As a result of higher prices and improved marketing, cashew (Anacardium occidentale) farmers in Tanzania are trying to improve production through improved husbandry. The main production constraint is powdery mildew disease which causes large reductions in tree yields. Although fungicides can control this disease, the majority of farmers are unable to afford them. Recently, cashew material with some tolerance to the disease has been released to growers and use of this material will be one of the main ways for farmers to cope with the disease. Cashew is grown principally by smallholders in Tanzania and since 1993 ways for farmers to increase production by including improved material on their farms have been investigated in participatory trials. The most important initial step is to fell non-productive trees. Where there is sufficient space these can be replaced by improved material established either as grafted plants, polyclonal seed or by top-working. Improved material can also be planted in gaps amongst the trees.

The photothermal flowering responses of 25 diverse genotypes of common bean (Phaseolus vulgaris L.) were examined in 25 African Bean Yield Adaptation Nurseries (AFBYAN) in the Eastern, Southern and Great Lakes regions of Africa during 1988 and 1991. The trials were located at latitudes between 0.6 and 29.3° and at altitudes from 780 to 2200 m asl. In those 13 trials where daily records of maximum and minimum temperature were available, mean pre-flowering temperatures for individual genotypes ranged from 17.9 to 24.6 °C and mean pre-flowering photoperiods varied from 12.7 to 14.7 h d−1. The time from sowing to first flowering (f) for the 25 genotypes varied from 26 to 42 d in the most-inductive regime to as late as 47 to 80 d in the least-inductive circumstances. The stepwise linear regression on daily mean temperature during the pre-flowering period explained most (52–86%) of the variation in the rate of progress from sowing towards flowering of 21 genotypes. In contrast, in four genotypes (GLPx 92, Ikinimba, G 13671 and G 2816) the fitted values of days to flowering using temperature alone were much earlier than the times observed in the two trials at Maseru in Lesotho (the highest latitude and coolest location). These differences may well reflect photoperiodic effects but from the photothermal combinations encountered this could not be confirmed and so remains to be proven. The overall mean absolute difference between the observed and fitted time to flowering was just 2.6 d. The estimated optimum temperatures ranged from 20.4 to 23.3 °C, at which the minimum times taken to flower were between 28 and 44 d. The derived base and ceiling temperatures ranged from 7.1 to 13.2 °C and from 29.1 to 40.2 °C respectively. Not surprisingly, the use of long-term monthly temperatures (for those trials from which daily temperature records were not available) gave poor agreement between predicted and observed flowering times. The significance and implications of these findings are discussed in relation to those from other studies on the photothermal flowering responses in common bean and the breeding and testing of common beans in Africa.

Two studies were conducted in Kenya during 1993 and 1994 to determine the yield responses of kale (Brassica oleracea var. acephala D.C.) intercropped with beans (Phaseolus vulgaris L.) under different redroot pigweed (Amaranthus retroflexus L.) densities. Redroot pigweed significantly reduced both kale and bean yields, the reduction being greater in 1993 than in 1994, and being greater for beans than for kale. Redroot pigweed growth was suppressed more by beans than by kale. Food output per unit area, measured by Land Equivalent Ratios, was increased by 22–115% by intercropping kale with beans and the increase was greater under weedy conditions (38–115%) than under weed-free conditions (22–74%). The presence of beans did not affect the leaf yield of kale. The presence of kale did not affect the seed yield of beans in 1994, but consistently reduced it by about 50% in 1993, though the difference was not significant.

Plantain hybrids and landraces, and banana cultivars (Musa spp. L.) were evaluated for three years in the plant and ratoon crops at three locations in the humid lowland forest (Mbalmayo and Onne) and derived savanna (Ibadan) agro-ecozones of sub-Saharan Africa. Additive main effects and multiplicative interaction (AMMI) models accounted for a significant percentage of the genotype × environment interaction (GE) affecting bunch weight (kg plant−1) and yield potential (t ha−1 a−1). Obino l'Ewai, a plantain landrace, showed little GE for bunch weight, whereas the exotic cooking banana cultivar Cardaba had the most stable yield potential as revealed by the biplots of the GE analysis (AMMI-2 biplots). Plantain hybrids achieved high yield potential due to their short growth cycle. The high yield potential of the cooking bananas was mainly the result of their fast sucker development.

The coconut yield is harvested in six picks per year at two-monthly intervals. The yield variation between and within years is very complex and this variability has not yet been explained. The analysis of long-term nut yield and monthly climate data: rainfall (RF), pan evaporation (EV), sunshine duration (SS), wind velocity (WV), minimum and maximum air temperatures (TMIN and TMAX), and relative humidity in forenoons and afternoons (RHAM and RHPM), using multivariate methods enabled the use of the variables TMAX, RHPM and EV as significantly important determinants (parsimonious set of variables) to represent the effects of climate on coconut irrespective of picks. Parsimonious models developed using these three variables explain how the development of bunches during the active growth period responded to climate variables without physiological parameters. The models are desirable where interpretation is concerned. The yields of picks one to six were determined by the climate variability during February, June, July, September, December and February respectively. Based on the models the proper timing of the use of some agronomic practices to enhance the productivity was recommended. A common model was also fitted (R2 = 0.81; p < 0.002) to estimate the annual yield 18 months in advance using EV, RHPM and TMAX. The three variables influence the microclimate around the crown of the palm for utilizing solar radiation in dry matter partitioning and thereby nut production. The method used to screen climatic variables so as to develop parsimonious crop–weather models using multivariate and univariate techniques can be used for other tree crops.

The effects of temperature (13–20 °C) and potential soil water deficit (0–350 mm on the leaf appearance rates of six contrasting clones of tea (Camellia sinensis) were studied over twenty-five months to provide guidance to tea growers in southern Tanzania on the choice of harvest intervals. Within the fully irrigated treatments (potential soil water deficit <65 mm) the mean time period between a shoot unfurling its second and third true leaf (a phyllochron) ranged from 5.8–7.9 d during the warm–wet season to 11–19 d during the cool-dry season. Between 61 and 79% of the weekly variation in the mean leaf appearance rate (1/phyllochron) for each clone could be explained by an asymptotic relation with the mean air temperature. Building on research in India which has suggested that appropriate harvest intervals for tea can be derived from measurements of leaf appearance rates, a simple procedure is described for determining harvest intervals from the daily mean air temperature. Corrections to account for the effects of drought and clonal differences in responses to temperature are also explained.

Data from 110 on-farm vegetable trials conducted in Jamaica were examined to seek guidelines as to how on-farm trials should be executed in order to obtain quality data. The results show that while one-way blocking is useful in designing experiments it may sometimes be inefficient and that two-way blocking is generally preferable. If only a small number of trials can be conducted then it is important that up to four or five replications of each treatment are used at each site. Plot sizes should be larger than those used for on-station trials. Due to low correlations between results from different sites, experiments should be conducted at many sites. Thus a large number of trials should be planned to allow for treatment–environment interactions and trial failures.

Changes in soil pH water (pHw) were investigated on a sugarcane plantation in the Ramu Valley of Papua New Guinea. The plantation was established in 1979 from natural grassland and the dominant soils were Fluvents and Vertisols. Statistical analysis of the topsoil pHw data (n = 541) showed a significant (α = 0.01) decrease from 6.5 to 5.7 between 1979 and 1996. Based on samples from 80 fields at different sampling times, the average decrease in topsoil pHw was calculated to be 0.4 units after 10 years of continuous sugarcane cultivation (r2 = 0.481). Between 1986 and 1996, subsoil pHw also decreased significantly (α < 0.05) by 0.4 and 0.3 units in the 0.30–0.45 and 0.45–0.60 m horizons respectively. The acidification trend accelerated in the 1990s when trash-harvesting replaced pre-harvesting burning and sulphate of ammonia became the dominant nitrogen fertilizer. Between 1991 and 1995, average nitrogen application rates were 90 ka ha−1 a−1 which resulted in an annual addition of 11.6 kmol H+ ha−1. The soil buffer capacity was estimated to be 125 kmol H+ ha−1 pH−1 which implied that the pHw could further decrease by 0.5 unit after five annual applications of 90 kg N ha−1 pH−1 as sulphate of ammonia. Although these soils were young in pedological terms and they had been cultivated for less than 20 years, they had acidified significantly and this could affect sugarcane production adversely if such trend were to continue.