Unshaded Plots Research Articles

Restoring Caribbean Dry Forests: Evaluation of Tree Propagation Techniques

AbstractSurvival and height growth of tree seedlings and rooted cuttings introduced into artificially shaded and unshaded plots in a degraded dry forest were measured at intervals for nine months. Ten tree species were selected to represent a range of ecological characteristics of the dry–forest plant community on St. John, U.S. Virgin Islands. Of three propagule types – seeds, seedlings, and rooted cuttings – introduced to field plots, seedlings survived best (52%) over the initial nine‐month period. Cuttings of six species rooted successfully in a shadehouse, but only two of these species survived the nine–month field experiment. Seed germination was low, under 11% for eight of ten species tested, and four species did not germinate. Subsequent mortality of seedling recruits was moderately high. Plumeria alba was the only species for which seedling height growth was not significantly greater than cutting height growth. Shading treatment (25% of full sun) significantly increased seedling survivorship (p= 0.03) but suppressed growth slightly for some species. Shading enhanced survival of seedlings produced from broadcast seeds, but not seed germination. Mortality occurred during dry periods, apparently from drought stress. Results suggest (1) that seedling introductions are the preferred propagule type (over seeding or rooted cuttings) for ecological restoration of degraded tropical dry forests, and (2) that some level of shading is required to increase the survivorship of many dry‐forest species or to avert complete mortality of some species. This study suggests that early secondary dry forest may be best restored by underplanting within the existing vegetation. Sufficient shading suitable for growth of native dry‐forest trees may be attained using a nurse crop of fast‐growing leguminous trees.

Changes in pigments and phenolics and their relationship with black tea quality

AbstractThe pigmentation pattern of tea leaf shoots grown under a canopy and without shade were analysed in order to investigate the effects of some cultural practices on North East Indian made tea quality. The chlorophyll, carotenoid and anthocyanin contents of tea shoots grown in the shade of trees were significantly higher than those from unshaded plots. On the other hand, the lower accumulation of catechins and/or higher pigment contents in shaded plants makes tea less astringent and with better colour and appearance. Furthermore, all the pigment contents, except chlorophyll, were found to be higher in pruned tea leaf than unpruned tea, thus enhancing the quality of made tea.

Effect of shade and environmental conditions on the initiation and development of garlic cloves ( Allium sativum L.)

The rate of initiation, differentiation and development of garlic cloves increased with increasing light transmission through shade covers and was maximal on unshaded plots. The time for complete clove differentiation and development ranged from 90 days in full light to 140 days in 25% full light. Cloves differentiated up to six foliage leaves in the open (100% light), but only up to four under conditions of heavy shade (25% light). Stepwise regression analysis on data from the tropical cultivar ‘Bangladesh Local’, collected from experiments conducted during 1985 and 1986, showed the rate of clove differentiation to be highly correlated with solar radiation and that both soil temperature and photoperiod had little influence in this respect. The best fitting model from the combined 1985/86 data, when tested against data of the same cultivar from experiments conducted in 1987, accounted for ∼86% of the observed variance. Furthermore, the same model, which had been derived on data from ‘Bangladesh Local’, accounted for similar levels of variance in the temperate cultivar ‘Fructidor’.

Voluntary feed intake by sheep and digestibility of shadedStenotaphrum secundatumandPennisetum clandestinumherbage

SUMMARYThe effects of shade (50% of ambient light transmission) on the quality of established swards of buffalo grass (Stenotaphrum secundatum) and kikuyu grass (Pennisetum clandestinum) were examined at Wollongbar Research Station, northern New South Wales. Sarlon cloth was used to shade plots of the two species, after cutting to 8 cm, from November 1985 to March 1986. Herbage was harvested from shaded and adjacent unshaded plots for chemical analyses and for feeding as dry chaff to penned sheep at the University of Queensland research farm at Mt Cotton.Shade markedly decreased the voluntary feed intake (VI) ofP. dandestinumby 30·7% over the two harvests while VI ofS. secundatumwas not significantly affected. Shade had no effect on thein vitroandin vivodigestibility ofP. clandestinumherbage but marginally increased that ofS. secundatum. These shade effects resulted in a 14·2% increase forS. secundatumand a 34% decrease forP. clandestinumin the intake of digestible dry matter of shaded compared with unshaded herbage.The reduced VI of the shade-grown herbage ofP. clandestinumwas associated with a higher proportion of stem (21v. 8% for unshaded herbage), a lower proportion of leaf (48v. 54%), and a lower concentration of total nonstructural carbohydrates (TNC) (0.9v. 2.1%). InS. secundatum, there were similar, but smaller, changes in proportion of stem and TNC percentage in shade-grown herbage but, in contrast toP. clandestinum, these potential detriments to VI were offset by an increase in proportion of leaf and a decrease in the proportion of dead material. Average moisture content of shaded herbage (76%) was higher than that of unshaded herbage (70%). Nitrogen and potassium concentrations in plant tissue were higher in the shaded herbage.The higher yielding capacity and maintenance of nutritive quality of shadedS. secundatumcompared with shadedP. clandestinumindicates the potential usefulness ofS. secundatumfor plantation agriculture.

Atrazine, Bifenox, and Shade Effects on Crownvetch (Coronilla varia) Nodulation and Nodule Activity

Studies were conducted to determine whether photosynthesis-inhibiting herbicides atrazine or bifenox, and shade affect the number, weight, senescence, and N fixation activity of nodules on the roots of the perennial legume crownvetch. Atrazine and bifenox were applied at rates of 2.24 kg ai/ha to shaded and unshaded plots. The shade was varied during the growing season to simulate changing irradiance levels beneath a corn canopy. Atrazine and bifenox treatments reduced nodule number to 13 and 42% of the untreated control, respectively, in 1980, and 18 and 35% in 1981. Shade treatments reduced nodule number to a low of 40% of the control in 1980 and 50% in 1981. Combined effects of herbicides and shade on nodule numbers were more than additive. Nodule fresh weights were reduced an average of 37% by herbicide treatments and 39% by shade treatments. Sloughed nodule numbers decreased in the herbicide and shaded treatments, suggesting that the reduction in nodule numbers was due to fewer nodules being produced. Nodule numbers were reduced a greater percentage by herbicides and shade than was herbage dry matter production. Specific nodule activity (SNA) did not differ in nodules from the atrazine, bifenox, or shade treatments on the six sampling dates in 1980 or on two of three sampling dates in 1981.

Solar Injury of Raspberry Fruit

Abstract Red raspberry (Rubus idaeus L.) is prone to a “white drupelet” disorder on the sun-exposed side of the fruit, largely during those harvest periods when daytime temperatures exceed about 33°C. In mid-August, more than 40% of the fruit were affected. Three types of shade covers (30% and 60% black shade fabric and 25% shade white polyester), placed over raspberry plots for 1 to 3 weeks prior to fruit harvest, reduced the amount of solar-injured fruit from 41% in unshaded plots to between 8% and 16%. Fruit surface temperature was reduced about 4° by both black shade fabrics, but only 1° by the polyester cover. Fans cooled fruit by about 2°, but the reduction in solar injury was less than with shade covers.

Bulb Development in Onion (Allium cepa L.) III. Effects of the Size of Adjacent Plants, Shading by Neutral and Leaf Filters, Irrigation and Nitrogen Regime and the Relationship between the Red: Far-red Spectral Ratio in the Canopy and Leaf Area Index

Field experiments were done to investigate why onion crops with a high leaf area index (LAI) initiate bulb scales and mature sooner than those with a low LAI. When small plants were grown either mixed with large plants or in pure stands, those in the mixed stands initiated bulb scales earlier than those in pure stands. The timing of bulb development therefore depended on the size of neighbouring plants and the LAI of the stand and was not simply determined by the size or age of individual plants. Shading plots with neutral filters which caused no spectral changes slightly accelerated bulb development compared to unshaded plots but shading by a canopy of climbing pea and bean leaves had a larger effect. Lack of irrigation advanced bulb maturity but in the highly irrigated treatments plots of high plant density still initiated bulb scales and matured before those of low density. Quantitative relationships between the change in R : FR and either LAI or total radiation interception were determined for onion leaf canopies. It is suggested that the decrease in the red to far-red spectral ratio (R : FR) as LAI increases may be the cause of the earlier bulb scale initiation and maturity that occurs as LAI increases.

Effect of Increased Soil Moisture and Reduced Soil Temperature on a Desert Soil Arthropod Community

The effects of soil moisture and temperature on arthropod communities were experimentally examined in the northern Chihuahuan Desert of New Mexico. Shaded plots were established which lowered the soil temperature several degrees; some plots received artificial rainfall to increase soil moisture. Shading reduced soil temperature at 5-cm depth 7-10 C. Soil moisture at 5 cm accounted for most of the variation in surface activity of subterranean termites (r values between 0.3 and 0.7). Termites did not respond to temperature differences. When all soils were at field capacity, there was no difference in termite activity in shaded and unshaded plots. There were higher densities of microarthropods in litter bags on the shaded plots than on the unshaded plots. Numbers of microarthropods were an order of magnitude larger in litter bags on watered and shaded plots than on other plots. Lower litter temperatures apparently affect litter arthropods more than increased soil moisture. Shade had no effect on ant colonies but there were fewer colonies on the watered plots. There was between 40 to 50% mass loss from creosotebush leaf litter after 7 months on all plots. Water and soil temperature had no effect on decomposition rates. INTRODUCTION Temperature extremes and water availability are considered to be the most important factors limiting production, activity of desert organisms and ecosystem processes in deserts (Noy-Meir, 1973, 1974; Whitford et al., 1981, Whitford et al., 1983). The frequency, amount and seasonal occurrence of precipitation are thought to affect productivity, litter decomposition and behavior of soil biota (Whitford et al., 1981). Noy-Meir (1973) proposed a pulse-reserve hypothesis for desert organisms in which rainfall sets off a of activity that is rapidly reduced, but some energy is stored reserved to await the next pulse. If desert organisms behave as predicted by the pulse reserve hypothesis, simulated rainfall events should trigger intense activity of various groups of soil organisms. Recent work indicates that moisture may not be as important as once thought as a regulator of the activity of soil biota. Whitford et al. (1982a) found no effect of rainfall on disappearance of leaf litter. They suggested that the desert soil decomposer community has evolved adaptations that allow those organisms to process surface litter independently of rainfall, and that soil temperature could be the most important parameter affecting the rate of litter removal. Hence, rates of decomposition in North American deserts are considerably greater than predicted based on the actual evapotranspiration and lignin content, which are good predictors of decomposition in more mesic environments (Whitford et al., 1983). Subterranean termites Gnathamitermes tubiformans are the most important processors of dead plant material and dung in the northern Chihuahuan desert (Johnson and Whitford, 1975; Whitford et al., 1982b). Termites are active aboveground during the rainy seasons, especially in the autumn, when they can be found in accumulations of litter or producing mud galleries on dead plant material (MacKay et al., 1985). Ettershank et al. (1980) reported that termites locate large food objects such as cow dung 'Send reprint requests to W. G. Whitford.

Observations on the insect fauna of shaded and unshaded Amelonado cocoa

AbstractThe insect fauna of a block of Amelonado cocoa trees at Tafo, Ghana, partly shaded by Gliricidia sepium and partly unshaded was sampled. Crematogaster clariventris (Mayr) and Oecopyhlla longinoda (Latr.) were the most numerous species of ants, the former occurring on 84% of the trees and the latter on 17%. There was a considerable overlap in the distribution of the two species. Thirty-two other species of ant were collected by pyrethrum knockdown sprays from the cocoa canopy, and 47 species were collected from leaf litter beneath the trees. More species of ant were recovered from litter on shaded plots than on unshaded ones. There was some avoidance of trees occupied by O. longinoda by certain canopy .ants. A greater number of Lepidoptera larvae, Orthoptera and the mirid Sahlbergella singularis Hagl were collected by pyrethrum knockdown sprays from unshaded plots than from shaded ones, whereas Diptera and Hymenoptera other than ants were more numerous on shaded plots. The most abundant coccid was Stictococcus sjostedti Ckll., a species tended for its honeydew by both dominant ants; it was more common on shaded plots. Mealybug species, of which Planococcoides njalensis (Laing) was the most common, were more abundant on unshaded plots.

Effect of shading at different times on the growth and yield of the potato

The effect of shading during the periods of new tuber initiation and subsequent bulking were studied with three crops of field-grown potatoes cv Sebago Plots were shaded (34% reduction on full sunlight) up to or after the stage when the young tubers had formed (3 weeks after the onset of initiation), receiving full sunlight for the other half of growth In other treatments plots were shaded throughout growth or not shaded at all In two experiments plots were split for two planting densities (7.14 and 14.28 tubers planted m-2), but density had no effect on the response to shade. Shade during the first part of growth did not affect the numbers of tubers initiation but, compared with unshaded plots, did reduce the numbers which reached a size of 1 cm in diameter or more, which was the same as the final numbers harvested at maturity Shade also delayed by a few days the onset of the rapid tuber-bulking period. Shade during later growth had some additional effect In reducing the maximum bulking rate achieved, so that the final yields from the differentially shaded plots were intermediate between those from the plots either unshaded or shaded throughout Plants receiving late shade had a higher percentage of their total dry weight In the haulm than did unshaded plants.

Productivity of vegetable crops in a region of high solar input. II. Yields and efficiencies of water use and energy

Details are given of final yields and size gradings of three potato crops grown under conditions of high solar input and high temperatures in the Murrumbidgee Irrigation Areas of New South Wales. Total yields were up to 50 t ha-l. Differences resulting from different irrigation treatments were surprisingly small, although mean tuber weight was slightly less in the drier treatments. Water use was about 300 g for each 1 g dry weight produced, and efficiency was slightly greater in the wetter irrigation treatments. Reductions of 21 %and 34 % of the total solar input, using shade covers, markedly reduced yields, and there was no statistical interaction with irrigation treatment. Tuber numbers also decreased with decreasing solar input, though not as much as yields, and mean tuber size was greatest on unshaded plots, least under 34% shade. Tuber moisture percentage at harvest was not affected by the different irrigation treatments, but was reduced in two experiments as shading increased. There were only small differences in plant and stem numbers per unit area between any of the treatments, though stem numbers decreased significantly as shading increased. High crop growth rates were achieved especially during the tuber bulking periods, when up to 22.8 g m-2 day-1 of dry matter were produced in each of two experiments, achieved with conversion efficiencies of photosynthetically active radiation of 3.5 % (spring-planted crop) or 6.1 % (summer-planted crop). The results are in agreement with the hypothesis that assimilation in the potato depends primarily on the 'sink' strength of the developing tubers, which is determined in the 2 or 3 weeks following the onset of initiation. The main effects of differences in solar input appear to be determined in this period. It is suggested that a practical approach to increasing yields in this region may be to increase the numbers of tubers which develop per unit area by increasing plant density and encouraging early haulm growth.

Effects of shading and of seasonal differences in weather on the growth, sugar content and sugar yield of sugar‐beet crops

SUMMARYIn 1967 and 1968 plots of sugar beet in two identically grown crops were shaded for successive four week periods starting on 13 June, 18 July and 22 August, and the growth of the plants compared with that on unshaded plots. At the beginning of each period in 1967 some shaded and unshaded plants received additional nitrogen, and in 1968 plants continuously shaded from June to September were compared with unshaded plants irrigated to equalize their water losses with those of the shaded plants.The weather in 1967 was sunny and dry and that in 1968 dull and wet, but the yields of dry matter, and particularly of sugar, of the unshaded crop in the 2 years were similar because, although net assimilation rate (E) was greater in 1967 than 1968, mean leaf area index (L) in 1968 was almost double that in the 1967 crop. Shading decreased the incoming radiation by 56%; it decreased E proportionally in 1967, increasing L slightly, but it decreased both E (by 44%) and L in 1968. The weights of dry matter and sugar in the roots of the shaded crop were consistently smaller at the end of shading and at final harvest in October in both years, and their weights, but not those of the tops or the whole plant, at final harvest over all shading treatments in both years were proportional to the amount of radiation received by the crop between June and September. Although shading greatly decreased the supply of photosynthate to the roots, it did not change the sugar content percentage of dry matter, except in the early stages of growth when the sugar content was rapidly increasing. Sugar content percentage of fresh weight of the roots was consistently decreased by shading, wholly because water content was increased relative to dry matter. Therefore the sugar yield of shaded plants was less because the dry weights of the roots were less, not because the partition of photosynthate between sugar storage and root growth changed.There appears to be a mechanism within the root operating over a wide range of photosynthate supply that maintains a nearly constant proportion of sucrose to non‐sugar, contrary to the hypothesis that sugar stored in the roots is photosynthate in excess of what can be used in growth of the plant. However, in the extreme condition of continuous shading which drastically decreased the dry weights of all parts of the plant, sugar percentage of dry matter in the roots was decreased, but only from 80 to 70%.In 1967 extra nitrogen applied at the start of shading increased L and the dry weight of the tops in all periods, but had no effect on the dry weight of roots. Because 1968 was a wet year the irrigation treatment had no effect on E or L except for a slight increase in L during the first period; it had no effect on plant dry weight. Both irrigation and additional nitrogen decreased the sugar content percentage of fresh weight of the roots only by altering their water content; sugar percentage of dry matter was unaffected. None of these changes persisted until the final harvest in October.

Influence of the Shading Culture on Catechin Composition in the Tea Leaves

The influence of shading culture on the catechin composition in the tea leaves was examined.During the developing period of the tea shoots, the tea plants were covered with several sheets of black net for 8-13 days. The light intensity under the shade was reduced to 1.6-6.4 percent of the open field. The shoots were plucked at different intervals from the shaded and the unshaded plots and subjected to the estimation of each catechin fraction.As a result of shading, the yield of the plucked leaves and the content of total catechins decreased, however, a uniform tendency of decreasing in catechin content was not observed with each catechin fraction. The decreasing of the contents of (-) epicatechin and (-) epigallocatechin was characteristic of variation by shading. A significant difference of gallate content between the shaded and the unshaded shoots was not observed. In consequence, the tea shoots grown under the shade were rich in the proportion of (-) epigallo catechin gallate. After removal of the shade, a remarkable restoration of catechin content occurred quickly.It seems that the results mentioned above involve a suggestion of the possible pathway of catechin formation in the tea leaves.

New developments in cocoa shade studies in Ghana

AbstractAttention is drawn to the lack of confirmation for the results of the Amelonado cocoa shade and manurial experiment, Tafo, K1. The shade of this experiment has recently been determined as reducing the illumination of the cocoa to about 30% ambient light intensity. A survey of local farms has shown their shade to be highly variable on average reducing illumination to about 40% ambient light.Results of another experiment, and recent yield trends of various unshaded plots at Tafo, are reported. They are in some disagreement with conclusions previously drawn from the results of Tafo K1 and with previous reports of establishing cocoa on clear‐felled land. It appears that the maintenance of a closed canopy is essential to the success of deshaded cocoa. Possible factors are reduction of insect attack, suppression of weed growth, preservation of soil structure, and provision of suitable microclimate.It is suggested that the use of herbicides may be a critical adjunct to the rehabilitation of unshaded cocoa whose canopy has become broken. Breeding programmes should consider variation in capacity to flourish in bright sunlight.

Sombreamento dos cafezais IV - resultados de mais dois biênios: 1963/1964 - 1965/1966

This paper deals with data obtained in 1963, 1964, 1965 e 1966 in shaded and unshaded coffee plots at Piracicaba, Sao Paulo, Brazil. The results can be summarized as follows: a. the production, in shaded and unshaded plots, did not show differences statisticaly significant; b. the percentage of coffee berry borer infestations was higher in shaded plots as compared with unshaded ones; c. the percentage of green, ripened and dry fruits depends on the year and on the harvest time.

Sombreamento dos cafezais: III - Resultados do 5º biênio (1961/1962)

This paper deals with data obtained in 1961 and 1962 in shaded and unshaded coffee plots at Piracicaba, Sao Paulo, Brazil. The results can be summarized as follows: a - the production, in shaded and unshaded plots, did not show differences statistically significant; b - the percentage of coffee berry borer infestation was higher in shaded plots as compared with unshaded ones; c - coffee fruits brought from the field in the harvest time yielding up in sunshaded plots as compared with shaded ones.

Sombreamento dos cafèzais II: resultados do 4.° biênio (1959/1960)

This paper deals with data obtained in 1959 and 1960 in shaded and unshaded coffee plots at Piracicaba, Sao Paulo, Brazil. The results can be summarized as follows: a) the production, in shaded and unshaded plots, did not show differences statisticaly significant; b) the percentage of coffee berry borer infestation was higher in shaded plots as compared with unshaded ones; c) the percentage of green, ripened and dry fruits depends of the year and of the harvest time. In the same harvest time, both for shaded and for unshaded plots the percentages in the shaded plots were higher for green fruits and lesser for ripened and dry fruits; d) coffee fruits brought from the field in the harvest time yielding up in unshaded plots as compared with shaded ones; e) the relation grains/dry fruits was better in shaded plots.

Sombreamento dos cafèzais I.: resultados de três ciclos bienais (1953/1958) obtidos na escola "Luiz de Queiroz"

The present paper discusses the data obtained in shade and unshaded coffee plots at Piracicaba, Sao Paulo, Brazil. The results, analysed statistically, can be summarized as follows: a) unshaded plots produced 17% more than shaded ones; b) the percentage of coffee berry borer infestation was higher in shaded plots as compared with unshaded ones; c) the percentage of green (not ripened fruits) depends of the harvest time. When the harvest was retarded, the percentage of green fruits was higher in the shaded plots. When the percentage of green fruits was the same, both in shaded and unshaded plots, the percentage of ripened was higher and the percentage of dried fruits was lesser in the shaded plots as compared with unshaded ones; d) other comparisons as production of dried grains by the field fruits, relation between dried fruits and dried grains and cup-test by expert coffee-taster, did not show differences among shaded and unshaded plots.