In South and Central America, tens of thousands of hectares of oil palms (Elaeis guineensis Jacq.) are affected by bud-rot types of disease. Having destroyed entire estates in Panama, Colombia, Suriname, Brazil and Ecuador, they are holding back the development of oil palm cultivation in Latin America. The cause is unknown. Indeed, 30 years after these diseases first wreaked havoc on a large scale, it is still not known whether we are dealing with one or more diseases of infectious origin, or with a physiological disorder. Despite lengthy research launched in the early 1980s, no pathogens or insect vectors have been clearly identified. At present, genetics look likely to offer a solution in the medium- to long term, using traits of resistance transmitted by the native species on the American continent, Elaeis oleifera, to the interspecific hybrid E. oleifera×E. guineensis.

The effects of root inoculation with mycorrhizal fungi (Glomus mosseae) on the water relations and carbon dioxide assimilation rates of grapevine (Vitis vinifera cv. Cabernet Sauvignon) plants are reported. Cuttings of Cabernet Sauvignon were grafted onto eight different grapevine rootstocks and the composite plants were grown in pots. The potting media of half the pots of each rootstock were inoculated with Glomus mosseae. Half of each of the inoculated and the non-inoculated pots were subjected to five-day and eight-day drought periods. The control (non-stressed plants) was watered throughout the experiment three times per week to maintain pot media close to field capacity. Foliar growth, leaf phosphorus concentrations and drought tolerance were greater in the inoculated than in the non-inoculated plants. After five days of drought stress, predawn leaf water potentials ranged between −0.5 and −1.07 MPa in non-mycorrhizal vines and between −0.32 MPa and −0.61 MPa in mycorrhizal vines. Similarly, net carbon dioxide assimilation rates in five-day stressed plants ranged from 1.5 to 4.6 μmol m−2 s−1, and from 2.9 to 6.1 μmol m−2 s−1 respectively. Some drought-sensitive rootstocks (775P, 101–14Mgt and 5BB) infected with mycorrhizal fungi and subjected to drought for eight days showed much-improved drought resistance compared with non-infected rootstocks of the same varieties. In drought-stressed plants, differences between the various rootstocks were significant. For example, rootstocks 110R, 140Rug, 1103P and 44–53 M had the highest predawn leaf water potentials and photosynthetic rates after five days of drought, independent of the mycorrhizal infection. These findings show that colonization of the root system by mycorrhizal fungi, may improve the water status of non-irrigated vines.

A combination of agro-ecological and socioeconomic factors gave rise to the current weed epidemic of Phalaris minor, threatening the sustainability of wheat (Triticum aestivum) production and rural livelihoods across a large area of the Indo-Gangetic plains in northern India. This paper presents the results of a system audit describing the current status of the P. minor epidemic in Haryana State, India, in a broad agronomic and socioeconomic context. The audit showed that the P. minor epidemic is a major production constraint for many farmers, and seriously affects farm profitability. It suggests that the epidemic is closely entangled with geographic factors, as well as farm management systems and farmers' socioeconomic positions. Since the farmer community is not a homogeneous group with respect to P. minor management, nor in ability to change farm management practices, farmers are not equally receptive to technical innovations aimed at improving sustainability of wheat production.

In southern Bénin, the legume cover crop Mucuna pruriens var. utilis has been widely promoted for soil fertility improvement. Recent findings have shown, however, that the majority of farmers have not adopted it, and that alternative technologies are needed that are both attractive to farmers and beneficial in terms of soil fertility. A survey was carried out in southern Bénin to determine farmer perception and use of traditional grain legumes and to assess the adoption potential of new low-harvest-index grain legumes. Grain legumes were shown to be integral components of traditional cropping systems and constituted farmers' most important technology for soil fertility maintenance. More than 80% of respondents expressed interest in testing new, low-harvest-index varieties. Preferred grain characteristics and farmers' culinary preferences for grain legumes varied between locations and need to be taken into account if new germplasm is to be introduced. It is argued that farmers' interest and experience in legume cultivation provide an opportunity for the introduction of alternative legume-based technologies such as low-harvest-index grain legumes and techniques for the detoxification of mucuna seed. In addition, efforts should be made to increase the productivity of current legume production systems and to develop mucuna cultivars with reduced L-dopa content.

Farmers in the southern Kilimanjaro region of Tanzania have a strong preference for maize as their staple crop and have resisted attempts to introduce sorghum as an alternative in spite of the high drought risk associated with maize production. This paper presents the results of a seven-year period of field experiments to assess the benefits of a modified cropping system for maize, which aims to reduce drought risk through rainwater harvesting. In-situ, microcatchment and macrocatchment rainwater harvesting systems were tested against the local practice of flat cultivation as control. All were managed according to local extension recommendations, and the benefits were measured in terms of grain yield. In-situ rainwater harvesting provided no benefit. Microcatchment rainwater harvesting resulted in increased yield per unit area cultivated. On a total system area basis (i.e. including the uncropped catchment), however, production decreases were observed. A cost-benefit analysis, however, does show a benefit in the short rainy season. Macrocatchment rainwater harvesting provided increases in grain yield in both the short and the long rainy seasons.

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.

Phosphorus (P) deficiency is a major constraint to pearl millet (Pennisetum glaucum L.) growth on acid sandy soils of the West African Sahel. To develop cost-effective fertilization strategies for cash poor farmers, experiments with pearl millet were conducted in southwestern Niger. Treatments comprised single superphosphate hill-placed at rates of 1, 3, 5 or 7 kg P ha−1 factorially combined with broadcast P at a rate of 13 kg ha−1. Nitrogen was applied as calcium ammonium nitrate at rates of 30 and 45 kg ha−1. At low soil moisture, placement of single superphosphate in immediate proximity to the seed reduced seedling emergence. Despite these negative effects on germination, P placement resulted in much faster growth of millet seedlings than did broadcast P. With P application, potassium nutrition of millet was improved and seedling nitrogen uptake increased two- to three-fold, indicating that nitrogen was not limiting early millet growth. Averaged over the 1995 and 1996 cropping seasons, placed applications of 3, 5 and 7 kg P ha−1 led to 72%, 81% and 88% respectively, of the grain yield produced by broadcasting 13 kg P ha−1. Nitrogen application did not show major effects on grain yield unless P requirements were met. A simple economic analysis revealed that the profitability of P application, defined as additional income per unit of fertilizer, was highest for P placement at 3 and 5 kg ha−1.

Striga gesnerioides is a serious parasite of cowpea (Vigna unguiculata) on the Abomey plateau of southern Bénin. S. gesnerioides in southern Bénin has been characterized as a race that is different from those found in the dry savanna of West Africa. IITA breeding line IT93KZ-4-5-6-1-5 was used in a trial to study fertilizer response of cowpea on two farmers' fields in 1998. No emerged S. gesnerioides plants were observed on this breeding line while heavy parasite loads were observed on local cultivars growing in adjacent fields. In 1999, IT93KZ-4-5-6-1-5 was grown again on seven fields and no emerged S. gesnerioides plants were observed. In 2000 the same line was grown on 18 farmers' fields with local cowpea cultivars in adjacent control plots. The mean number of S. gesnerioides plants on the local cultivars was 0.92 per cowpea plant (s.d. 0.72) while the improved line carried none. The mean yield gain from the improved cowpea line was 156% and varied from 20 to 680 kg pods ha−1. Thus it appears that progress has been made in developing cowpea lines that are resistant to S. gesnerioides and the potential impact of adoption of resistant cowpea is high.