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.

Genotype × environment interaction plays an important role in the identification of genotypes with high and stable yields. The environmental components of such interaction can be attributed to location (spatial) and year (temporal) factors. This study considers a specific aspect of the location factor, i.e. that locations not geographically close to each other are likely to vary in terms of the conditions that determine the effect of the year factor, even during the same calendar year. In these situations, the year effects are considered to be random variables within each location. This study addresses the question of whether genotype × location interactions are consistent (or repeatable) over time: a question which is crucial when defining the target environments in a plant breeding programme and when deciding the optimum environment for selection. Using three sets of data from field experiments, various computation methods were developed to estimate variance components; the methods and estimates are presented here. Using the bootstrapping procedure to sample one year from each location within a given calendar year, we obtained bootstrap replicated values of genotype × location interaction and their summary statistics, including the coefficient of variation (CV). We suggest that the CV can be used to measure the repeatability of genotype × location interactions. A Genstat program that can be used to perform the required computations is available from the authors upon request.

Reducing soil evaporation by different agricultural practices is important not only for water saving but also for its applicability by farmers. In wheat fields, the goal of efficient water management is to save water and increase yield. At present, the combined effects of maize-straw mulching (M) and crop density (D) on soil evaporation and temperature, wheat performance, and water use efficiency (WUE) are not clear. A field experiment was conducted for winter wheat (Triticum aestivum L.) in the North China Plain (NCP). The two levels of crop density included high (HD) and normal density (ND), and the three levels of mulch included high (HM), low (LM), and no mulch (NM). The results indicated that both straw mulching and high crop density had significant inhibitory effects on soil evaporation. Normal crop density with high mulch gave the lowest yield among all treatments because high mulching reduced the soil temperature and hindered the soil temperature increase in early spring. Compared with normal crop density with no mulch, the yield and WUE of winter wheat for high crop density with low mulch (HDLM) were enhanced by 20.6% and 21.9%, respectively. Compared with other treatments, HDLM gave the higher WUE due to the higher soil temperature, leaf area index, and biomass. Therefore, HDLM was an effective way to maximize the WUE of winter wheat in the NCP.

Pot experiments were used to test the effect of incorporating various organic materials in the soil on the nodulation of peas (Pisum sativum). Only farmyard manure gave a consistent increase in the number and weight of nodules, and also in plant growth, increases which were also produced by the aqueous extract of farmyard manure, although none of these increases were as large as those obtained by the addition of a combination of P and K fertilizers or activated vermiculite. Field beans (Vicia faba) and French beans (Phaseolus vulgaris) in general reacted in the same way as peas.

The introduction of appropriate crop rotations is known to be beneficial in many farming systems. One feature of rotations is that it takes a valuable length of time for the advantage of the rotation to take effect. In long-term rotation trials, the observations from the same plot over years are correlated; ignoring such correlations may affect the precision of the estimates of rotation effects. We examined five covariance structures between the plot errors over time to assess the effect of correlations on the standard errors of rotation means and rotation x cycle combination (interaction) means on wheat yields using eight years of data from six two-phase rotations with wheat. Based on wheat yield data from the four cycles of the rotations considered, the compound symmetry covariance structure (constant correlation) between plot errors arising over alternate years gave more efficient estimates of rotation means compared with the other four covariance structures.

Information on the influence of date of planting on protein, oil and fatty acid composition of soybean seeds is meagre, whilst similar studies on lipoxygenase isozymes and trypsin inhibitor contents are lacking. A field experiment was conducted with nine Indian genotypes and three planting dates (spread over 23 days) to study the influence of planting dates on these seed traits. Results based upon a one-year study indicated that oil content declined with delays in planting. Oleic acid content increased from the first to third planting, while the reverse trend was observed for linolenic acid. Lipoxygenase-1 activity was reduced by delayed plantings. Protein content was the lowest and trypsin inhibitor content was the highest for the second planting. However, no differences were observed for protein and trypsin inhibitor contents between the first and third planting. Significant interactions. observed between genotype and planting date for most of the seed compositional characters suggest that the influence of late planting is genotype-dependent.

Insects cause serious problems during the storage of cassava chips, when quality may be reduced and significant quantities of the product consumed. The major species naturally infesting chips were Rhizopertha dominica, Lasioderma serricorne and Araecerus fasciculatus. Infestation occurs during the sun-drying process, and up to 16% reduction in chip weight due to insect feeding was recorded after 2 months storage. Chips that had not received any pre-drying storage, but contained salt as a preservative, were infested by fewer insects than chips without salt. The poorest quality chips had significantly more insects than better quality ones.

This paper describes the design of six data-recording forms which have been found to be acceptable by both field workers and data-processing staff. The reasons for the choice of design and hints on how to present the data are also given.

The results are presented of a trial with coconuts, testing progeny of 104 unselected seed parents. The progenies of the best 5 per cent of the parents, selected on their phenotypic values, gave yields 14 per cent above the progeny population mean, indicating that mass selection is effective. There was considerable variation in breeding values between the palms tested, and a higher frequency of desirable genotypes could be isolated when the parents were selected on yield of copra rather than when they were taken at random. Prepotency in coconut palms is discussed. Leaf production of the young palms within a family, during the first 40 months of their growth, was correlated with the breeding value of the parent.

Grain barley was grown either continually or in rotation with fallow in a 12-year experiment. Annual rainfall ranged from 120 to 297 mm. As the water requirement of the crop is 240 mm, growth in most seasons occurred under water stress. The amount of water conserved under fallow was only significant (75–100 mm) in three of the 12 years and only once did the water conserved increase barley yield in the following year. The total grain yield over the experimental period was twice as high in the barley–barley sequence as in the barley–fallow sequence.

Cultiuo continuo de cebada o después de barbecho

The feasibility of commencing tapping (‘opening’) of rubber trees for latex extraction at a lower stem girth (40 and 45 cm) than the currently recommended 50 cm was investigated in three different genotypes. The possibility of combining early opening with low frequency tapping and yield stimulation using Ethrel (LFT + E) was also examined. One of the genotypes tested, RRIC 121, gave a higher dry rubber yield, both per tapping and cumulatively over a given period, when opened at 40 cm than at 50 cm. Of the other two genotypes, one (RRISL 211) showed a clear reduction in yield with early opening, while the other (RRIC 102) did not show a significant yield response. Among the three genotypes tested, RRIC 121 showed the minimum depression in trunk girth increment. Analysis of yield components showed that the response of a given genotype to early opening and LFT + E is determined by the interaction between latex volume per tapping and dry rubber content (DRC), which were negatively correlated. RRIC 121 had a significantly greater DRC, which enabled it to maintain a higher dry rubber yield under early opening and LFT + E despite producing a lower latex volume than both the other genotypes. In contrast, despite producing a substantially greater latex volume than the other two genotypes, RRISL 211 did not produce a higher dry rubber yield because of its lower DRC. The higher DRC was also responsible for the greater response of RRIC 121 to yield stimulation with Ethrel, which reduced the plugging index and increased the initial latex flow rate. Early commencement of tapping in combination with LFT + E is therefore possible in rubber when amenable genotypes are selected, offering the potential of improving the economics of rubber production, especially for smallholders, in West Asia.

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.

Highly weathered soils from humid tropics naturally have low contents of available potassium (K) to plants. Under these conditions, the K deprivation can change the equilibrium among cations in the soil and the nutritional status of some crops as soybean (Glycine max (L.) Merrill). A field experiment related to K fertilisation, spring soybean and diverse species of fall/winter crops, such as wheat (Triticum aestivum L.), corn (Zea mays L.), sunflower (Helianthus annuus L.) or oat (Avena strigosa L.), has been carried out in Southern Brazil since 1983. The K deprivation for 8 years reduced soybean grain yield and the K contents in soil and plant tissues. K extractants, such as Mehlich-1 and ion exchange resins, had diverse sensitivities with the variation in the K exchangeable contents induced by K rates. The increased soil K content after K fertilisation reduced calcium (Ca) and magnesium (Mg) contents in index leaves and altered its contents in the soil extracted by 1 mol L−1 KCl and ion exchange resins. Among the micronutrients, only B contents changed due to increased K rates, and had significant correlations with K and Ca contents in index leaves. The calculated Diagnosis and Recommendation Integrated System (DRIS) indices were compatible with soybean yield and K contents in soybean index leaves.

In tropical Africa, pepper (Capsicum spp.) is grown as a rainfed crop, and its production is limited by the long, hot growing season. Field experiments were conducted in Nigeria to evaluate the effects of cassava (Manihot esculenta) on the growth and yields of three pepper cultivars and gross returns in 2001–2003. In Experiment 1, pepper (cv. Sombo) was planted between rows of cassava cvs Idileru (PI), Odongbo (PO) and TMS 30572 (PT). In Experiment 2, pepper cvs Sombo, Tatase and Atarodo, were mixed with TMS 30572 (MS, MT or MA). The growth environment for the intercropped pepper differed from sole crops of pepper. Radiant energy reaching the soil surface, maximum diurnal soil and canopy temperatures, and weed growth were lower with intercropping, with the lowest values being observed in the PI and PT intercrops. Similarly, soil moisture content and the number of earthworm casts were greater with intercropping, with the highest values also occurring in the PI and PT intercrops. In both experiments, fresh fruit yields of pepper depended on the duration of harvest, the number of fruits per plant and the weight of fruits. In Experiment 1, although the number of fruits and fruit yield of cv. Sombo were greater in the sole crop (SP) than the PO intercrop, the fruit yields in the PI and PT intercrops were similar to those of the SP plot. In Experiment 2, the number of fruits and yield of intercropped pepper cvs Tatase, Sombo and Atarodo were 25–28 % higher, on average, than in pure stands. Cassava tuber yield was not affected by intercropped pepper in either experiment. Total gross returns were greater than growing either pepper or cassava in monoculture. Increased total gross returns in the intercrops were obtained in the PI and PT treatments and in the MS and MA treatments without a significant reduction in pepper fruit yield. By promoting early fruit set and harvest, and bearing in mind the cumulative gross returns, mixing pepper and cassava enhanced the value of the vegetable, as early fresh pepper fruits command a premium price. It is concluded that pepper can be grown between cassava rows to provide a suitable environment for growth, but that this depends on the cassava cultivar. Using the less tall early cassava cultivar, with a relatively moderate leaf area index in a mixture with pepper is therefore recommended.

Leucaena leucocephala is cultivated at close spacings that do not permit intercropping. This has been a discouraging factor for small landholders who need regular income to establish leucaena plantations and benefit from the rapidly expanding market for wood. Therefore, on-farm experiments were conducted near Bhadrachalam, Khammam district, Andhra Pradesh, India, from August 2001 to January 2006, to study the effect of reducing tree density and modifying tree geometry on the growth of leucaena and productivity of intercrops. The inter-row spacing of 1.3 m in farmers' practice was increased up to 13 m to examine whether wide-row planting and grouping of certain rows would facilitate extended intercropping without sacrificing wood yield. Tree density treatments tried were 1.3 × 1.3 m, 3 × 0.75 m, 3 × 1 m, 5 × 0.8 m and 3 × 2 m which gives densities of 5919, 4444, 3333, 2500 and 1666 trees ha−1, respectively. Tree geometry treatments tested were 7 × 1 m paired row spacing (7 × 1 PR), 10 × 1 m triple row spacing (10 × 1 TR), and 13 × 1 m four rows (13 × 1 FR) with a constant tree population of 2500 trees ha−1. Cowpea (Vigna unguiculata) was the intercrop. While changes in tree density affected diameter at breast height (DBH) significantly, modification of tree geometry did not affect tree height and DBH. Marketable wood and dry biomass productivity was highest with 3 × 0.75 m spacing, and reducing tree density and alteration of tree geometry reduced the biomass considerably. In 2001, 2002 and 2003 seasons, respectively, tree spacing at 3 m produced mean yields of 97, 23 and 11% of the sole crop cowpea yield whereas modified tree geometry treatments produced mean yields of 97, 61 and 20% of sole crop yield. The widest spacing (13 × 1 FR) recorded 95, 73 and 30% of the sole crop yields during 2001, 2002 and 2003, respectively. Net returns from intercropping of leucaena in 3 × 0.75 m spacing was 36% higher than that of the farmers' practice. Although wider tree geometry treatments recorded lower net returns, they provided higher intercrop yields and returns in the first two years of plantation establishment. Therefore, it can be concluded that in regions where annual rainfall is around 1000 mm, leucaena can be planted at a spacing of 3 × 0.75 m for improving intercrop performance, higher tree productivity and returns.

The effects of levels of soil moisture and plant population on lodging and associated losses from mechanical harvesting of two lentil genotypes, one susceptible and one resistant to lodging, were investigated during 1986–87 and 1987–88 at Tel Hadya in northern Syria. High plant population increased lodging because the crowded plants had thin stems, while high levels of soil moisture caused lodging because biological yield was increased. When biological yields were high a two tonne increase in biological yield led to a one point increase in lodging score. Mechanical harvesting increased losses in biological yield due to lodging by 12% compared with yields obtained by hand harvesting under rainfed conditions and by 24% at the highest level ofsoil moisture. It is suggested that supplementary irrigation should be used in dry seasons in trials to select genotypes resistant to lodging.

Decaimiento de la lenteja

Fluid-drilling is the term used to describe sowing seed in a liquid carrier. Elliot (1966) used a tractor-mounted fluid drill designed by the National Institute of Agricultural Engineering to sow normal seed into killed grassland, and a similar but modified drill was subsequently used at the National Vegetable Research Station to sow pre-germinated vegetable seeds (Gurrah et al., 1974; Gurrah, 1975). It then became necessary for compact and economical experiments to be carried out, both on and off the Station, creating a requirement for a small, portable, easily operated, hand-powered drill of simple and robust construction (Gurrah, 1975). Such a drill was built in 1975 and is described in this paper.

A farm survey conducted in Ethiopia in 1986 identified seasonal food shortage as an important problem facing farmers. The researchers proposed the development of an early maturing maize variety to alleviate the problem and by 1988, on-farm trials of a selected variety were initiated. About two-thirds of the farmers retained part of the harvested crop as seed for planting, indicating their strong interest in the variety. Farmer-designed trials were found to be especially effective for obtaining farmers' assessment of the new variety and for monitoring how they incorporated it into the farming system.

Maíl con maduración temprana para Etiopía

Trials on cotton in Uganda show that four DDT sprays give substantial increases in yields and a reduction in percentage of stained cotton. Benefits were obtained from early ploughing prior to sowing and there were positive interactions between time of ploughing and spraying. Fertilizer applications of superphosphate and sulphate of ammonia generally produced marginal benefits but more cotton was obtained from fertilized plots if they were sprayed, though not if unsprayed. The effect of fertilizer on the pest complex was slight, though one pest appeared to be attracted to lush fertilized cotton. Spraying gave excellent control of bollworms and mirids.

In the process of developing an improved fallow system based on forage legumes, the potential interest of crop-livestock farmers in enhancing soil fertility restoration and dry-season feed supply was assessed during a socio-economic study on 11 farms of settled agro-pastoralists in the subhumid zone of West Africa. Simultaneously, eight farmers in the group participated in simple and largely farmer-managed on-farm experiments testing the establishment of selected forage legumes on fallow land. In addition to agronomic parameters, the participatory approach included an evaluation of the technology by farmers both during farm visits and field days.

With cropping and dry-season feeding strategies increasingly being limited by land availability, the agronomic performance of some of the tested legume species, in particular Stylosanthes guianensis, promised substantial productivity gains once they could be integrated into the traditional fallow system. The major concerns of the farmers were animal health and labour supply for cropping activities, rather than soil fertility and feed constraints. The need for initial weed control within most of the legume species, therefore, limited their acceptability by farmers at this early stage of innovation testing. Nevertheless, farmers' interest grew remarkably in the course of the study. Options for the selection of appropriate species and management practices, which aimed at facilitating the establishment of legumes on fallow land, are discussed as a means of enhancing further adoption of the innovation.