Drawing on ideas advanced during the course of an international workshop, this paper reviews agricultural research priorities in the dry areas of the developing world, where economic and demographic pressures are driving a rapid intensification of production, even on very fragile lands. Current priorities for research and research funding reflect a strongly felt need, among governments and donor agencies, for rapid problem-solving to relieve poverty. In this context, traditional long-term agronomic research trials, with essentially strategic and basic objectives, are often seen as irrelevant. Yet the need to anticipate problems impending in environments where intensification is consuming the natural resource base and degrading the production potential is an urgent one. To accommodate this need to the perceptions of the different stakeholders, a new research paradigm, ‘Anticipatory Long-Term Research for Sustainable Productivity’, is proposed. It invokes a holistic approach, building a longer view and greater dynamism into traditional agronomy, enhancing ties to socio-economic and resource management disciplines, and reconciling the immediate demand for high-yielding technology with the strategic issues of sustainable production.

The aims and design features of historic long-term experiments are discussed and modern perceptions are presented of long-term studies to address sustainability and research impact in farming communities. A research strategy is proposed combining on-station and on-farm research whose results influence dynamically the directions of the component studies. Guidelines are given for choosing well-controlled designs, appropriate data and sampling procedures and for maintaining quality control in data collection and indicator formation over anticipated lengthy periods of time.

Trends over time in annual crop yields potentially provide measures of the likely long-term sustainability of cropping systems. However, where large annual variability in the growth environment is responsible for most of the large year-to-year yield differences, appropriate analytical techniques must be developed to distinguish real long-term trends from the ‘background noise’. This paper presents models for the estimation of time trends in the yield data from crop rotation systems and discusses the results of applying these models to yield values from two types of long-term trial involving barley, each conducted at two sites in northern Syria.

The models used were linear with respect to time (years) and allowed for seasonal effects by means of a quadratic relationship on total rainfall and a linear relationship on planting date. A more complex model might account for more of the variance, but restrictions were imposed by the limited number of degrees of freedom (number of years of data less one) and the choice of meaningful single-valued parameters of growth-season conditions. For many experimental treatments the model accounted for less of the total variance at the wetter site. This may be due to seasonal bufferring by soil moisture stored at depth from one year to the next, and future iterations of the analysis will try to allow for this. The appropriateness of the linear time function is also questioned, and alternative functions will be tested along with alternative structures for plot errors over time.

A participatory on-farm research project was started at Tah village, 100 km south of Aleppo, Syria in 1984. The objective was to introduce annual medics (Medicago spp.) as a replacement for fallow in dryland wheat (Triticum durum)/fallow farming systems. About 50 farmers were directly involved in the project while an equal number were passive participants, receiving seed but no technical advice. The project did not attain its original intention of introducing a ley-farming system into Syria. The Syrian Government decided to eliminate fallow – which was to receive medics – in the agricultural planning for 1989–90. An array of profitable crops such as lentil (Lens culinaris), cumin (Cuminum cyminum), sesame (Sesamum indicum) and watermelon (Citrullus lanatus), together with price supports on wheat presented formidable economic competition to the use of pasture on cultivated land. Technical constraints include insufficient farm size, lack of a medic phase in every year, deep ploughing, overgrazing and uncontrolled grazing. The Tah project experience also suggests that feed production projects must include an assessment of how the feed benefits animals and be designed to demonstrate the economic advantages of integrating livestock and crops in dryland farming systems.

Over a period of seven years farmers participated in trials in which common vetch (Vicia sativa (V)) or chickling (Lathyrus sativus (C)) replaced the fallow in a barley (Hordeum vulgare)–fallow rotation (F) or were introduced into continuous barley cropping (B) – giving a total of four rotations, B–F, B–B, B–V and B–C. Trials on 4 ha, 2 ha per phase of each rotation, were replicated on 6–8 farms. Some vetch and chickling crops were grazed in spring. Mean seven-year dry matter yields were 2.91 t ha−1 for B–F, 4.82 t for B–B, 5.02 t for B–C and 5.32 t for B–V; total crude protein outputs were twice as high from rotations including legumes; and the B–V rotation yielded most metabolizable energy. Realizing the benefit, farmers started to adopt vetch. In 1991 three farmers were growing vetch on 7 ha but by 1997 174 farmers in 15 villages were growing vetch on 420 ha. Forage legumes will not, however, become more widely grown until inexpensive and efficient mechanized methods of harvesting the mature crop are available in order to avoid the high cost of hand labour. Drought and cold tolerance, early maturation and high harvest index may also enhance farmers' interest in forage legumes.

In southern and central India, farmers crop Vertisols only in the post-rainy season, to avoid land management problems in the rainy season. In 1983 ICRISAT established a long-term trial seeking to intensify cropping. The trial included intercrops, sequential crops and appropriate Vertisol management technology to allow consecutive rainy-season and post-rainy season crops to be grown. Benefits provided by legumes to succeeding rainy-season sorghum (Sorghum bicolor) were analysed in relation to a non-legume system of sorghum + safflower (Carthamus tinctorius). Rainy-season sorghum grain yield production was sustained at about 2.7 t ha−1 over 12 years within a continuous sorghum–pigeonpea (Cajanus cajan) intercrop system. With a cowpea–pigeonpea intercrop system, succeeding sorghum benefitted each year by about 40 kg N ha−1 (fertilizer nitrogen (N) equivalent). Without N fertilizer application the sorghum grain yield was around 3.3 t ha−1. Legume benefits were less marked in the chickpea (Cicer arietinum)-based rotation than in the pigeonpea system, in which a 12-year build up of soil total N (about 125 μg g−1) was observed. Although sorghum benefitted from this system, pigeonpea yields declined over time due to soil-borne fungi and nematodes. Wider rotations of crops with pigeonpea may help to overcome these problems, while sustaining sorghum production.

The effect of tillage and crop rotations can only be seen over many crop years. Crop yield and soil results are evaluated from two long-term trials, established in 1978–79 and 1985–86 to investigate various forms of tillage and the timing of such operations in various wheat (Triticum aestivum)-based rotations on a Calcixerollic Xerochrept in northern Syria. In a tillage systems trial involving two wheat–legume–watermelon (Citrullus lanatus) rotations, deep tillage showed no advantage over a shallow sweep-tillage system, either for soil moisture storage or yield increase of any crop. The zero-till system suited legume crops but gave lower productivity in wheat due to a build up of grassy weeds, and was not suitable for watermelon. Minimum tillage, with its higher energy-use efficiency and yield levels equal to or even slightly above those of deep-tillage systems, appears promising for the lowland areas of West Asia and North Africa. In a tillage timing trial, wheat in a wheat–lentil (Lens culinaris) rotation yielded best after conventional deep disc-plough tillage, but lentil yields were higher in a zero-till system.

The millet (Pennisetum glaucum)-based cropping systems that dominate the Sudano–Sahelian Zone of West Africa cannot, as they are currently practised, meet the growing food needs of the region. They must therefore be intensified in a sustainable manner. The present study was initiated in 1986 and continued until 1996 to evaluate the effects of phosphorus (P) fertilization, tillage and rotation with sole cowpea (Vigna unguiculata) on an operational scale with two cropping systems, namely, sole millet and millet–cowpea intercropping. A randomized complete block design with four replications was used. The effects of P fertilization, ridging with animal traction and planting on ridges (AT), and rotation with sole cowpea increased the productivity of millet substantially in 10 of the 11 years. Based on the 11-year average, P fertilization alone improved grain yield by 52%, and AT with P fertilization improved grain yield by nearly 135%. Combining AT, P fertilization and the sole cowpea rotation resulted in a 200% increase in grain yield compared with the traditional system of production. Millet productivity did not show a significant decline when intercropped with cowpea. Stability and relative stability analysis showed that the traditional system was more stable than the various agronomic packages, but had the least yield. Conversely, the agronomic package with the highest yield advantage over the traditional system was the least stable. A major portion of the annual variation in the environmental index for grain yield and total dry matter was attributed to the seasonal variation in rainfall and organic matter depletion. Organic matter levels declined linearly with years of cultivation. Significant differences were found in the rate of depletion between the various agronomic treatments tested. After 11 years, nearly 60% of the organic matter was depleted irrespective of the agronomic treatments.

Sustainability of intensive irrigated agriculture in Egypt has become a critical issue, as land and water resources are limited on the one hand and population is increasing rapidly on the other. Salinization, heavy input use, nutrient export and pollution all threaten the health of soils that have been feeding Egypt for centuries. At the same time, the build-up of newly reclaimed desert soils to economically sustainable productive capacity is a major challenge. In a collaborative effort between the Agricultural Research Center (ARC) of the Ministry of Agriculture and Land Reclamation in Egypt and the International Center for Agricultural Research in the Dry Areas (ICARDA), a long-term resource management programme, funded by the European Union, has been developed to address the issue of resource management in a multidisciplinary way. Long-term agronomic trials (with such variables as water quantity, water quality, nutrient inputs and crop rotations) have been set up at sites representing the old lands, the newly reclaimed areas and the rainfed areas. These trials are complemented by extensive long-term monitoring in villages close to the experimental sites. This covers farmers' perspectives, farming practices and the condition of farmers' soils and crops and is aimed at identifying over time the sustainable and non-sustainable production practices and the social and economic factors that underline them. The project activities began with a Preparatory Phase which comprised inventory studies, rapid rural appraisal and multi-disciplinary surveys. This knowledge was used in the planning of the two closely related activities of long-term trials (LTT) and long-term monitoring (LTM). As the programme was implemented, the complementarity of the LTT and LTM approaches became the most important feature of this programme.

Green revolution technologies of the 1960s and 1970s have led to the emergence of rice (Oryza sativa)–wheat (Triticum aestivum) (R–W) as a major cropping system in the Indo-Gangetic Plains (IGP). Expansion of irrigation through a network of canals and privately owned tube wells was one of the key factors in the success of the new technologies. Since canal water supplies are not demand-driven, farmers increasingly relied on the use of ground water by installing shallow tube wells. The strategy of ground water development and its use in conjunction with canal supplies paid rich dividends in control of waterlogging and secondary alkalization and in increasing the pace of alkali soils reclamation programmes in areas underlaid with fresh quality aquifers. Rice–wheat systems were the preferred choice of farmers. Adoption of the R–W system, however, changed the salt and water balance in north-western parts of the IGP. In the north-east of Punjab and Haryana states it led to receding water tables and waterlogging, and in south-west parts to associated problems of secondary salination. In eastern parts of the IGP in West Bengal, development of ground water aquifers to meet irrigation water requirements for the intensification and diversification of agriculture has led to serious problems of ground water contamination due to dissolution of arsenic-bearing minerals under altered soil moisture regimes, conducive to oxidation of pyritic sediments. These experiences suggest that there is an urgent need for a change in the way food is produced in the IGP for sustainability of the natural resource base. This will depend on the ability to predict long-term consequences of intensification and diversification of agriculture on the farm and regional scale. Whereas issues of favourable regional salt and water balances need attention in the north-west of the IGP, rain-water management and alleviating drainage congestion can facilitate the adoption of agricultural technologies and improve productivity of the R–W systems.