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.

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).

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.

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.

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).

In a field experiment initiated in the 1972/73 rabi season (November–March) on an acidic soil in the western Himalayas of India, continuous cropping for 25 years with nitrogen fertilizer alone reduced the grain yields of maize (Zea mays) and wheat (Triticum aestivum) to almost zero. Based on five-year moving average values, the application of 100% NP resulted in a reduction of grain yields of maize and wheat crops by 67 and 19% respectively during 1994 to1998 compared with 1973 to 1977. The crops did not respond to K application during the initial years of cropping, but a significant reduction in crop yields was observed in the absence of K after five years of continuous cropping. With the integrated use of chemical fertilizers (100% NPK) and farmyard manure, the pooled grain yields of 25 years were about 4600 and 3300 kg ha−1 for maize and wheat respectively. Corresponding yields with the use of chemical fertilizers and lime (100% NPK + lime) were 4000 and 3100 kg ha−1 respectively. The use of nitrogenous fertilizer alone aggravated the problem of soil acidity by lowering the pH from 5.8 to 4.7 after 25 years. In almost all the treatments, the organic carbon content increased: a marginal decrease occurred in the 100% N and control plots. Even under optimum application rates, the available N and K status decreased with time. Again with the exception of the control plots, the contents of the Diphenyl Triamine Penta Acetic Acid-extractable micronutrients were sufficiently high for the crops in all the treatments. The available sulphur decreased with the use of di-ammonium phosphate as the P source, which drastically reduced the yields of both crops. In the N-alone treatment the weed flora also changed with the change in soil environment. There is a need to review fertilizer recommendations in this region of India.

The first ever on-farm soil fertility research in the rainfed lowland rice (Oryza sativa) fields of Sukumaland, in northwest Tanzania, was carried out between 1990 and 1996 in response to farmers' complaints about declining rice yields. From diagnosis to extension, the research approach followed that of the International Maize and Wheat Improvement Center (CIMMYT). In 1990/91, rice yields in the Maswa district increased sharply when nitrogen at a rate of 30 kg ha−1 in the form of urea was broadcast in flooded rice fields at tillering. Similar research was subsequently conducted in other parts of Sukumaland to evaluate this type of low-dose nitrogen application under varying circumstances. In 1995/96, higher doses of nitrogen (60 and 120 kg ha−1) and a high dose of phosphorus (17.5 kg ha−1) were applied for comparison in Sengerema district. Between 1990 and 1996, the average increase in rice yield from the application of 30 kg N ha−1 varied between 463 and 986 kg ha−1. In 1995/96, the same application of N was more economical than both 60 and 120 kg N ha−1, and no phosphorus deficiency was found. The deteriorating ratio between the price of rice at the farm gate and that of urea, however, threatens the adoption of this technology by farmers. Adaptability analysis showed that the relatively small differences in response per field (environment) in all years did not justify a need for multiple different extension messages. Until more detailed recommendations can be made, therefore, a single dose of 30 kg N ha−1, in the form of urea, applied to rice at tillering is recommended for the whole of Sukumaland to reverse the decline in yields. Further on-farm research should concentrate on improving the efficiency of nitrogen fertilization and on determining the optimum rates of other major nutrients to refine this initial recommendation.

This paper presents the results of:

(a) On-farm trials (eight) over a two-year period designed to test the effectiveness of leguminous cover crops in terms of increasing maize yields in Igalaland, Nigeria.

(b) A survey designed to monitor the extent of, and reasons behind, adoption of the leguminous cover crop technology in subsequent years by farmers involved, to varying degrees, in the trial programme.

Particular emphasis was placed on comparing adoption of leguminous cover crops with that of new crop varieties released by a non-governmental organization in the same area since the mid 1980s. While the leguminous cover crop technology boosted maize grain yields by 127 to 136% above an untreated control yield of between 141 and 171 kg ha−1, the adoption rate (number of farmers adopting) was only 18%. By way of contrast, new crop varieties had a highly variable benefit in terms of yield advantage over local varieties, with the best average increase of around 20%. Adoption rates for new crop varieties, assessed as both the number of farmers growing the varieties and the number of plots planted to the varieties, were 40% on average. The paper discusses some key factors influencing adoption of the leguminous cover crop technology, including seed availability. Implications of these results for a local non-governmental organization, the Diocesan Development Services, concerned with promoting the leguminous cover crop technology are also discussed.

On-farm trials were conducted in the northern Guinea savanna of Nigeria. The objective was to compare integrated Striga hermonthica control measures (soyabean or cowpea trap crop in the first year followed by maize resistant to Striga in the second year) with farmers' traditional practices (cereal-based cropping systems) under farmer-managed conditions.

Integrated control proved to be highly effective in terms of reducing Striga incidence both in terms of reduced seed density in the soil and decreased infection in maize. Resistant maize following the soyabean trap crop yielded 1.58 t ha−1 of grain and out-yielded local maize following traditional practices by more than 80%. Similarly, the overall productivity over the period of the experiment was highest with the integrated control treatment using soyabean. Conversely, resistant maize after the cowpea trap crop yielded only 0.92 t ha−1 (possibly due to the poor performance of the cowpea crop in the first year), and maize yields were similar to those obtained with farmer practices. Initial Striga seed density in the soil was negatively correlated (r = −0.33) with soil nitrogen, but nitrogen-fertilizer application rates did not seem to affect the level of Striga infection in maize.

Readers may be interested to know about the above publication received but not reviewed because of its limited relevance to the majority of readers of Experimental Agriculture.

Readers may be interested to know about the above publication received but not reviewed because of its limited relevance to the majority of readers of Experimental Agriculture.