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.

A simulation model describing the growth and yield of tea (Camellia sinensis L.) is described. The model simulates the behaviour of a population of shoots which develop and extend independently at different rates to simulate the variation observed in natural conditions. The development of each shoot is divided into three phases corresponding to the resting, quiescent and bud-burst phases in temperate trees, with the rate of development in each phase being influenced by temperature, photoperiod and saturation deficit. Photoperiod also influences the onset and release of bud dormancy, and therefore the numbers of actively growing shoots at any one time. As shoots are generally harvested at a specific developmental state or size, the number of shoots plucked at each harvest is the main determinant of yield variation. Sensitivity analysis using annual yields as the output indicated that the model was most sensitive to the values of the two critical photoperiod parameters controlling bud dormancy and shoot development. Good agreement was found between model predictions and observed yields for an experiment in well-irrigated tea in the Southern Highlands of Tanzania, but further testing is necessary before it can be used with confidence in a wider range of environments.

A long-term fertilizer experiment was conducted on the rice–wheat cropping system at four locations in India. Trends in partial factor productivity of applied nitrogen, benefit : cost ratio of fertilizer application, grain yield, changes in soil organic carbon, and available nitrogen (N), phosphorus (P) and potassium (K) were studied in control (N0P0K0), N (N120P0K0), NP (N120P80K0), NK (N120P0K40) and NPK (N120P80K40) fertilizer treatments. On average at all locations, continuous rice–wheat cropping for 16 years decreased the yield of rice by 57% in unfertilized plots and by 32% in plots receiving nitrogen and phosphorus fertilizers. Over the same period wheat yields only declined in unfertilized plots by 18%; in plots receiving nitrogen, phosphorus and potassium yields increased by 18% and they increased by 33.6% in plots receiving nitrogen and phosphorus fertilizer. Partial factor productivity of applied nitrogen (the ratio of output value to the cost of a specific input) exhibited similar trends. Profit from fertilizer application, however, increased over the 16-year cycle by 130% in rice and by 262% in wheat in the treatment given nitrogen and phosphorus fertilizers. The long-term rice–wheat cropping system became depleted in soil organic carbon and available nitrogen and phosphorus at two locations but increased in organic carbon, available nitrogen and potassium at the third location. The available phosphorus and potassium content of the soil also increased at the fourth location.

Plants of the photoperiod-sensitive, late-maturing pigeonpea (Cajanus cajan) cv. KAT777 were grown in pots in modified field environments at Katumani, Kenya. They were transferred at different durations after emergence from natural short days (SD, 12.6 h d−1) to artificially-extended long days (LD, 15.0 h d−1), and vice versa, under both ambient (19 °C) and warmer (26 °C) temperatures created beneath p olythene enclosures. All plants at 19 °C flowered within 106–160 d after emergence whereas only those transferred from LD to SD flowered at 26 °C during the investigation (202 d). A well-defined photoperiod-insens itive pre-inductive phase (a1) was detected after emergence; it lasted for 26 d at 19 °C but increased to 49 d at 26 °C. Thereafter, SD hastened and LD delayed progress to flowering until a third pha se, the photoperiod-insensitive post-inductive phase (a3) of pre-flowering development. At 19 °C, a3 was 66 d while the duration of the inductive phase in SD (IS) was 25  d and in LD (IL) it was 72 d. Plants were also moved from ambient to warmer temperatures and vice versa within either SD or LD at different durations after emergence. In SD all plants flowered during the investigation ( 250 d) whereas in LD only the plants transferred from the warmer to the ambient temperature regime flowered. During the initial stages of development plants were less sensitive to supra-optimal temperatures so that developmental progress from emerg ence to first flowering was the same whether plants were held at warmer or ambient temperatures during the first 35 d from emergence. Furthermore, plants transferred from the ambient to the warmer temperature in SD at any time from 49 to 77  d from emergence flowered at similar times to those kept at ambient temperature from emergence. Since a1 = 26 d and a1 + IS = 51 d, we sugg est that these results imply that exposure to supra-optimal temperature in SD during the latter 60% of the photoperiod-sensitive inductive phase (IS) of pre-flowering development delayed progress to flowering. In contrast, expos ing plants to supra-optimal temperature during either the photoperiod-insensitive pre-inductive phase (a1) or part of the photoperiod-insensitive post-inductive phase (a3) or during the first 40% of the photo period-sensitive inductive phase did not delay progress to flowering.

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.

A model predicting biomass production and water use in tea plantations is described. Biomass production is calculated from the amount of light intercepted and a radiation conversion efficiency. Available assimilate (current production plus reserves) is distributed according to the ‘potential’ demand of each of the shoots, stems and roots. Any excess is stored in the stem and root reserve pool. In the case of the demand for assimilate exceeding the supply, allocation is according to the relative demands of each component. Simulations with the model suggest that assimilate supply is unlikely to limit shoot growth under most conditions. Soil water movement and crop water uptake are simulated using the water balance sub-model used by the CERES crop growth models. The model calculates a water stress factor (Φ) as the ratio of actual to potential crop transpiration, and uses this factor to adjust various crop processes such as dry matter production and shoot development and extension rates. Predicted yields match observed yields well across a range of watering treatments and for different years at sites in Tanzania and Zimbabwe, providing some degree of confidence in the model's ability to predict tea yields for environments in East Africa.

The effects of pre-flowering drought on millet were studied in two experiments, an on-station, dry-season trial under irrigation and an on-farm trial where drought was induced by natural rainfall regimes (one wet, two dry years). The on-station experimental conditions were adjusted to those of Sahel farms, particularly through low plant density, low soil fertility and an irrigation regime that simulated the natural rainfall pattern. The replanting (5–10%) of missing hills in the on-farm trial increased stand variance significantly, whereas small quantities of applied N reduced it. Grain yield and grain number were equally seriously affected by drought in both experiments; yields were 700–800 kg ha−1 in the control years compared with 200–300 kg ha−1 in drought years. Both experiments showed sub-populations of early-, intermediate- and late-flowering millet plants. Fertile tillers were concentrated in the group of early-flowering plants. Only this group when subjected to moisture stress could secure part of the grain production by delaying, to a maximum of 18 d, the development of fertile tillers beyond the period of stress. Later-flowering plants, mostly uniculm, would be either sterile or unaffected by drought, depending on the exact coincidence of panicle development and drought. Drought did not alter the number of fertile hills per stand, because earlier- or later-flowering plants in the same hill compensated for sterile plants. The period of flowering in a stand was stretched over 40–45 d independently of drought, and this occurred both in the on-station experiment comprising 19 plants per treatment and in the on-farm experiment comprising about 700 hills. Although stand variance was reduced by better crop management and resulted in more fertile hills, more panicles per hill, and taller hills of more uniform height, the spread in flowering period of the millet population tended to be unaffected. Stand variability therefore appeared to be of paramount importance in accounting for drought avoidance.

Most farming systems in semi-arid West Africa rely on organic matter recycling for maintaining soil fertility. The cycling of biomass through ruminant livestock into dung (faeces) and urine that fertilize the soil has long been an important factor in t he nutrient cycling processes of these integrated, mixed crop/livestock systems. While dung greatly improves soil properties and crop yields, little is known about the effects of urine on soil chemical properties and the impact of dung and urine on crop p roduction. An average voiding of sheep urine applied to a sandy, siliceous soil in the Republic of Niger increased soil pH, available phosphorus and ammonium levels dramatically in the upper 10–15 cm of soil, especially during the first week following application. Losses of applied urine nitrogen via volatilization were in the order of 30–50%. A four-year field trial was conducted on the same soil type to evaluate the effects on pearl millet and weed yields of corralling cattle o r sheep overnight on cropland (dung plus urine application) for one, two or three nights, every one, two or three years versus the effects of applying only dung at the same application rates and intervals achieved with corralling. The main results of this field trial were that (1) urine had large positive effects on millet grain, threshed panicle, leaf, stem and weed yields, (2) sheep dung was more effective than cattle dung in increasing yield, (3) two nights of dung application was adequate for maximum yield and (4) the positive effects of dung and urine on yield lasted two to three cropping seasons after application.

An experiment was carried out to determine the partitioning and accumulation of nitrogen in plant components, nitrogenase activity and their relationships with seed yield of a local cultivar of winged bean (Psophocarpus tetragonolobus (L.) DC.) grown on three support systems of 0, 1, and 2 m height under field conditions. Total nitrogen accumulation and nitrogen partitioning were determined throughout the growing season by measuring nitrogen content and concentration in above-ground plant tissues (leaves, stems, petioles and pods). Support heights of 1 and 2 m significantly increased total nitrogen accumulation in component parts of the plant, nitrogenase activity, nodulation, total dry matter accumulation and seed yield compared with the control. Plants grown on supports accumulated significantly higher leaf nitrogen at the vegetative stages and the contribution of seed nitrogen was also significantly higher compared with unsupported plants. Nitrogenase activity increased with onset of flowering but declined during the pod formation stage in plants grown on a support system. Unsupported plants showed higher nitrogenase activity prior to flowering possibly due to lack of photosynthate and, consequently, early senescence of leaves.

Four experiments were conducted to facilitate the improvement of degraded grasslands in north Syria. The first examined the survival of legume seeds fed to penned Awassi wethers. The second and third observed the germination and establishment of legumes from faecal pellets in the field and in a glasshouse respectively. The fourth explored the possibility of transporting seeds from legume-rich (source) to legume-poor (target) grasslands using commercial flocks on communally-owned land. Seeds of small-seeded clovers passed through sheep in greater numbers (58–72%) than did seeds of larger-seeded species (10–40%). Of the clover seeds Trifolium campestre (seed size 0.45 mg) disintegrated least (72% passage) and T. haussknechtii (seed size 2.68 mg) disintegrated most (10% passage). Recoveries of Medicago noeana and Scorpiurus muricatus seeds were larger than expected on the basis of their seed sizes. Maximum rate of recovery was at 36 h after the seed meal for all species, all seeds were recovered by 120 h and 90% of the recovered seeds were passed in 72 h. Ingestion had little effect on the hardness and viability of most seeds. Experiments 2 and 3 suggested that seeds in pellets germinated and established as successfully as naked seeds. Burial increased establishment, whether in the field or under conditions of low moisture stress in the glasshouse. The small-seeded clovers, T. tomentosum and T. campestre, established most successfully whether from pellets or from naked seeds. About 500 seeds m−2 were successfully transported from the source to the target grassland. About half were Trigonella monspeliaca, a naturally-occurring legume found on both the source and target grasslands. Of the species sown on the source grassland, 115 seeds m−2 of Trifolium campestre (33% of the source seed bank), 62 seeds m−2 of T. tomentosum (27%) and 78 seeds m−2 of T. purpureum (21%) were detected in the target. Few medics were transported (for example, <2% of M. noeana). Apart from Trigonella monspeliaca, Trifolium tomentosum (16 plants m−2) was the most frequent species found in the target grassland in the following April. The results suggest that using sheep is a cheap and practical way of dispersing the seeds of pasture legumes and thereby improving the degraded grasslands of north Syria. They clearly demonstrate the role of small-seeded legumes (<1 mg) in grassland improvement, especially the small-seeded clovers.

An experiment to determine weed spectrum, weed seedling numbers, temperature and nutrient changes in manure heaped for one to five months was undertaken over two seasons. Weed seedling numbers in manure heaped for one to five months decreased significa ntly by 65–70%. The weed spectrum comprised 17 broadleaf weed species of which Amaranthus hybridus, Leucasmartinicensis and Nicandra physalodes were most prevalent. There were six grasses with Eleusine indica and Cynodon dactylon being dominant. Temperature increased from 20 °C in the unheaped manure to averages of 34 and 42 °C in manure heaped for three and five months respectively in the two seasons. In both season s nitrogen and potassium became more available as the period of manure heaping increased while phosphorus decreased. It was concluded that heaping manure for three months significantly reduces weed seed viability and enhances the availability of some nutr ients.

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.

Farmer-managed tests of Striga hermonthica-resistant maize varieties were conducted in 1994 in a moderately intensified zone in the northern Guinea savanna of Nigeria. Field history, soil properties, current season fertility management, and crop management observations were recorded for 37 farmer-managed trials. Site averages for maize grain yield varied from 300 to 4000 kg grain ha−1. In spite of the tremendous variability observed, the grain yield was significantly higher for the striga-resistant hybrid 8321-18 compared with an improved open-pollinated variety, STR Syn-W, and the farmers' current variety. Correlation analysis and stepwise regression analysis of grain yield on measured variables suggested that maize yield was a function of plant density for all three varieties. The rate of nitrogen fertilizer application was an important variable only for the hybrid, while the day of first weeding was most important for the improved varieties. The yield of the local varieties and STR Syn-W was related to the number of emerged striga at harvest in the stepwise regression, and the yield of the local varieties was highly correlated with the striga-damage score on maize. The striga-damage score was significantly lower on 8321-18 than on the other varieties, suggesting some degree of resistance in the hybrid. The number of emerged striga was lower for the hybrid but not significantly different. Farmers were almost unanimous in ranking the hybrid as least damaged by striga and highest yielding. Besides being related to maize variety, striga-damage score was lower if crop residue was observed on the field at the time of site confirmation. Highest yields (approximately 4 t ha−1) were recorded on fields near the homestead (compound fields) where soil organic carbon values were 2.0–2.5%. Realization of maize yield potential in the absence of manure or fertilizer will only be possible on long-term compound fields. Striga-resistant maize can maintain high yields under S. hermonthica infestation.

Erosion changes soil properties, removes nutrients and alters crop yields. A knowledge of these impacts on soil productivity is needed for economic analyses of erosion and conservation. Based on a United Nations Food and Agriculture Organization experimental design to monitor these changes, results are reported from four research sites in southern Brazil on Ferralsols and Cambisols, enabling the construction of erosion–yield–time and nutrient loss relationships. Plot experiments ran for up to seven years of natural erosion, followed by one or two years of maize cropping. A remarkably consistent composite erosion–yield relationship in logarithmic form was found, showing a sharp yield decline with initial soil loss. Soil ‘resilience’ was identified through erosion–time relationships, ‘sensitivity’ through erosion–yield equations. As erosion progressed, losses of nutrients, especially of organic carbon and calcium, were significant. In situ changes in soil properties were far less marked. Together with measured yield reductions caused by cumulative erosion, these results enabled the modelling of changes in soil productivity over time with respect to both soil quality and impact on yields. A production ‘half-life’ of between one and 39 years according to soil type and level of erosion was also identified.

An experiment with the objective of evaluating the performance of 15 clones of rubber (Hevea brasiliensis) was conducted in the Konkan region of Western India. The clones under evaluation were RRII 5, RRII 6, RRII 105, RRII 208, RRII 308, RRIC 52, RRIC 100, RRIC 102, RRIC 105, RRIM 605, PB 260, PB 310, PB 311, PR 255, and PR 261. The region is a trial environment for the crop and experiences more than seven rainless months and severe drought in the summer months. Data on monthly girth growth w ere collected for six years from a trial with randomized block design. The growth of clones in terms of monthly girth increment growth (GIN, cm month−1) seasonal mean girth increments (MGIN, cm season−1) and mean relative increment rates (MRIR, mm cm−1 season−1) as well as annual MGIN (cm a−1) and MRIR (mm cm−1 a−1) was studied. Correlation analysis was performed to understand the effect of seasonal growth on the final growth. At the beginning of the study, the largest girth noted was for the clone RRII 6 (22. 5 cm) followed by RRII 208 (22.0 cm). PR 261 with a girth of only 14.2 cm was the least vigorous among the clones. A large portion of the growth occurred in the wet season only. During the dry season the growth rates of the clones declined substantially and decreases in girth ranging from 0.2 mm to 0.5 mm were noticed in most of the clones. At the end of the study period the largest girth observed was for clone RRII 208 (49.3 cm) and the lowest for PR 261 (39.3 cm). The highest proportion of tappable trees noted was for clone RRII 208 (52.4%) and the lowest for PR 261 (2.7%). The pooled average of tappable trees was on ly 17.5%. The data revealed that the immaturity period for Hevea in the region will not be less than 9 years under rainfed conditions. From the analysis based on the final girth it was concluded that clones RRII 208, RRIC 52, RRII 6, RRIC 100 and RRIC 102 are more tolerant to drought while RRII 105, RRIC 105, RRII 5, RRIM 605, PB 310, PB 260, PB 311, PR 255, RRII 308 and PR 261 are less tolerant. The results of correlation indicated that by analysing the growth, potentially drought-toleran t clones can be identified.

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 contribution of root and leaf litter to soil nitrogen dynamics, nitrogen uptake and balance was evaluated under cereal–legume rotations in a tropical moist savanna soil. Two legumes, soyabean (Glycine max) and stylo (Stylosanthes hamata), and maize (Zea mays) as a control were grown in four farmers' fields of different native fertility in 1993. At the end of the season, soyabean grain and stover were harvested and stylo biomass was removed for fodder. At the beginning of the 1994 season levels of total mineral nitrogen at a soil depth of 0–30 cm were 75, 52 and 44 kg ha−1 following soyabean, stylo and maize respectively. Total nitrogen uptake by maize was over 25% higher following legumes than following maize. Maize yield was 20 and 24% higher when grown after stylo and soyabean than after maize in spite of the removal of the standing legume biomass from the plots. Sorghum grain yield and nitrogen uptake were not significantly affected by the previous crops. Nitrogen balance estimates indicated that loss of nitrogen, probably due to leaching, was lowest in the plots previously planted with stylo. Results indicated opportunities to integrate appropriate legume-based technologies into the farming systems based on an identification of inherent nitrogen-release patterns.

Peri-urban dairy producers in West Africa face major production constraints including inadequate and poor quality feeds. In view of the high cost of traditional supplementary feeds such as oilseed cakes, the production of forage, especially legumes, is increasingly being advocated. However, it has not been established whether returns in terms of increased livestock productivity from sown forages will be adequate to encourage smallholder livestock owners to undertake forage production for indigenous livestock.

In three trials involving indigenous Bunaji cows biological and economic responses in terms of milk yields to farmer-planted forage legumes and tree legumes from home gardens were evaluated. Synthesis of the resulting data on labour inputs, forage yields, feed intakes, milk yields, value of outputs and cost of inputs such as seeds and fertilizers showed that for the semi-intensive smallholder and zero-grazed models considered in this study, the margin or profit from using home-grown fodder was 5–8 times the cost of acquiring the feed. The opportunity cost of using the land for forage production rather than for cultivating sorghum, a highly favoured cereal crop, was only 67% of the accrued benefits from milk yields produced by cows supplemented with the forage hays. Thus, there is a real potential for profitable dairy production in peri-urban areas using home-grown fodder.

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.

Plants of yam, taro, tannia, cassava and sweet potato were raised under shade or in full sunlight and the effect of shade on leaf chlorophyll and carotenoids was examined to determine and compare the relative shade tolerance and adaptability of the var ious species. All five species of root crops adapted to shade. The chlorophyll concentration was higher, while the chlorophyll a:b ratio, carotenoids per unit chlorophyll and the weight per unit area of leaf were lower in the shade than in the su n in yam, tannia, taro, cassava and sweet potato. All species had larger leaves and more chlorophyll per leaf in the shade. The extent of the changes, however, differed between species. The aroids (taro and tannia) appeared to be shade-tolerant species as their chlorophyll a:b ratios changed less than those of the other species in the shade, suggesting that their light-harvesting systems may be normally adapted to shade conditions. Taro and tannia also adapted to shade by a greater proportional i ncrease in leaf size, a smaller reduction in leaf weight per unit area and a greater proportional increase in chlorophyll and carotenoids per leaf than the other species. Yam compensated for shade by having a large proportional increase in leaf size and a ppeared to be moderately tolerant of shade. Sweet potato and cassava appeared to be the least tolerant of shade of the major tropical root crops.