Results of farm-level experiments with pearl millet are reported from four villages in semi-arid Niger in 1982 and 1983. Crop establishment, yield loss factors (insects, diseases, striga) and economics of new practices were studied in a randomized design which included density, fertility, cultivar, and intercropping with cowpea as treatments. Improved cultivars did not establish significantly better than local ones, but fertilizer occasionally improved establishment. Incidence of yield loss factors was low, and only small effects of cultivar and fertilizer were seen. Fertilizer increased grain yields of the local cultivar by as much as 153%. The use of fertilizer and improved cultivars increased grain yields by as much as 171% over an unfertilized local millet. Even without government subsidies, fertilizer use was profitable for 56% of farmers on all cultivars. In general, fertilizers and improved cultivars had a small positive impact on profitability, with little adverse impact on grain yield variability, so that they could be recommended to farmers with some prospect of success. The intercropping treatment failed in both years, and would have to be modified before extension.

The effect of strain of Rhizobium and of temperature on nodule formation and early growth of Trifolium semipilosum was studied in controlled environment cabinets. Time required for nodules to form was affected by strain of Rhizobium and by root temperature, acting independently. Strains CB788 and CB2116 required only 9.5 to 10.0 days, averaging over temperatures, whereas strains CB782 and CB526 required 12.8 to 13.0 days. Nodulation was earliest at whole-plant temperatures of 25/20°C and 30/25°C day/night (average 9.5 days); 15 days were required at 20/15°C. Nodule number was independent of bacterial strain but dependent on temperature; nodules were fewest in the lowest and most in the highest temperature regime. Plant yield was determined by interactions between temperature and strain and was generally greatest at whole plant temperatures of 25/20°C.

When nodulated plants growing at 25°C were transferred to a range of root temperatures, plants grew best at 20° and 25°C and with strains CB782 and CB2116.

A two-year study was conducted at two locations in Niger to compare the response of five cowpea cultivars to two planting patterns and two sowing dates relative to the sowing date of pearl millet. All the cowpea cultivars took less time to mature when planted three weeks after millet than when sown one week after. Early-maturing cowpea cultivars had the smallest yield, whereas the yield of the local indeterminate cultivar was nearly double that of the other cultivars at both dates of sowing. Early planting of cowpea significantly depressed millet yield, but when cowpea was planted late millet yields approached those of the sole crop. The local cultivar depressed millet yields more than the other cowpea cultivars. Planting pattern had no significant effect on the yield of either cowpea or millet. Cowpea yield was reduced by more than 50% by two weeks delay in sowing, confirming that the sowing date of cowpea relative to millet is a critical factor in the Sahelian pearl millet/cowpea intercropping system. There were marked differences in the effect of cowpea cultivar on millet yield but these differences were consistent over sowing dates.

Date palm is a crop suited to hot, arid regions. It originated in Mesopotamia and the centres of production are in West Asia and North Africa. Despite its regional and international importance, and its dependence on irrigation or a shallow water table for survival, relatively little research has been published on the water relations and irrigation need of date palm. Following early work in California, the majority of the recent research reported in the literature has been conducted in Saudi Arabia and Tunisia. The date palm has a terminal crown of 100–120 leaves. At the base of each leaf is an axillary bud, most of which develop in the winter as flower buds. It takes 150–200 days from pollination to fruit maturity. Stomata occur on both leaf surfaces. Different techniques have been used to measure the water use of date palm, including micrometeorological and sap flow methods. In Syria, mean actual evapotranspiration rates varied between 0.5 mm d−1 (winter) and 3.5 mm d−1 (summer), in Saudi Arabia from 2–3 to 8–11 mm d−1 depending on location and in Jordan from 2 to 8–10 mm d−1 respectively. In Tunisia, there was some (limited) evidence of stomatal control of transpiration rates (seasonal range 0.5 to 3.5 mm d−1) when temperatures exceeded 32 °C. Experimentally determined values of the crop coefficient were inconsistent, varying from 0.6–0.7 to 1.18. In the vicinity of an oasis, advection may increase potential water use substantially above that of a reference crop. In the absence of a shallow water table, roots can extract water from soil depths greater than 2 m. There is little published information on the water productivity of date palm. A target benchmark figure is probably about 1.3-kg fresh fruit m−3 of irrigation water applied. Under controlled conditions, phenotypes differed in their responses to water stress. The date palm is traditionally considered to be relatively salt-tolerant, with a threshold electrical conductivity value for the saturated soil extract of 4.0 dS m−1, but recent evidence from Israel suggests that this view may be mistaken. Since early times, flood irrigation has been used to irrigate date palm and it is still probably the most common method in many countries. Since the 1980s, farmers have been encouraged by governments to use localised irrigation methods (e.g. micro-sprinklers, drip and bubbler) as a means of saving water. Since water is a scarce resource in the West Asia and North Africa region, research should focus on developing ways to improve the water productivity of this high value crop.

Yields of pearl millet were significantly increased when grown after legume crops such as groundnut (22·6%), cowpea (24·2%) or pigeonpea (12·1%) instead of after pearl millet. A previous crop of short-duration mung did not affect the yield of pearl millet. Benefits from previous crops of groundnut and cowpea were equivalent to about 60 kg N/ha applied to a pearl millet crop following a previous crop of pearl millet.

Knowledge of agro-physiological traits associated with drought tolerance would be useful for developing breeding materials for drought-prone environments. This study was conducted (i) to estimate genetic variability among 25 durum wheat genotypes in response to drought based on grain yield and 15 agro-physiological traits in single and multi-year trials; and (ii) to compare genotypes on the basis of multiple investigated traits using genotype by trait (GT) biplot technique and then recommend possible selection strategies. We found large genetic differences among durum wheat genotypes for agro-physiological traits in response to drought stress within and between single years, which revealed good promise in their further exploitation for selection in durum wheat breeding program. High broad-sense heritability and expected genetic advance as percent of mean observed in plant height (90.8%; 52.7%), grain yield (53.6%, 23.5%) and relative water loss (47.2%, 41.3%), respectively, indicated a major role of additive gene action. The results showed that the performance of genotypes was influenced by the year. The traits with high consistence across years were heading date, plant height and peduncle length. The potential quantum efficiency of photosystem II (Fv/Fm) and thousand-kernel weight (TKW) were positively associated with grain yield, while heading date, plant height and canopy temperature (CT) were negatively associated with grain yield under the drought conditions. In conclusion, based on across-year analyses, Fv/Fm, TKW, heading date, plant height and CT are the most promising traits for indirect selection.

Sequential sowings were carried out at Dodoma, Tanzania, to examine the effect of changing climatic parameters on the growth and yield of bambara groundnut (Vigna subterranea). Sowings took place on 4 January, 4 February and 4 March 1994; 4 and 24 January, and 13 February 1995; 4 and 21 January, and 7 February 1996. Rainfall during the crop life cycle varied from 163 to 611 mm, mean photoperiod from 11.82 to 12.09 h d−1 and mean temperature from 22.6 to 24.4 °C. In 1994, the highest pod yields were achieved at the earliest sowing date, with a maximum of 2.87 and 1.42 t ha−1 for the red- and cream-seeded landraces, representing pod harvest indices of 0.56 and 0.34 respectively. A 30-d delay in sowing caused >60% reduction in pod yield, and a further 30-d delay resulted in no pods at all. Similarly, in 1995 successive delays in sowing caused dramatic yield declines, and the maximum yield was much lower, at 0.44 t ha−1. In 1996 there was no significant difference in pod yields between the two early sowing dates for the red-seeded landrace and yields were again lower than in 1994 with a maximum of 1.02 t ha−1. Differences in dry matter production between sowings and years were attributed mainly to differences in the amount and distribution of rainfall and to declining temperatures towards the end of the season; however, partitioning to pods was remarkably consistent across sowings.

Enset [Ensete ventricosum (Welw.) Cheesman (Musaceae)] is a multi-purpose and drought-tolerant crop, traditionally grown in Ethiopia. Food from enset has nutritive values similar to potato; it could improve food and livelihood security for many in larger geographical areas. Agronomical advice is needed which requires increased knowledge of management techniques. The purposes of this study were to (i) compare traditional corm pre-treatments when planting for sucker production, (ii) compare all six officially released cultivars regarding sprouting and (iii) investigate the effect of watering on newly buried corms. Emergence rate and number and characteristics of sprouts were recorded. Corms, from 63 two year old plants, were buried in local soil supplied with cow manure in Wolaita Sodo, Ethiopia. Emergence was recorded daily. After nine months, including one rainy season, all suckers (totally 4405) were harvested and individually recorded. Regardless of cultivar, minimum time to emergence was 50 days. Sprouts from split parent corms emerged earlier than from entire. Emergence occurred from 100% of corms, number of sprouts was strongly correlated to cultivar: average 28–106. The cultivars responded similarly to corm splitting: the more pieces the corm was split into, the more sprouts per parent corm. Average pseudostem diameter of the seven largest per parent corm: 8–10 cm for all cultivars, leaf length: 3.1–3.7 m, remaining 2700 smaller suckers: diameter 3 cm (SD 1.8). Watering decreased the average time to emergence and levelled out the differences between pre-treatments. The traditional belief is that watering as well as manure on corm cause rotting; manure is therefore usually put on the soil surface. On the contrary, full emergence and unexpected large suckers may be a result of careful soil preparation with manure applied on corm directly; watering resulted in an even emergence and growth. In conclusion, vegetative propagation of enset is efficient, but methods used and agronomical advice can be improved.

If corn-soyabean intercrops are to replace corn grown alone, maintenance of yield and improvements in forage quality are important. Total yields and inter-crop competition in corn-soyabean intercropping experiments have been discussed previously (Putnam et al., 1985). In Part II yield composition, components and protein content are presented for intercrops of varying planting patterns and corn densities. Most intercrop patterns produced more forage than sole crops compared at the same yield ratio of corn-soyabean as in the intercrop harvested mixture. At high plant density ear yields in the intercrop were increased while in sole crops they were reduced or unaffected. The increase was a result of an increased number of ears, weight per ear and kernel, and number of kernels per row in the intercrops. Increases in crude protein content over sole crop corn of 11–51% were shown for the various intercrop treatments. Crude protein yields in the intercrops were greater than either sole crop in 1981 and greater than corn and similar to soyabean in 1982, and greater than the crude protein yields expected from an equal planted area of sole crop corn and soyabean in both years. Intercrop forage quality was improved over sole corn both by the addition of protein from soyabean pods and an increased ear: stover ratio of the intercropped corn.

At a field site in central India, four populations of groundnut (Arachis hypogaea L.) were grown on stored water to investigate how the production of shoot and root dry matter is related to transpired water and intercepted radiation. Throughout the season, total dry matter was closely related to transpiration (slope = 3.0 mg dry matter g−1 water) and the amount of radiation intercepted by foliage (slope = 0.74 g dry matter MJ−1 radiation intercepted). Accumulated transpiration increased linearly with intercepted radiation at 0.37 kg water MJ−1 in the sparser stands. In the densest spacing, the initial slope of the relation at 0.28 kg MJ−1 decreased later in the season because water deficits curtailed growth without a concomitant reduction in the interception of radiation.

At Hyderabad, India, stands of pearl millet were grown after the monsoon (a) with no irrigation after establishment and (b) with irrigation as needed to avoid stress. Increases of dry matter and leaf area were determined by regular harvesting. The interception of radiation by the foliage, uptake of water from the soil and stomatal conductance were monitored. Before anthesis at 42 days after sowing (DAS), the rate of dry matter production and the transpiration rate in the unirrigated stand were about 80% of the corresponding rates for the irrigated control, mainly because of a smaller stomatal conductance from 30 DAS. After anthesis, the unirrigated stand grew little and used only 10% of the water transpired by the control. This large difference was partitioned between loss of leaf area and smaller stomatal conductance in the ratio of approximately 2:1. Radiation intercepted by foliage in the irrigated stand produced 2.0 g of dry matter per MJ compared with 2.5 g MJ−1 for the same variety growing in the monsoon, a difference consistent with a smaller stomatal conductance in drier air.

Thirteen cultivars of cassava were planted, widely spaced, and harvested after two, three, five and seven months. Differences in root yield after seven months were caused by variations in rate of root bulking, and were not associated with differences in onset of root bulking, which occurred during the second month of growth in all varieties that produced thickened roots.

Mixed cropping of teff (Eragrostis tef) with faba bean (Vicia faba) was compared with sole cropping in the 2002 and 2003 growing seasons at Holetta Research Centre, in the central highlands of Ethiopia. The treatments were sole teff (25 kg seed ha−1), sole faba bean (200 kg seed ha−1) and 12.5, 25, 37.5, 50 and 62.5 % of the sole seed rate of faba bean mixed with a full teff seed rate. A randomized complete block design replicated four times was used. Treatment effects were significant for seed and biomass yields of each crop species. Increasing the seed rate of faba bean in teff/faba bean mixture increased faba bean seed yield but decreased teff grain yield. Nonetheless, mixed cropping of faba bean with teff increased land use efficiency and gave higher total yields compared to growing either species in sole culture. Teff yield equivalent, land equivalent ratios (LERs) and system productivity index (SPI) of the mixtures exceeded those of sole crops especially when the seed rate of faba bean in the mixture was increased to 50 kg ha−1 (25 %) or more. The relatively high crowding coefficient values indicated yield advantages from mixed cropping of the two species. The highest values of teff yield equivalent, LER and SPI were obtained when faba bean was mixed at a rate of 62.5 % with the full seed rate of teff. We suggest that, at the current prices of the respective crops, up to 62.5 % of faba bean can be mixed in normal teff to get better total yield and income than sole culture of either species.

In the oil palm plantations of Ecuador, two factorial trials (namely CP06 and CP08) were used to assess the effects of N, P and K fertilization on the soil chemical characteristics after 10 years of fertilizer application. The use of ammonia-based fertilizers has resulted in a drop in soil pH, which has reached 1.2 units in one of the two trials. A drop in cation exchange capacity (CEC) was also found, and a loss of exchangeable cations that probably reflected leaching of excess N as nitrates. The use of KCl enriched the soil in K, which contributed to impoverishment in Ca and Mg. In both trials, the highest N and K application rates had no significant effect on yield in comparison with an intermediate fertilization rate; however, their effects on the fertilized soil significantly increased the risk of N and cation leaching towards the deep soil layers. We also compared the effects of the N, P and K factors on soil properties outside the fertilizer application zone. In both trials, the mineral reserves played a major role in meeting the needs of the control palms, which had not been fertilized for 10 years, as no significant yield drop has been observed except in trial CP06 when no KCl was applied. However, uptake of nutrient in the control plots did not lead to significant impoverishment of the soil.

The yield gap has arisen again as a focus for agricultural research to ensure food security and economic growth for farmers around the world. To examine this renewed interest, we carried out a review of key literature in the field of yield gap analysis to identify important gaps in research and analysis. In so doing, both the complexities in yield gap studies emerged along with some significant omissions. Much of the literature and research on the yield gap has been framed by larger concerns and initiatives to raise agricultural productivity. This focus has led to an emphasis on technical solutions such as crop breeding, fertilizer application and other methods to increase production. However, this concentration on the technical usually ignores the wider social, economic and political context that shapes farmer decision-making about agricultural production. This context can either discourage or enable farmers to close their yield gap. Additionally, the impact of increased agricultural production through certain technical solutions also often overlooks the wider impact on the landscape and the ecosystem services which underpin agricultural production and livelihoods. We argue that increasing agricultural productivity, and closing the yield gap, must be addressed with this broader approach.

Proximal plant sensing with active canopy sensors offers a leap in the non-destructive assessment of crop agronomic information. For managing fertilizer nitrogen (N), sensor readings must be translated using functional models or algorithms to fertilizer amounts. Six field experiments were conducted in three wheat seasons in the West Nile Delta in Egypt to develop and validate an algorithm based on GreenSeeker canopy reflectance sensor for field-specific fertilizer N management in wheat, which takes into account both spatial and temporal variability of N during the crop growth season. The proposed algorithm is based on the prediction of total N uptake and response index of N uptake determined from normalized difference vegetation index measured by the sensor from plots differing in yield potential as established by applying a range of fertilizer N levels in the four experiments conducted in the first two wheat seasons. The treatments in the two experiments conducted in the third wheat season were designed to define appropriate fertilizer N management prior to applying a sensor-based dose at Feekes 6 stage (jointing stage). The application of 40 and 60 kg N ha−1 at 10 and 30 days after sowing of wheat and a sensor-guided dose of N estimated by using the algorithm developed in this study resulted in yields similar to those obtained by following the general recommendation, but with an average of 66 kg N ha−1 less fertilizer N. These results were also reflected in a substantial increase in N recovery (21.9%) and agronomic (7.7 kg grain kg−1 N) efficiencies compared with the general recommendation, thereby proving the usefulness of the sensor-based algorithm in optimizing fertilizer N management in wheat.

Seed inoculation with Bacillus polymyxa markedly increased the yields of rice and chickpea crops, while Pseudomonas striata caused a greater impact on crop production when used with rock phosphate or super-phosphate in a wheat crop. The effect of the phospho-microbe inoculants was greater in phosphorus-deficient soils.

Surveys and on-farm trials are frequently used to facilitate farmer participation in agricultural research. This paper reports on a less common method-farmer involvement in on-station trials. Thirty-nine farmers were invited to multipurpose-tree screening trials in Burundi. Three different methods were used to determine which species the farmers wanted to test on their own farms. Private interviews and voting by a show of hands in plenary sessions gave very similar results whereas focus group interviews produced different and contradictory results. Researchers also learned what criteria farmers used to evaluate trees and the reasons for their choices. A supplementary survey of farmers’ preferences for trees grown on their own farms confirmed the findings and more clearly defined their criteria. In this survey, farmers used a local board game, Bao, to rate tree species across criteria they considered important. Overall, the visit to the trials and follow-up survey proved to be a useful and cost-effective method for getting farmer input and applying it in the screening process.

La participación de los agricultores en la selección de especies de árboles

In order to assess the response of cocoa trees to drought, changes in water status, gas exchange, leaf carbon isotopic ratio (δ13C), photochemical activity, and leaf N and chlorophyll content during the rainy and dry season were measured in 31 Venezuelan cocoa clones (17 Trinitarios, 6 Criollos, and 8 Modern Criollos) grown in a common garden. Drought caused a 40% decrease in water potential (ψ) in all but the Modern Criollos, and a reduction in net photosynthetic rate (A) and stomatal conductance (gs) without an increase in instantaneous water use efficiency (WUE) in 93% of clones, and an increase in δ13C (long-term WUE) in 74% of clones; these responses suggest differences in tolerance to drought among clones. A positive correlation between A and both gs and leaf N content was found for all genotypes. Leaf N content, chlorophyll content, and photochemical activity were reduced during drought, suggesting that metabolism was also inhibited. The best performance during drought was shown by Modern Criollos with the highest WUE, while five Trinitario clones seemed to be less sensitive to drought, since neither chlorophyll, N, total soluble protein concentration, nor gs changed with drought, indicating that those Trinitario clones, with lower A, have a conservative water use. Modern Criollos showed no reductions in either ψ or gs; A remained unchanged, as did WUE, which was the highest, suggesting that these clones would be more successful in environments with low water availability. Our results indicate large variation in physiological response to drought over a range of parameters, suggesting possible differences in tolerance among clones.

Mixed tree and food crop farming systems are being developed in the humid tropics. They offer one solution to the problems caused by population pressure and de-forestation, since they can provide a satisfactory income to the subsistence farmer, while adequately protecting the environment In seeking to develop optimal systems, examples and information can be drawn from traditional mixed cropping systems, from taungya systems of forestation, and from other systems developed within the commodity cropping sector. However, the full potential of mixtures involving perennials and food crops can only be realised within the limitations of local socio-economic and political circumstances.