Long-term data (20 years) on wheat (Triticum aestivum) grain yield under various fertilizer-nitrogen (N) and water conditions in rainfed and irrigated environments of sub-tropical north India were used to assess the magnitude and economics of N response in relation to amount and timing of irrigation. Treatments comprised combinations of fertilizer N rates (ranging from 0 to 150 kg ha−1) and irrigation regimes (rainfed, supplemental, limited, and adequately irrigated). Regression analysis of wheat yield against available water supply and fertilizer N showed a strong interaction between the two variables for grain yield and input use efficiency. The effect, on grain yield and returns, of increasing the N rate for a given water supply was influenced by the irrigation regimes. Economic optimization of water and N, based on constrained profit maximization technique, showed that optimum amounts of available water (or irrigation) and fertilizer N are related directly to the capital investment. Increased input prices lowered their optimum levels for a given investment. The analysis suggests an approach for resource allocation that relates to capital investment and input prices.

A two-year field trial was conducted to study the effects of prolonged water stress on cassava (Manihot esculenta) productivity, and on nutrient uptake and use efficiency. Four contrasting cultivars were supplied with adequate fertilization and watering, except when water was excluded by covering the soil with plastic sheets for different periods, depending on treatment: from two to six months, four to eight months, or from six to twelve months after planting (early, mid-season and terminal stress respectively). Sequential harvests were made at 2, 4, 6, 8 and 12 months after planting to determine leaf area index and shoot and root biomass. At final harvest, nitrogen, phosphorus, potassium, calcium and magnesium concentrations in shoots and storage roots were determined.

During both early and mid-season stress, leaf area index and shoot and root biomass were significantly smaller than those in the controls across all cultivars. After recovery from stress, leaf area index was greatly enhanced with less dry matter allocated to stems, and root yields approached those in the controls. One cultivar, CMC 40, had greater final root yield under stress treatments. Nutrient concentration in roots and shoots was less in all cultivars with early stress and resulted in higher nutrient use efficiency in all elements for root production. The same trend was observed under mid-season stress, except for nitrogen concentration, which remained unchanged.

Terminal stress did not affect leaf area index, but reduced the shoot biomass in all cultivars. Final root yields were smaller than those in the controls except for CMC 40 whose final root yield was greater under stress. Nitrogen concentration was greater in root biomass but less in shoot biomass of all cultivars, resulting in lower nitrogen–use efficiency for root production. Across cultivars, only potassium- and magnesium-use efficiencies were greater than in the controls. CMC 40 was the only cultivar with consistently greater use efficiency of nitrogen, phosphorus, potassium, calcium and magnesium for root production under terminal stress. This higher nutrient use efficiency was due, mainly, to a greater root production rather than to smaller nutrient concentration. This cultivar is suitable as a gene source for improving cassava in order to maximize root production per unit nutrient extracted under stressful environmental conditions.

Farmers hosted on-farm trials and demonstrations involving three new groundnut (Arachis hypogaea) varieties in Malawi to assess their acceptability and adoption potential. Patterns of seed diffusion among trial farmers were examined as well as among non-trial farmers who were members of seed banks. The study showed that trial follow-up surveys provide a cost-effective approach for assessing early adoption and providing feedback to researchers. While useful, however, such studies are not an end in themselves. Rather they need to be perceived and designed as one of several studies that help researchers understand the complexity of farmers' adoption decisions.

In any experiment the land will not be completely uniform and it is helpful to have ways of allowing for the variation. Some sources, for example altitude, will be obvious; some will be permanent but less obvious, such as depth of topsoil; and some may depend upon season and so be unpredictable. Various methods of local control have been suggested. Where the experimenter has good knowledge of the land it can be divided into blocks, each as far as possible uniform within itself. Then comparisons are made within the blocks rather than within the area as a whole. Where such knowledge does not exist, it is sometimes reasonable to make an assumption about the fertility pattern and make use of that, as in a row-and-column design like a Latin square. There is also the possibility of judging the fertility pattern from the data themselves and assessing the performance of a plot by reference to that of its neighbours.

The approach will be to generate bodies of data on the computer to form realizations of diverse fertility patterns and to use all methods on all realizations, noting success and failure.

When the variation forms a trend, blocks succeed only if they are aligned along fertility contours; the other methods do not depend upon orientation. Row-and-column designs can fail badly if the rows and columns interact. Some random variation is inevitable and it makes all methods less effective, especially nearest-neighbour methods, which can fail also when there are discontinuities. Random patches of different soil types are very difficult to deal with and any method might fail.

The duration of the residual effect of sesbania (Sesbania sesban) fallow on subsequent crops will determine the interval at which sesbania must be grown to replenish N in a planted fallow–crop rotation cycle. An experiment was conducted from 1995 to 1998 (seven cropping seasons) on two farms in western Kenya, an area subject to a bimodal annual rainfall pattern. The aim was to compare the effect of a single-season sesbania fallow with continuous annual cropping with and without phosphorus fertilizer, on a P-deficient soil. Phosphorus was applied at a rate of 500 kg ha−1 in a single application to meet the phosphorus needs of subsequent crops for the next five to ten years. Sesbania was established simultaneously with maize by direct seeding in the first rainy season of 1995 and allowed to grow as a pure fallow through the second rainy season. Following the harvest of this fallow crop, sole maize in the first post-fallow season and maize-bean intercrops in the subsequent four seasons were grown with and without nitrogen at a rate of 100 kg ha−1. Added phosphorus on average increased maize yields by 3.7 times over the control, indicating that phosphorus fertilizer is essential for good yields. The amount of phosphorus recycled by sesbania fallow was inadequate to meet the crop needs in P-deficient soils. While continuously cropped maize in the presence of phosphorus responded to nitrogen in all seasons, the crop following sesbania responded only from the third season. In the first post-fallow season, sesbania increased maize grain yields over continuous maize by 1.4 t ha−1 with phosphorus fertilizer and by 1.3 t ha−1 without phosphorus fertilizer. The residual effect of sesbania with phosphorus fertilizer lasted for two seasons, while without phosphorus it lasted for only one. In these Kenyan highlands, farmers who can afford fertilizer should buy phosphorus fertilizer and rely for nitrogen on planted fallow with species such as sesbania grown for one season every two years. For farmers who cannot afford fertilizer, one-season fallow every year may be more attractive because of labour savings and the firewood produced by sesbania.

Output:input ratios and apparent balances for nitrogen (N), phosphorus (P) and potassium (K) were measured in a rice-wheat system at Modipuram (29.4°N, 77.46°E, 237 m asl), India, under two planting densities (P1 = 200×200 mm for rice, 230 mm row spacing for wheat, and P2 = 200×100 mm for rice, 150 mm row spacing for wheat), and two levels of fertilizer NPK (100% F = recommended levels of fertilizer N, P and K for each crop, i.e. 120 kg N, 26 kg P and 33 kg K ha−1, and 150% F = 150% of the recommended levels) with and without 5 t ha−1 farmyard manure (M) to each crop. After two cycles of the rice-wheat rotation at a fixed site, N and K balances were negative for all treatments, but P balance was negative only in plots treated with P1 + 100% F treatment. The largest yield in the system, 15.7 t ha−1, was obtained in plots receiving P2 planting density with 150% F + M treatment, and the smallest (13 t ha−1) in plots of P1 planting density with 100% F treatment. In plots with the largest yield, total removal of NPK was 659 kg ha−1 (310 kg N, 62 kg P and 287 kg K ha−1), and in plots with the smallest yield, NPK removal was 411 kg ha−1 (188 kg N, 34 kg P and 189 kg K ha−1). At these nutrient uptakes, output:input ratios were 0.74 for N, 0.57 for P and 1.80 for K in plots receiving P2 + 150% F + M treatment, and 0.78 for N, 0.65 for P and 2.86 for K in plots receiving P1 + 100% F treatment.

The effects of ten rootstocks on tree development, leaf nutrient levels, fruit internal quality and yield were studied. Plantings of the mandarin cultivar ‘clementine’ were established at the Agricultural Research Station of Rhodes on the rootstocks Cleopatra mandarin, Troyer and Carrizo citranges, rough lemon, Palestine sweet lime, Volkameriana, Citrus macrophylla, Rangpur lime and C. moi with sour orange as a standard for comparison. Data indicated that rootstocks significantly influenced tree development and fruit quality characteristics as well as foliar nutrient concentrations. The largest trees were on Volkameriana and the smallest on the two citranges. In terms of trunk cross-sectional area, the most vigorous trees were on C. moi and the least on Palestine sweet lime and the two citranges. Cleopatra mandarin, the two citranges, and Palestine sweet lime showed a tendency to biennial bearing. The highest cumulative yield of clementine trees was on C. macrophylla and Volkameriana and the lowest on Troyer and Carrizo citrange. C. macrophylla and Volkameriana produced the most efficient trees with the largest and heaviest thin-skinned almost seedless fruit. Fruit on C. macrophylla produced the highest juice content but also the lowest concentration of total soluble solids. Differences were observed in leaf nutrient contents between the rootstocks. These trials showed that C. macrophylla and Volkameriana could be used successfully as alternatives rootstocks to sour orange.

Data from a long-term trial on rates of fertilizer nitrogen (N) application to maize (Zea mays) were used to validate a cropping systems simulation model (APSIM) and then to apply the model to explore the risk associated with N fertilizer use by smallholder farmers and management strategies to minimize that risk. On average, maize growth and development in response to N was simulated with a degree of accuracy that justified its use in analysis of risk associated with N use in these semi-arid regions of Zimbabwe. APSIM was then configured to simulate the response to N over a 46-year climate record in order to assess the long-term risks associated with N use. The simulated long-term distribution indicated that negative responses to N could be expected in 15% of years, whereas no negative response to N was recorded in the experiments at the Makoholi Research Centre. Median responses were 20–30 kg maize grain kg−1 N for observed and simulated results. In terms of return on fertilizer investment, the observed and simulated distributions were also similar: in about 20% of years, a negative return could be expected, while in the best 20% of years a return of $Z5000 or more could be expected given the grain:fertilizer price ratio which, at March 2000, was about 1:7. The model analysis has suggested moderate rates (approximately 30 kg N ha−1) of N fertilizer would give greater responses per unit N applied than smaller rates (15 kg N ha−1). There was no evidence that conditional fertilizer strategies based on early-season rainfall would offer significant benefits over fixed application strategies. Early sowing at recommended population densities gave higher responses to N than were achieved for late sown or low-density crops.

This paper presents the results of extensive experience in the development and promotion of tobacco-based insecticides for the control of field crop pests in Igalaland, Nigeria. A non-governmental organization (NGO), the Diocesan Development Services (DDS), became involved in the development of tobacco-based insecticides in the early 1990s, and facilitated a series of ‘on-farm’ trials between 1997 and 2000 designed to test the effectiveness of such insecticides for two crops that are particularly vulnerable to pest attack in Igalaland: cowpea (Vigna unguiculata) and maize (Zea mays). The results suggest that even crude tobacco formulations had a significant benefit on cowpea and maize yields relative to the absence of pest control, although commercial insecticides were more effective. However, while having advantages of cost and availability over commercial insecticides, tobacco-based products appear to have serious internal and external disadvantages that limit their widespread use, and some of these are discussed. It is concluded that while technical efficacy of botanicals is an important element, there are others such as the logistics of production and preparation that need to be considered. A better understanding of the balance between these factors and how context-specific they may be is required in order to maximize their adoption by farmers under ‘resource-poor’ conditions.

Wheat (Triticum aestivum) production using no-tillage is becoming an increasingly accepted management technology. Major obstacles to its adoption in Morocco, however, are exportation of wheat straw from the field and stubble grazing. Among pertinent solutions is the control of these practices. A four-year field study was conducted to determine the effect of residue level under no-tillage on wheat grain and total dry-matter yields, water use and water-use efficiency, and to compare this with conventional tillage systems. The aim was to evaluate whether all the straw produced is needed for no-till cropping or whether partial removal of straw from the field is possible without any adverse effect on production. No-tillage and deep tillage with disk plough performed equally well and subsurface tillage with an off-set disk produced the lowest yields. Both bare and full no-tillage covers depressed wheat production. Uo to 30% of straw produced under no-tillage can be removed without jeopardizing wheat crop performance.

Canopy characteristics (leaf area index, fractional light interception, extinction coefficient) of mature trees of ten clonally propagated cacao cultivars were measured over a period of 14 months at an experiment site in Bahia, Brazil. Differences in leaf area index between clones became more pronounced over time. When an approximately constant leaf area index was reached (after about nine months), the leaf area index varied between clones from 2.8 to 4.5. Clonal differences in the relationship between leaf area index and fractional light interception implied differences in canopy architecture, as reflected by the range of extinction coefficients (mean values ranged from 0.63 for the clone TSH-565 to 0.82 for CC-10). The results demonstrate the potential for breeding more photosynthetically efficient cacao canopies.

Ranking and scoring exercises are common in participatory research work, for example in determining farmer preferences for crop varieties, tree species or other commodities. However, they rarely involve eliciting opinions of many individual farmers so as to establish the repeatability of study findings. This paper demonstrates ways in which ranking of evaluation criteria can be combined with evaluation scores to produce generalizable results concerning farmers' overall preference for a set of bean (Phaseolus vulgaris) varieties. The use of weighted indices is explored. Results were found to be robust across all indices. However, farmer evaluations for yields did not correlate well with actual yields measured on their own plots. Farmers often gave high evaluation scores for yield performance of new bean varieties, even when they yielded quite poorly in plots in their own fields. Reasons for this are discussed.