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.

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.

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.

A hydraulic press (the J-14) was compared with a Scholander pressure chamber to measure leaf water potential in Theobroma cacao, Gliricidia maculata, Cajanus cajan and Elaeis guineensis. Although the press satisfactorily estimated water status in soft, unhardened leaves of T. cacao, G. maculata and C. cajan at high water potential, it underestimated water status in hardened leaves of T. cacao. Satisfactory estimates were obtained at low water potential for hardened leaves of T. cacao but not for the others. There was a poor relation between readings of the two instruments for E. guineensis over a wide range of water potentials because press readings appeared to be influenced by leaf structure.

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.

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.

Increasing image resolution and shrinking camera size facilitates easy mounting of digital cameras on Unmanned Aerial Vehicles (UAVs) to collect large amounts of high-resolution aerial photos for soil surface and vegetation monitoring. Major challenges remain geo-referencing of these images, reliable stitching (mosaicking), elimination of geometric image distortions and compensation of limited image quality and high cost of the equipment. In this study, we report upon the design and field-testing of a custom-made, cost-effective mini-UAV allowing the acquisition of RGB and near-IR images covering areas of 1–2 km2 in each flight and the development of a software tool to automatically combine the geo-referenced images into a seamless image mosaic. Object-orientated image classification was used to estimate plant biomass. The images allowed to determine the distribution and biomass of selected plant species and other landscape features such as field borders and settlement patterns as well as to construct a simple 3D model of the topography of the surveyed area. The setup facilitates the cost-effective acquisition, mosaicking and classification of hundreds of RGB and near-IR images with a spatial resolution of 5–10 cm.

Cocoyam (Xanthosoma spp.) is the most important export crop of all the root and tuber crops grown in Nicaragua. Despite its importance, the total planted area and yield have significantly decreased during the past few years, a decrease that is mainly due to diseases that are disseminated through the planting material. In this study virus-free (NI) and virus-infected (I) in vitro plants from three genotypes were established in a non-traditional production area. The aim was to evaluate their agronomic performance, and to study the re-infection of dasheen mosaic virus (DsMV) and its effect on yield. Repeated measurements of morphological traits were made during the experimental period. The height of the plants, the diameter of the pseudo-stem and the leaf area increased continuously up to 217 days after planting after which the growth curves declined. The genotypes differed in all yield components, except in yield per plant. Regardless of genotype, the NI plants produced a larger number of cormels that were heavier and longer than the cormels produced by I plants. This resulted in a higher yield from NI plants (18.2 t ha−1) compared with I plants (13.6 t ha−1). Seven months after planting between 60 and 90 % of the NI plants, depending on genotype, were infected with DsMV. Aphis gossypii was the only aphid observed in the field trial and is therefore most probably the vector responsible for the transmission of the virus.

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.

Parthenium hysterophorus is a prolific invasive weed species, which infests many crops in over 40 countries around the world. A 2-year field study was carried out to quantify the potential impacts of this weed on direct-seeded rice. Parthenium weed was allowed to compete for 2, 4, 6 or 8 weeks after crop emergence, while full season weedy and weed-free plots were maintained as controls. Parthenium weed plants grew taller and attained more biomass as the competition duration prolonged. The yield and yield-related attributes of rice were negatively affected with increasing competition duration. The season-long competition caused the highest reductions in panicle number (28–34%), panicle length (26–27%), grains per panicle (22–23%) and grain yield (33 and 38%) of rice in both years. Weed competition for 2–8 weeks caused 5–34% and 6–33% losses in rice grain yield during both years, respectively. Importantly, Parthenium weed control after 8 weeks of competition did not improve rice yield significantly. The results suggested that Parthenium weed should be controlled in rice fields between 4 and 8 weeks after crop emergence under direct-seeded conditions to avoid over 10% yield losses.

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.

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 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.

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.

Effects of N, P and K on yields of cotton were investigated using data obtained over an 18-year period from a factorial experiment comparing various combinations of the three nutrients. The results clearly indicated a significant and fairly consistent response of cotton to the application of fertilizer nitrogen, but the rate of increase in yield with increased N gradually diminished. The response to P was erratic and to K was negligible. The response to N did not vary with levels of P or K. Whether lack of response to P on the alkaline soils of the Gezira was due to sufficient already available in the soil, or because the added fertilizer was fixed and rendered unavailable to the plant needs further investigation. Lack of response to added K was attributed to the high content of available K already in the Gezira soil.

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.

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.

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 objective of this study was to investigate the user communities' understanding and interpretation of changes in rangeland use and productivity in the communal lands of Zimbabwe. While external knowledge has been instrumental in defining the drivers and effects of ecological changes hitherto, the role of local knowledge is becoming increasingly important in explaining factors that inform user community perceptions and guide their decisions on the use of rangeland resources. Data on community perceptions were collected in four villages, using Participatory Rural Appraisals in each village and household surveys with a total of 104 households. This study showed that user communities in Nkayi district differentiate rangelands among seven categories of livestock feed resources and how these have changed over time. Communities viewed rangelands not as one continuous, designated and specialized land parcel, but differentiated the land by location, productivity, management and uses in different times of the year. Although land use changes affecting these livestock feed resources were considered to be widespread and multi-directional (both negative and positive) they did not cause widespread degradation. Rangelands converted to croplands were not completely lost, but became important dual purpose land parcels fulfilling both household food security needs and dry season livestock feed requirements. The importance of croplands as a feed resource is reflected in the emergence of new institutions governing their use for livestock grazing and to guarantee security of tenure. On the other hand institutions governing the use of common property rangelands decreased or weakened in their application. The study concludes that while this situation presents ecological challenges for the rangelands, it offers opportunities to find innovative ways of utilizing croplands as the new frontier in the provision of dry season feed resources to smallholder farmers in highly variable environments. Implications for livestock water productivity need to be investigated and water saving technologies should be promoted in the land use intensification processes.