An experiment conducted from 1988 to 1997 to determine the effects of the timing of application and nutrient supply (particularly of phosphorus) is reported. The sources of applied nutrients that were compared were farmyard manure, pre-rice green-manuring with Sesbania aculeata and fertilizer application in a rice-wheat rotation on a typic ustifluvent. The application of seven tonnes farmyard manure per hectare to both the rice and the wheat crops over eight years increased organic carbon levels from 1.4 to 1.6% but had no yield effect on either crop. Phosphorus application through farmyard manure was not adequate for rice, whilst an application of 34 kg P ha−1 to the rotation gave an economic yield increase only in rice and then only in the first four years of the experiment. From the third year, green manuring was able to replace the effects of the recommended nitrogen, phosphorus and potassium fertilizer applications in increasing rice yield. Green manuring had no effect on the wheat yield but the recommended fertilizer application increased yield. Green manuring increased soil total nitrogen and available potassium levels and reduced base saturation. After adjusting rice yields for variation in transplanting date between years there was no statistical evidence of a yield trend in either crop over the period of the experiment. Farmers' practice of applying seven tonnes farmyard manure per hectare appears adequate to produce stable rice paddy yields of 4–6 t ha−1 a−1.

To understand the impact of residue and tillage management on crop productivity of rice and barley (including grain yield) and soil fertility in a tropical dryland agro-ecosystem, the following six treatments were established: (a) conventional tillage and residue removed (CT−R); (b) conventional tillage and residue retained (CT+R); (c) minimum tillage and residue removed (MT−R); (d) minimum tillage and residue retained (MT+R); (e) zero tillage and residue removed (ZT−R); and (f) zero tillage and residue retained (ZT+R). Minimum total net productivity (TNP) in both barley (the winter season crop) and rice (the rainy season crop) was recorded in the ZT−R treatment and the maximum in the MT+R treatment. In these crops, 83–88% of TNP was represented by above-ground net productivity (ANP). A reduction in tillage, from conventional to zero, especially when combined with residue retention, reduced the crop TNP/weed TNP ratio, reflecting the abundance of weeds with zero tillage. In both crops, minimum tillage increased grain yields, compared with conventional, but zero tillage resulted in reduced yields. Soil microbial biomass carbon (MBC) and nitrogen (MBN) and N-mineralization rates were higher in rice than in barley, and were maximum in the MT+R treatment. Crop productivity and grain yield in different treatments were positively correlated with MBC, MBN, N-mineralization rate and available-N. Strong negative correlations between crop productivity and grain yield with weed TNP and N-uptake were recorded. This study suggests that retention of a small fraction (one-third) of above-ground biomass from the previous crop and its incorporation in the soil through minimum tillage enhances the crop productivity and grain yield of succeeding crops and promotes soil fertility in a cereal based tropical dryland agro-ecosystem.

Farmers around the world are concerned about the effects of human-induced salinity on crop yield and quality. Therefore, researchers are actively testing wild relatives of cultivated plants to identify candidates to improve crop performance under salt stress. A study was conducted to understand the effects of salt stress (Sodium chloride, NaCl) on cultivated tomato species (Solanum lycopersicum var. cerasiforme L.) and a wild tomato relative (Solanum chilense Dun.) from the Northern part of Chile. Plants were cultivated hydroponically under controlled environmental conditions for 112 days with nutrient solution containing 0 mM (3 dS m−1), 40 mM (6 dS m−1) and 80-mM (9 dS m−1) NaCl. Salt stress reduced the shoot biomass in S. lycopersicum but not in S. chilense. Both species were able to maintain the leaf water content; however, the cultivated S. lycopersicum showed osmotic adjustment, while S. chilense did not. Salt stress reduced the total fruit yield in S. lycopersicum based on a decrease in the mean fruit weight, but it had no impact on the number of fruits per plant. In contrast, salt stress had no significant impact on the fruit yield in S. chilense. Salt stress increased the total soluble solids content in S. lycopersicum and the titratable acidity in S. chilense. It was concluded that S. chilense displays a contrasting behaviour in response to prolonged exposure to moderate salinity compared with S. lycopersicum, and that this related species could be an interesting plant for breeding purposes.

Field trials in Northern Nigeria have shown that the yield of introduced varieties of maize can be economically improved with combinations of nitrogen and phosphorus fertilizer. Three response areas have been defined. In the south, where most of the maize is grown, the initial response is to nitrogen. Further north, with the exception of one small area in which the response is almost entirely to phosphorus, phosphorus and nitrogen and equal limiting factors. Estimates of the most profitable combinations of nitrogen and phosphorus to use in each area have been obtained from quadratic response surfaces fitted to the yield data of the experiments.

Simple models of the growth and development of legume cover crops in different environments may aid the selection of species and genotypes most suitable for particular farming systems. The effects of temperature and photoperiod on the daily rate of seedling emergence (1/t50%) and the rate of leaf appearance (leaves d⊃−1&/sup;) were quantified for 12 diverse legume cover crop species. Six tropical or subtropical species were grown in 12 combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (11.5, 12.5, 13.5 and 14.5 h d⊃−1&/sup;). Another six genotypes of temperate species were grown in nine combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (12.5, 13.5 and 14.5 h d⊃−1&/sup;). Durations from sowing to 50% seedling emergence (t50%) were recorded and the number of leaves on the main stem counted during early vegetative growth. Photoperiod did not affect either 1/t50% or leaves d⊃−1&/sup;. However, the effects of temperature, photoperiod response group (short-day or long-day response), genotype or species and their interactions were all significant. An optimal temperature between 21.8 and 26.8 °C for leaves d⊃−1&/sup; was identified for Vicia sativa, Vicia dasycarpa and Lupinus mutabilis. Below the optimum temperature, 1/t50% and leaves d⊃−1&/sup; were positive linear functions of temperature for all legume species except Vicia dasycarpa. Estimates of base temperature (Tb) and thermal time (θ) for 1/t50% and leaves d−1 were obtained for each legume cover crop from these functions. Common values of Tb were found within each photoperiod response group: 9 °C and 1 °C for 1/t50%, and 10 °C and −2 °C for leaves d⊃−1&/sup; for short-day and long-day species respectively. Differences among species were represented by variant estimates of θ. The practical consequences of the combined effects of these values of Tb and θ for selecting legume cover crops for particular farming systems are discussed.

Cassava (Manihot esculenta Crantz) has generally been reported to possess hypostomatal leaves. Several cultivars have now been found to possess clusters of functional stomata around the veins on the upper leaf surface and two cultivars (M Col 88 and M Col 90) have significant numbers of stomata (83–140 mm−2) dispersed over the entire upper leaf surface. Stomatal density on the lower leaf surface ranged from 322–553 mm−2 among cultivars, with a relative stomatal area of 3.4–6.1%. The CO2 uptake by the upper leaf surface (27% of total) and the transpiration loss (32% of total) corresponded closely to the ratio of relative stomatal areas on the upper and lower leaf surface of cv. M Col 88.

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.

Shoot production was examined for two clones at four sites in western Kenya, differing by up to 300 m in altitude and from 16.4 to 18.1°C in mean air temperature. The duration of the shoot growth cycle increased with altitude, and the rate of shoot extension decreased, mainly because of the temperature differences. Outside a dry season, linear regressions of both extension rate and 1/duration on temperature were significant for Clone S.15/10, and gave apparent base temperatures around 7.5°C, but were not significant for Clone TN.14/3 which responded only slightly to temperature. The dry weight per shoot was stable and the growing point frequency did not change systematically with altitude. Analysis that excluded the effects of drought indicated that the yield of Clone S.15/10 decreased from 740 g m-2 at the lowest site by about 10% per degree fall in temperature, whereas the yield of TN.14/3 did not change systematically with altitude.

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.

Herding and farming environments in sub-Saharan Africa are described briefly. The relative importance of crops and livestock is described for each environment. A matrix of crop-livestock interactions is defined for each environment and the reasons for each type of relation are noted. Farming systems are defined as segregated or completely integrated, according to the degree of crop-livestock integration on the farm. Points at which farming systems research (FSR) might be undertaken to improve interactions between crops and livestock are noted for both systems.

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.

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.

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.

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.

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.

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.

Modern maize varieties have been bred for drought tolerance and early maturity, to assist farmers in avoiding or escaping the effects of moisture stress in drought-prone areas. This study evaluates the prospects for widespread adoption of these modern maize varieties as a climate change adaptation strategy for smallholder farmers. Data are from a detailed household survey completed in four rural villages in Southern Malawi between May and July 2010. The empirical analysis involves estimation of an ordered logit regression model because the dependent variable is categorical, with one category for nonadoption (has never grown modern maize varieties) and three categories for the duration of growing a modern maize variety among adopters (this year only, 2 to 5 years and 6 years or more). The empirical findings indicate a positive association between a farmer's perception of drought risk and the adoption and continued use of modern maize. Regression results also show that farmers that value the traits of early maturity and drought tolerance are more likely to adopt modern maize varieties. There is evidence of some disadoption among farmers dissatisfied with maize genotype performance, in terms of poor storability and yield under drought conditions. Finally, the study highlights the urgent need for maize breeders interested in sustained use of modern varieties to simultaneously address robust drought tolerance, early maturity and storability. This underscores the importance of cognizance of local farmer preferences in crop breeding efforts.

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.

The results of international research on the water relations and irrigation needs of onions have been synthesised in an attempt to link fundamental studies on crop physiology to irrigation practices, and consequent impacts on crop yield, quality and storage. Following a brief introduction on its origins and centres of production, a synthesis of research on crop development including plant water relations, crop water requirements, yield response to water, irrigation systems and scheduling are presented. Most of the evidence stems from research conducted in arid and semi-arid regions, notably the USA, India, Spain and Turkey. The findings confirm that onion seasonal water requirements are highly variable depending on agroclimate, location and season, as are the crop coefficients (Kc) which range from 0.4 to 0.7 (initial stage), 0.85 to 1.05 (middle development) and 0.6 to 0.75 (final stage). Seasonal irrigation needs are reported to vary from 225 to 1040 mm to produce between 10 and 77 t ha−1. The most sensitive stages for water stress are at emergence, transplanting and bulb formation. Final crop quality can also be affected by water excess. Water stress at specific stages can negatively impact on quality leading to reduced size and multi-centred bulbs. In recent years, pressure on water resources, retailer demands for quality assurance and rising production costs have meant that onion irrigation has switched from traditional low efficiency (furrow) methods to more efficient advanced (sprinkler and drip) technologies. For scheduling, optimal soil water potential thresholds for triggering irrigation were found to be between −17 and −27 kPa for drip and furrow irrigation. Research is underway to maximise water use efficiency in onions, but the deficit irrigation regimes being tested under experimental conditions have yet to be adopted commercially.