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.

Irrigation, mulch and N-fertilizers increased the yield of fresh fruit/tree by 66 per cent due to increases of 42 per cent in the number of fruiting nodes/tree, 14 per cent in number of fruits/node and 15 per cent in fresh weight/fruit; these three yield components accounted for 42, 13 and 6 per cent of the variation in yield among all treatment combinations. Bean/fruit weight ratios and times of flowering were not affected. Correlations between yield components were positive, suggesting that still more nodes could be produced per tree and per unit area before physiological limits to yield were reached.

To assess the potentialities of Ph. vulgaris for haricot type bean production in Britain, a large collection of types was surveyed. One hundred varieties, mostly but not exclusively bush types, were grown both in the greenhouse and in the field. Characters of agronomic importance were evaluated. The morphological basis of the difference between the climbing and the bush habit was shown to be the interaction between two character contrasts, indeterminate versus determinate vegetative growth, and long versus short internodes. The four classes resulting from this interaction were identified and are described. Flowering habit, pod type and seed size were surveyed. Among the bush beans, wide variation in day length sensitivity in flowering was shown, and it is clear that day length neutral types can easily be selected. Among the determinate dwarfs, pods are either leathery or fleshy. Leathery types dry out readily, and do not dehisce freely in the field, and are therefore agronomically desirable in dry bean production. Fleshy pods are used for culinary purposes. The indeterminate bush types included in this survey have parchmented pods, which tend to dehisce when dry, and hence are subject to crop loss in the field. A wide range of seed size and seed colour is available for selection according to requirement. Two small variety trials yielded evidence that Colombian determinate bush types grow and crop satisfactorily within the limits of the growing season in eastern England. From two spacing trials, optimum within-row spacing was deduced.

A trial was carried out at Pantnagar in India during 1984–85 and 1985–86 to study the productivity of Egyptian clover and oats under intercropping. Cross sowing of both the crops either at full or half seed rates and line sowing of oats in broadcast Egyptian clover was better than other intercropping systems or sole cropping in respect of herbage production, digestible dry matter yield and land equivalent ratio but crude protein yield from the mixed crops was similar to that from sole cropped Egyptian clover.

Effects of environmental temperature on boll maturation period of cotton and the genotype response, investigated in a 3-year field experiment, showed a negative correlation between period and mean temperature and revealed genotypic differences regarding degree of temperature influence and sensibility to temperature changes. The observed genotype × temperature interactions may help cotton breeders in establishing breeding centres and in creating desirable gene combinations for wider adaptability to temperature.

A small farmer in the tropics often grows a range of crops to protect himself against failure in a bad season. It is suggested that guidance on the choice of species, and the proportions between them, can be gained by studying past cropping figures, such as those collected for FAO purposes. Two cases are distinguished for systems using two species, (a) when the crops serve much the same purpose and are interchangeable in use, and (b) when they serve different purposes and a certain minimum is required of each. Special attention is given to intercropping, in which the two species are grown in close association.

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.

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.

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.

Root traits, such as depth and root biomass, have been identified as the most promising plant traits in chickpea for terminal drought tolerance. With this objective, five contrasting genotypes of chickpea, viz. ICCV-4958, H-208, HC-5, RSG-931 and CSJ-379, having wide adaptability to drought prone areas at national level were assessed for various root characteristics under two environments, i.e. irrigated and rain-fed. The sampling was done at full bloom stage and there were significant differences in the rooting depth among the genotypes both under irrigated and rain-fed conditions. The chickpea roots penetrated to a minimum depth of 92 cm in CSJ-379 and maximum of 122 cm in ICCV-4958 under rain-fed conditions. The rooting depth remained higher under rain-fed than irrigated environment. Under irrigated conditions, the chickpea roots were able to grow to a maximum depth of 99 and 97 cm in HC-5 and ICCV-4958, respectively. Among the genotypes, biomass per plant of the root was higher in ICCV-4958 (6.7 g) and HC-5 (5.6 g) under rain-fed conditions. Similar observations were recorded for root/shoot ratio, dry weights of stem, leaf, nodules and total dry weight per plant. The moisture stress increased the biomass partitioning towards the roots. The water potential (ψw), osmotic potential (ψs) and relative water content (RWC %) of leaf were –0.98 MPa, –1.82 MPa and 60%, respectively, in the genotype HC-5, and –1.02 MPa, –1.72 MPa and 64%, respectively, in ICCV-4958 under rain-fed conditions. The rates of photosynthesis, and transpiration, values of the stomatal conductance and photochemical efficiency/quantum yield as indicated by Fv/Fm ratio were in the range of 6.7 to 10.6 (μmol m−2 s−1), 1.27 to 2.38 (mmol m−2 s−1), 0.23 to 0.48 (mol m−2 s−1) and 0.457 to 0.584, respectively, under rain-fed conditions. Genotypes HC-5 and ICCV-4958 also maintained higher photosynthetic and transpiration rates and Fv/Fm ratio than others. The maximum Fv/Fm values in these genotypes were correlated with the higher photosynthetic rate and dry matter yield per plant. Relative stress injury (RSI %) values in HC-5 and ICCV-4958 noticed were 25.3% and 23.7%, respectively. The results of this study indicate that under rain-fed conditions, genotypes ICCV-4958 and HC-5 had higher dry weight of stem, leaves, roots, nodules and total dry weight per plant, rooting depth, root/shoot ratio, photosynthetic and transpiration rates, photochemical efficiency and better plant water status but lower stomatal conductance than other genotypes. These traits are directly associated with maximum seed yield per plant, i.e. 15.6 g and 14.7 g per plant, respectively, in these genotypes. Therefore, both the genotypes in future can be used in crop improvement programme of chickpea breeding for drought tolerance.

The effects of variety and fertilizer on wheat and barley production, and of inoculation with rhizobium on Vicia crop production under rain-fed conditions were observed in farmers' fields in Balochistan from 1985 to 1988. Weeding and application of phosphate fertilizer had little effect on wheat yields, but in the ‘good‘ rainfall year, 1986/87, application of nitrogen fertilizer resulted in increased economic yields. Barley varieties from Syria generally produced better grain yields and, with the exception of Arabi abiad, poorer straw yields than a local variety. Genotype–environment analyses indicated that Arabi abiad could be expected to produce more grain, similar amounts of straw and larger gross benefits than the local variety in all except the most severe environments, when crop failure was inevitable. V. villosa ssp. dasycarpa showed negligible amounts of cold damage, and produced greater herbage and straw yields than the other legume crops. Inoculation with Rhizobium leguminosarum produced large yield increases in 1986/87.

The economic returns from crop production were poor and variable, but the results suggest that the productivity of the crop–livestock system could be increased by greater emphasis on barley, and by the introduction of Arabi abiad barley and V. villosa ssp. dasycarpa.

D. J. Rees et al.: Cultivos regadospor la lluvia de las tierras altas de Balochistan.

Examples are presented of tropical tree commodity plantation crops, tea, coffee, rubber and oil palm, as models for farm system development. They are environmentally benign in comparison with annual food crops, have been organized on a large scale with smallholder participation, and make significant contributions to local and national economies. It is suggested that lessons learned in their development might be used in the large-scale development of other potentially major tree crops, including timber, fruit and nut producing species.

Grassland productivity was studied for four years near Terbol, Lebanon. In the first year pasture availability and plant numbers were monitored along transects, and in the following three years the effects of sowing four Mediterranean annual legumes (three cultivars of subterranean clover and a local ecotype of Medicago rigidula) and top-dressing with super-phosphate were studied. The results indicated that natural grasslands were dominated by annual grasses (Aegilops, Hordeum, Bromur, Lolium and Poa). Legume density was low, which resulted in poor legume productivity, especially in winter. Exotic legumes only resulted in a slight improvement in pasture productivity even when phosphate fertilizer was added. However, partial protection from grazing (for one or two months in late winter and spring) more than doubled the number of legume seeds in the seed bank compared with full protection and open grazing. The build up of seeds in the soil is an essential step towards the improvement of productivity in these degraded pastures, which form a large part of the land surface in Lebanon and on which small ruminant production largely depends.

Dryland agriculture is critically important to food security and rural livelihoods in Tanzania, but crop production is seriously constrained throughout the semi-arid lowlands by the rainfall regime. A major challenge is to develop improved cropping systems to alleviate the moisture constraint. Experimental evidence indicates that adoption of rainwater harvesting systems can bring benefits, but the restricted spatial and temporal extent of the experimental work leads to difficulties in extrapolation. This paper shows how the PARCHED-THIRST model can add value to the experimental results and provide important insights into their transferability. The model is seen as an aid to researchers, planners and extensionists in interpreting experimental results and designing locally appropriate interventions. Simulation based on 30 years of daily meteorological data provides an opportunity for temporal extrapolation. The long-term simulation allows an objective assessment of the risks and benefits associated with alternative rainwater harvesting systems. Simulation for different soils and modified rainfall regimes permits objective analysis of spatial transferability of experimental results to any other site for which rainwater harvesting interventions might be considered. It is shown that macrocatchment rainwater harvesting reduces drought risk within the target area, but may bring a serious risk of erosion due to excessively high flow rates. The overall assessment of the twin-track approach (experimentation+simulation) is that rainwater harvesting has potential for increasing productivity and sustainability of maize cropping systems in semi-arid Tanzania provided that the innovations are properly matched to the site-specific environmental conditions.

High temperature stress at flowering can adversely affect rice yield, largely due to failure of fertilization. Oxidative damage can be a major reason inducing spikelet sterility in rice. In the present study, the effect of high temperatures on antioxidant metabolism in rice spikelets was characterised using nine different genotypes. Exposure to different temperatures at flowering stage revealed significant differences among various antioxidant enzymes in spikelets, both quantitatively and qualitatively. Spikelets of susceptible genotypes withstood temperature stress of up to 35 °C, those of moderately tolerant between 35 °C and 38 °C and those of tolerant genotypes up to 40 °C. Presence or absence, and changes in the isozyme intensities were consistent with alterations in their activities. Superoxide dismutase (SOD) isozymes II and III were present after exposure at 30 °C and 35 °C, while SOD I appeared above 40°C. Intensities of catalase isozymes I and III and the only isozyme of ascorbate peroxidase altered, while the only isozyme of guaical peroxidase and two (III and IV) of the four isozymes of catechol peroxidase disappeared after high temperature exposure of 45 °C. Thus, this work provides an evidence of the role of antioxidant metabolism in spikelets under high temperature stress conditions. Hence, changes in antioxidant isozymes in rice spikelets can be used as a biomarker for characterizing high temperature stress tolerance in rice spikelets.

The growth and grain production of four rice varieties were compared under controlled environment conditions at two minimum night temperatures (15 and 23°C) and at two daylengths (11½ and 13 hours) where the period of daylight for active photosynthesis was kept constant at 8 hours. The lower night temperature prevented flowering but at the higher one grain yields were associated with panicle weights rather than panicle numbers, and production of so-called photoperiod-insensitive varieties was affected by photoperiod. Although the periods of natural light were constant, and photoperiods were extended by low intensity incandescent light, in-creased total plant weights, not due to effects on tillering, were observed under longer days.

Responses of nodulating and non-nodulating isolines of Clark and Harosoy to applications of N were studied, to evaluate the suitability of symbiosis versus N fertilization for soybean. Nodulating lines did not respond to N when they were either effectively inoculated or raised on a field which had been under inoculated soybean in the past. On a field brought under soybean for the first time, uninoculated Clark and Harosoy needed 300 and 235 kg. N/ha. respectively to give maximum yields. Symbiosis proved better than N fertilization for the N nutrition of soybean.

The dry-matter and organic-matter digestibilities of eight samples of fodder maize and five samples of maize silage were measured, using sheep. The maizes were harvested and ensiled in such a way that comparisons could be made between the digestibilities of either the same maturity types, harvested on different dates, or of different maturity types harvested on the same date, or of maize and silage made from similar material. The total range of organic matter digestibility for all types of maize on all dates was within the range 70·6 to 75·2 per cent. The digestibilities of maize silages were found to be slightly lower than those of the original materials.

The effect of four crops of maize on the distribution of organic nitrogen in ten West Indian soils, given either lime, P, K, Mg and trace elements or no fertilizers, was studied in a greenhouse experiment. The soils were also analysed for ‘available N’ by incubation and chemical methods. Variations in the redistribution of organic N fractions during the greenhouse experiment did not permit conclusions to be drawn on the source of N used by the maize, although the amount of hydrolysable N, particularly hexosamine, amino and hydroxy-amino N, in the initial samples was closely related to N uptake. Part of the chemically stable, non-hydrolysable organic N was broken down by soil organisms during the experiment; this was increased by liming acid soils.

Agricultural systems of Northern Ethiopia are under pressure from demographic expansion leading to land degradation and increasing water scarcity. Livestock water productivity (LWP) is an important component in improving overall productivity in mixed crop-livestock systems. The objective of the study was to characterize the existing farming system in a typical water stressed environment in the Ethiopian highlands in terms of crop and livestock production and to assess LWP at household level. To this end, the characteristic watershed of Lenche Dima watershed was chosen. An exploratory assessment of LWP variables and potential differences between farmers' wealth classes was conducted based on a survey of 54 sample households and focus group discussions. LWP was determined as the ratio of beneficial outputs over used water. We used market values of livestock products and services to unify the livestock outputs. Water used to produce the livestock outputs was determined based on water consumption to produce the feed. The overall water used per household for livestock production ranged from 3079 ± 2335 (s.d.) m3 per year to 11 975 ± 4080 (s.d.) m3 per year for poor and better-off households, respectively. If fully valued as fuel and fertilizer, manure contributed an overall 34% of the total financial livestock output, followed by draught power (22%), transport (17%) and milk production (16%). LWP ranged from 0.07 to 0.09 US$ m−3 and was not significantly different between farmers' wealth classes. The small differences were an indication that all farmer types had very limited access to potential LWP improvements through increased feed quality and quantity, improved animal husbandry and better veterinary care.