Nitrate-nitrogen was analysed over two cropping seasons in 57 farmers' fields in the northern Guinea savanna of Nigeria. Differences between fields were at least five-fold and often ten-fold irrespective of fertilization rates. Average concentrations were highest at the beginning of the rainy season. Loamy soils had a later peak for nitrate release and maintained high concentrations for a longer period after the start of the rains than the more sandy soils. Nitrate-N was not correlated with soil organic carbon or total nitrogen content. Grain yield of maize was closely associated with nitrate-N in the soil but not with organic carbon or total N. Four patterns of nitrate-N release over the season could he differentiated using cluster analysis. Soil texture, soil pH, soil organic carbon, stover management and cropping history contributed most to a differentiation of the four cluster groups in a discriminant model. There was wide variability in the inherent soil-nitrate level and in its importance in explaining differences in yield among farmers' fields. The development of technologies resulting in improved nitrogen availability or better nitrogen utilization should be based on research of inherent soil processes. For the transfer of such technologies, recommendation domains should be defined based on different native patterns of soil-nitrogen availability.

The yield of cowpeas could be increased by judicious defoliation of the older leaves or by topping the growing apices at the onset of flowering. Limited defoliation at the pre-flowering stage did not reduce the yield of beans significantly but severe defoliation at any stage prior to maturity drastically reduced yield. Satisfactory yields of cowpea could be obtained by maintaining only about one-half to two-thirds of the potential leaf-area of the plants, suggesting that a reduction in the number and area of leaves, coupled with a better display of the fewer remaining leaves, could make cowpeas more productive than hitherto.

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.

Six intercropping systems and four levels of nitrogen were compared at the Indian Agricultural Research Institute, New Delhi, in the summer rainy seasons (July-October) of 1978 and 1979. The maximum increase in sorghum yield was obtained when it was associated with fodder cowpea, followed by association with grain cowpea and greengram. The application of 40, 80 and 120 kg N ha−1 increased sorghum yield by 8.6, 16.1 and 18.2% in 1978 and by 2.9, 8.1 and 14.1% in 1979, respectively, compared with unfertilized sorghum. The nitrogen uptake by sorghum, and by the total system, was greater in sorghum-legume intercropping systems than in sole sorghum. Nitrogen application also increased the nitrogen uptake by sorghum and by the whole system.

Farm households in the Andean region of South America face serious livelihood challenges, including a poor natural resource base and declining agricultural yields. Conservation agriculture has been identified as a potential solution to environmental degradation and the associated poverty and food insecurity in the region. This study analyses the potential economic impact of conservation agriculture in two sub-watersheds in central Ecuador utilizing a linear programming model and data from experiments in farmer fields. The model found that specific cover crops, crop rotations and reduced tillage designed to reduce soil erosion and increase soil organic matter can lead to increased incomes for farm households in a time period of as short as two years. It appears that conservation agriculture practices have the potential to improve the livelihoods of the rural poor in Ecuador because conservation agriculture activities entered the revenue-maximizing model solution for both sub-watersheds.

Transplanting single seedlings rather than seedlings in clumps has been increasingly attractive in hybrid rice production in China due to reduced seed requirements and higher grain yield. This study was conducted to determine grain yield and nitrogen (N) utilization in response to reductions in the N rate in hybrid rice under single-seedling transplanting. Field experiments were done in 2015 and 2016 on a moderate to high fertility soil at the Experimental Farm of Hunan Agricultural University, China. The hybrid rice cultivar Liangyoupeijiu (LYPJ) was used in 2015, and two hybrid cultivars LYPJ and Xiangliangyou 900 were used the next year. In each year, the rice plants transplanted with a single seedling per hill were grown with three N rates, including the usual N rate (150 kg ha–1) and two reduced N rates (120 and 90 kg ha–1). Grain yield, yield attributes, and N uptake and use efficiency were determined for each N rate. Significant reduction in grain yield was observed in only one of three cultivar-year combinations when N rate was reduced by 20% (from 150 to 120 kg ha–1), and the magnitude of yield reduction was only 4%. Although significant reduction in grain yield was observed in two of the three cultivar-year combinations when N rate reduced by 40% (to 90 kg ha–1), the highest yield reduction was only 7%. Yield attributes were generally changed slightly when N rate was reduced by 20%, while compensation among yield attributes and N utilization characteristics could explain why a 40% reduction in N rate did not result in substantial yield loss. Partial factor productivity of applied N (PFPN) was increased by 21–24% and 56–63% with 20% and 40% reductions in the N rate, respectively. The higher PFPN with a reduced N rate was attributed to higher recovery efficiency of applied N (REN) or to both higher REN and internal N use efficiency. Our study suggests that reducing N rate does not necessarily result in yield loss due to compensation among yield components and increased N use efficiency in hybrid rice transplanted as single seedlings under moderate to high soil fertility conditions.

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.

High yield in the tapioca varieties studied appears to be associated with sink activity of the tubers and consequently with crop index. Growth measurements indicate that assimilation is significantly affected by sink activity as well as by the functioning of the assimilation apparatus. The form of the crop growth curve, and the effect of spacing on yield and distribution of dry matter are also considered.

Seed of the new heavy yielding bean cultivar Carioca was distributed directly to 400 farmers in Zambia during 1986 in order to speed its adoption and diffusion. Three years after distribution, 55% of the farmers who participated in a follow-up survey were still sowing Carioca. Diffusion of the new cultivar had occurred, with 3.7 times as many farmers estimated to be growing Carioca in 1988/89 as in 1986, an annual rate of diffusion of approximately 49%. Use of a logistic modelling framework suggested that the variables directly associated with the decision to adopt the cultivar were the farmer's total area in cultivated crops and the area in local maize. Variables indirectly associated with adoption were the level of education of the household head, the average number of years that the fields had been in continuous cultivation and the number of cattle owned. These results will help guide the development of effective strategies for the release and distribution of new bean cultivars from national bean research programmes in sub-Saharan Africa.

Adopción y difusión del poroto Carioca en Zambia

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.

Two cocoa progenies, T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid), were compared for degree of infestation by 17 insect species comprising a Coccid, an Aphis, a Mirid and six ants. A significantly greater proportion of trees of the second variety was infested by the mealybugs Planococcus citri Risso and Pseudococcus hargreavesi Laing, by the Lecaniid scale Gascardia sp. nr. zonatus Newst., by the aphis Toxoptera aurantii Boys, by attendant ants Camponotus spp., and Crematogaster spp., and by the ant Polyrhachis laboriosa F. Smith. Because of differences in habitat requirement between the four Hemiptera, it is postulated that it is more likely that the response is due to a physiological difference between the two progenies than to a purely environmental difference.

Topsoil nitrate was measured every few days under grass, sorghum and bare fallow at two sites in lower Embu District, Kenya. Concentrations were highest soon after the start of rain and within a week most nitrate had been lost. Under bare fallow and sorghum, nitrate concentration increased during dry weather and losses occurred when soil water content exceeded 10%. Modelling of soil water movement indicated that there was no leaching below the rooting zone, so denitrification may be the main route for loss of soil nitrogen. Application of nitrogen fertilizer early in the season is not recommended as it would be lost with the native soil nitrate. The use of phosphorus fertilizer at the phosphorus-deficient site reduced soil nitrate concentration throughout the season and increased nitrogen uptake by sorghum. At the phosphorus-rich site, vigorous sorghum growth kept the soil nitrate concentration low, even though much nitrate was produced and lost in bare fallow. Adequate soil phosphorus is considered essential if the natural nitrogen resources of the soil are to be managed efficiently.

The effects of sole and intercropping of rainfed maize (Zea mays L.) were evaluated with soybean (Glycine max L.) and groundnut (Arachis hypogea L.) on crop yield, weed smothering efficiency (WSE) and nutrient (NPK) balance at Eastern Himalayan Region (EHR), India. Grain yield of maize was highest (3886 to 4110 kg ha−1) in the solitary system followed by maize-soybean intercrops at 1:2 rows. However, system productivity as well as production efficiency was higher by 47.3-63.3% and 39.5-58.4%, respectively in intercropping with groundnut at 1:5 rows compared to solitary maize. WSE was relatively higher to solitary soybean and was comparable to maize-groundnut intercropping at 1:5 row proportions. Similarly, NPK uptake was higher in intercropping of maize-soybean systems at 1:5 row proportions. Inclusion of legumes as intercrops in predominantly solitary rainfed maize may improve the system productivity while sustaining the nutrient availability in the vast uplands of the EHR and other similar rainfed hilly ecosystems.

Two field experiments were conducted during the rainy seasons of 2013 and 2014 to evaluate the effects of biological nitrogen fixation (BNF) and/or sowing N fertilization on the growth and yield of Phaseolus vulgaris L. In addition, leaf soluble protein content (LSPC) was measured at four growth stages in both seasons. Plants were subjected to the following treatments: only fertilized with 20 kg N ha−1 at sowing and with 40 kg N ha−1 at 25 days after emergence (DAE) (F); only inoculated with Rhizobium tropici strain SEMIA 4080 at sowing and fertilized with 40 kg N ha−1 at 25 DAE (I+N); and inoculated and fertilized with 20 kg N ha−1 at sowing and with 40 kg N ha−1 at 25 DAE (IF). An additional treatment was done only in the second season and plants were inoculated with no N fertilization at any phase (I−N). Crop growth rate and leaf area index were enhanced by IF and F treatments as compared to I+N treatment, however, net assimilation rate did not differ among the treatments. At the pollination and flowering stages for seasons, LSPC was significantly increased by IF treatment, which also caused the highest final yield compared with the remaining treatments in both seasons. Therefore, the fertilization with 20 kg N ha−1 at sowing together with inoculation and 40 kg N ha−1 at 25 DAE is recommended for obtaining high yield in bean cultivation with high technology. As the inoculation with Rhizobium at sowing and fertilization with 40 kg N ha−1 at 25 DAE (I+N) had the same crop yield as plants fertilized at sowing and at 25 DAE (F), it can be recommended for a low-cost technology cultivation employed by small farmers.

Pearl millet topcross hybrids (inbred male-sterile seed parent × open-pollinated variety restorer) based on locally adapted varieties and publicly available seed parents provide an ideal entry point into the commercial hybrid seed business, which can stimulate commercial investment by prospective seed producers. To demonstrate this potential, fifteen topcross hybrids made with the widely adapted variety ICMV 221 were evaluated in Eritrea, Sudan and Kenya for overall field performance, and in India for mechanisms of expression of heterosis and for terminal drought tolerance. Across all evaluation environments, the mean yield heterosis was 8%, with a range of −1% to +19%; six hybrids had a statistically significant, positive across-environment yield heterosis (ranging from +11% to +19%). Significant grain yield heterosis in rainy season environments was a consequence of heterosis in both biomass and harvest index, but not necessarily in any specific yield component. Positive grain yield heterosis under terminal drought stress, a common occurrence in millet-growing environments, was related to positive heterosis for grain size. These results are discussed in terms of their support for topcross hybrids as an entry point for prospective millet seed producers, and a scheme presented for the rapid creation, evaluation and marketing of locally adapted topcross hybrids.

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.

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.

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.

To assist commercial producers with optimizing the use of irrigation water, the responses to drought of mature and young tea (Camellia sinensis) crops (22 and 5 years after field planting respectively) were compared using data from two adjacent long-term irrigation experiments in southern Tanzania. Providing the maximum potential soil water deficit was below about 400–500 mm for mature, and 200–250 mm for young plants (clone 6/8), annual yields of dry tea from rainfed or partially irrigated crops were similar to those from the corresponding well-watered crops. At deficits greater than this, annual yields declined rapidly in young tea (up to 22 kg ha−1 mm−1) but relatively slowly in mature tea (up to 6.5 kg ha−1 mm−1). This apparent insensitivity of the mature crop to drought was principally due to compensation during the rains for yield lost in the dry season. Differences in dry matter distribution and shoot:root ratios contributed to these contrasting responses. Thus, the total above-ground dry mass of well-irrigated, mature plants was about twice that for young plants. Similarly, the total mass of structural roots (>1 mm diameter) to 3 m depth was four times greater in the mature crop than in the young crop and, for fine roots (<1 mm diameter), eight times greater. The corresponding shoot:root ratios (dry mass) were about 1:1 and 2:1 respectively. In addition, each unit area of leaf in the canopy of a mature plant had six times (by weight) more fine roots available to extract and supply water than did a young plant. These results show that young tea should be irrigated in preference to mature tea, especially where the maximum soil water deficit is likely to exceed 250 mm.