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

Reports that an Indonesian soyabean (Glycine max) line (TGm737p) shows greater seed storage longevity than an American cultivar (Bossier), and that the cross between them (TG×536–02D) is intermediate between the two parents in this regard, were investigated by growing all three genotypes under identical conditions (30°C/20°C, 12 h d-1 photoperiod) in a plastics house. Seeds were harvested when moisture content had declined naturally to 14–15% (wet basis), and then stored hermetically at five different moisture contents at 40°C. Analyses of the resultant seed survival curves revealed that the seed lot constant Ki (a measure of potential longevity) was greatest in TGm737p and least in cv. Bossier, the cross being much closer to the American parent in this regard. The negative logarithmic relation between σ (standard deviation of the frequency distribution of seed deaths in time) and moisture content did not differ (p > 0.10) among the three genotypes. Moreover, this relation was close to that predicted by earlier results for four different genotypes. Similarly, there was no significant difference (p > 0.25) among genotypes in the negative semi-logarithmic relation between σ and seed equilibrium relative humidity (rh): the regression slope was equivalent to a doubling of longevity for each 8.0% reduction in rh. Finally, comparison of the negative logarithmic relation between absolute longevity (50% viability period) and seed moisture content confirmed that TGm737p showed greatest longevity (p > 0.005), but failed to show a difference in absolute longevity between cv. Bossier and the cross (p > 0.25). The results confirm that the seed viability equation of Ellis and Roberts (1980a, b) provides a framework within which the seed longevity of different genotypes can be compared. They suggest too that there is considerable doubt as to whether or not the greater potential longevity of the Indonesian line TGm737p has been incorporated successfully into the cross TG×536–02D.

Longevidad de la semilla de soja

The effects of levels of soil moisture and plant population on lodging and associated losses from mechanical harvesting of two lentil genotypes, one susceptible and one resistant to lodging, were investigated during 1986–87 and 1987–88 at Tel Hadya in northern Syria. High plant population increased lodging because the crowded plants had thin stems, while high levels of soil moisture caused lodging because biological yield was increased. When biological yields were high a two tonne increase in biological yield led to a one point increase in lodging score. Mechanical harvesting increased losses in biological yield due to lodging by 12% compared with yields obtained by hand harvesting under rainfed conditions and by 24% at the highest level ofsoil moisture. It is suggested that supplementary irrigation should be used in dry seasons in trials to select genotypes resistant to lodging.

Decaimiento de la lenteja

Although the relationship between the length of a growing tea shoot and time is not truly exponential, the exponential relative shoot extension rate (ERSER) can be used for comparisons when both the initial shoot lengths and the periods of measurement are identical. An empirical method to adjust ERSER for variations in initial shoot length was developed for weekly field measurements of seven tea clones in Malawi. ERSERs, measured throughout the two growing seasons after the bushes had been pruned, were standardized to an initial shoot length of 2.5 cm and were then related to mean weekly air temperatures and to vapour pressure deficits. There were large clonal differences in the response of ERSER to temperature within the range 18–23°C. Shoots of the vigorous Malawi clone SFS 150 elongated rapidly at all temperatures, but notably at the lower temperatures (18–20°C). Two Kenyan clones, BB/35 and K6/8, did not grow well at about 18°C, which is normal for growth in Kenya but which coincides with the period of short daylengths (less than 12 h) in Malawi. A significant decrease in ERSER was found with increased vapour pressure deficit over the whole range of field measurements and ERSERs were uniformly lower in the second year after pruning. The results suggest that the usual calculations to derive an inherent base temperature for elongation are not valid unless elongation is truly exponential and therefore, in general, base temperatures should not be used for comparisons between experiments.

Coconut is harvested at bimonthly intervals (six picks per year) in all field experiments carried out by the Coconut Research Institute in Sri Lanka. Because recording of individual picks is costly and time consuming, it is of interest to know whether or not recording can be restricted to fewer picks without prejudicing the results of experiments. Yield data from five long-term field experiments conducted at five different locations showed that the sum of the first, third and fifth picks could provide a good estimate of the sum of six picks. Yield recording can therefore be confined to these three picks and the cost and time of recording in an experiment reduced by 50%. These three picks can conveniently be used to assess treatment effects on total annual yield.

Análisis estadístico del rendimiento de coco

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

Seven sorghum lines, flowering from 50 to 87 days after sowing, were subjected to early drought stress, late stress, and both early and late stress in the field during the dry season in India. Panicle initiation was delayed by 2–25 days and flowering by 1–59 days by the drought stress treatments, the greatest effect being in the treatment subjected to both early and late stress. Stress increased the period between panicle initiation and flowering by retarding the rate of panicle development; when stress was severe panicle development stopped. Upon relief of stress following irrigation, panicle development resumed at rates comparable to those in a fully irrigated control. The rate of leaf appearance was affected in a similar manner to panicle development soon after water was withheld. Rate of leaf appearance and panicle development decreased as pre-dawn leaf water potential decreased and ceased at water potentials of −0.55 and −0.7 MPa, respectively.

The fate of seed of six annual medics produced in spring 1987 and used in the pasture phase of cereal-pasture rotations was followed over four years. The medics were sown at low and high density, and seed set beyond 1987 was prevented by cultivation in 1988, and by herbicides in 1989 and 1990. The breakdown of hard seed was measured in the summer and autumn of each year, and the number of seedlings was counted after the first seasonal rains in the final three years. The survival of seeds buried at three depths was monitored. Seed of Medicago noeana lived longer than that of M. rotata and M. polymorpha. Survival of M. rigidula and M. truncatula seed was intermediate and there was no effect of planting density on survival. Breakdown of hard seed was least in the first year and increased in the second and third years. Within any year breakdown began in late summer or early autumn, beginning earlier as the seed aged. Seed burial enhanced germination in the year following seed set, depressed it in the second and third years, and had little effect in the fourth year. The net effect of seed burial on survival was therefore slight. The results suggest that the use of medics that have harder seeds than currently available cultivars, and medics in which germination is delayed until late in the autumn, will increase the sustainability and productivity of cereal-pasture rotations in semi-arid areas.

Dinámica de semilla de los Medicago spp anuales en Siria

Four peanut cultivars of Spanish or Virginia botanical type and varying time to maturity were grown at a range of plant densities (44 000 to 352 000 plants ha-1) and spatial arrangements under irrigated conditions in sub-tropical southern Queensland, Australia. Total and pod dry matter production of the very early maturing Spanish cultivar Chico showed strong positive responses to increased plant density up to the highest density tested. Responses were less pronounced for the later maturing Spanish cultivar McCubbin and were minimal for the Virginia cultivars Early Bunch and Mani Pintar. All cultivars were insensitive to spatial arrangements. Accumulation of total dry matter, adjusted for the higher synthesis costs of oil and protein during seed filling, was well correlated to intercepted photosynthetically active radiation (PAR). Much of the variation in dry matter production among cultivars and plant populations could be accounted for by the effects of differing leaf area duration on cumulative intercepted PAR. Radiation use efficiency was negatively associated with the canopy extinction coefficient (k) within most sowing dates, and also negatively associated with minimum temperature across sowing dates for all cultivars except Mani Pintar.

Crecimiento y eficacia del use de radiación en el maní

A field technique to screen pearl millet genotypes for their emergence and survival at high soil surface temperatures is described. Genetic variation in seedling emergence and survival is shown and it is argued that this variation is largely due to tolerance of high temperatures rather than tolerance of soil moisture deficit, although some interaction occurred. An index for ‘thermotolerance’ is defined and genotypes are ranked accordingly for this trait, which is shown to be highly heritable. The technique is repeatable and allows a large number of genotypes to be screened at the same time.

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

Three early and four later flowering lines of sorghum were subjected to three drought stress treatments (early, late and early plus late stress) in the field during the dry season at Hyderabad in India. Mean diurnal temperature and evaporation rate were uniformly high throughout the experiment. The late and early plus late stress conditions were severe, while the early stress was mild.

Grain yield was affected by both the timing and the severity of the stress. The largest reduction (87%) in grain yield resulted from stress imposed during booting and flowering (late stress) in the early flowering lines; the same stress treatment on vegetative plants had no effect on grain yield. Increasing the duration of severe stress on vegetative plants (early plus late stress) reduced grain yield by 50–60%.

Grain yield was strongly and positively correlated with the number of grains m-2. Variation in grain yield was associated with variation in total dry matter rather than with harvest index, which was only reduced when stress occurred at flowering. Treatment effects on thermal growth rates (g m-2 °Cd-1) during the phase from booting to flowering confirmed that growth during this phase is the major determinant of yield potential (number of grains). The importance of phonology in research into drought resistance is discussed.

A study conducted at Ibadan, Nigeria, showed that some community water supplies were slightly polluted by the pesticides applied on adjacent farms. There was also evidence of soil degradation as a result of agrochemical use, with differences in the physico-chemical properties of soils in fields where agrochemicals had been applied and in adjacent fields that had not been cultivated. Measures that can be taken to minimize some of the environmental dangers inherent in the application of agrochemicals are discussed.

The partitioning of dry matter between vegetative and reproductive yield components was analysed for four diverse peanut cultivars at a range of sowing dates and plant populations in sub-tropical Queensland, Australia. Rates of accumulation of pods (pod addition) varied significantly with both cultivar and sowing date. Within cultivars, much of this variation could be attributed to variation in crop growth rate during the critical pod addition period. The proportion of current assimilate distributed to pods depended on inherent cultivar characteristics and also correlated well with the current crop growth rate relative to the crop growth rate during pod addition (that is, with relative source activity). Neither plant density nor spatial arrangement had any significant effects on patterns of assimilate distribution. All cultivars appeared capable of remobilizing stored assimilate to maintain constant rates of pod yield increase despite fluctuations in crop growth rate which might be expected to produce short term source limitations to pod yield accumulation. The harvest index (HI) increased linearly during the entire pod fill period in all cultivars except the very early maturing Spanish cultivar Chico. Neither density nor spatial arrangement affected rate of increase in HI except in Chico, where increased density produced increased rates of increase in HI. Variation in the rate of HI increase among sowing dates was small.

Distributión de la materia seca en el maní

Gliricidia sepium is a leguminous tree native to Mexico and Central America, and is utilized for fuelwood, animal fodder and green manure in rural communities. It is widely distributed throughout the tropics, but many populations of the tree have arisen from haphazard introductions of unknown quality. Methods for determining the genetic structure and origin of populations are therefore required as a basis for genetic improvement. In order to test the effectiveness of various measures of genetic diversity, provenances of G. sepium from Panama, Guatemala, Mexico and Honduras were studied by electrophoresis of seed storage proteins and the enzymes leucine aminopeptidase (LAP) and acid phosphatase (ACP), and by measurement of plant morphological characteristics. Study of seed storage proteins and morphological characters was very informative, and there was some genetic variation for ACP, but LAP showed no clear variation. In the cases where genetic variation was present, the different methods of study showed a consistent pattern of variation: genetic diversity was greatest in the population from Honduras, and least in that from Panama. This was contrary to expectations on the basis of the locations of origin of the populations and the range in which G. sepium is believed to be native. Electrophoresis of the storage proteins of Gliricidia maculata confirmed the status of this species as a distinct taxon.

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

The adaptation of extra short duration (ESD) pigeonpea (Cajanus cajan) genotypes to rainfed environments was studied on Alfisols and Vertisols at the ICRISAT Center between 1987 and 1989. Despite a slightly shorter crop duration, the grain yield of ESD genotypes was twice as large on Alfisols as on Vertisols. On both soil types, the rate of growth and grain yield were better in crops sown on time than in those where sowing was delayed. The population levels necessary to maximize yield varied among genotypes on Alfisols, where the grain yield of several ESD genotypes compared favourably with that of ICPL 87, a standard short duration genotype. However, none of the ESD genotypes yielded more than ICPL 87 on the Vertisols.

After farmer-to-farmer training, farmers at an upland research site in the Philippines adapted and adopted contour hedgerows over a period of four years. They developed hedgerow establishment methods that required less labour, eliminated grasses that were too competitive with crops, stopped planting trees that were initially intended to produce green manures, and planted species that might provide direct cash returns. The different systems they used controlled soil erosion equally and effectively, although grazing of hedgerows by neighbours’ cattle was a problem. The farmers who learned about the technology but who did not establish contour hedgerows on their farms were those who had a higher proportion of flat land and/or off -farm or non-farm income opportunities.

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

The diffusion of rice varieties introduced into an area with poor production potential and problems of soil degradation was studied in a farming systems research and extension programme. Two rice varieties, BW. 272–3 and At. 85–1 were identified as appropriate for the area and efforts made to transfer the experimental results to the farmers. BW. 272–3 was widely adopted by farmers in the lower, intermediate and upper areas of the recommendation domain but adoption of At. 85–1 was confined to the intermediate and upper areas. Adoption of rice varieties was mainly governed by the characteristics that allowed a variety to perform well under adverse conditions and by the farm gate price it could command, which depended on grain pericarp colour.

Difusión de nuevas variedades de arroz