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.

Long-term indicators of soil fertility were assessed by measuring grain yield, soil organic carbon (SOC) and soil Olsen phosphorous for a P-deficient soil. In one set of treatments, goat manure was applied annually for 13 years at 0, 5 and 10 t ha−1, and intercrops of sorghum/cowpea, millet/green gram and maize/pigeonpea were grown. Yield depended on rainfall and trends with time were not identifiable. Manure caused an upward trend in SOC, but 10 t ha−1 manure did not give significantly more SOC than 5 t ha−1. Only 10 t ha−1 manure increased Olsen P. Measurements of both SOC and Olsen P are recommended. In another set of treatments, manure was applied for four years; the residual effect lasted another seven to eight years when assessed by yield, SOC and Olsen P. Treatment with mineral fertilizers provided the same rates of N and P as 5 t ha−1 manure and yields from manure and fertilizer were similar. Fertilizer increased Olsen P but not SOC. Management systems with occasional manure application and intermediate fertilizer applications should be assessed. Inputs and offtakes of C, N and P were measured for three years. Approximately 16, 25 and 11% of C, N and P respectively were stabilized into soil organic matter from 5 t ha−1 a−1 manure. The majority of organic P was fixed as soil inorganic P.

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.

The effect of Rhizobium strain and low levels of nitrogen on growth and nitrogen fixation was studied on 5 seedlines of Phaseolus vulgaris. All plants responded to irrigation when low levels of nitrogen were supplied throughout each experiment during vegetative growth, but the final seed yield was not significantly affected. All strains induced less nodule tissue and lower nitrogenase activity per plant when nitrogen was applied; some strains were less sensitive than others. The proportion of the plant's nitrogen estimated to be derived from fixation (based on acetylene reduction) and fertilizer was affected by host genetics. Nodulated plants had nitrogenase activities comparable with other grain legumes and responded to combined nitrogen during vegetative growth, but this was not reflected in grain yield.

An intercropping experiment is described, using a parallel-row systematic design, to examine four plant populations of chickpea in all combinations with 15 systematically arranged populations of safflower in 1:1 and 2:1 row arrangements; four populations of the sole crops were included. Safflower was usually dominant and increasing the total population (i.e. both crops combined) made it more so. Safflower yield was little affected by changes in its own population and was independent of changes in the chickpea population. Chickpea yield increased with increase in its own population and it was the dominant crop at high chickpea/low safflower populations. An initial increase in safflower population caused an increase in chickpea yield at the 1:1 row arrangement; otherwise increasing safflower population decreased chickpea yield. LERs at 2:1 indicated no real evidence of yield advantages for intercropping. At 1:1 advantages ranged up to 19%, with a maximum where the highest chickpea population was combined with a low safflower one. This optimum combination could not have been identified with earlier designs.

Field trials designed to investigate the effects of nitrogen, phosphorus and potassium on the yield, starch and dry matter content of white guinea yam were conducted over a four year period in south western Nigeria. The optimum level of nitrogen for successful production of white guinea yam was 35 kg ha−1 in a forest Alfisol that had been under cultivation for at least two years. Nitrogen, phosphorus and potassium had no significant effect on starch content, but large applications of phosphorus and potassium significantly decreased dry matter accumulation.

A previously presented model for one-dimensional soil movement by repeated tillage is extended for use under the more complex conditions of long-term field experiments, for (i) following the two-dimensional movement (along and across the plots) of accumulating substances (nutrients, disease organisms, etc.) caused by tillage; (ii) determining the smallest acceptable plot size from given conditions, when planning new long-term field experiments and (iii) determining the size of the discard relative to the size of the treated plot.

Diagrams are given from which rough estimations can be made of both the movement of accumulating substances in long-term field experiments and the smallest acceptable plot size, when a computer with the necessary facilities is not available.

The decline in fertility of red ferrallitic soils in Uganda under arable cropping, and its restoration under permanent vegetation, is shown to be associated with losses and gains of major nutrients by the top-soil. A fertilizer mixture formulated to correct the losses and imitate the gains of nutrients consistently increased crop yields and maintained soil fertility over 4 years. Reasons for the success of the fertilizer mixture and its potential use in other tropical areas are discussed.

Daily courses of leaf gas exchange and leaf water potential (Ψleaf) of green dwarf coconut palm (Cocos nucifera) were measured in irrigated plantations on the wet coastal plateau and in a dry semi-arid area of northeast Brazil. At both sites, significant correlations were obtained between stomatal conductance (gs) and vapour pressure deficit (VPDair), Ψleaf and VPDair, leaf transpiration (E) and gs, and E-Ψleaf. Despite these similar relationships between sites, stronger correlations involving gs-VPDair and E-Ψleaf were found at the semi-arid site, where whole-plant hydraulic conductance (gp) was correlated significantly with VPDair. In addition, at the semi-arid site, only, the net photosynthesis (PN) was not correlated with E and Ψleaf, and the intrinsic water use efficiency (WUEi) was disconnected from VPDair and Ψleaf. The different behaviour of leaf gas exchange and Ψleaf between sites was probably caused by low gs in response to high VPDair at the semi-arid site. Our results indicate potential for significant alterations in the pattern of leaf gas exchange during future climatic changes with increasing temperature and concomitant increases in VPDair. The atmospheric water stress will probably reinforce the strength of connection among water relation variables (E, Ψleaf, gs, gp, and VPDair), but it will disrupt the linear relationship between net CO2 assimilation and leaf water relations such as PN-E, PN-Ψleaf, WUEi-VPDair and WUEi-Ψleaf.

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.

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.

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.

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

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 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.

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.

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.

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.

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.

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.