Norman Simmonds was an outstanding member of the group of British Tropical Agriculturalists who served overseas with great distinction during and immediately after the Second World War. He was then equally successful and influential in British academia and as an internationally respected researcher. He will be remembered as a plant breeder, a geneticist, a teacher and author, and as incisive commentator on current affairs in tropical agriculture. Simmonds had a long association with Experimental Agriculture, serving on its Editorial Board from 1978 to 1998, and as a Book Review Editor from 1978 to 1987.

A. H. Bunting was born in Johannesburg, South Africa on 7 September 1917 and died peacefully in his sleep at his home in Berkshire, UK on 8 May 2002.

The residual effects of subsoil compaction (below 0.15 m depth) on soil properties, growth, yields and nutrient uptake by irrigated wheat (Triticum aestivum) and cotton (Gossipium hirsutum) are reported. The study was initiated during 1997 on a sandy clay loam soil in a semiarid region of Pakistan. Results showed that the adverse effects of subsoil compaction on bulk density, penetration resistance, total porosity and air-filled porosity of soil persisted for at least four years. In the third and fourth years after the imposition of treatments, compaction decreased yields of wheat by 12–18% and by 7% for cotton. The corresponding reductions in nutrient uptake by wheat were 11–16% for N, 11–15% for P and 5–10% for K. For cotton, the values were 9% for N, 3% for P and 7% for K. Subsoil compaction decreased nutrient use efficiency by 16% in wheat and 5% in cotton. The reductions in water use efficiency were estimated to be 11% in wheat and 7% in cotton. Wheat root length density was also decreased in the subsoil.

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.

Maize (Zea mays)-mucuna (Mucuna pruriens) systems have been promoted to the smallholder farmers of the Los Tuxtlas region of southeastern Veracruz, Mexico. To determine on-farm performance, an agronomic assessment was conducted in 1995–97 replicating farmer conditions in four fields. Treatments were first- and second-season maize with first-season mucuna (system Zm-Mp/Zm), first-season maize with first- and second-season mucuna (system Zm-Mp/Mp), second-season maize following first-season mucuna (system Mp/Zm), and first- and second-season maize, no mucuna control. Data on mucuna biomass amount and quality as well as maize yield, yield components, and nutrient status were collected. Highest mucuna biomass was obtained in system Mp/Zm (leaf-stem-mulch biomass in 1996/97, 7.34 t ha−1, 147 kg ha−1 N), followed by systems Zm-Mp/Mp (5.06 t ha−1, 101 kg N ha−1) and Zm-Mp/Zm (2.75 t ha−1, 50 kg N ha−1). Second-season maize yield was increased over that of the control by 45–58% (0.15–0.23 t ha−1) in system Zm-Mp/Zm and by 118% (0.60 t ha−1) in system Mp/Zm. Mucuna did not increase first-season maize yield. Climatic constraints make second-season maize production risky and yield increases due to mucuna are low in absolute terms, perhaps not offsetting labour costs (systems Zm-Mp/Zm and Mp/Zm) or loss of first-season maize (Mp/Zm).

An experiment conducted from 1988 to 1997 to determine the effects of the timing of application and nutrient supply (particularly of phosphorus) is reported. The sources of applied nutrients that were compared were farmyard manure, pre-rice green-manuring with Sesbania aculeata and fertilizer application in a rice-wheat rotation on a typic ustifluvent. The application of seven tonnes farmyard manure per hectare to both the rice and the wheat crops over eight years increased organic carbon levels from 1.4 to 1.6% but had no yield effect on either crop. Phosphorus application through farmyard manure was not adequate for rice, whilst an application of 34 kg P ha−1 to the rotation gave an economic yield increase only in rice and then only in the first four years of the experiment. From the third year, green manuring was able to replace the effects of the recommended nitrogen, phosphorus and potassium fertilizer applications in increasing rice yield. Green manuring had no effect on the wheat yield but the recommended fertilizer application increased yield. Green manuring increased soil total nitrogen and available potassium levels and reduced base saturation. After adjusting rice yields for variation in transplanting date between years there was no statistical evidence of a yield trend in either crop over the period of the experiment. Farmers' practice of applying seven tonnes farmyard manure per hectare appears adequate to produce stable rice paddy yields of 4–6 t ha−1 a−1.

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 nutrient-balance model was used to investigate the nitrogen contributions of cowpea (Vigna unguiculata) to pearl millet (Pennisetum glaucum) intercropping systems in semi-arid northern Namibia. Data on nitrogen fixation, production, crop nitrogen off-take and competition effects came from two seasons of fieldwork. Supplementary data were taken from secondary sources. The model was used as a tool to attempt to identify grain legume management options with the potential to make significant contributions to soil fertility. The crop parameters pearl millet grain yield, nitrogen fixation rates, nitrogen harvest index and biomass production were found to be critical in determining system nitrogen inputs and outputs as was the form of residue management. The model indicated that it is extremely difficult to manage grain legumes in dryland environments in ways that lead to consistent increases in pearl millet grain yields, measurable against season-to-season variation due to other factors. Several of the options for improved legume management conflict strongly with farmers' risk-avoidance strategies and their tendency to invest preferentially in off-farm activities in an environment where livelihoods have diversified considerably away from agriculture. Potential routes for increasing grain legume contributions to soil fertility in dryland areas are discussed.

Despite interest in mucuna (Mucuna pruriens) as a green manure/cover crop, biomass production of its accessions has been poorly quantified, including in the Los Tuxtlas region of Veracruz, Mexico where smallholders have used maize (Zea mays)-mucuna systems increasingly since 1991. This on-farm research compared the biomass production of three mucuna varieties (white-, mottled-, and black seeded) in a rotational maize-mucuna system. Mucuna was sole-cropped during the first season (on eleven and five fields in 1996 and 1997 respectively), and its impact on the second-season maize yield was measured (on seven fields in 1996). White and mottled varieties produced equal biomass (7.92 and 6.74 t ha−1 in 1996 and 1997 respectively), and more than the black variety (6.85 and 4.90 t ha−1 in 1996 and 1997 respectively). Mucuna increased 1996/97 second-season maize grain yields by 50 % (from 0.97 to 1.46 t ha−1). Plots previously cropped with white and mottled varieties produced greater maize yield (1.55 t ha−1) than did black-variety plots (1.29 t ha−1). The research confirmed the higher productivity of the white and mottled varieties and the potential of the rotational system. Allocating the more desirable first-season growth period to mucuna and the riskier second season to maize is problematic, but the system may have potential in the region as a short-term fallow that permits second-season maize production.

A modified technique for measurement of nitrogen fixation by blue green algae and Azolla sp. using intact, moist soil cores was developed for use in field studies in which chemical fertilizers, blue green algae and Azolla biofertilizers had been used in association with a rice crop. This method involves collection of fresh and moist soil cores (0–30 mm) using a soil auger, incubation with 10% acetylene in airtight glass vials under field conditions for three hours, and measurement of the ethylene produced using a gas chromatograph. Experiments carried out over a period of three consecutive years revealed that the estimates of nitrogen fixation were comparable with data of other researchers obtained through the use of soil water columns, sophisticated chambers and automated sampling devices. This simplified technique, therefore, can provide rapid and reliable measurements of nitrogen fixation in field experiments.

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.

Management deficiencies on the part of the pastoralists were claimed to be one of the major causes of the high losses of camel (Camelus dromedarius) calves contributing to low productivity of camel herds. In the present study, calf deaths, and the causes thereof, were analysed in connection with pastoral calf management in order to assess possible relationships. Progeny history data on 1506 Rendille, 789 Gabra and 1206 Somali calves born between 1980 and 1995 provided quantitative information on losses and the underlying causes. Assessment of the causes of death, and analysis of related management practices, led to suggestions for management changes. In feedback seminars with pastoralists, however, it became apparent that these management changes would not be adopted because they contradicted the pastoralists' assumptions on the causes of calf mortality. The discussions revealed that differences between pastoralists' and scientists' perceptions determined different opinions on proper calf-rearing management practices. Combining different knowledge systems offers the possibility of a more complete understanding, which is required for the derivation of adoptable calf mortality-reducing interventions that are compatible with the knowledge and production systems of the pastoralists.

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.

Pulses of potassium (K+) applied to columns of repacked calcium (Ca2+) saturated soil were leached with distilled water or calcium chloride (CaCl2) solutions of various concentrations at a rate of 12 mm h−1. With increased Ca2+ concentration, the rate of movement of K+ increased, as did the concentration of K+ in the displaced pulse, which was less dispersed. The movement of K+ in calcite-amended soil leached with water was at a similar rate to that of the untreated soil leached with 1 mM CaCl2, and in soil containing gypsum, movement was similar to that leached with 15 mM CaCl2. The Ca2+ concentrations in the leachates were about 0.4 and 15 mM respectively, the expected values for the dissolution of the two amendments. Soil containing native K+ was leached with distilled water or CaCl2 solutions. The amount of K+ leached increased as Ca2+ concentration increased, with up to 34 % of the exchangeable K+ being removed in five pore volumes of 15 mM CaCl2. Soil amended with calcite and leached with water lost K+ at a rate between that for leaching the unamended soil with 1 mM CaCl2 and that with water. Soil containing gypsum and leached with water lost K+ at a similar rate to unamended soil leached with 15 mM CaCl2. The presence of Ca2+ in irrigation water and of soil minerals able to release Ca2+ are of importance in determining the amounts of K+ leached from soils.The LEACHM model predicted approximately the displacement of K+, and was more accurate with higher concentrations of displacing solution. The shortcomings of this model are its inability to account for rate-controlled processes and the assumption that K+: Ca2+ exchange during leaching can be described using a constant adsorption coefficient. As a result, the pulse is predicted to appear a little earlier and the following edge has less of a tail than that measured. In practical agriculture, the model will be more useful in soils containing gypsum or leached with saline water than in either calcareous or non-calcareous soils leached with rainwater.

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.

Spatial variability in field trials is a reality. A proportion of this is accounted for as inter-block variability by using block (complete or incomplete) designs. A large amount of spatial variability still remains unaccounted for, however, and this may lead to erroneous conclusions. To capture this inexplicable variation (which is mainly due to intra-block variation), yield data from a series of variety yield trials, using cereals and legumes, were analysed using various spatial models. The most suitable of these, selected on the basis of the Akaike Information Criterion, were used to assess the relative performance of genotypes. Although incomplete-block designs have been found to be effective in variety trials, spatial models have added considerable value to trials with legumes and cereals. The ‘best’ spatial models gave efficiency values of over 330% in winter-sown chickpea (Cicer arietinum), 140% in lentil (Lens esculenta), and 150% in barley (Hordeum spp.) trials. Furthermore, the use of these best models resulted in a change in the ranking of genotypes (on the basis of mean yield), which resulted, therefore, in a different set of genotypes being selected for high yield. It is recommended that: (i) incomplete block designs be used in variety trials; (ii) the Akaike Information Criterion be used to select the best spatial model; and (iii) genotypes be selected after the use of this model. The selected model would account most effectively for spatial variability in the field trials, improve selection of the most desirable genotypes and, therefore, improve the efficiency of breeding programmes.

The effect of Ethrel on the yield and sugar content of coconut (Cocos nucifera) inflorescence sap and sustainability of productivity was investigated on forty-year-old tall coconut palms (var. typica) at Bandirippuwa Estate, Lunuwila, Sri Lanka. Ethrel was applied at a concentration of 2.5% and the volume and sugar content of the sap were measured. Application of Ethrel consistently increased the yield per day, yield per spadix, yield per palm per annum and sugar content in the sap for a period of four years. The removal of carbon, nitrogen, phosphorus, potassium and magnesium with the sap was greater from Ethrel-treated than from untreated palms, and this was attributed mainly to the enhanced sap yields and sugar concentrations.

Most of the agricultural lands in the highlands of western Kenya are depleted of plant nutrients, particularly phosphorus. This depletion has resulted in a continued decline in crop production in the area. Recent experiments, in which direct application of indigenous phosphate rocks were evaluated, have yielded variable results, depending on the relative reactivity of the rock phosphate tested. The effectiveness of rock phosphate was generally low compared with fertilizers such as triple super phosphate. This is attributed to the relatively low solubility of the rocks as opposed to the readily water soluble phosphorus fertilizers. Phosphate rocks are available locally and are cheaper than triple super phosphate. If the solubility of these phosphate rocks could be improved, the resource-poor smallholder farmers in western Kenya would have an affordable source of phosphorus for their crops. Greenhouse and field experiments were conducted to evaluate the effects of combining different on-farm organic materials with the Minjingu rock phosphate (from Tanzania) on the availability of phosphorus to maize (Zea mays) in western Kenya. The greenhouse results indicated that there were significant positive linear relationships between rock phosphate application rates and (i) the Olsen-extractable soil phosphorus in the soil samples taken four weeks and nine weeks respectively after the application of the treatments; (ii) the dry matter yield, and (iii) phosphorus uptake. Results of the field experiments showed that rock phosphate combined with farmyard manure or crop residues (maize stover) generally increased the Olsen-extractable soil phosphorus, maize yields and phosphorus uptake, particularly in the first season when both the Minjingu rock phosphate and organic materials were applied, but the effectiveness of the materials and their combinations varied between the two sites. Combining Minjingu rock phosphate with the organic materials improved its relative agronomic effectiveness for maize.

In Mozambique, the sweet potato (Ipomoea batatas) is grown in the dry season in areas with a high water table, or as an irrigated crop. It is also grown in the rainy season when short-term droughts can occur. This paper reports the results of experiments designed to evaluate the effects of water availability and vine-harvesting practices on actual crop water use (cv. TIS 2534), during two contrasting seasons in the south of the country. Rain-fed crops extracted water to soil depths (variable sandy loam) of 0.75 m, with most (90%) taken from the top 0.25 m. Well-irrigated crops apparently obtained some (10%) water from below 0.75 m, but most (75%) came from the upper 0.25 m. Total water use from well-watered crops was about 800 mm during the rains, and 550 mm during the dry season. The corresponding values for rain-fed crops were 360 and 180 mm respectively. Peak rates of water use averaged 8 mm d−1 in the rainy season, and 5–6 mm d−1 in the dry season. Water use was not modified by the frequency of vine harvests. Actual rates of evapotranspiration fell below maximum values when the soil water deficit exceeded only 20 mm. By comparison, the maximum depth of extractable water in the root zone was 80–90 mm. The crop coefficients (Kc) for each stage of growth were consistent over both seasons and estimated to be: 0.55–0.7 (crop establishment), 1.1–1.2 (mid-season), and 0.8 (end-season).

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.