Changes in soil moisture and nitrate content in the top 75 cm of soil in bare and cropped plots were followed throughout the growing season in a Ferruginous savanna soil. A low leaching efficiency, of 0.38–0.66 cm/cm rainfall, was related to very slow wetting of the subsoil, a phenomenon which could be explained satisfactorily only by assuming that part of the rain passed through the profile relatively quickly in the larger pores. However, losses of fertilizer nitrate to deep drainage by this rapid percolation were only 25% of that applied, at most, the greater part remaining in the top 45 cm of soil for almost the whole growing season, thus explaining why only small responses have been obtained at this site to delayed or split applications of nitrogen.

Cross-inoculation tests, based on nodule formation and nitrogen fixation, were made on 21 species of legumes commonly found in the Sudan. The results showed that they may be grouped according to the accepted system of classification, but there were some important inconsistencies in the cowpea group. For instance, Arachis hypogaea and Acacia spp. have their own strains of Rhizobium. The cultural and physiological characters of the rhizobia studied were generally similar to those known for other species of the organisms.

Controlling weeds until 6 weeks after crop emergence gave a yield of soyabeans only 85 per cent that of the clean-weeded control treatment. Delaying weeding until 3 or 6 weeks after emergence gave yields 89 per cent and 69 per cent respectively of the control. Narrow crop rows (30.5 cm.) gave higher yields than wide rows (61 cm.). Defoliation of soyabeans reduced pod number, seed size and yields more with late and severe defoliation, and with lower plant populations. Delayed harvesting during the dry season led to seed shedding and yield was at the maximum for only about one week.

Seed cotton yield in Northern Cameroon has been declining since the 80s despite breeding efforts. In order to evaluate the impact of genetic improvement on this decline, we conducted field experiments in two locations with 10 widely grown cotton cultivars released in Cameroon between 1950 and 2009. The rate of genetic gain (GG) was estimated with a linear regression of the cultivar mean on its year of release (YR). Contrasts between rates of GG observed with different planting dates were estimated and tested. Our results revealed a rate of GG on fibre yield of 3.3 kg ha−1 year−1 due to increased ginning out-turn (3.9% and 6.2% in 60 years in Garoua and Maroua, respectively). There was no GG on leaf area index (LAI), radiation use efficiency (RUE), aerial biomass, harvest index and on seed cotton yield. We concluded that cotton breeding efforts in Cameroon have successfully improved cotton fibre yield but there is still some room for seed cotton yield improvement.

In an experiment on genotype × environment interactions in tea (Camellia sinensis), yield differed between the genotypes at all sites. The highest yield in the third year after planting was 3760 kg ha−1 for clone S15/10 at site 4 (1800 m altitude), while the lowest was 1610 kg ha−1 for clone 6/8 at site 1 (2200 m). The dry matter contents of harvested shoots from each clone ranged from 0.24 for clone TN14-3 down to 0.19 for clone S15/10. Yield response to soil water deficits was more pronounced at site 4, where larger deficits were observed. Hail damage affected the yield of two sites and a temperature influence on recovery was evident.

General mathematical relations between yield parameters, plant populations and rainfall were developed for an indigenous sorghum from the results of 28 population/row spacing trials conducted at four sites over five seasons. Populations maximizing yield increased from 25 000 to 69 000 plants ha−1 over the rainfall range 200–700 mm (pre-planting to harvest total). Tillering partly compensated for low populations but yields from 10000 plants ha−1 at 300 and 600 mm rainfall were only 80 and 61% of potential maximum, respectively. Row spacing at constant population affected tiller numbers and eventual panicle weights but not panicle numbers, and any yield differences were unrelated to rainfall.

A participatory method that promotes farmer involvement in systems-problem research was developed in response to the failure to adopt improved cropping patterns among upland farmers. Techniques to identify systems problems involved group and individual farmer meetings. Problems concerning the cultivation of marginal cogonal (Imperata cylindrica) uplands were identified. An informal random sample survey, guided by topics of inquiry and biological measurements that employed systems analytical tools, was used to obtain a farmers' perception of ‘systems-problems’. Systems diagrams also provided a framework for searching and screening solutions. A sequence of vining legumes was tested in rehabilitating the marginal uplands. For this experiment farmers elaborated hypotheses on control of Imperata, recovery of soil fertility, and reduced labour costs in re-cultivation. Extensive research activity among the farmers indicates the value of this participatory method.

Aerobic rice is considered a viable agro-technology to cope with the looming crisis of water supply that threatens the sustainability of irrigated rice production systems. Rice adapted to aerobic conditions requires less water than that grown under conventional irrigation management. A field study was conducted at Cuttack, India, during the dry season (January–May) in 2005 and 2006 to determine the critical soil moisture regime at the root-zone depth (30 cm) for sustaining optimum growth and grain yield of aerobic rice variety ‘Apo’ (IR 55423-01). Irrigation at 0, 20 and 40 kPa soil moisture tension resulted in similar grain yields (4.90–5.25 t ha−1 in 2005 and 4.35–4.50 t ha−1 in 2006). The seasonal water requirement in treatments receiving irrigation at 20, 40 and 60 kPa soil moisture tensions was 28.4, 42.8 and 60.7% lower than that at 0 kPa soil moisture tension, but the yield declined significantly at 60 kPa, i.e. by 42.8% in 2005 and 36.7% in 2006. Irrigation at 40 kPa soil moisture tension ensured maximum water productivity of 0.90, 0.47 and 0.53 g grain kg−1 water with respect to evapotranspiration, irrigation plus rainfall and irrigation alone, respectively. Thus, irrigation at 40 kPa soil moisture tension may be considered critical for optimum grain yield and maximum water productivity of aerobic rice in Indian cultivation conditions.

Echinacea purpurea has been introduced in to Taiwan and grown successfully. However, information regarding the effects of the growing climate on its active constituents (e.g. caffeoyl derivatives) and biomass production is very limited. In this study the biomass of field-grown E. purpurea plants harvested during three different crop seasons was compared. The content of caffeoyl phenols and the production of aerial plant parts were also assayed. The results indicated that both morphological and agronomic traits were affected by crop season, with spring-grown plants producing more stems and flowers but fewer leaves than autumn-grown plants. Autumn-grown plants produced more caffeoyl phenols, particularly cichoric acid and caftaric acid, in leaf and flower tissues than spring grown plants. Thus, transplanting E. purpurea seedlings in the autumn and harvesting the aerial parts at the beginning of winter first, and then harvesting the rhizome-regenerated plants again in the following summer are technically feasible. This farming system would give commercial cultivation of E. purpurea in Taiwan a great competitive advantage over other growing regions, provided that an environmentally suitable population is selected and established in Taiwan.

Three alternate-row intercrop experiments of sorghum (Sorghum bicolor)–cowpea (Vigna unguiculata) and/or millet (Pennisetum glaucum)–cowpea were grown at plant densities of 20 000 to 80 000 plants ha−1 at two locations in northern Nigeria between 1990 and 1992 to examine relations between yield and plant density. These relations were examined using the reciprocals of yield per plant to determine effects of environment, species and genotype on the theoretical maximum yield and optimum plant density. The intercrops were dominated by cereals, and cowpea biomass (BY) and seed yield (SY) were <10% of cereal BY and SY. Cowpea yields decreased as cereal plant density (D) increased, whereas cereal and total intercrop yields increased asymptotically with increasing D. Biomass yield of all intercrops responded to increasing D in a similar manner and the theoretical maximum intercrop BY was 12 290 kg ha−1 in all experiments. The response of SY to D varied among intercrops and was greatest and least with early and late maturing cereals respectively. The optimum D required to produce 90% maximum intercrop BY and SY varied between 15 600 and 30 000 plants ha−1, and 0 (no response to D) and 120 000 plants ha−1 respectively, and was higher for sorghum than for millet intercrops. The implications of these responses for agronomic management and germplasm improvement of cereal–cowpea intercrops are discussed.

A field technique to screen large numbers of pearl millet and sorghum lines for seedling emergence through soil crusts is described. Seeds were sown on raised broad beds in an Alfisol field. The beds were smoothed after sowing with a bed shaper. Thirty five mm of water was applied from two parallel lines of sprinklers at a rate of 14 mm per hour. A crust of relatively constant strength in different tests developed as the surface dried out. The crust was broken in the control treatment with a crust breaker. The ratio of emergence under crust to that under control (c/u ratio) was used to classify the test materials.

The after effects of three years' continuous cropping with sole millet, sole cowpea or a traditional millet/cowpea intercrop were compared using five levels of nitrogen fertilizer. The continuous sole cowpea system had reduced the carbon to nitrogen ratio more than the continuous sole millet or the traditional intercrop. The test crop millet yielded much more, and its uptake of nitrogen and phosphorus was greater, when it followed sole cowpea than when it followed sole millet or the traditional millet/cowpea intercrop. The three years' continuous sole cowpea had an effect equivalent to the application of 205 kg N ha−1 on the test crop of millet. It also caused the greatest reduction in Striga infestation in the test crop. It is therefore recommended that cowpea cultivation be increased in the Sahel.

Trials on leaf abscission of cassava led to the conclusion that the leaf lamina is necessary, and must receive light, to prevent abscission of the petiole. The abscission rate of old leaves is increased by the presence of an active apex, but is not affected by the carbohydrate requirements of the roots.

Smallholder farmers in Malawi are faced with the challenge of managing complex and dynamic farming systems while also adapting to change within volatile agroecological conditions. Moreover, management decisions are influenced by a combination of local knowledge, expert recommendations and on-farm experimentation. Although many smallholder farmers actively experiment with new crops and technologies, little is known about the prevalence of experimentation or the types of experiments farmers conduct. This study examined the decision-making processes of experimenting farmers to explore the drivers of on-farm experimentation. Using a mixed-methods design that incorporated field observations, survey data and in-depth interviews, we identified numerous examples of experiments with new crops, varieties and techniques that had been executed either independently or through participation in an agricultural development project. Results of quantitative and qualitative analysis reveal that smallholder farmers in Malawi across a range of socioeconomic characteristics are inclined to experiment, and gender roles in agricultural experimentation vary widely. While experimental methods differ between farmers, there are commonalities in the drivers of experimentation, including adapting to climate change, improving soil health, improving nutrition and generating income. Smallholders have a great capacity for experimentation, and their knowledge, experience, preferences and priorities – if properly understood and incorporated – could ultimately benefit both future agricultural development projects and their participants.

Soybean yields on smallholder farmers’ fields in Malawi are constrained by poor soil fertility, limited application of external inputs and poor crop husbandry. We tested crop management practices through on-farm experimentation and participatory technology evaluation. Two agronomic soybean trials were established in 2009 and 2010 in three contrasting agro-ecologies resulting in 72 replications per trial. Treatments in the first trial included several combinations of inoculation with Bradyrhizobium japonicum, inorganic fertiliser application and compost manure. In the second trial, farmers tested an improved variety, optimal weeding regime, increased plant population and chemical pest and disease control. A combination of inoculation, inorganic fertiliser (10 N, 8 P, 20 K in kg ha−1), and 6 t ha−1 compost manure increased yields from 0.86 t ha−1 under farmers’ practice to 1.56 t ha−1 and resulted in average profits of US$222 ha−1. Increased plant populations and biocide spraying also resulted in substantial yield increases. Inoculation and increased plant population resulted in an average value to cost ratio (VCR) > 2. Low investment costs make inoculants, compost manure and increased plant populations interesting options, whereas adoption of inorganic fertiliser application in soybean may be limited due to high costs and low VCR. The farmers ranked eight technologies in descending order of preference as: (i) early planting, (ii) plant population, (iii) variety choice, (iv) compost manure, (v) weeding, (vi) inoculant, (vii) fertiliser and (viii) spraying. Our participatory research approach demonstrated that there is a wide range of technologies with different levels of human and financial investment costs that smallholder farmers can adopt to enhance their soybean yields and profits.

Agronomists have increasingly conducted experiments on-farm, in an attempt to increase the wider applicability (external validity) of their experimental findings and their relevance for agricultural development. This review assesses the way in which on-farm experimental studies address the scope or generalisability of their findings when based on a limited number of farms. A central question is how on-farm studies define the environment or research population in which the on-farm trial findings are valid, or are valuable for. Such an assessment is, of course, conditional on the (internal) validity of the experimental findings. We therefore first analyse how authors of on-farm experimental studies describe the factors that may shape experimental outcomes. As agronomic experiments often use ‘yield’ as dependent variable to assess treatment effects, we developed a procedure to score studies on their descriptions of yield-determining factors. Although experimental validity principally rests upon the reproducibility of the experiment and its findings, we found that on the basis of the information provided in published on-farm experimental studies, it is often difficult or impossible to reproduce the experimental design. Nutrient management, weed management and crop information are best described, whereas land preparation, field history and management of pests and water are rarely described. Further, on-farm experimental studies often compare treatments to a ‘farmer practice’ reference or control treatment which is assumed to be widely and uniformly practiced and known to the reader. The wider applicability or external validity is often poorly addressed in the reviewed studies. Most do not explicitly define the research population and/or environment in which (they expect) the experimental findings to work. Academic textbooks on agronomic experimentation are remarkably silent on both the internal and external validity of on-farm experimentation. We therefore argue for more systematic investigations and descriptions of the research population and settings to which on-farm experimental studies seek to generalise their findings.

Two maize cvs, FARZ 23 and FARZ 25, were grown at three densities (37,000, 53,000 and 80,000 plants/ha) in 1979 and 1980. Leaf area index (LAI) increased with increase in plant population and was at a maximum at mid-silk. Grain yield was highest at 53,000 plants/ha. There was no relation between LAI and grain yield but there was a positive correlation between LAI and total dry matter yield.

This study demonstrates a relationship between earliness of ripening and stalk elongation which could be useful in a sugarcane selection programme. Sixty-four sugarcane genotypes with contrasting ripening behaviour were grown in a quadruple-lattice design and ordinary logistic curves were shown to give the best fit between stalk height and time. Genotypes with early high sucrose contents gave logistic curves with earlier inflection points and steeper slopes at the point of inflection. The inflection point was shown to be a reliable indicator of time of ripening and it was suggested that stalk height per se could be considered as a selection criterion for earliness of ripening in sugarcane.

Soil fertility decline and fallow effects were studied in Ferralsol-Acrisol catenas of plantations of sisal (Agave sisalana) in north-east Tanzania. The fertility of Ferralsols that had been subject to continuous sisal cultivation in the absence of fertilizers was extremely low but that of Ferralsols that had been under 18 years of bush fallow or under secondary forest was slightly better. Acrisols that had been under continuous sisal cultivation were less depleted than the Ferralsols because of greater intrinsic fertility. A comparison of soil analytical data from the 1950s and 1960s with recent data from the same sisal fields showed that the topsoil pH of the Ferralsols had decreased by 1.5 (r2 = 0.807) and that of the Acrisols by 1.2 (r2 = 0.494) under continuous sisal cultivation. Thus there had been a serious decline in soil fertility under sisal cultivation, and this decline was not adequately reversed by fallowing.

This paper aims to determine the influence of family farming features on efficient use of water. The analysis focusses on a random sample of family farms in the province of Almería, southeast Spain. A hierarchical regression model was conducted to determine how the water efficiency is related to environmental awareness and certain characteristics of farmers, decision-makers and the family farm itself. The results show that these family farms strive to be more efficient in their use of water when they are going to be inherited, when there are younger decision-makers who have received a better education, and also when women are involved. Moreover, this efficiency is positively related to more ecological production and to the farmer's habitual behaviour with respect to water economy. The study provides evidence regarding the influences of socio-economic and environmental features of family farming on water use efficiency that may prove useful for other analyses and policy makers on water management in agriculture.