Management deficiencies on the part of the pastoralists were claimed to be one of the major causes of the high losses of camel (Camelus dromedarius) calves contributing to low productivity of camel herds. In the present study, calf deaths, and the causes thereof, were analysed in connection with pastoral calf management in order to assess possible relationships. Progeny history data on 1506 Rendille, 789 Gabra and 1206 Somali calves born between 1980 and 1995 provided quantitative information on losses and the underlying causes. Assessment of the causes of death, and analysis of related management practices, led to suggestions for management changes. In feedback seminars with pastoralists, however, it became apparent that these management changes would not be adopted because they contradicted the pastoralists' assumptions on the causes of calf mortality. The discussions revealed that differences between pastoralists' and scientists' perceptions determined different opinions on proper calf-rearing management practices. Combining different knowledge systems offers the possibility of a more complete understanding, which is required for the derivation of adoptable calf mortality-reducing interventions that are compatible with the knowledge and production systems of the pastoralists.

In western Kenya, severe nutrient depletion, especially that of nitrogen and phosphorus, has drastically reduced crop yields over the past two to three decades. The potential effects of P application, with a single direct application of Minjingu phosphate rock (MPR) at 20, 40 and 60 kg P ha−1, and fallow biomass in terms of nutrient replenishment on maize and bean yields were investigated on N and P deficient soils of western Kenya for six cropping seasons (three years). The agro-forestry shrubs tested were one season (six months) Crotalaria grahamiana and Tephrosia vogelii followed by maize monocrop. These fallow species were intercropped with beans in the 2000 long rains season to provide a food benefit to the farmer. Soil samples were taken at the end of each season and analyzed for soil pH and extractable P. The results showed that soil available P increased significantly following application of MPR. Significant increases in bean yields were obtained when 60 kg P ha−1 as MPR were applied, and contributed to a 260 % increase above the control. Significant maize grain yield increases were obtained when MPR was applied alone or in combination with fallow biomass as compared with treatments with either no external nutrient addition (control) or with fallow biomass alone in all seasons. The 60 kg P ha −1 MPR rate gave the highest cumulative maize grain yields (9.6 t ha−1) over the five consecutive maize growing seasons, followed by 40 kg P ha−1 (8.8 t ha−1). The residual benefits of MPR at modest rates of application (60 kg P ha−1) were found to persist in the soil for only three cropping seasons. Thereafter, there was a steady decline in soil chemical properties (pH and available P), grain yields and net benefits. The study demonstrated the need for frequent additions of P especially in the fourth consecutive season to ensure sustained availability of P, favorable pH, and increased crop yields and net benefits on the nutrient-depleted soils of western Kenya.

The response of potatoes (Solanum tuberosum L.) to application of inorganic and organic fertilizer was studied in long-term field experiments between 1987 and 1994. Responses to phosphorus and nitrogen were tested at 27 sites and to potassium at 17 sites. The sites represented various agro-ecological zones in Kenya. Phosphate (triple superphosphate, TSP) and nitrogen (calcium ammonium nitrate, CAN) fertilizer were applied at 0, 25, 50 or 75 kg P2O5 ha−1 and 0, 25, 50 or 75 kg N ha−1. Potassium (muriate of potash) was tested mainly on sites with low levels of K in the soil at rates of 0 or 50 kg K2O ha−1. Farmyard manure was applied at 0 or 5 t ha−1 with or without N and/or P2O5 fertilizer.

Over the study period average yields varied considerably between sites and agro-ecological zones. At 16 of the 27 sites, potatoes responded strongly to the application of P2O5 and at 9 sites to N application. A significant response to K2O application was found at three out of the 17 sites. Nutrient use efficiency ranged from 13 to 214 kg tubers per kg P2O5 and from 20 to 113 kg tubers per kg N applied. In the majority of the sites, both N and P response followed a linear function which suggests that application rates higher than 75 kg N ha−1 and/or 75 kg P2O5 ha−1 could be beneficial. Economic analysis revealed that in most cases fertilizer application was highly profitable for potatoes.

The critical soil P value was about 15 ppm (mod. Olsen) for optimal potato nutrition; on soils with higher P levels generally no P response was found. The respectively critical soil K value was found to be about 0.55 meq 100 g−1 (modified Olsen). Farmyard manure at 5 t ha−1 significantly increased yields of potatoes at 9 of the 27 sites. On soils with P levels below 12 ppm, there was a positive effect on potato yields with a combination of 50 kg P2O5 ha−1 and farmyard manure, although significant differences were achieved in only one out of the 19 sites.

Two experiments to investigate the micronutrient requirements of cassava (cv Black Twig) on Malaysian peat soil are described. Cu was found to be the only essential micronutrient and Mn, Zn, Fe, Mo and B were not needed. Fertilizing with 20 kg/ha of copper sulphate approximately tripled tuber dry matter, and starch and Cu uptake, but applying 10 kg/ha of copper sulphate gave the same results. Each crop of cassava absorbed only about 2% of the applied Cu, giving a leaf Cu content of about 14 ppm compared with about 7 ppm in Cu-deficient plants. Cu deficiency symptoms were invariably observed in Cu-deficient plots and these are also described.

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.

Multivariate statistical methods are used increasingly in biological research to investigate the responses of organisms considered as a whole, whereas established statistical methods are usually concerned with measured characteristics considered one at a time. Multivariate techniques are mostly explained in terms of matrix algebra, which is a way of dealing with groups of numbers rather than individual ones. A brief description is given of some elementary results of matrix algebra and a method is presented whereby hypotheses can be generated about interrelations within an organism. Two techniques, principal component analysis and canonical analysis, are described in greater detail. It is emphasized that hypotheses need to be tested even though they have been generated by objective statistical means.

The yield, variability and quality of 16 sweet potato cultivars, harvested after 21 weeks growth, were evaluated in sub-tropical Australia. The coloured-flesh cultivars L8-92, Centennial, HAC-Pink, Copperskin Goldrush and Nemagold produced yields of marketable storage roots in excess of 19,000 kg ha−1, which was three to four times the yield of the local commercial cultivar, White Maltese. The high variability in mean yield per plant of all cultivars offers scope for selection within cultivars. Those with a deep orange flesh and high soluble solids content, i.e. L8-92, Copperskin Goldrush and Centennial, were preferred by members of a taste panel. A high carotene cultivar L8-92 has the greatest commercial potential because it produced the highest yield of marketable storage roots and had the highest taste panel rating for eating quality of stored roots.

Field experiments at 26 sites, selected on the basis of their varying degrees of zinc deficiency, showed that the critical deficiency levels of zinc for wheat were 0.60 mg kg−1 in the soil and 19 μg g−1 dry matter in 45-day-old plants. Further field trials at nine locations with varying levels of zinc deficiency showed successive increases in the grain yield of wheat with increases in zinc application, emphasizing the need for zinc fertilization when wheat is grown on zinc-deficient soils.

Intercropping is considered as a promising system having multi-dimensional advantages such as improved yield on sustained basis, effective use of land and other resources and reduction in cost of production. The present study was carried out using pea and three non-legume winter vegetables, i.e. garlic, turnip and cauliflower, by planting as sole crops and in pea–garlic, pea–turnip and pea–cauliflower intercropping systems to determine the competition among these vegetables and economics of each intercropping system. The intercropping systems were assessed on the basis of existing competition and economic indices such as land equivalent ratio (LER), relative crowding coefficient (K), aggressivity (A), competitive ratio (CR), actual yield loss (AYL), intercropping advantage and monetary advantage index (MAI). Yields of individual vegetables were higher when grown as sole crops compared with their intercropping with pea. Harvest index for pea was higher when grown alone or intercropped with garlic and was significantly reduced when intercropped with turnip or cauliflower. Harvest indices for garlic, turnip and cauliflower were statistically similar when grown as sole crops or intercropped with pea. The partial LER, K, A and CR for pea were higher in pea–garlic intercropping. However, partial LER, K, A and CR for intercrop were significantly higher for cauliflower and turnip in pea–cauliflower and pea–turnip intercropping systems respectively. The product of relative K values was greater for pea–garlic intercropping system, indicating a definite yield advantage. A similar trend to LER was followed by AYL. These results indicate that pea was more competitive than garlic, and cauliflower and turnip were more competitive than pea for exploiting the available growth resources. The highest MAI value was recorded for pea–garlic intercropping, reflecting that this intercropping system was more advantageous compared with other intercropping systems, indicating definite yield and economic advantages. However, pea–cauliflower intercropping system resulted in higher net income and benefit cost ratio.

Over an eight-year period, harvesting methods based on simple mechanical aids (blade and shear) were evaluated against hand harvesting on mature morphologically contrasting tea clones in Southern Tanzania. The effects of shear step height (5–32 mm) and the harvest interval (1.8–4.2 phyllochrons) were also examined. Except in the year following pruning, large annual yields (5.7–7.9 t dry tea ha−1) were obtained by hand harvesting at intervals of two phyllochrons. For clones K35 (large shoots) and T207 (small shoots), the mean harvested shoot weights were equivalent to three unfurled leaves and a terminal bud. The proportions of broken shoots (40–48 %) and coarse material (4–6 %) were both relatively high. Using a blade resulted in similar yields to hand harvesting from K35 but larger yields from T207 (+13 %). The yield increase from clone T207 was associated with the harvest of more shoots and heavier shoots, smaller increases in canopy height, and a higher proportion (7–9 %) of coarse material compared to hand harvesting. On bushes, which had been harvested by hand for two years following pruning, using flat shears (no step) supported on the tea canopy resulted, over a three year period, in yields 8–14 % less than those obtained by hand harvesting and, for clone K35, a reduction in the leaf area index to below 5. The development of a larger leaf area index is made possible by adding a step to the shear. However, since annual yields were reduced by 40–50 kg ha−1 per mm increase in step height, the step should be the minimum necessary to maintain long-term bush productivity. As mean shoot weights following shear harvesting were about 13 % below those obtained by hand harvesting, there is scope, when using shears, to extend the harvest interval from 2 to 2.5 phyllochrons.

Upland rice (Oryza sativa L., UR) could be an option under soybean–maize crop rotation system. However, the recommended row spacing for UR (0.30 m) is shorter than that recommended for soybean and corn (0.40 m), limiting the use of UR in this rotation. We hypothesize that cultivar adaptation to wider than recommended row spacing and local environmental conditions harbour significant potential for overcoming the yield constraints of wider row spacing. We evaluated the row spacing effects on rice grain yield and their components in UR cultivars grown under different water deficit conditions. The experiments were designed as a randomized block in a split–split-plot scheme with sites (the cities of Santo Antônio de Goiás, Porangatu and Formoso) as main plots, row spacing (0.25, 0.35, 0.45 and 0.55 m) as the subplots and UR cultivars (one old and two modern genotypes) as the sub-subplots. We found that, in the less stressful environments, the modern cultivars, BRSMG Curinga and BRS Primavera, presented the highest grain yield. By contrast, in environments with moderate to intense water stress, the traditional cultivar, Douradão, presented the best performance, regardless of row spacing used. We conclude that UR is a viable option for soybean–maize rotation systems, as the UR cultivars tested presented no noticeable yield losses when sown with the same row spacing used for soybean and maize crops (0.40 m). In terms of impact, it can lead to an increase in UR cropped area in Brazil, and decrease in dependence on flooded rice harvested in the south of the country.

With a focus on eastern Africa, the results of research on the water requirements and responses of tea to irrigation and drought are reviewed. In particular, work undertaken at the Ngwazi Tea Research Station (formerly Unit) in southern Tanzania is synthesized. Topics covered include: crop water use, yield responses to water for mature and immature tea, comparisons between clones (including composite plants), plant density/water availability interactions, dry matter production and partitioning, drought mitigation, crop modelling and irrigation systems. Emphasis is placed on the practical aspects of the work and its relevance to the tea industry it serves. A companion paper reviews our understanding of the water relations of the tea plant and, in particular, the mechanisms responsible for the responses observed in the field.

Photosynthesis and biomass production by millet (Pennisetum glaucum) and taro (Colocasia esculenta) grown under baobab (Adansonia digitata) and néré (Parkia biglobosa) was studied at Nobéré (Burkina Faso) with the aim of optimising parkland systems productivity. Millet yielded the highest biomass under Baobab and the lowest biomass was recorded in the zone close to the tree trunk of néré. In contrast, the biomass of taro was higher in heavy shaded zones under néré and the zone close to baobab's trunk. The two crops showed an increasing trend of photosynthesis rate (PN) from tree trunk to the open area. However, the increase in the PN of taro from tree trunk to the open field was lower compared to that of millet. By increasing its leaf area index (LAI) under shade, taro displayed higher biomass production under tree compared to the open area while an opposite trend was observed in millet. The high millet biomass production under baobab could be explained by light availability and the reduction of temperature under shade compared to the open field. The adaptation of taro to shade by increasing its LAI and thus avoiding drastic reduction in PN under shade resulted in better biomass production under heavy shade. Therefore, it was concluded that by replacing millet with taro under dense tree crowns the productivity of agroforestry parkland systems could be increased.

The effects of different soil temperature regimes on vegetative growth, symbiotic nitrogen fixation and seed yield of two cowpea cultivars (K 2809 and Prima) were investigated in experiments carried out in plastic houses during the UK summer. Mean maximum soil temperatures above 32°C significantly reduced vegetative growth of both cultivars, through their effects on branch, peduncle and root dry weight per plant and, to a lesser extent, leaf production. The warmest temperature regime (35.4°C) also reduced nodule activity, especially in cv. Prima. Seed yields were adversely affected, due largely to changes in the number of peduncles per plant, as mean maximum soil temperature increased from 25.8 to 35.4°C.

Although bambara groundnut (Voandzeia subterranea) is an important pulse crop in Africa and particularly in Ghana, information on the crop is not only very limited but conflicting, especially as regards flowering and mode of pollination. Both self- and cross-pollination can take place in varying degrees, depending on variety or strain, and this is brought about by two species of ants, Pheidole megacephala and Monomorium pharaonis, without which pollination might be severely limited or prevented altogether. The extent of cross pollination may be greater in varieties or strains with a more open habit, i.e.. varieties resembling the wild uncultivated ancestors, whereas the bunch cultivated types are more likely to be self-pollinated. It is suggested that varieties or strains may show differences in their ability to cross with one another.

In Mozambique, the sweet potato (Ipomoea batatas) is grown both as a leafy vegetable, the terminal shoots or vines being progressively harvested during the season, and as a root crop. It is produced in the dry season, in areas with a high water table or with irrigation, and in the rainy season. This paper reports the results of measurements made during the 1995 dry season to evaluate the effects of water availability and the frequency of vine harvesting on the processes of radiation interception, dry matter production and partitioning. An irrigated crop (cv. TIS 2534) with a single, end of season vine-harvest (H1) intercepted 71% of the total solar radiation, reducing to 52% with weekly (H4) harvests. The corresponding values for a rain-fed crop were 33 and 20% respectively. When the leaf area index (L) exceeded 3–4, virtually full interception of photosynthetically active radiation (PAR) occurred, except when frequent vine-harvests modified the architecture of the leaf canopy. The extinction coefficient (k, PAR) was highly variable: at a given leaf area, interception was greatest earlier in the season, with infrequent harvests and with irrigation. Total dry matter production (vines, foliage and storage roots), over a period of 161 days, reached 23 t ha−1 in the single harvest (H1), irrigated crop, less when the vines were harvested weekly (H4). The corresponding value for the rain-fed crop, which was able to resume active growth immediately after a rainfall event, following a prolonged dry period, was 7 t ha−1. The efficiency of conversion of PAR into dry matter (εs) was 2.74 g MJ−1 in the irrigated treatments combined, decreasing to around 73% of this without irrigation. The value of εs appeared not to be influenced by dry air or high temperatures. The reduction in εs due to drought was less than the corresponding reduction in intercepted PAR. Increasing the frequency of vine harvests increased the partitioning of assimilates to vines. Irrigation had similar effects early in the season, but afterwards it encouraged preferential growth of the storage roots. The end of season harvest index (h) for vines increased with harvesting frequency from, for example, 0.08 (H1) to 0.38 (H4) in the irrigated crop. By comparison, irrigation increased ‘h’ for storage roots from 0.24 (rain-fed) to 0.57 in the H1 treatment. The total harvest index (vines plus roots) increased with the number of vine harvests from 0.32 (H1) to 0.55 (H4) in the rain-fed crop, and from 0.62 (H1) to 0.72 (H4) in the irrigated crop. Clearly, ‘h’ is not a conservative parameter in the sweet potato, but is sensitive to crop management practices and to soil water availability.

Field experiments were conducted to standardize protocols for site-specific fertilizer nitrogen (N) management in Bt cotton using Soil Plant Analysis Development (SPAD) chlorophyll meter. Performance of different SPAD-based site-specific N management scenarios was evaluated vis-à-vis blanket fertilizer N recommendation. The N treatments comprised a no-N (control), four fixed-time and fixed N doses (60, 90, 120, and 150 kg N ha-1) including the recommended dose (150 kg ha-1), and eight fixed-time and adjustable N doses based on critical SPAD readings of 45 and 41 at first flowering and boll formation stages, respectively. The results revealed that by applying 45 or 60 kg N ha-1 at thinning stage of the crop and critical SPAD value-guided dose of 45 or 30 kg N ha-1 at first flowering stage resulted in yields similar to that recorded by applying the recommended dose of 150 kg N ha-1. However, significantly higher N use efficiency as well as 30–40% less total fertilizer N use was recorded with site-specific N management. Applying 30 kg N ha-1 at thinning and SPAD meter-guided 45 kg N ha-1 at first flowering were not enough and required additional SPAD meter-guided 45 kg N ha-1 at boll formation for sustaining yield levels equivalent to those observed by following blanket recommendation but resulted in 20% less fertilizer N application. Our data revealed that SPAD meter-based site-specific N management in Bt cotton results in optimum yield with dynamic adjustment of fertilizer N doses at first flowering and boll formation stages. The total amount of N fertilizer following site-specific management strategies was substantially less than the blanket recommendation of 150 kg N ha-1, but the extent may vary in different fields.

A better understanding of the agronomic and economic benefits of integrating organic and inorganic fertilizers is essential for their wide-scale dissemination and adoption in smallholder farming systems in developing countries. Field studies were conducted for 10 cropping seasons (1996–2000) on a Kandiudalfic Eutrudox soil to compare the effects of Minjingu phosphate rock (MPR) and triple superphosphate (TSP) on the yield of maize (Zea mays), in combination with three nitrogen (N) sources: urea, Tithonia diversifolia and Sesbania sesban leafy biomass. Urea and tithonia were applied to provide 60 kg N ha−1. Phosphorus (P) from either MPR or TSP was added either once at 250 kg P ha−1 at the beginning of the experiment or annually at 50 kg P ha−1 for five years, the two rates representing two P recapitalization strategies. From the second year, potassium (K) was added to half of each plot to correct for the deficiency that emerged. Over the 10 cropping seasons, the agronomic and economic benefits of the two P recapitalization strategies were similar and were not influenced by the P sources used. With N and K application, both P sources resulted in at least a two-fold maize grain yield increase over the control with no P application that averaged 1.1 tons ha−1. Comparing the N sources, although urea and tithonia had similar net benefits when P was applied, the total cost associated with tithonia was considerably higher. Without P application, sesbania fallow was the most financially attractive option. Sesbania fallows as an N source were also least sensitive to increases in the price of fertilizers and the cost of labour although the financial benefits of this system remained low in the absence of P and K application.

An action research process was conducted with communities in Gununo, southern Ethiopia (2000–2003), to develop alternative cropping strategies for achieving their food security and cash needs. Farmers identified three major production objectives depending on their household priorities and socio-economic status. In Group I, farmers are currently food insecure and want to produce enough food from their own farms. In Group II, they produce enough food but want to fulfil their financial needs. In Group III, farmers rely on off-farm activities and want to increase cash income. The current system mostly fulfils the nutritional requirement of Group II. Groups I and III were highly food deficit from their own farms, with production covering less than seven months per year and fulfilling <50% of the recommended daily allowances (RDA) for human nutrition. Using a linear programming optimization model, it was possible to fulfil the RDA of Group I by reallocating the cropping area of maize, sweet potato, coffee and wheat to potato, enset and kale in proportions of 50, 29 and 15%, respectively. To satisfy both financial and nutritional needs of Group II, an increase in the proportion of coffee and beans by about 29 and 7.3%, respectively, over the current land allocation was needed. This shift would triple their cash income. The cash income of Group III increased four-fold by full replacement of the cereals and root crops by coffee (48%) and teff (52%), though the total income was not enough to secure food security due to their small landholdings. In farms of Groups I and II, the shift to the suggested cropping will reduce soil erosion by about 40%, while it will have no effect on farms of Group III. This shift will reduce the quantity and quality of livestock feed, except for Group I. Moreover, it will increase the farm crop water requirement 17.5 and 37% in Groups I and III (resource poor households) and reduce it in resource rich households of Group II. These changes did not imply extra labour in any groups. Whilst this model can optimize systems for food security and cash income, its research for development value is in identifying possible intensification strategies for farming systems and their implications on the farming systems, rather than generating practical recommendations for all cropping systems.

Simultaneous undersowing of upland rice with Stylosanthes guyanensis at Khon Kaen, north-east Thailand did not affect vegetative growth of rice but reduced grain yield by 19 per cent. Grain yield was not significantly affected if stylo undersowing was delayed by 10 days. Stylo growth was reduced by one half by delayed sowing and was negatively related to dry matter yield of rice variety.