Three early and four later flowering lines of sorghum were subjected to three drought stress treatments (early, late and early plus late stress) in the field during the dry season at Hyderabad in India. Mean diurnal temperature and evaporation rate were uniformly high throughout the experiment. The late and early plus late stress conditions were severe, while the early stress was mild.

Grain yield was affected by both the timing and the severity of the stress. The largest reduction (87%) in grain yield resulted from stress imposed during booting and flowering (late stress) in the early flowering lines; the same stress treatment on vegetative plants had no effect on grain yield. Increasing the duration of severe stress on vegetative plants (early plus late stress) reduced grain yield by 50–60%.

Grain yield was strongly and positively correlated with the number of grains m-2. Variation in grain yield was associated with variation in total dry matter rather than with harvest index, which was only reduced when stress occurred at flowering. Treatment effects on thermal growth rates (g m-2 °Cd-1) during the phase from booting to flowering confirmed that growth during this phase is the major determinant of yield potential (number of grains). The importance of phonology in research into drought resistance is discussed.

The role of water in the development and yield of the coffee crop (Coffea arabica L.) is reviewed. A period of water stress, induced either by dry soil or dry air, is needed to prepare flower buds for blossoming that is then stimulated by rain or irrigation. Although attempts have been made to quantify the intensity and duration of stress required, these have not yet been specified in ways that are commercially useful. Water must be freely available during the period of rapid fruit expansion to ensure large, high-quality seed yields. Depending on the time and uniformity of flowering this can occur at times when rainfall is unreliable, particularly in equatorial areas.

Although there are differences in their responses to drought, commercial cultivars have retained many of the characteristics adapted to the shady environment of the forests in the Ethiopian highlands in which C. arabica is believed to have originated. These include partial closure of the stomata when evaporation rates are high as a result of large leaf-to-air saturation deficits (>1.6 kPa), even if the soil is at field capacity. This is thought to be an adaptive mechanism that minimizes transpiration at high irradiances when the leaves are light-saturated.

Our understanding of the actual water use of coffee crops grown in diverse ways is imperfect. For mature crops, well supplied with water, the crop coefficient (Kc) appears to have a value in the range equivalent to 0.7–0.8 times the evaporation from a US Weather Bureau Class A pan. There is some evidence that Kc values are less than this on days when evaporation rates are high (>7 mm d−1). For immature crops allowance has to be made for the proportion of the ground area shaded by the leaf canopy, but this alone may underestimate rates of water use. Present methods of calculating crop water requirements for the purposes of irrigation scheme design and management are imprecise and, probably, subject to large errors depending on local circumstances.

The need for irrigation, and its role in controlling the timing of flowering, varies depending on the rainfall distribution, the severity of the dry season, and soil type and depth. Two geographic areas need to be distinguished in particular; those close to the equator with a bi-modal rainfall pattern and those at higher latitudes with a single rainy season and an extended dry season. Despite the international importance of irrigation in coffee crop production, the benefits to be derived from irrigation, in yield and in financial terms, have not been adequately quantified in either location. Allowable soil-water deficits have been specified for deep-rooting crops (2–3 m) on water retentive soils, usually linked to conventional over-tree sprinkler irrigation systems. Other, potentially more efficient, methods of irrigation are now available for coffee grower use, in particular, micro-jet- and drip-irrigation systems. However, there appears to be little advice, based on sound experimental work, on how to design and operate these to best advantage.

There is a need to interpret and apply the scientific understanding of the role that water plays in the growth and development of the coffee plant into practical advice that can assist the grower to plan and to use water efficiently, whether rainfall or irrigation, for the production of reliable, high-quality crops. Future research opportunities are identified.

Approaches using breeding, physiology and modelling for evaluating adaptation of plant genotypes to target environments are discussed and methods of characterizing the target environments outlined. Traditional approaches, and their limitations, to evaluation of genotypic adaptation using statistical and classificatory techniques with a phenotypic model are discussed. It is suggested that a simple biological model is the most appropriate framework in which to integrate physiology and modelling with plant breeding. Methods by which physiology and modelling may contribute to assessment of adaptive traits and to selection for adaptation in a breeding programme are considered.

Conducting farmers participatory field trials at 40 sites for 3 consecutive years in four rice-wheat system dominated districts of Haryana state of India, this paper tested the hypothesis that zero tillage (ZT) based crop production emits less greenhouse gases and yet provide adequate economic benefits to farmers compared to the conventional tillage (CT). In each farmer's field, ZT and CT based wheat production were compared side by side for three consecutive years from 2009–10 to 2011–12. In assessing the mitigation potential of ZT, we examined the differences in input use and crop management, especially those contributing to GHGs emissions, between ZT wheat and CT wheat. We employed Cool Farm Tool (CFT) to estimate emission of GHGs from various wheat production activities. In order to assess economic benefits, we examined the difference in input costs, net returns and cost-benefit analysis of wheat production under CT and ZT. Results show that farmers can save approximately USD 79 ha−1 in terms of total production costs and increase net revenue of about USD 97.5 ha−1 under ZT compared to CT. Similarly, benefit-cost ratio under ZT is 1.43 against 1.31 under CT. Our estimate shows that shifting from CT to ZT based wheat production reduces GHG emission by 1.5 Mg CO2-eq ha−1 season−1. Overall, ZT has both climate change mitigation and economic benefits, implying the win-win outcome of better agricultural practices.

It is proposed that two distinct objectives should be recognized in the evaluation of intercropping advantages: (i) a biological objective to determine the increased biological efficiency of intercropping and (ii) a practical objective to determine the advantages that are likely to be obtained by a farmer. The sole crop systems with which intercropping must be compared to satisfy these objectives are defined. Evaluation in relative, absolute, monetary and nutritional units is discussed and some aspects of presenting intercropping data in graphical form are illustrated.

Declining soil fertility is a major cause of low per capita food production on smallholder farms of sub-Saharan Africa. This study attempted to provide an empirical explanation of the factors associated with farmers' decisions to adopt or not to adopt newly introduced integrated soil fertility management (ISFM) technologies consisting of combinations of organics and mineral fertilizer in Meru South district of the central highlands of Kenya. Out of 106 households interviewed, 46% were ‘adopters’ while 54% were ‘non-adopters’. A logistic regression model showed that the factors that significantly influenced adoption positively were farm management, ability to hire labour and months in a year households bought food for their families, while age of household head and number of mature cattle negatively influenced adoption. The implication of these results is that the adoption of ISFM practices could be enhanced through targeting of younger families where both spouses work on the farm full-time and food insecure households. It is also important to target farmers that lack access to other sources of soil fertility improvement. Examples include farmers that do not own cattle or those owning few and who, therefore, have limited access to animal manure.

Organic coffee is one of several types of speciality coffees selling at a premium over mainstream coffees because of distinct origin and flavour, environment-friendly production or socio-economic concerns for the smallholder coffee growers. The demand for organic coffee in Western Europe, North America and Japan exceeds the present supply, which is still small (<1% of annual world production). More than 85% of organic coffees come from Latin America and practically all is (washed) arabica coffee. The production of certified organic coffee follows the principles of organic farming developed in Europe and the United States out of concern for the perceived negative effects of conventional high-input agriculture on health and environment. It claims superior ecological sustainability in combination with sound economic viability. A rather complex and expensive system of certification has to be passed before such coffees can be sold as truly organic. Growers adhering to the strict rules of organic coffee production may to some extent share the concern of the health- and environment-conscious consumers, but they are motivated primarily by the economic benefits from the premium received for certified organic coffee. Nevertheless, there appears to be considerable injustice between the extreme preconditions demanded for ‘organics’ by the largely urban consumer of the industrialized world and the modest rewards received by the organic coffee growers for their strenuous efforts. From an agronomic point of view, there is also considerable ground for criticism on the principles of organic farming when applied to coffee. For instance, to sustain economically viable yield levels (1 t green coffee ha−1 year−1) large additional amounts of composted organic matter will have to come from external sources to meet nutrient requirements (especially N and K). Most smallholders will be unable to acquire such quantities and have to face declining yields. Organic farming does not necessarily reduce incidence of diseases and pests below economically harmful thresholds, while the humid conditions of heavily shaded coffee may actually stimulate the outbreak of others. These and other aspects peculiar to the preconditions of organic coffee production are addressed in this review. It is concluded that the concept of organic farming in its strict sense, when applied to coffee, is not sustainable and also not serving the interests of the producer and consumer as much as the proponents would like us to believe. On the other hand, agronomically and economically sustainable coffee production is feasible by applying best practices of crop production and post-harvest processing.

Cowpea (Vigna unguiculata) has relatively higher drought tolerance than other legume crops. It is widely grown in semi-arid regions, particularly in West Africa. One objective of the present study was to determine the effects of soil moisture stress on the length, dry matter and distribution of the roots of two cowpea varieties with different drought tolerances. Another objective was to evaluate the pin-board root-box as a method for identifying the role of root characteristics in drought tolerance. Two cowpea varieties, IT96D-604 (drought tolerant) and TVu7778 (drought susceptible), were used in this study. There were three watering treatments, T1 (well-watered), T2 (mild water stress) and T3 (severe water stress). Between varieties, there were no significant differences in shoot and root characteristics except for leaf area in T1. Under T2, the shoot:root ratio (S:R ratio) of IT96D-604 was significantly decreased compared with that under T1 as a result of the increase in root dry matter and decrease in leaf area without significant differences in total dry matter. In addition, the root dry matter per leaf area, which indicates the capacity to absorb water, of IT96D-604 was significantly higher than that of TVu7778. Under T3, the total dry matter of TVu7778 was about one third of those of the other treatments for the same variety, whereas that of IT96D-604 was more than half. Regarding root distribution, the centres of root dry matter and root length density of both varieties moved downwards significantly under water-stress conditions compared with those of the well-watered condition. This tendency was more pronounced in IT96D-604 than in TVu7778. Drought tolerance in IT96D-604 was associated with the increase in root dry matter per leaf area under mild water-stress conditions, and downward movement of roots (increasing access and use of soil moisture in deep soil layers) under mild and severe water stress conditions. In addition, the root-box method was versatile and can be used for studying root responses to edaphic factors relevant to root growth.

The results of research on the water relations and irrigation need of oil palm are collated and summarized in an attempt to link fundamental studies on crop physiology to drought mitigation and irrigation practices. Background information is given on the centres of origin (West Africa) and of production of oil palm (Malaysia and Indonesia), but the crop is now moving into drier regions. The effects of water stress on the development processes of the crop are summarized followed by reviews of its water relations, water use and water productivity. The majority of the recent research published in the international literature has been conducted in Malaysia and in Francophone West Africa. The unique vegetative structure of the palm (stem and leaves) together with the long interval between flower initiation and the harvesting of the mature fruit (ca. three years) means that causal links between environmental factors (especially water) and yield are difficult to establish. The majority of roots are found in the 0–0.6 m soil horizons, but roots can reach depths greater than 5 m and spread laterally up to 25 m from the trunk. The stomata are a sensitive indicator of plant water status and play an important role in controlling water loss. Stomatal conductance and photosynthesis are negatively correlated with the saturation deficit of the air. It is not easy to measure the actual water use of oil palm, the best estimates for mature palms suggesting crop evapotranspiration (ETc) rates of 4–5 mm d−1 in the monsoon months (equivalent to 280–350 l palm−1 d−1). For well-watered mature palms, crop coefficient (Kc) values are in the range 0.8–1.0. Although the susceptibility of oil palm to drought is well recognized, there is a limited amount of reliable data on actual yield responses to irrigation. The best estimates are 20–25 kg fresh fruit bunches ha−1 mm−1 (or a yield loss of about 10% for every 100 mm increase in the soil water deficit). These increases are only realized in the third and subsequent years after the introduction of irrigation and follow an increase in the number of fruit bunches as a result of an improvement in the sex ratio (female/total inflorescence production) and a reduction in the abortion of immature inflorescences. There is no agreement on the allowable depletion of the available soil water, or on the associated optimum irrigation interval. Drip irrigation has been used successfully on oil palm.

Using experience with bambara groundnut (Vigna subterranea), this paper examines how local knowledge, genetic evaluation, research in fields, glasshouses and laboratories, and crop simulation modelling might be linked within a methodological framework to assess rapidly the potential of any underutilized crop. The approach described is retrospective in that each activity was not clearly defined and structured at the outset. However, the experience gained may help to establish a methodology by which growers, researchers and international agencies can integrate their knowledge and understanding of any particular underutilized crop and apply similar principles to accelerate the acquisition of knowledge on other underutilized species. The use of a methodological framework provides a basis for activities that maximize knowledge, minimize duplication of effort, identify priority areas for further research and dissemination, and derive general principles for application across underutilized crops in general. It also allows policy makers and planners to make comparative decisions on the nutritional, economic and research importance of different underutilized and more-favoured species. In particular, the incorporation of a generic crop simulation model within the methodological framework may assist growers, extension agencies and scientists to refine general recommendations for any particular crop to local conditions. Also, the incorporation of information gathered from the field, laboratory or market can be used to update rapidly the predictive capacity of the model for each crop.

Drought is one of the major factors limiting crop production worldwide. Dry areas are a much less homogeneous population of target environments than areas with high and reliable rainfall. In this paper we argue that a decentralized participatory plant breeding programme can address the complexity of dry areas, characterized by high and repeatable genotype × locations and genotype × years within locations interactions, more efficiently and effectively than a centralized non-participatory plant breeding programme. This is because varieties can be tailored not only to the multitude of target environments typical of dry areas, but also to diverse clients needs. In addition, varieties can be delivered in a shorter time and with a higher probability of adoption. Decentralized participatory plant breeding also has beneficial effects on biodiversity because selection is for specific adaptation rather than for broad spatial adaptation. The paper gives examples of methodological aspects including the modes of farmer selection, the precision of the trials, the efficiency of selection, the response to selection, the role of the type of germplasm and the role of molecular breeding in a participatory breeding programme. The paper gives the example of drought-resistant barley lines identified through extensive field testing and selection in a decentralized participatory breeding programme, and concludes that this type of plant breeding may be better targeted, more relevant and more appropriate for poor farmers in marginal areas.

Despite numerous altempts, the development of generalixed models capable of accurate predictions of the times from sowing to flowering (f) of crop plants in field environments has remained elusive. Models which seek to correlate ;ʃ with various states of environmental factors such as photoperiod, P, and temperature, T, using formal statistical procedures arc often complex. Here, we describe a family of photothermal responses (involving unambiguous parameters and limits) which quantify the linear, non-interacting effects of P and T not on ʃ but on 1/ʃ, i.e. on the rate of progress towards flowering. Based on these relations we suggest that the modelling of crop phenology will be simplified, more reliable and more biologically plausible.

Ethiopia has an irrigation potential of 5.3 million ha (Mha) of which 3.7 Mha can be developed using surface water sources, and 1.6 Mha using groundwater and rainwater management. Irrigation contributes to rapid transformation of agriculture as present-day agriculture is dominated by rainfed single crops. The current irrigation development in Ethiopia is about 0.7 Mha, and the performance of the existing schemes is not well understood. As the country is planning to expand irrigated agriculture in the next five years, it will be useful to review existing performance and to identify areas for interventions that help revitalize underperforming systems. In this paper, we have investigated the performances of irrigation at three levels: (a) national level for broad performance, (b) regional level for small-scale irrigation and (c) scheme level for large-scale irrigation. National level indicators measure (i) the relative proportion of operating schemes, (ii) ratio of actually cultivated area to planned command area and (iii) relative number of benefited to targeted number of households. The result shows that 86.5% of schemes are operating, 74.1% of command area is under cultivation and only 46.8% of the planned beneficiaries have benefited from implemented irrigation. For regional level irrigation performances, the regions of Southern Nations and Nationalities and Oromia Regions were investigated. We used technological (structural) and management factors as measures of performances. Sixty-four underperforming schemes were sampled from the two regions to analyse the causes. About 30 parameters were identified as causes of underperformance. Watershed degradation related problems that are causing erosion and sedimentation of water control and conveyance structures are found to be the major cause for structural failures, while lack of sustainable funding, extension of agronomic practice, and post harvest technologies are identified as the top management-related problems. For evaluating performances of large-scale schemes, we used irrigation water delivery performance and output performance indicators applied to six large-scale schemes. Scheme level performance indicators results showed that all of the schemes considered have supplied adequate to excess amounts of water during the period. The Wonji scheme that uses pump diversion showed higher water use efficiency than other schemes that are using simple gravity diversion types. In this case it might be the running costs of pumps that have encouraged efficient management of water. In terms of output performance, sugarcane based irrigation schemes are superior and up to ten times that of banana, cotton, and maize or tobacco production. The results of these assessments are useful for decision-makers and disclosed the low performance of the existing irrigation schemes. They also indicated the need to revitalize existing schemes to improve performance in parallel to the implementation of new projects. The paper also provided new indicators of evaluation of performance with respect to national level, structural and management related performance.

Global food security is under threat by climate change, and the impacts fall disproportionately on resource-poor small producers. With the goal of making agricultural and food systems more climate-resilient, this paper presents an adaptation and mitigation framework. A road map for further agricultural research is proposed, based on the CGIAR Research Program on Climate Change, Agriculture and Food Security. We propose a holistic, integrated approach that takes into account trade-offs and feedbacks between interventions. We divide the agenda into four research areas, three tackling risk management, accelerated adaptation and emissions mitigation, and the fourth facilitating adoption of research outputs. After reviewing specific technical, agronomic and policy options for reducing climate change vulnerability, we acknowledge that science and good-faith recommendations do not necessarily translate into effective and timely actions. We therefore outline impediments to behavioural change and propose that future research overcomes these obstacles by linking the right institutions, instruments and scientific outputs. Food security research must go beyond its focus on production to also examine food access and utilization issues. Finally, we conclude that urgent action is needed despite the uncertainties, trade-offs and challenges.

In the last 35 years, the population of sub-Saharan Africa has increased nearly threefold and is expected to reach 681 million by the year 2000, with nearly 50% of the population living in urban centres. Such population pressures, exacerbated by a range of social and political factors, have already resulted in widespread land degradation in areas of high population densities and the expansion of agriculture on to marginal and sloping land. Declining soil fertility and soil erosion are increasingly threatening the sustainability of small scale farming systems throughout Africa, and affordable external nutrient inputs are seldom available to farmers. In addition, shortages of wood for construction and fuel and high-quality dry-season fodder for livestock are widespread and serious constraints to farm productivity.

Agroforestry, the deliberate integration of woody perennials into crop and livestock systems, has the potential to mitigate many of these constraints through both the service and production functions played by trees. In recent decades much agroforestry research has been undertaken in sub-Saharan Africa. In this review we focus specifically on research which addresses the potential of agroforestry systems to enhance soil fertility, prevent soil erosion, provide high-quality dry-season fodder or generate much needed income through the production of high-value goods.

Much emphasis has been placed on a wide range of agroforestry systems for the maintenance of soil fertility and the prevention of soil erosion losses, and encouraging results, both in technical performance and farmer enthusiasm, have occurred. However, it is clear that agroforestry solutions to land degradation are always likely to be location-specific in their relevance, performance and farmer acceptability. It is essential that farmers are included as research partners to determine what is appropriate for their conditions.

Good progress has also been made on identifying fast-growing leguminous trees and shrubs for high-quality livestock fodder supplements. Where livestock enterprises, such as peri-urban milk production, are market-oriented the adoption and impact of such systems have been high. Given population and urbanization projections, it is likely that fodder trees and shrubs will have a major role to play in meeting future feed demands for both milk and meat production. Research on the potential of high-value indigenous and exotic trees to generate income has been less extensive in Africa, although the huge potential of this approach has been clearly demonstrated by farmers in south-east Asia. We suggest that there is a need for increased research emphasis on the domestication of high value indigenous trees, and their integration into more sustainable, diverse and intensive land use systems.

We conclude that, although good progress has been made in agroforestry research in Africa and farmer adoption is occurring, future population projections pose a clear challenge. Agroforestry systems which provide solutions for today's land degradation problems will need to evolve in both diversity and intensity if they are to remain relevant and effective for tomorrow's Africa.

Field experiments were conducted in 2005 and 2006 to investigate the impacts of alternative rice cultivation systems on grain yield, water productivity, N uptake and N use efficiency (ANUE, agronomic N use efficiency; PFP, partial factor productivity of applied N). The trials compared the practices used with the system of rice intensification (SRI) and traditional flooding (TF). The effects of different N application rates (0, 80, 160 and 240 kg ha−1) and of N rates interacting with the cultivation system were also evaluated. Resulting grain yields with SRI ranged from 5.6 to 7.3 t ha−1, and from 4.1 to 6.4 t ha−1 under TF management. On average, grain yields under SRI were 21% higher in 2005 and 22% higher in 2006 than with TF. Compared with TF, SRI plots had higher harvest index across four fertilizer N rates in both years. However, there was no significance difference in above-ground biomass between two cultivation systems in either year. ANUE was increased significantly under SRI at 80 kg N ha−1 compared with TF, while at higher N application rates, ANUE with SRI was significantly lower than TF. Compared with TF, PFP under SRI was higher across all four N rates in both years, although the difference at 240 kg N ha−1 was not significant. As N rate increased, the ANUE and PFP under both SRI and TF significantly decreased. Reduction in irrigation water use with SRI was 40% in 2005 and 47% in 2006, and water use efficiency, both total and from irrigation, were significantly increased compared to TF. With both SRI and TF, the highest N application was associated with decreases in grain yield, N use efficiency and water use efficiency. This is an important finding given current debates whether N application rates in China are above the optimum, especially considering consequences for soil and water resources. Cultivation system, N rates and their interactions all produced significant differences in this study. Results confirmed that optimizing fertilizer N application rates under SRI is important to increase yield, N use efficiency and water use efficiency.

Declining land productivity is a major problem facing smallholder farmers today in Sub-Saharan Africa, and as a result increase in maize grain yield has historically staggered behind yield gains that have been achieved elsewhere in the world. This decline primarily results from reduction in soil fertility caused by continuous cultivation without adequate addition of external nutrient inputs. Improved soil fertility management practices, which combine organic and mineral fertilizer inputs, can enable efficient use of inputs applied, and can increase overall system's productivity. The trials were established at two sites with different soil fertility status to determine the effects of various organic sources (Tithonia diversifolia, Mucuna pruriens, Calliandra calothyrsus and cattle manure) and their combinations with mineral fertilizer on maize grain yield, economic return and soil chemical properties. Drought spells were common during the peak water requirement periods, and during all the seasons most (90%) of the rainfall was received before 50% flowering. In good and poor sites, there was a significant (p < 0.001) effect of season on maize grain yield. Tithonia diversifolia recorded the highest (4.2 t ha−1) average maize grain yield in the poor site, while Calliandra calothyrsus gave the highest (4.8 t ha−1) average maize grain yield in the good site. Maize grain yields were lower in treatments with sole fertilizer compared with treatments that included organic fertilizers. The maize grain yields were higher with sole organics compared with treatments integrating organic and inorganic fertilizers. Soil pH increment was statistically significant in the sole manure treatment in good and poor sites (t-test, p = 0.036 and 0.013), respectively. In the poor site, magnesium increased significantly in the sole manure and manure + 30 kg N ha−1 treatments with t-test p = 0.006 and 0.027, respectively. Soil potassium was significant in the sole manure treatment (t-test, p = 0.03). Generally the economic returns were low, with negative net benefits and benefit cost ratio of less than 1. Inorganic fertilizer recorded the highest net benefit and return to labour (p < 0.001 and <0.01, respectively) in the good site. The treatments that had very high maize grain yields did not lead to improved soil fertility, thus there is need for tradeoffs between yield gains and soil fertility management when selecting agricultural production technologies.

Farmer participatory varietal selection (PVS) was used to identify farmer-acceptable cultivars of rice and chickpea. Farmers' requirements in new crop cultivars (varieties) were determined, a search was carried out for released and non-released cultivars that matched these needs, and they were tested in farmer-managed, participatory trials. Farmer-acceptable cultivars were found amongst released material, but not among the recommended material for the area. Lack of adoption is, therefore, because resource-poor farmers have not been recommended or exposed to the most appropriate cultivars under the existing system of varietal identification and popularization. Adoption rates of cultivars would be improved by increased farmer participation, the systematic testing in zonal trials of locally popular cultivars to define their domains properly, a more liberal release system, and a more open system of providing seeds of new cultivars to farmers.

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.

The results of research on the water relations and irrigation needs of sugar cane are collated and summarized in an attempt to link fundamental studies on crop physiology to irrigation practices. Background information on the centres of production of sugar cane is followed by reviews of (1) crop development, including roots; (2) plant water relations; (3) crop water requirements; (4) water productivity; (5) irrigation systems and (6) irrigation scheduling. The majority of the recent research published in the international literature has been conducted in Australia and southern Africa. Leaf/stem extension is a more sensitive indicator of the onset of water stress than stomatal conductance or photosynthesis. Possible mechanisms by which cultivars differ in their responses to drought have been described. Roots extend in depth at rates of 5–18 mm d−1 reaching maximum depths of > 4 m in ca. 300 d providing there are no physical restrictions. The Penman-Monteith equation and the USWB Class A pan both give good estimates of reference crop evapotranspiration (ETo). The corresponding values for the crop coefficient (Kc) are 0.4 (initial stage), 1.25 (peak season) and 0.75 (drying off phase). On an annual basis, the total water-use (ETc) is in the range 1100–1800 mm, with peak daily rates of 6–15 mm d−1. There is a linear relationship between cane/sucrose yields and actual evapotranspiration (ETc) over the season, with slopes of about 100 (cane) and 13 (sugar) kg (ha mm)−1 (but variable). Water stress during tillering need not result in a loss in yield because of compensatory growth on re-watering. Water can be withheld prior to harvest for periods of time up to the equivalent of twice the depth of available water in the root zone. As alternatives to traditional furrow irrigation, drag-line sprinklers and centre pivots have several advantages, such as allowing the application of small quantities of water at frequent intervals. Drip irrigation should only be contemplated when there are well-organized management systems in place. Methods for scheduling irrigation are summarized and the reasons for their limited uptake considered. In conclusion, the ‘drivers for change’, including the need for improved environmental protection, influencing technology choice if irrigated sugar cane production is to be sustainable are summarized.