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.

Studies on the effect of climatic factors such as rainfall, relative humidity, temperature, sunshine hours, pan evaporation, evapotranspiration, solar radiation, vapour pressure and wind velocity on the button shedding, premature nut fall, and final nut yield of coconut, and crop-weather models developed to predict nut yield, are reviewed. The type of data and statistical analyses techniques used and the areas of research poorly addressed under the different topics are highlighted.

Efectos de las condiciones climáticas y el tiempo en el coco

Field experiments were carried out under irrigation in Central Saudi Arabia during the winters of 1987–88 and 1988–89 to examine the productivity and quality (grain protein content) of wheat intercropped with inoculated and uninoculated alfalfa with or without additional nitrogen. Nitrogen increased wheat grain yield and protein percentage but inoculation of the alfalfa had no additional effect. Herbage yield of intercropped alfa4fa was unaffected by nitrogen application. Added nitrogen reduced the protein percentage in alfalfa but increased its protein yield. Intercropping had benefits for alfalfa, increasing its protein content and yield.

Siembra simultánea de trigoy alfalfa

Root and tuber crops make a major contribution to the food supply in many developing countries. Most of the relatively limited research effort on tropical root crops has focussed on improved production technologies, especially with regard to genetic improvement. Interest in post-harvest technologies and crop use has increased recently with the growing recognition of their importance in the marketing of these perishable crops. This paper reviews recent advances in storage research for three of the principal root crops: cassava (Manihot esculenta C), yam (Dioscorea spp.) and the edible aroids (Colocasia spp.).

R. D. Cooke, J. E. Rickard y A. K. Thompson: El almacenamiento de tubérculos tropicales - mandioca, ôame y aráceas comestibles.

Stands of groundnut were grown at four densities on water stored in a medium depth alfisol in central India. Evaporation was estimated from changes in soil water content, and partitioned between transpiration and evaporation from the soil surface. Seasonal transpiration was strongly influenced by plant population, and approached a maximum as the population density increased to 23 plants m−2. Evaporation from the soil surface was only a small component of the seasonal water balance in dense stands, and was little affected by planting density. Differences in transpiration rate between spacings were greatest early in the season, but diminished when the denser stands ran out of water. The denser stands extracted more water from deep in the profile. Plants in widely spaced rows preferentially extracted water from near the row; water mid-row was only used later in the season.

The phenology of mung beans is extremely plastic; responsiveness to both photoperiod and temperature is known to modulate flowering. A previous conclusion, perpetuated uncritically now for almost forty years, has been that both (quantitative) short- and long-day flowering responses exist in the mung bean germplasm. However, our re-analysis of the original data leads us to an alternative conclusion: that genotypes of mung bean are quantitative short-day plants with different optimum mean diurnal temperatures for flowering. This alternative interpretation (which is plausible biologically and in evolutionary terms) is discussed.

Field trials conducted previously in Niger have shown that in years when the onset of the rains is 15–20 days earlier than average, the long growing season can be exploited by growing a relay crop of millet (Pennisetum glaucum) and cowpea (Vigna unguiculata). In the trials reported here, the advantages of relay cropping were compared with intercropping with improved management and intercropping under traditional management during the 1989, 1990 and 1991 rainy seasons at the ICRISAT Sahelian Center, Sadore, Niger. The length of the growing season varied from 139 to 150 days over the three seasons. The relay crop produced more dry matter and leaf area and yielded more than the intercrops in all three years, confirming that in years when the onset of the rains is early, relay cropping with millet and cowpea is a better option than growing the same two species as an intercrop. Relay cropping avoids the competitive effects inherent in intercropping systems, while offering the additional advantages of rotating cereals with legumes.

Mijo y caupí en sistemas de relevo y de cultivo simultáneo

The main objective of this study was to determine the best soil amendment and tillage practices for sustainable millet yield and grain and stover quality. The treatments included tillage practices (immediate-, late- and no-till) and soil amendments (sheep manure plus urine, manure, millet stover (stalks, leaf blades and leaf sheaths) and millet stover ash) in factorial combinations with fertilizer nitrogen levels of 0, 15 and 30 kg ha−1 plus controls. Results showed that (i) higher yields were obtained in tilled plots than in no-till plots; (ii) tillage timing may not be a significant yield determining factor; (iii) the application of animal urine resulted in significantly higher yield and greater nitrogen, phosphorus and potassium uptake than the application either of manure alone or of millet stover. Urine application (ruminant urine contains virtually no phosphorus), which elevates soil pH especially during the first week after application, may have resulted in the dissolution of phosphorus from the aluminium–iron complexes of kaolinitic clays. This is corroborated by the significantly higher phosphorus uptake from the manure-plus-urine plots than from plots amended with either manure alone or millet stover. Long-term implications of ‘mining’ soil phosphorus with repeated applications of animal urine in these fragile ecosystems remains unclear.

Insect infestation and damage in cowpea (Vigna unguiculala), planted sole or intercropped with tomato (Lycopersicon esculentum) was monitored in 1987 and 1988 in Akure, Nigeria. Infestation of cowpea by Empoasca dolichi was significantly reduced by intercropping with tomato in both years, except in the early season of 1988. Infestation of cowpea by Ootheca mutabilis, Aphis craccivora, Megalurothrips sjosledti and Maruca testulalis was not affected by intercropping with tomato in either year. Damage by pod-sucking bugs and Heliothis armigera was significantly higher in sole cowpea than in cowpea intercropped with tomato, in both years. Sole cowpea had a significantly lower seed yield than cowpea intercropped with tomato.

Observaciones en cuanto a la infestación de insectos y daños en el caupí (Vigna unguiculata) sembrado en forma simultánea con tomate (Lycopersicon esculentum) en una zona de bosque tropical en Nigeria

The yield response to drought and temperature of six contrasting tea clones was studied in a line-source irrigation experiment in Southern Tanzania. The selected clones, all commercially and/or scientifically important in eastern Africa, embrace a range of morphological and physiological types. The bushes were planted in August 1988 and differential drought treatments were imposed for 16 and 13 weeks towards the end of the dry seasons in 1990 and 1991, respectively. The resulting soil water deficits were successfully simulated using a water balance model. Under well-watered conditions Clone S15/10 (from Kenya) gave the highest yield of dry tea, reaching 5600 kg ha−l in the fourth year after planting (1991/92) compared with 3640–4420 kg ha−1 for the other five clones. During the cool season Clone SFS150 (from Malawi) yielded more than Clones 1, 207, 6/8 and K35. Although annual yields decreased curvi-linearly as the maximum soil water deficit increased, single values for the drought sensitivity of each clone could be derived by using stress time as an index of drought. On this basis Clones S15/10 and 207 were identified as being the most sensitive to drought; Clones SFS150 and 1 were drought resistant. The reasons for these differences in yield responses and the importance of determining drought sensitivity over an appropriate time period are discussed.

There are currently concerns within some sugar industries that long-term monoculture has led to soil degradation and consequent yield decline. An investigation was conducted in Swaziland to assess the effects of fallowing and green manuring practices, over a seven-month period, on sugarcane yields and the physical properties of a poorly draining clay soil. In the subsequent first sugarcane crop after planting, yields were improved from 129 t ha−1 under continuous sugarcane to 141–144 t ha−1 after fallowing and green manuring, but there were no significant responses in the first and second ratoon crops. Also, in the first crop after planting, root length index increased from 3.5 km m−2 under continuous sugarcane to 5.2–6.8 km m−2 after fallowing, and improved rooting was still evident in the first ratoon crop where there had been soil drying during the fallow period. Soil bulk density, total porosity and water-holding capacity were not affected by the fallowing practices. However, air-filled porosity increased from 11 % under continuous sugarcane to 16% after fallowing, and steady state ponded infiltration rates were increased from 0.61 mm h−1 to 1.34 mm h−1, but these improvements were no longer evident after a year back under sugarcane. Levels of soil organic matter were reduced in all cases, probably as a result of the tillage operations involved. In the plant crop, root length was well correlated with air-filled porosity, indicating the importance of improving belowground air supply for crop production on poorly draining clay soils.

Most oil palm pollen is produced by male inflorescences 2–3 days after anthesis, and this pollen is the most viable. When protected, pollen viability on female inflorescences is good up to 6 days, after which it declines. The majority of the pollen remains below the canopy, especially at bunch level. Results of quantitative evaluation of pollen dispersal showed that atmospheric pollen density is very variable and is governed by numerous factors. There is a marked diurnal variation, with highest pollen density during the afternoon and a negligible amount during the night and early morning. Rain causes an immediate drop in concentration, but pollen densities were influenced more by the number of days on which rain was recorded than by total rainfall. A relationship exists between pollen density, the number of male inflorescences in the vicinity, and rainfall, but the effects of relative humidity, sunshine and wind are obscure. Whilst pollen density drops rapidly within a short distance from the inflorescence, there is a significant dispersal over greater distances than previously thought.

An experiment was conducted on peanut inoculation with Rhizobium inoculum, introduced below the planting level at three different soil depths (8, 12 and 15 cm.), to ensure more favourable moisture conditions for proliferation of the root nodule bacteria, and to obviate the need for frequent irrigation. Inoculation on both sides of the peanut rows, after the plants had emerged, was also tested. The number and weight of nodules per plant decreased with increase in placement depth. Side inoculation after emergence of the plants resulted in significantly less plant infection than placement of the inoculum at 8 and 12 cm. depths. Peanut yield and quality after inoculation at 15 cm. depth were significantly lower than at 8 cm. inoculation.

To improve the national average yield of potato in Ethiopia, which is very low as compared to its potential, factors that influence technical efficiency of potato production need to be determined. Therefore, the objective of this study was to investigate the determinants of technical efficiency using a cross-sectional data collected from 368 randomly selected potato producers in Northern Ethiopia using a multi-stage sampling technique. The study employed Cobb–Douglas stochastic frontier model to get farm-level technical efficiency scores. Tobit model and principal component analysis were used to determine the factors that influence technical efficiency of farm households. The results revealed that chemical fertiliser, seed potato, plot size and labour are statistically significant factors that affect potato yield. The average technical efficiency score was estimated to be 75%; and education, experience, off-farm income, household size, membership in a farmers’ association, use of irrigation water, extension contact, use of improved seed, access to product market and weak coordination of stakeholders’ were significant factors influencing technical efficiency. The findings of the study suggest that there is a need for government intervention to create strong market linkage between producers and buyers and to give appropriate training to agricultural extension agents.

Inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) improved growth of chick-pea (Cicer arielinum L.) and doubled phosphorus (P) uptake at low and intermediate levels of P fertilization in a pot experiment on sterilized low-P calcareous soil. In field experiments at Tel Hadya, northern Syria, growth, shoot P concentration and seed yield of spring-sown chickpea remained unaffected by inoculation with VAMF or by P fertilization. The mycorrhizal infection of chickpea was high (approximately 75% of root length mycorrhizal at the flowering stage) irrespective of inoculation with VAMF or P fertilization and may ensure efficient P uptake under field conditions.

This paper evaluates 30-year (2013–2042) projections of the selected climatic parameters in cotton/wheat agro-climatic zone of Pakistan. A statistical bias correction procedure was adopted to eliminate the systematic errors in output of three selected general circulation models (GCM) under A2 emission scenario. A transfer function was developed between the GCM outputs and the observed time series of the climatic parameters (base period: 1980–2004) and applied to GCM future projections. The predictions detected seasonal shifts in rainfall and increasing temperature trend which in combination can affect the crop water requirements (CWR) at different phonological stages of the two major crops (i.e. wheat and cotton). CROPWAT model is used to optimize the shifts in sowing dates as a climate change adaptation option. The results depict that with reference to the existing sowing patterns, early sowing of wheat and late sowing of cotton will favour decreased CWR of these crops.

Previously published data from two tea experiments in Tanzania and Malawi were re-analysed to identify factors responsible for the marked seasonal peaks and troughs of production observed at the two locations. Simulation modelling indicated that the influence of seasonal variations in temperature or photoperiod on shoot growth rates alone were not able to explain the occurrence of a large peak in September/October followed by smaller and progressively wider peaks in December, February and April in well-irrigated, well-fertilized tea at the two sites. Various mechanisms to explain these seasonal variations in yield are discussed, but it is concluded that the best explanation is the regulation of the numbers of shoots available for harvesting through the effect of photoperiod on shoot activity. The significant production peak normally obtained in September/October at both locations can then be explained by the release of a large number of buds from their resting state around the time of the winter solstice in June. Subsequent peaks are due to successive cohorts of shoots released from apical dominance when the preceding peak is harvested.

Thirty on-farm trials were conducted in northwest Syria over a period of four seasons to examine the main effects and interaction of sowing date, sowing method, Rhizobium inoculation, phosphate application and weed control on chickpea (Cicer arietinum). Advancing the sowing date from spring or late winter to early winter resulted in substantial yield increases. The effects of Rhizobium inoculation were small and inconsistent. Chemical weed control significantly increased grain yield compared with the unweeded control treatment in winter-sown crops but was less effective than hand weeding. Phosphate application significantly increased yield in the first three seasons, the overall increase being 10%. Drilling chickpea seed gave an overall 10% increase in yield compared with the broadcast sowing commonly practised by farmers. There is no economic or environmental risk to the farmer in adopting the proposed practices either singly or in combination. However, the greatest gains in yield and net revenue are derived from a combination of early winter sowing, drilling, weeding and, where appropriate, phosphate application.

Average seed yields of effectively nodulated cowpea plants were 38% greater than those of non-nodulated plants when both received applied nitrogen at concentrations ranging from 60 to 240 ppm during one of three periods: emergence to first flower, first flower to mid pod-fill, or mid pod-fill to maturity. Nodulation increased seed yields by 45% when plants received a ‘basal’ level of 30 ppm N throughout growth. None of the combined nitrogen treatments could compensate non-nodulated plants for the loss of symbiotic nitrogen fixation. Non-nodulated plants relying on applied N branched less, produced fewer peduncles and set fewer pods on each peduncle than nodulated plants.