more, and its uptake of nitrogen and phosphorus was greater, when it followed sole cowpea than when it followed sole millet or the traditional millet/cowpea intercrop. The three years' continuous sole cowpea had an effect equivalent to the application of 205 kg N ha−1 on the test crop of millet. It also caused the greatest reduction in Striga infestation in the test crop. It is therefore recommended that cowpea cultivation be increased in the Sahel.

The effect on Coffea arabica cv. Ruiru 11 of training the trees on a single or two stem system at planting densities of between 1600 and 4800 trees ha−1 during the first production cycle after establishment was studied at three contrasting sites in Kenya. Training tree growth in the two stem system significantly depressed yields from the first two crops at all sites, irrespective of plant density, but yields caught up with the production levels of the single stem system faster in the wetter than in the drier zone. Yields of clean coffee increased with tree density up to 4000 trees ha−1 at all sites, irrespective of tree training method, but increased more slowly at populations of more than 4000 trees ha−1, especially in the drier zone. The proportion of large, grade A, coffee beans was not significantly influenced by the treatments studied.

Beusani is a rice crop management system practised in rainfed lowland areas of eastern India whereby rice is dry-seeded, then wet-ploughed at 30–50 days after emergence and the land levelled by drawing a board across the field. Field experiments showed that beusani enhances rooting, especially in shallow soil layers, as a result of reduced penetration resistance. Although beusani reduced weed biomass by 38%, it was not as effective as application of herbicide followed by hand weeding, which reduced biomass by 87%. Yields were directly related to weed control, so beusani treatments did not yield as much as the herbicide plus hand weeding treatments in these experiments.