Hot Tropics Research Articles

Growth and biomass production in potato grown in the hot tropics as influenced by paclobutrazol

Two similar field trials were carried out during 2003 in a hot tropical region of eastern Ethiopia to investigate the effect of leaf and soil applied paclobutrazol on the growth, dry matter production and assimilate partitioning in potato. A month after planting paclobutrazol was applied as a foliar spray or soil drench at rates of 0, 2, 3, and 4 kg a.i. paclobutrazol ha−1. Plants were sampled during treatment application and subsequently 2, 4, 6 and 8 weeks after treatment application. The data was analyzed using standard growth analyses techniques. None of the growth parameters studied was affected by the method of paclobutrazol application. Paclobutrazol decreased leaf area index, crop growth rate, and total biomass production, and increased specific leaf weight, tuber growth rate, net assimilation rate, and partitioning coefficient of potato. At all harvesting stages, paclobutrazol reduced the partitioning of assimilate to the leaves, stems, and roots and stolons and increased allocation to the tubers. Although paclobutrazol decreased the total biomass production it improved tuber yield by partitioning more assimilates to the tubers. Paclobutrazol improved the productivity of potato under tropical conditions by redirecting assimilate allocation to the tubers.

Pavement evaluation for thermal/glare comfort during footdrills

The conventional material used for military parade squares in Singapore is dense asphaltic concrete, which is the black material used commonly in road paving. In recent years red coloured concrete interlocking blocks have also been used for the parade squares and service roads in selected military camps. For the Singapore Armed Forces Military Institute (SMI) complex, the Defence Ministry has decided to use alternative paving materials (granite and concrete with exposed aggregates) to enhance the aesthetics, ambience and thermal environment of the Institute. In this paper the study conducted to evaluate the use of these materials for a parade square in outdoor conditions in the hot tropics is reported. In particular, the pavement serviceability for thermal and glare comfort, and troop marching-suitability are evaluated.

Coat characteristics of goats in relation to heat tolerance in the hot tropics

Heat tolerance in relation to coat characteristics was studied by exposing Sirohi goats to the sun for more than 8 h each day continuously for 5 days during the hot summer. Morning rectal temperatures and pulse rates were not influenced by coat type but dermal temperatures and respiratory rates were lower in long haired goats. In the afternoon after exposure, the short haired goats had higher respiratory and pulse rates than long haired goats. The increase in afternoon rectal temperatures, respiration rates and pulse rates over those recorded in the morning was higher in black followed by dark brown, light brown and white goats, in descending order. Water consumption was higher and feed intake during the hotter part of the day was lower in coloured goats than in white goats; feed intake was lowest in black goats. It was concluded that long haired goats tolerate radiant heat better than short haired goats and that white or light brown goats do better than dark brown or black goats. Short haired black goats had lowest tolerance of radiant heat as seen from physiological responses related to heat tolerance, water and feed intakes. Thus, it will be important to select long haired white or light brown goats for breeding and rearing in the hot tropics for higher productivity during summer months.

Overview of Biological Control of Lepidoptera in the Caribbean

Some previous biological control programs in the Caribbean are listed. Three cases are considered in detail: 1) Biocontrol of the sugarcane borer (Diatraea saccharalis) has been a notable success, with effective control in several countries in the Caribbean. The braconid parasitoid Cotesia flavipes has been shown to be particularly adaptable to new hosts and future studies should exploit this quality still further. 2) Biocontrol of the diamondback moth on the other hand has been generally less successful, mostly due to the very low economic threshold required of crucifers but also because the parasitoids that have been tried up to now do not seem to work as well in the hot tropics as in more temperate areas. 3) Biocontrol of the pigeonpea pod borer is still in its infancy but is a suitable case for treatment. The past history of lepidopteran biocontrol in the Caribbean suggests that prolonged effort over many years yields results. It is difficult to finance years of sustained effort; the challenge for the future is to coordinate the endeavors of several Caribbean organizations in order to focus them on a few key pest problems.

Influence of production and storage conditions on subsequent growth and tuber yield of potato (Solanum spp.) in the hot tropics

SummaryA series of experiments to quantify the response of diverse potato genotypes to production and storage conditions in hot climates was carried out in 1984–87 at three sites in Peru, two of which were characterized by at least one hot season per year. Yield stability and field performance of seed tubers of six clones produced in situ, and stored in diffused light (DLS) or cold stored (CS), were compared with those of good quality seed tubers produced and stored in cool conditions. The yield potential of tubers produced in hot climates and grown as (i) a double crop per year with short DLS (1–4 months) (ii) a single crop per year with long DLS (c. 8 months) and (iii) a single crop per year with long CS (c. 8 months) was compared with that of seed tubers produced in cool conditions and introduced in successive crops.The first replanting of tubers produced in hot climates resulted in lower yield than that of coolproduced tubers. Yield reductions in clones ranged from 30 to 93% when replanted within 4 months, from 10 to 100% when replanted after 7–10·5 months of DLS and from 0 to 82% after similar periods of CS. Reduced yield was often due to poor plant vigour and crop growth leading to inefficient interception of solar radiation. There was, however, no evidence that the efficiency of utilization of intercepted radiation for tuber dry matter production was influenced by storage treatment. Poor sprout growth at planting reduced yield considerably for late clones in double cropping. Low dry matter content of tubers produced in hot climates did not influence emergence rate, but was related to poor plant vigour in the first replant under warmer conditions. Replanting and storage in hot climates did not enhance the initial reduction of tuber dry matter, which was evident after the first hot season. Tuber yields continued to decline, particularly under single cropping with long DLS.For the clones studied, CS would be a feasible storage method for potato production in hot climates if replanted tubers were used on an annual basis. For double cropping, short dormancy is essential; however, poor plant vigour results in additional yield reductions. Our data indicate that clonal selection for maximum production in hot climates should take into account the proposed or existing production and storage schemes.

Potato ( Solanum spp.) in the hot tropics. VI. Plant population effects on soil temperature, plant development and tuber yield

Nine experiments were run at three hot tropical sites (5–12°S, 180–800 m) within Peru to quantify the influence of plant population on soil temperature and growth and yield of the potato. Radiation interception was greatest at the highest plant populations and soil cooling was directly proportional to the amount of crop cover over the soil, but no appreciable effect on the timing of tuber initiation was apparent. More stems per unit land area leading to a higher leaf area index ( lai) were primarily responsible for greater interception of radiation at the higher plant populations, although some compensation in stem number per unit land area and in lai at lower populations was evident later in the season. In general, tuber yield increased linearly with increases in planted population over the range studied (2.7–12.5 plants m −2, and in one experiment to 31.7 plants m −2), and was proportional to increases in the amount of intercepted radiation. Tuber yields ranged from 8 to 60 t ha −1 over sites and populations. Vigorous clones with Solanum tuberosum spp. andigena in their genetic background constituted the exceptions to this linear trend, and for these clones yields declined at the highest populations, particularly when the rectangularity of planting vastly deviated from square patterns. Tuber yield of Solanum tuberosum spp. tuberosum and Neotuberosum ( S. tuberosum spp. andigena selected for tuberization under long-day conditions) clones did not respond to variations in rectangularity of planting and, probably due to their small stature and early maturity, did not demonstrate signs of intense between-plant competition for tuber yield as measured with the Kira competition density index. In contrast, for clones with Solanum tuberosum ssp. andigena in their genetic background, maximum tuber yield at populations greater than 5.5 plants m −2 was dependent on the rectangularity of planting, and declined as the latter deviated from squareness. Since the proportion of marketable tubers was scarcely affected by the planting densities, plant population of S. tuberosum ssp. tuberosum clones planted in hot climates should be as close as possible without limiting the amount of soil available for hilling-up.

Potato ( Solanum spp.) in the hot tropics V. Intercropping with maize and the influence of shade on tuber yields

The influence of various shade treatments on tuber yield of potato in three hot tropical sites (5–12°S, 180–800 m a.s.l.) within Peru was evaluated. Shade treatments comprised (a) artificial screens imposed throughout the season of the potato crop; (b) relay-cropping with maize for a short (10–30-day) period following planting of potato; and (c) planting maize and potato simultaneously such that maize shaded potato from 40 days after planting onwards. Variables tested included periodicity of shading throughout the day, duration of shade, and density of shade, the last-mentioned accomplished by variations in population and rectangularity of maize plantings. Artificial shade (50% reduction of light transmission) during midday or in the afternoon favoured tuber yield more than morning shade, and shaded plants were in general 35–39% more efficient than non-shaded plants in their conversion of available solar energy to tuber fresh weight. When relay-cropped with maize, potato plant population at harvest was superior to that of a sole crop of potato, an effect mediated through faster emergence and achievement of a greater maximum population and not through differential survival of shaded or sole potato plants. Enhanced final population was often offset by reduced individual yield per plant, particularly at dense or extended periods of shade, and shade for 20 days appeared optimal, although during the dry season 30-day periods were not always detrimental to yield. Tuber yields of relay-cropped plots ranged from +89% to −53% those of sole potato plots, the latter following a 31-day period of shade at a density of 4.76 maize plants m −2 during the rainy season. Yields of maize increased with increase of maize planting population, and at a given population were greater for square than for rectangular plantings. Tuber yield of potato planted simultaneously with maize was not significantly less than potato yield of sole crops until maize population exceeded 0.6 plants m −2, i.e. the population reducing transmission by more than 30% to the understory potato crop. In a replacement-series experiment, at the hottest site, tuber yield was greater in mixed than in sole plots at 1:11 and 1:9 maize:potato proportions (375 and 391 g m −2 vs 273 g m −2 for sole plots) and the maximum reduction in tuber yield at the densest maize population (1:6) at any site was 34% (1030 and 1563 g m −2 for mixed and sole plot). However, land equivalent ratios always exceeded unity since maize yield in mixtures was disproportionally greater than yield based on per-plant yields of sole-maize plots. In relay cropping treatments, and those in which maize and potato were simultaneously planted, a delicate balance existed between the ability of shade to reduce air and soil temperatures, without causing reductions in tuberization and photosynthesis. Our results indicate that there would appear to be potential for intercropping potato and maize in the hot tropics.

Potato ( Solanum spp.) in the hot tropics IV. Intercropping with maize and the influence of shade on potato microenvironment and crop growth

Fourteen experiments at three hot tropical sites (5–12°S, 180–800 m a.s.l.) within Peru were conducted over a 5-year period using artificial or natural shades. Shade was provided (a) artificially throughout the potato crop, (b) by a maize crop for a short (10–30-day) period following planting (relay cropping), or (c) by a maize crop during the last 30 days of the potato crop (mixed cropping). Increase of shade effected a linear reduction of soil temperature (7-cm depth) and significantly hastened emergence in all artificial-shade and relay experiments but one. Irrespective of sites, experiments, or cultivars, days to 50% emergence ( y) was closely related to the accumulated heat sum at tuber depth during the day ( x, Σ°h>20°C, 08.00–18.00 h) through the quadratic relationship y=17.65−0.215 x+0.00196 x 2( r 2=0.704). Marked delay of emergence was noted when the weighted daytime soil temperature exceeded 30°C. Shade treatments also resulted in conservation of soil moisture, which may have contributed to improved emergence. Plant height was positively related to intensity and duration of shade in relay and artificial shade treatments, and tuber initiation was delayed by shade, despite the earlier emergence. Branching and dry-matter production were reduced by shade, in a quantitative manner depending upon shade intensity, except in one apparently shade-tolerant clone, DTO-33. Later-season shading in mixed-cropping experiments resulted in a reduction of up to 40% transmission of irradiance to understorey potato plants.

Management of environmental temperature and rations for poultry production in the hot and humid tropics

This paper reviews studies that have been conducted to determine how environmental temperature affects productivity of poultry and how these effects can be alleviated so that the bird will realise its full productive capacity. It is shown that temperature primarily affects production of poultry meat and eggs through food consumption. A key factor in efficient weight gain and/or egg production of poultry is optimum nutrient intake. High environmental temperatures cause food intake to decrease and often result in inadequate nutrient intake contributing to poor performance. When nutrient intake is shifted by the influence of temperature on food intake, the adverse effect on productivity (growth or egg output) may be alleviated through improved feed formulation by adjusting the nutrient density to compensate for the altered intake of food. Improved feed management and better housing systems can partially compensate for low feed intake caused by high environmental temperatures.

Potato (Solanum spp.) in the hot tropics II. Soil temperature and moisture modification by mulch in contrasting environments

Abstract In order to quantify the effects of mulch on soil temperature and soil moisture regimes during the growth of the potato crop, seven experiments were conducted at three contrasting hot tropical sites (latitude 5–12 °S) varying in altitude from 180 to 800 m. Mean maximum and minimum temperatures during the crop seasons ranged from 27° and 30° and 16° to 21°C respectively. Various mulches, mostly organic, were tested either singly or in combination with other agronomic practices, and in one experiment the interactions between mulch and three radiation levels (0, 50, and 75% reduction of incoming radiation) were studied. Mulch always enhanced soil moisture retention, but the improvement was less evident under increasing shade. Daily soil temperature fluctuations at tuber depth were damped by mulch, and maximum reduction of daytime soil temperature was recorded immediately following planting, before the crop emerged. Reductions of daytime soil heating and retention of heat within the soil at night by mulch were influenced by various edaphic and weather conditions. Maximum reduction during the day was achieved under conditions favouring soil heating (e.g. high irradiance, low soil moisture content, ridged soil, soil of low albedo) whereas heat retention at night by mulch, although greater in shaded than non-shaded plots, in general was relatively greater under conditions that favoured longwave re-radiation from the soil (e.g. ridged and dry soil).

Potato (Solanum spp.) in the hot tropics III. Influence of mulch on weed growth, crop development, and yield in contrasting environments

Abstract Eighteen experiments at three hot tropical sites (5–12 °S, 180–800 m) within Peru were run with various mulches over a 4-year period. Mulch, although suppressing weed growth, favoured both crop emergence and the stand of tuber-bearing plants at final harvest. Canopy development, crop cover and light interception over the season were almost invariably improved by mulch. Tuber initiation, when measured, was earlier and tuber growth rates greater for mulched plants. Tuber yield was consistently increased by mulch in all but two experiments, averaging 25% over all experiments. Yield improvements due to mulch were less evident at the hottest site, where high soil temperature (> 25 °C) during the night at tuber depth, high natural reflectivity of the soil (0.18), a large sand fraction in the soil, and cloudy days and nights, were considered responsible for inconsistent benefits of mulch on tuber yield. At another site, where mulch was also tested during the rainy season, yield was on average improved by mulch in a proportion similar to that during the dry season at the same site. Mulch was particularly beneficial in improving all measured aspects of crop growth and yield when combined with agronomic treatments that, on their own, predisposed plants to greater heat stress. For example, mulch was more effective in ridge than on the flat plantings, at planting depth less than 7 cm, at lower plant populations and for small-canopied determinate clones. Environmental and biological criteria for the successful use of mulch for potato cultivation in hot climates are discussed.

Potato (Solanum spp.) in the hot tropics I. Soil temperature effects on emergence, plant development and yield

Abstract In order to measure the influence of day or night soil temperature on the growth and yield of potato in the hot tropics, various soil temperature regimes were effected by spreading a reflectant or clear polyethylene sheeting, in a number of day/night combinations, over the soil surface. The soil reflectant reduced day time soil temperatures (at 5 cm depth) by a maximum of 7°C (e.g. 37°C control reduced to 30°C), and polyethylene increased it by 3–5°C. During the night soil temperature of reflectant treatments was generally cooler than the control, with little difference apparent by dawn, whereas polyehtylene maintained a temperature differential of approximately 2–3°C throughout the night. Treatments that reduced soil temperature hastened emergence, foliage development and canopy cover of the soil, the latter in turn further reduced day time soil temperature and favoured tuber initiation. The rapid rate of increase in leaf area observed in cooler soil treatments more than compensated for their early tuber initiation such that at early tuber initiation leaf area indexes were greater than those of later initiating treatments. Soil heating delayed emergence and reduced the final number of plants emerging, but tuber initiation, although delayed, was never inhibited. Tuber growth rates and final yields were markedly greater for cool soil treatments. Although the heating/cooling effect was negligible for the main bulking period (due to self shading), during the last 3–4 weeks of bulking, lodging of stems and branches caused the soil surface to become exposed and soil cooling in reflectant plots was again evident. Tuber yield ranged from 5 to 37 t/ha; for non-adapted clones yields were improved more than 100% by treatments effecting soil cooling whereas for those heating the soil yields were reduced by approximately 50%. The treatment influence on tuber yields was less notable for the clone DTO-33, selected for its heat tolerance. Tuber deformities were reduced in cooler soil treatments and tuber dry matter content was marginally greater, both indicative of less heat stress. Reduction of day, rather than night, soil temperature would appear to have a more practical application for yield improvement within the range of temperatures recorded in these experiments. Criteria for the selection of better adapted clones, on the basis of results from these experiments, are presented.

A note on crossbreeding for fat-lamb production in the hot tropics

ABSTRACTTo compare the genetic group differences in live-weight gains, efficiency of food conversion (in terms of dry matter, total digestible nutrients, digestible crude protein, digestible energy and metabolizable energy) and physiological responses related to heat balance, a total of 24 male lambs (91 to 180 days old), four each of Malpura, Sonadi, and their crosses with Dorset and Suffolk breeds, were given a ration having a roughage to concentrate ratio of 250:750g/kg and metabolizable energy content of 100MJ/kg dry matter. Live-weight gain per day was higher and the food conversion ratio (the intakes of total digestible nutrients, digestible energy and metabolizable energy per kg gain) was lower in the crossbreds than in the native sheep. The crossbreds had higher respiratory rates (153 per min) than the natives (140 per min) but there was no significant difference in rectal temperature between purebreds and crossbreds. The crossbred lambs in the present experiment grew faster, consumed more food and utilized the food more efficiently than did the native lambs, despite the fact that they dissipated more energy as body heat. It was, therefore, concluded that the crossbreds performed better than the native breeds between 3 and 6 months of age, even though they were not permanently acclimatized to hot environmental conditions.

Housing In The Hot Arid Tropics

(1962). Housing In The Hot Arid Tropics. Architectural Science Review: Vol. 5, No. 1, pp. 3-12.

Heat and water in tropical Merino sheep

The relation between environment and the water intake and output of young Merino sheep living in the hot dry tropics on lat. 21° S. has been studied for 3 years. The tip wool of sheep standing in the sun heats to 189°F by absorption of radiant energy, most of which is re-radiated. Wool, especially when it is more than 3 cm long, assists in protecting sheep from radiant energy. The respiratory rates of sheep shorn during summer were more than twice those of unshorn sheep standing in the sun. On the open plains summer shearing appears to add to the thermal strain. Acclimatizing sheep respired more rapidly in the sun than tropical sheep. Evaporative cooling, by panting, increases water demand, and in summer merinos drank on the average 12 times as much water as in winter, when they took 7.3 ml/kg/day. Water intake is related closely to respiratory rate. Urine output was lower in summer than in winter.