Showing papers on "Shading published in 1976"

Production of epibenthic salt marsh algae: Light and nutrient limitation1

Abstract: Epibenthic algal production was measured in Great Sippewissett Marsh, Falmouth, Massachusetts, in plots treated with two levels of a mixed fertilizer and with urea or phosphate. Production, which followed a consistent seasonal pattern with short-lived peaks in spring and fall, was increased by the highest dosage of mixed fertilizer but not by the other treatments. Fertilization also increased production of the marsh grasses. Algal production at the marsh surface was limited due to shading by the grass canopy. The production rate decreased with increasing biomass of the grasses. To separate the effects of light and nutrients in the treated areas, additional small plots were enriched with three levels of nitrogen (suspected as the limiting nutrient) and provided with three levels of canopy cover cross-classified to the nitrogen treatments. Shading by the grasses reduced, while fertilization with nitrogen significantly increased, production. When the grasses were dormant, prediction from a model of epibenthic production based on limitation by light compared well with observed measurements. The predicted production rate was higher than that observed during the growing season of the grasses. In the plots receiving the highest doses of mixed fertilizer the added nutrients comoensated for the light limitation. since the discrepancy between predicted and observed valuis was smaller than in the control plots.

Some effects of environmental stress on seed yield of cowpea (Vigna unguiculata (L.) walp.) cv. Prima

Abstract: Separate experiments examined nodulation and seed yield of cowpea cv. Prima after (a) changes in the level of combined nitrogen from 25 to 0 or 60 ppm N, (b) cycles of wilting and rehydration, and (c) shading to ca 50% full daylight. Plants were grown in the simulated tropical environment of a plastics ‘bubble’ house and experienced these changes over the growth stages: emergence to first flower, first flower to mid pod-fill or mid pod-fill to maturity. Seed yields of nodulated plants were unaffected by combined nitrogen supply and almost double those of non-nodulated plants (100 g cf 56 g per plant)-due mainly to increases in pod number per plant and mean seed weight. Reducing the nitrogen level from 25 to 0 ppm N, especially between mid pod-fill and maturity, reduced seed yields of non-nodulated plants to 36 g per plant. At the first flowering stage, plants grown without combined nitrogen had nitrogenase activities less than 10% of those supplied with 25 ppm N; 60 ppm N at any stage of development more than halved nitrogenase activity when compared with plants supplied with 25 ppm. Repeated wilting prior to flowering markedly reduced seed yields compared with the unstressed controls (41 g cf 76 g per plant)-mainly by decreasing subsequent pod production. Nodule weight and nitrogenase activity per plant were also much reduced. Wilting after flowering did not reduce yield, and nitrogenase activity was less affected. Shading throughout, or from first flower onwards, reduced seed yield by about 25% because fewer pods were produced. All shading treatments significantly increased mean seed weight compared with unshaded controls (116–121 mg cf 105 mg).

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

Abstract: 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.

Mask pattern printing method and the equipment

Abstract: PURPOSE:To do as to be able to do, uniformly, pattern printing of the dry plate by controlling and measuring the illumination which corresponds to the shading of the mask pattern.

Studies on the relative contribution of stem sugars and various photosynthetic plant parts to the grain development at various moisture levels in pennisetum typhoides (burm) s & h.

Abstract: One pot culture cxperlment was conducted during df1 975 with two brjra hybrids( HUS and New HBS) The plants were subjected to varlou8 defoliation and shading trulmontr from anthesis to maturity under three moisture levels