Eleven genotypes of soyabean (Glycine max) of tropical, sub-tropical and temperate origin and one accession of G. soja were grown in six locations in Australia during 1986–88, and at one location in Australia and two in Taiwan during 1989–91. Dates of sowing were varied within and among locations so as to expose plants to as many as 32 environments of widely different diurnal temperature and daylength. Times from sowing to flowering (f) were recorded, from which rates of progress towards flowering (1/f) were calculated. These derived data were then related to mean pre-flowering values of temperature (T¯) and photoperiod (P) using a three-plane linear model developed from controlled environment data. Among genotypes, mean values of f varied between 24–49 d and between 139–291 d in the most- and least-inductive environments, respectively. These differences were associated with variations in P from about 11 to 16 h d-1, in daily mean maximum temperatures from about 17° to 36°C, in daily mean minimum temperatures from about 5° to 25°C, and in T¯ from about 11° to 30°C, that is, a very wide range of photothermal regimes. The relations of 1/f to T¯ and P can be described in photoperiod-insensitive genotypes by a thermal plane defined by two constants, a and b, and additionally by a photothermal plane defined by three constants, a′, b′ and c′, in the more numerous photoperiod-sensitive genotypes. If photoperiod-sensitive genotypes are grown in sufficiently long days then a third photoperiod and temperature-insensitive plane is exposed, defined by a constant, d′; this plane indicates the maximum delay in flowering of which the genotype is capable. The constants a′, b′, c′ and d′ define the delay in flowering caused by photoperiod-sensitivity genes. The two intercepts between the three planes define, respectively, the critical photoperiod, Pc, above which increase in daylength delays flowering, and the ceiling photoperiod, Pcc, above which there is no further delay. The values of the six constants for any genotype can be estimated from observations of fin several natural environments. Comparisons between years in Australia and between Australia and Taiwan show that these genotypic constants can predict 1/f, and so the time taken to flower, given data on latitude, sowing date and daily values of maximum and minimum air temperatures. This model is more accurate than an alternative logistic model; we also believe that all six constants in the three-plane rate model described here have biological meaning. They indicate separate genetic control of flowering responses to P and T¯ and could form a rational basis for the genetic characterization and analysis of these responses in the soyabean germplasm.

Pronóstico del momento de floración II

Photosynthetic rates were monitored during the warm dry season in tea Clone 6/8 in a line-source irrigation × fertilizer experiment in the Southern Highlands of Tanzania. Irrigation and fertilizer increased photosynthetic rate both by enhancing photosynthetic rate per unit leaf area (A) in healthy leaves and by increasing the proportion of sunlight intercepted by photosynthetically efficient leaves. Irrigation-induced increases in A could be accounted for by increases in stomatal conductance (g) and associated reductions in leaf temperature. Fertilizer at an annual application rate of 225 kg N ha-1 caused increases in A associated with increases in g and improved responses to ambient CO2 concentration and illuminance (photon flux density, PFD). However, a further increase in fertilizer application rate to 375 kg N ha-1 a-1 decreased A in spite of increasing g. Light-saturation of photosynthesis occurred only at the higher fertilizer application rate. In unfertilized tea or tea fertilized at the lower rate, A decreased at a PFD of between 1400 and 2000 μmol m-2 s-l. These results are discussed in terms of the relation between photosynthesis and yield in tea.

Fotosíntesis en el té

Extra-short-duration pigeonpea (Cajanus cajan) genotypes generally yielded more than short-season legumes when sown at the normal time on rainfed medium-deep Alfisols. However, their growth and yield were more reduced by delayed sowings and varied more widely between seasons than those of the short-season legumes, especially cowpea and black gram. All the crops gave lower yields on shallow Alfisols than on medium-deep Alfisols and none was consistently superior. Partitioning of dry matter into grain yield was less affected by time of sowing, soil and season in extra-short-duration pigeonpea genotypes than in short-season legumes. Less sensitivity of biomass accumulation to various abiotic constraints is therefore a major objective in improving the adaptation of extra-short-duration pigeonpea genotypes.

Cajanus cajan de duración extra-corta

The effect of managing hedgerow foliage for mulch and fodder in Leucaena leucocephala and Gliricidia sepium alley farming systems on maize grain yield and soil chemical characteristics was studied in on-station and on-farm experiments in southwestern Nigeria. Yields increased as the proportion of mulch applied increased but the extra increases obtained when more than half the foliage was applied as mulch were relatively small, suggesting that half the foliage may be removed as feed without detrimental effect. Soil organic carbon, nitrogen and available phosphorus tended to increase with increasing proportion of prunings applied as mulch.

Follaje para ‘mulch’ y forraje en la agricultura de sendero

Rates of shoot extension and development (the unfolding of leaves) were recorded in an irrigation × fertilizer experiment on Clone 6/8 at Ngwazi Tea Research Unit in southern Tanzania. The wide range of mean temperatures (from 15–20°C) meant that the duration of the shoot replacement cycle (the time taken for an axillary bud released from apical dominance to develop three leaves and a terminal bud), in fully irrigated tea receiving 450 kg N ha-l, varied from 65 d in the warm wet season to 95 d in the cool dry season, compared with 75 to 180 d for unirrigated and unfertilized tea. Regression analysis indicated that the base temperature for extension, for Clone 6/8 in high-input plots, was about 10°C, some 2–3°C more than that for development. As a result of these differences in base temperature, the length of shoots with three leaves and a bud varied considerably between treatments and seasons, ranging from 15 mm in the unirrigated plots (at the end of the dry season) to 130 mm in the high-input plots at the start of the rains. Shoots from well fertilized tea were always longer (at a given stage of development) than those from unfertilized tea. The results are discussed in terms of the possible mechanisms responsible for the observed responses (changes in partitioning between roots and shoots), commercial harvesting practices and yield modelling.

Extensión y desarrollo de broies en el té

Prolonged moisture stress and high vapour pressure deficits reduced the shoot water potential, shoot population density, rate of shoot extension and yield of clonal tea. The more drought susceptible Clone 6/8 had a lower shoot water potential, rate of shoot extension, number of shoots per unit area, rate of shoot regeneration and yield than the more tolerant Clones 31/8, 57/15 and 15/10 during the periods of low soil moisture, which coincided with high vapour pressure deficits. The changes in the shoot growth components could be used as an index of the suitability of different clones for different regimes of soil moisture and vapour pressure deficits.

Factores ambientales que afectan el rendimiento del té

The effects of temperature and soil water potential on maize germination were investigated in controlled environment conditions and the effects of depth of planting and a mulch on maize emergence were studied in a field experiment in eastern Kenya. The rate of germination increased to an optimum temperature of 33.6°C above a base temperature of 6.1°C and decreased above the optimum to zero germination at 42.9°C. The thermal time for median germination increased from 51.5°Cd to 56.4°Cd as soil matric potential decreased from -5 to -40 kPa. Soil water content, depth of planting, and their interaction had significant (P < 0.001) effects on final germination and emergence but mulch, or any interactions involving mulch, had no such effects. Increasing depth of planting by 1 cm increased the thermal time required for emergence by 2.8°Cd, and decreasing water content by 1% increased the thermal time required for emergence by 3.2°Cd.

Germinación y emergencia del maíz

Spatial nutrient distribution was studied under a three-and-a-half-year-old fallow of Dactyladenia barteri, Alchornea cordifolia, Senna siamea and Gmelina arborea hedgerows grown on an acid Ultisol in southeastern Nigeria. The objectives were to evaluate the nutrient cycling capacity and suitability of the hedgerow species for alley cropping. No consistent patterns were observed in the lateral distribution of soil pH, total nitrogen, organic carbon, available phosphorus, exchangeable cations (potassium, calcium, magnesium and sodium), total acidity and effective cation exchange capacity in the 4 m wide alleys formed between the hedgerow species. Senna siamea and Gmelina arborea tended to increase soil organic carbon, calcium, magnesium and effective cation exchange capacity, particularly in the top 50 cm, compared with Alchornea cordifolia and Dactyladenia barteri, and can therefore be recommended for soil fertility regeneration on acid Ultisols during periods of fallow. However, they appear to be less suitable for alley cropping than Dactyladenia barteri because they are shallow rooting.

Propiedades químicas delo suelo bajo cuatro especies de seto vivo

The effects of intercropping young plants of the compact arabica coffee hybrid cultivar Ruiru 11 with potatoes, tomatoes, maize and Phaseolus (dry) beans were studied between 1987 and 1989 at Ruiru in Kenya. Yields of clean (hulled) coffee were reduced by the maize intercrop by 59–100%. Coffee bean size, and raw, roast and liquor quality were not significantly affected by the potato, tomato and bean intercrops, which gave positive net economic benefits. Potatoes planted between all the coffee rows gave the largest marginal rate of economic return, followed by tomatoes in combination with beans. The technically and economically viable intercrops for coffee were potatoes, tomatoes, beans, and tomatoes in combination with beans.

Siembra simultánea de café Araébica y cultivos para la alimentatión

Seed of the new heavy yielding bean cultivar Carioca was distributed directly to 400 farmers in Zambia during 1986 in order to speed its adoption and diffusion. Three years after distribution, 55% of the farmers who participated in a follow-up survey were still sowing Carioca. Diffusion of the new cultivar had occurred, with 3.7 times as many farmers estimated to be growing Carioca in 1988/89 as in 1986, an annual rate of diffusion of approximately 49%. Use of a logistic modelling framework suggested that the variables directly associated with the decision to adopt the cultivar were the farmer's total area in cultivated crops and the area in local maize. Variables indirectly associated with adoption were the level of education of the household head, the average number of years that the fields had been in continuous cultivation and the number of cattle owned. These results will help guide the development of effective strategies for the release and distribution of new bean cultivars from national bean research programmes in sub-Saharan Africa.

Adopción y difusión del poroto Carioca en Zambia