In this study, different levels of defoliation were imposed on a determinate species (maize) and a relatively indeterminate species (cotton). The aim was to quantify the effects of defoliation on plant growth and production, under either optimum or water-stressed conditions. Under well-watered conditions, 33% defoliation twice (conducted 28 and 35 days after emergence) resulted in a 16% reduction in grain yield of maize while 67% defoliation once (conducted 28 days after emergence) had no significant effect on yield. Under water stress, the grain yields of maize plants with 33% (twice) and 67% defoliation were 13.5% and 25% greater than that of non-defoliated control plants, respectively. For cotton, the reproductive yields (seed and lint) with 33% and 67% defoliation (conducted 43 days after emergence) were reduced, under well-watered conditions, by 28% and 37% of that of the non-defoliated control, respectively. Defoliated cotton plants lost less fruiting forms (squares and young bolls) than non-defoliated plants during water stress. Therefore, under water stress the harvestable product of cotton plants with 67% defoliation was double that of non-defoliated control plants. In non-defoliated cotton plants, a second flush of flowering after release from water-stress permitted further compensatory fruit set and boll harvest. Defoliated plants did not show such levels of compensation. Defoliation significantly reduced water use by maize and cotton. The relative yield advantage of defoliated plants under water-stress conditions can be attributed to defoliation-induced improvement in water status as reflected in measures of photosynthetic rate and stomatal conductance. Under anticipated drought stress, defoliation could be an important management practice to reduce drought-induced yield decrease, but this needs to be tested under field conditions.

During the past two decades or so, rural population in Africa has increased slowly while urban population has grown dramatically. The hugely increased urban demand for cereals and pulses (which produce crop residues for livestock) and for livestock products is now the main force stimulating mixed farming systems in the semi-arid and sub-humid areas of sub-Saharan Africa. Grazing land has diminished, crop residues are becoming a more important element in raising livestock and fattening penned livestock has become profitable. The changes in land use, land tenure and the shift of livestock raising southwards in West Africa are illustrated. Farmers' adaptation to rapidly changing markets for their products and the factors of production are illustrated with examples from Senegal, Nigeria, Niger, and, by way of contrast, Kenya. The main challenges this sets to agricultural scientists are described. The livestock element in mixed farming system now requires careful economic analysis and participative research if scientists are to meet the evolving needs of farming as the urban sector enlarges.

The extent by which fertilizer nitrogen (N) may be reduced by the use of drip-fertigation in sugarcane was determined using 15N-labelled fertilizer in a field experiment in Mauritius. The data showed that, under the soil and climatic conditions that prevailed at the study site, fertilizer N could be reduced by 30%. Indeed, with 80 kg N ha−1 a−1 by drip-fertigation, total or fertilizer N recovered, growth pattern (as reflected by tiller density and leaf area development) and sugarcane yields were not inferior to those obtained with the standard practice of burying 120 kg N ha−1 a−1 along the cane rows. Applying more N than needed by the sugarcane in anticipation of a higher yield with drip irrigation would be wasteful of fertilizer N resources.

The use of cultivation techniques to conserve rainfall, by preventing runoff, and to improve the soil surface infiltration rate, has produced spectacular increases in the yield of cotton on the Loess Plain soils of Northern Nigeria, where yields of the order of 2000 lb seed cotton per acre can now be produced regularly irrespective of the rainfall pattern. As yields of this level had not been obtained previously, it has been concluded that lack of soil moisture and poor soil aeration have in the past set a ceiling to seed cotton yields. The effects of these cultivation treatments on the two other major crops of the area, sorghum and groundnuts, have now been examined, and results from a series of field experiments over six seasons indicate that adequate soil moisture is essential to the production of high yields, but that the other soil conditions which are alleviated by these cultivations are not so critical for these two crops as they are for cotton. Reasons are suggested why spectacular increases in yield in response to the treatments are not generally to be expected with sorghum and groundnuts.

The tea industry in Malawi is the oldest in Africa but in the past had always produced poor quality tea. A plant improvement programme was therefore started in 1956 at the Tea Research Stations in Mulanje. The improvement in made tea quality was assisted by an investigation into the biochemistry of tea fermentation. Early success was obtained with polyclonal seed varieties and the development of clones from field bushes. These were used in cross breeding to produce new progeny clones which are showing a steady improvement in quality and yield. The need for improved yield was recognised as the programme progressed and appropriate selection procedures adopted. Techniques for improved vegetative propagation for field planting, grafting ofseed bearer trees and composite plants were developed. Liaison with the tea industry has been good and all new plantings in southern Africa since about 1975 have been with improved material. The programme is continuing and future prospects are good.

Sorghum is the principal foodcrop grown in Northern Nigeria. A survey of local varieties grown during the rains was carried out in 1958 and the 821 samples collected were assigned to seven morphologically distinct races, of which four are important. Varieties belonging to the Guinea race, with loose, open panicles, are mainly cultivated in high rainfall areas south of latitude 11°30′N. Further north, three races, Kaura, Farafara and Chad are grown in the dry Sudan Savanna zone. Varieties of these races have compact panicles and bulging grains. Estimates of the contribution made by each of the four major races indicate that the Guinea race accounts for nearly 50 per cent of the total sorghum production in Northern Nigeria.

The rainfall erosivity (R) and soil erodibility (K) factors of the Universal Soil Loss Equation (USLE) were determined on two sites in the Colombian Cauca Department over a five year period when rainfall was mostly lower than average. The results showed that the high erosion potential of the soils can be attributed more to high rain erosivity than soil erodibility. The R factor explained between 59 and 81% of the variation in soil loss recorded on continuously clean-tilled fallow plots. The erodibility of Inceptisols in the study region is classified as low. Values for soil erodibility (K) ranged from 0.012 to 0.015 (measured in SI units) in the fifth year of permanent bare fallowing. K factors were higher in the rainy than in the dry season. Soils, previously under grass vegetation, were very resistant to erosion in the first two years of bare fallowing. In the third year erodibility increased sharply and continued to increase steadily until the sixth year. K factors predicted by the USLE nomograph underestimated the empirically-determined erodibility of these highly aggregated clay soils.

Using the sustainable livelihoods framework to evaluate the impact of a farmer-to-farmer video on the improved rice parboiling technology, women in Benin rated financial, social, human, natural and physical capital stocks for the baseline year (2006) and the impact year (2009) on a 0–5 scale. Women who had watched the video and those who had not, but who lived in the same villages, perceived a significant improvement in four out of five livelihood capitals while processors in control villages did not perceive any significant change. Apart from testing the sustainable livelihoods conceptual framework as a participatory impact assessment tool for video-mediated rural learning, this study shows how farmer-to-farmer training videos helped to improve multiple livelihood assets.

A field experiment to evaluate the effect of N, K and time of K application on the growth, yield and chemical composition of wheat (Triticum aestivum) grown in saline soil with subsurface drainage, was conducted at the Central Soil Salinity Research Institute, Karnal Research Farm, Sampla during the winter seasons of 1992–93 to 1994–95. The treatments consisted of three levels each of N (0, 120 and 150 kg ha−1) and K (0, 50 and 75 kg ha−1) with the K applied at two different times (full basal and half basal + half top dressed 30 d after sowing). The growth characteristics (plant height, number of tillers and dry matter weight m−2 recorded at 60 d after sowing) and yield-attributing parameters (number of productive tillers and length of spikes) increased significantly with increasing N levels up to 150 kg ha−1 and K levels up to 50 kg ha−1. Similar responses of N and K were also observed on grain and straw yields of wheat. Time of K application had no significant effect on growth and yields. The N concentration in grain and straw increased significantly with the application of 120 kg N ha−1 over control. Application of K had no significant effect on the concentration of N in grain and straw. The K concentration in grain and straw increased significantly due to the application of 50 kg K ha−1 but it was unaffected by the time of K application. Application of K increased the efficiency of utilization of applied N. A trend towards declining salinity of the soil profile due to leaching through the subsurface drainage system was observed from 1992–93 to 1994–95. For three consecutive years the status of available N and K in surface soil (0–30 cm depth) increased due to their respective applications. This field study indicates that 150 kg N and 50 kg K ha−1 should be applied under canal-irrigated conditions to get the sustainable and optimum yield of wheat in saline soils.

Potatoes (Solanum tuberosum L.) in central Africa are often grown between two rainy seasons to avoid late blight infection. The influence of planting date and setaria mulch treatment on soil temperature, soil humidity, late blight development, ground cover with green leaves, intercepted radiation and tuber yield of potato was studied in crops grown at 1850 m above sea level in Rwanda.

The planting dates towards the end of the rainy season resulted in the best yields and these were considerably increased by mulching which retained soil moisture and reduced soil temperature so resulting in a better ground cover. Increased yields in the mulched plots seemed to be due to increased radiation interception rather than to better radiation use efficiency.

An experiment designed to study differences in water requirements between some clones of tea suggests that clones which showed visual symptoms of being more susceptible to drought had a greater demand for water. Supplementary irrigation applied during the dry seasons prevented plants from dying and stimulated better early growth of clones tested. As a result of better early growth, the irrigated tea gave persistently and significantly larger yields than non-irrigated tea in the first 2 years of recording.

The conventional method of inoculating Phaseolus vulgaris with Rhizobium phaseoli, using a peat carrier and dry seeds, was compared with a method using a slurry inoculation of germinating seeds, which were subsequently sown with a fluid drill. The mean number of nodules per plant 28 days after sowing was 0·64 (uninoculated control), 2·14 (dry seed), and 7·0 (fluid drill), differences between treatments being significant at P=0·01. Two varieties included in the experiment gave similar responses, and it is concluded that the fluid drill technique has a useful potential as a method of ensuring good inoculation of legume seedlings.

Two contrasting clones of cassava (Manihot esculenta) were reciprocally grafted to test the hypothesis that the yield of cassava is limited by the number of storage roots. Effects of the root sink on leaf gas exchange were also tested under field conditions using a portable infra-red gas analyzer. Storage root number and root yield were affected by stock size and root yield was associated with the number of storage roots. The harvest index and sink-source ratio (root numberz/leaf area index) were correlated with root number. A feedback effect of root number on single-leaf photosynthesis was observed in one clone. It is concluded that the number of storage roots may be used as an indicator of sink strength.

The physiological basis for differences in yields from well-watered and draughted plants of four contrasting clones of tea was studied in terms of light interception, dry matter production and partitioning at a high altitude site in Southern Tanzania where there are marked seasonal variations in rainfall and temperature. The plant dry weights, including roots, were measured eight months after field planting and subsequently at intervals of three to four months, corresponding to the different seasons, during the following two years. Fully irrigated plants of one clone (S15/10) were also harvested after four years in the field. Clones differed in the rates of canopy spread and hence in their capacity to intercept solar radiation. The ‘radiation use efficiency’ (the net total dry matter production per unit of intercepted short-wave radiation) was similar for the four well-watered clones and ranged from 0.40 to 0.66 g MJ−1, which corresponds closely to values reported for other woody tropical plants. A 16-week drought treatment imposed two years after planting reduced the mean light interception of the four clones by about 25% and the mean radiation use efficiency by 78% to 0.09 g MJ−1. Clone S15/10, a cultivar from Kenya which produces large yields, partitioned a greater proportion of dry matter to leaves and harvested shoots than the other clones, and correspondingly less to large structural roots. This resulted in a maximum harvest index of 24%, substantially greater than other values reported in the literature. There were seasonal differences in partitioning, with more dry matter being diverted to roots and less to shoots during the cool season. Although the drought treatments had no significant effect on root growth, the amount of dry matter partitioned to leaves, stems and harvested shoots declined by 80–95%. The roots of all four clones extended in depth at similar rates (about 2 mm d−1), those of Clone S15/10 reaching 2.8m after four years. The results are discussed in terms of appropriate field cultural practices and possible selection criteria for high yielding clones.

The results of research into the water relations and irrigation requirements of lychee are collated and reviewed. The stages of plant development are summarised, with an emphasis on factors influencing the flowering process. This is followed by reviews of plant water relations, water requirements, water productivity and, finally, irrigation systems. The lychee tree is native to the rainforests of southern China and northern Vietnam, and the main centres of production remain close to this area. In contrast, much of the research on the water relations of this crop has been conducted in South Africa, Australia and Israel where the tree is relatively new. Vegetative growth occurs in a series of flushes. Terminal inflorescences are borne on current shoot growth under cool (<15 °C), dry conditions. Trees generally do not produce fruit in the tropics at altitudes below 300 m. Poor and erratic flowering results in low and irregular fruit yields. Drought can enhance flowering in locations with dry winters. Roots can extract water from depths greater than 2 m. Diurnal trends in stomatal conductance closely match those of leaf water status. Both variables mirror changes in the saturation deficit of the air. Very little research on crop water requirements has been reported. Crop responses to irrigation are complex. In areas with low rainfall after harvest, a moderate water deficit before floral initiation can increase flowering and yield. In contrast, fruit set and yield can be reduced by a severe water deficit after flowering, and the risk of fruit splitting increased. Water productivity has not been quantified. Supplementary irrigation in South-east Asia is limited by topography and competition for water from the summer rice crop, but irrigation is practised in Israel, South Africa, Australia and some other places. Research is needed to determine the benefits of irrigation in different growing areas.

Puddling coarse-textured soils for rice culture in the irrigated tract of the Indo-Gangetic Plains causes high soil strength in the upper layers. This may adversely affect growth and yield of following upland crops. It is possible that no-tillage (NT) in wheat (without residues of preceding rice crop) could aggravate this problem and reduce fertilizer nitrogen (N) use efficiency. In certain production scenarios, NT has been reported to be advantageous because it allows for earlier planting of wheat by eliminating delays caused by tillage. This study examined the combined effects of two crop establishment options for wheat in relation to fertilizer N and planting time following puddled rice cultivation in an irrigated environment of Punjab, northwest India. Combinations of two establishment systems, NT-direct planting and conventional-tillage (CT) with soil disruption to 0.10 m depth in main plots, with two N rates, 120 and 150 kg ha−1 in subplots, were evaluated. Variation in planting time, 31 October (D1) and 7 and 10 November (D2), was used to evaluate effect of planting-earliness. Under D1 in NT, grain yield of wheat was comparable to that under D2 in CT. However, under no advancement of wheat planting in NT, grain yield was 0.2–0.3 t ha−1 less than that in CT. This yield reduction in NT could be overcome by adding 30 kg ha−1 more fertilizer N suggesting that tillage enhanced N use efficiency. These tillage gains are ascribed to the greater extraction of profile stored and applied water and nutrients because of denser crop rooting caused by reduction in soil strength and less weed competition. Higher N use efficiency in CT suggests that farmers could achieve fertilizer N savings with this system. Comparing the tillage systems showed that NT was more cost-effective than CT even after accounting for the cost of additional fertilizer N (saving of Rs. 1685 ha−1) to overcome associated yield penalties under no advancement in planting time.

Overaged full-sun cacao plantations and the need for sustainable production systems call for combining rehabilitation of plantations with the establishment of agroforestry. We tested the effect of drastic rehabilitation pruning of old cacao tree stock and the introduction of both high- and low-diversity agroforestry on survival, growth and yield of T. cacao in a commercial plantation in peninsular Malaysia over a period of 5 years. We further determined the incidence of pests and diseases of cacao pods and assessed the performance of the whole system for smallholder farmers, including yields of by-crops. Rehabilitation pruning negatively affected cacao tree development and short-term yield. No more effects of pruning on cacao yield were observed starting in the third year on in the monoculture and starting in the fourth year on in low-diversity agroforestry. We found similar cacao tree development and yield in the low-diversity agroforestry and a common practice monoculture, suggesting that the implementation of agroforestry is a commercially feasible strategy, due to additional income generated through timber production. Reduced cacao tree development and yield in the high-diversity agroforestry were compensated by additional harvests of cassava and banana compared to monoculture. Incidence of cocoa pod borer (Conopomorpha cramerella) was lower in the agroforestry systems, especially the high-diversity system, while the incidence of black pod disease (Phytophthora spp.) did not differ between agroforestry and monoculture. The findings highlight the potential of agroforestry to reconcile ecologically sustainable land use with natural, cost-effective pest management. While pruning needs to be done with timing and disease pressure in mind to minimize short-term yield losses, this measure proved to be a feasible strategy for establishing agroforestry on extant plantations.

Pumpkin (Cucurbita maxima) is used for live mulch and edible apical shoots, seeds and fruits, and requires that a strategy for using it as ground cover in intercropping with food crops be developed while sustaining reasonable apical and fruit yields. Field experiments were conducted in 1999–2001 to investigate the effects of population density (5000, 10 000 and 15 000 plants ha−1) and sowing date (March, April and May) of pumpkin on the soil hydrothermal regime, earthworm casts, weed control, and crop growth and yields in a Yam–pumpkin intercrop. Growing pumpkin between yam mounds reduced maximum diurnal soil temperature by 4.3–8.1 °C, weeding frequency by 52% and weed dry biomass by 50–67%, while soil moisture was conserved by 48–62 g kg−1, earthworm casts were increased by 58–68% and yam tuber yield by 30–52%, irrespective of population density or sowing date, compared with yam monoculture. Intercropping had no effect on the growth and fruit yields of pumpkin, but leaf area index and apical shoot and fruit yields increased by 30–49% as the plant population increased to 10 000 plants ha−1, beyond which there was no further significant increase. Furthermore, apical shoot and fruit yields were remarkably reduced when pumpkin was sown beyond April. Increasing pumpkin population up to 10 000–15 000 plants ha−1 reduced soil temperatures by 0.7–1.2 °C, weeding frequency by 15–35% and weed dry biomass by 36–57%, conserved soil moisture by 46–63 g kg−1, and increased earthworm casts by 20% compared to 5000 plants ha−1 in both cropping systems. Although the sowing date did not affect earthworm casts and weeding frequency, pumpkin sown in March or April reduced soil temperatures by 2.6–4.0 °C and weeds by 27%, and conserved soil moisture by 15–37 g kg−1, compared with May-sown plants. Intercropping pumpkin up to 10 000 plants ha−1 with yam at an optimal sowing date target in March-April is recommended for maximum development and productivity, and when pumpkin is used for live mulch in yam plots to reduce supra-optimal soil temperature, excessive evaporation and weed growth.

The performance of newly developed extra-short-duration pigeonpea (Cajanus cajan) genotypes and traditional short-duration pigeonpea cultivars was compared in rotation with wheat in on-farm trials conducted in 1996–97 and 1997–98 in Sonepat (28° N) district in Haryana, and in 1996–97 at Ludhiana (30° N) district in Punjab, India. At both locations, a wheat crop (Triticum aestivum cv. HD 2329) followed pigeonpea. At Sonepat, an indeterminate extra-short-duration genotype ICPL 88039 matured up to three weeks earlier, yet gave 12% higher yield (1.57 t ha−1) and showed less susceptibility to borer damage than did the short-duration cv. Manak. At Ludhiana, extra-short-duration pigeonpea genotypes, ICPL 88039, ICPL 85010 and AL 201 gave similar grain yields to the short-duration T 21 in spite of maturing three to four weeks earlier. Yields of wheat crops following extra-short-duration genotypes were up to 0.75 t ha−1 greater at Sonepat and up to 1.0 t ha−1 greater at Ludhiana. The results of the study provide empirical evidence that extra-short-duration pigeonpea genotypes could contribute to higher productivity of pigeonpea–wheat rotation systems. Most of the farmers who grew on-farm trials in Sonepat preferred extra-short-duration to short-duration pigeonpea types for their early maturity, bold seed size, and the greater yield of the following wheat crop.

When water stress develops post-anthesis, wheat (Triticum aestivum L.) plants have to rely increasingly on remobilization of previously stored assimilates to maintain grain filling. In two-year field trials, we studied more than 20 agronomic and developmental traits in 61 wheat genotypes (27 F4:5 families, 17 parents used for the crosses and 17 standards), comparing plants that were defoliated (DP) by cutting off all leaf blades 10 days after anthesis with intact control plants (CP). Estimated contributions of stem and sheath assimilate reserves to grain weight/spike were from 10–54% and from 24–84% in CP and DP plants, respectively. Stem-related traits were among key traits determining stem reserve contribution (SRC). The most important genetic variables in differentiating genotypes for stress tolerance were biomass/stem, stem reserves mobilization efficiency and grain filling rate (GFR). Balance among traits related to yield maintenance in DP were more important than their high values. In general F4:5 families (FAM), that had been crossed to combine typical breeding traits such as biomass and yield components, showed better tolerance under moderate stress than standards and parents.