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- Author or Editor: Martin P.N. Gent x
Shading a greenhouse increased the fraction of tomatoes that were marketable, and the marketable yield, in a comparison of greenhouse tomato yields across years, in some of which the greenhouses were shaded. In 2003, the yield and quality of greenhouse tomatoes were compared directly when grown in spring and summer in Connecticut in identical greenhouses that differed only in the degree of shade. Each half of four greenhouses was either unshaded or shaded using reflective aluminized shade cloth rated to reduced light transmission by 15%, 30%, or 50%. Each shade treatment was repeated in two houses. Tomatoes were germinated in February and transplanted in March The houses were shaded when fruit began to ripen in early June. Picking continued through August. The effect of shade on total yield developed gradually. Yields in June were unaffected by shade, but in August yield under no shade was about 30% higher than under 50% shade. In contrast, there was an immediate effect of shade on fruit size. Fruit picked in June from plants under 50% shade was 16% smaller than from plants grown under no shade. This difference declined later in the season, to 6 and 9%, in July and August respectively. The highest yield of marketable fruit in 2003 was picked from houses under no shade, but this was only 10% more than picked from the houses under 50% shade. Shade increased the fraction of marketable fruit, from 54% under no shade to 63% under 50% shade. Certain defects were decreased by shade. For instance the fraction of fruit with cracked skin was decreased from 33% to 25%. In general, effects on fruit quality varied linearly with the degree of applied shade.
Efficacy of paclobutrazol was determined when applied to rooted cuttings before transplant. Cuttings of large-leaf Rhododendron catawbiense Michx. were treated with paclobutrazol applied as a 40-mL drench. In 1998, concentrations of 0, 1, 2, 10, or 20 mg·L-1 were applied to liners before root development was complete in February, or after cuttings were root-bound in May. The same volume of solution was applied to other plants at concentrations of 0, 5, 10, or 20 mg·L-1 in July 1998, after transplant to 1-gal pots. In 1999, a 40-mL drench of paclobutrazol at 0, 1, 2, 5, 10, or 20 mg·L-1 was only applied to liners in April. All cuttings were transplanted to 1-gal pots and set in the field. The elongation of stems was measured after each of three flushes of growth. Plants were far more responsive to paclobutrazol when it was applied before, rather than after transplant. There was a saturating response to paclobutrazol concentration and the half-maximal response occurred at 2 to 4 mg·L-1 (0.08 to 0.16 mg/plant). At low rates, later flushes of growth were affected less than earlier flushes. However if paclobutrazol was applied at 10 or 20 mg·L-1, later flushes of growth were inhibited more completely than early flushes. Flowering was enhanced by paclobutrazol. Paclobutrazol at 2 mg·L-1 applied to rooted cuttings before transplant was sufficient to inhibit growth of rhododendron, but not to the point where later flushes of growth were excessively short. Chemical name used: 2RS,3RS-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl)-pentan-3-ol (paclobutrazol).
Some amount of shade may be optimal to produce high-quality tomatoes in a greenhouse during summer months in the northeast United States. Simultaneous comparisons were made among greenhouse sections that were either not shaded or covered with reflective aluminized shadecloth that attenuated 15%, 30%, or 50% of direct sunlight. The shadecloth was applied at the start of warm weather in June. The houses were shaded for the rest of the summer, and fruit was picked until late August. Total yield decreased linearly with increasing shade, but there was no significant difference among shade treatments in marketable yield. The fraction of fruit that was marketable was greatest for plants grown under 50% shade. This fraction was 9% greater than in a greenhouse with no shade in 2003 and 7% greater in 2004 and 2005. Cracked skin was the defect most affected by shade. Among sensitive cultivars, up to 35% of the fruit produced in greenhouses with no shade had cracked skin, whereas in greenhouses covered with 50% shade, only 24% to 26% of the tomatoes had cracked skin. There was no consistent trend for shade density in the fraction of fruit with green shoulder, blossom end rot, or irregular shape. The effect of shade increased with duration of shading. There was no effect of 50% shade compared with no shade on total yield within 20 days, but yield decreased by 20% in the interval from 25 to 45 days after shading and by 30% after 50 or more days of shading in 2005. Marketable yield only decreased after more than 45 days of shading for cultivars that were not sensitive to cracked skin or uneven ripening. Shade decreased fruit size over the entire season only in 2003. In general, shading increased the fraction of marketable tomato fruit without affecting fruit size.
Tomatoes were grown in spring and summer in Connecticut in greenhouses covered with a double layer of 4-mL clear polyethylene film. Some sections were covered with reflective aluminized shadecloth that provided 85%, 70%, or 50% transmittance of direct radiation, respectively. This shading was applied in mid-June, after fruit began to ripen, and remained for the rest of the summer. Fruit was picked through August. A similar experimental protocol was used in 2003 and 2004. The maximum shading only decreased daily integrated solar radiation to 69% of that without shade, as measured by PARsensors set at a 2-m height in each greenhouse. Shading reduced yield of ripe fruit from 16.6 and 13.1 kg·m-2, proportional to the measured decrease in radiation. Neither fruit size nor weight fraction of marketable fruit was affected by shading in 2004. Nutrient content was analyzed in tissues of ripe fruits, and uppermost expanded leaves harvested in early August. As shading decreased transmittance, it increased the concentration of most elements in leaves. Total N, P, and K concentrations followed this trend; however, Ca was not affected by shading. Fruit dry matter content declined slightly, from 5.9% to 5.7% of fresh weight, for plants grown with no shade or shade with 50% transmittance, respectively. However, there was no significant effect of shading on K, Ca, Mg, or on minor elements in fruit tissue, whether expressed on a fresh weight or dry weight basis. Thus, shading a greenhouse to improve fruit quality had no effect on the value of ripe tomatoes as a dietary source of mineral nutrients.
The concentrations of metabolites in plants are affected by sunlight integral and other factors such as plant size, water content, and time of day. Tissue composition was measured for various sizes of hydroponic lettuce (Lactuca sativa L.) grown under seasonal variation in sunlight in a greenhouse and harvested in the morning or afternoon. Daily sunlight integral varied from 4 to 14 mol·m−2·day−1 photosynthetically active irradiance, and plant size varied from 2 to 260 g fresh weight (FW)/plant in this study. Much of the variation in tissue composition on a FW basis could be explained by the increase in dry matter content with irradiance normalized per unit area. Except for nitrate, metabolite concentrations on a FW basis increased with irradiance, and the changes resulting from irradiance were greater when harvested in the afternoon than in the morning. Nitrate concentration decreased with normalized irradiance, and the trend was the same whether measured in morning or afternoon. Malic acid increased with irradiance but not enough to counter the decrease in nitrate on a charge equivalence basis. Irradiance normalized per unit leaf area explained many effects of light and plant size on dry matter content and soluble metabolite concentrations. Lettuce for human consumption is best harvested in the afternoon after growth under high light, when it has the least nitrate and more of other nutrients.
Relative growth rate (RGR), the relative increase in weight per day, can analyze the effect of environment and nutrition on growth. I examined which of the parameters responding to plant growth scaled according to RGR for lettuce and spinach grown in heated greenhouses in hydroponics with control of the nutrient solution. The experiments for lettuce in 2006–08 included all times of year, high vs. low temperature, and effect of withdrawal of nitrogen. There were four parameters that were significant in multiple linear regression vs. RGR; irradiance divided by leaf area index if it was greater than one, or normalized daily light integral (NDLI), solution temperature, electrical conductivity (EC), and logarithm solution nitrate when it was between 3 and 55 mg·L−1 N. NDLI had the most significant coefficient, but the other parameters had regression coefficients more than three times se. For experiments on spinach in 2009–10, all the parameters mentioned previously were significant in multiple linear regression vs. RGR, except EC. The coefficient for NDLI in spinach was about half the value in lettuce. The coefficients for solution temperature and low nitrate were two and three times that in lettuce. In a third set of experiments on lettuce in 1996–98, solution temperature was the only significant parameter among those mentioned previously. The coefficient for solution temperature was similar to that for regression of lettuce in 2006–08.
How are C and N metabolites affected by a root-zone temperature (RZT) in phase or out of phase with the photoperiod? Tomato (Lycopersicon esculentum Mill.) was grown with an air temperature of 20C, and RZT that was in phase with a 12-h photoperiod, 28C in the light and 12C in the dark, or out of phase, 12C in the light and 28C in the dark. Seedlings were grown in flowing solution containing 200 μm NO3 and excess amount of other mineral elements. The flow rate increased with plant size. After 8 days, plants were harvested at the end of the day and at the end of the night. The relative growth rate (day–1) was slightly greater for in-phase (0.19) than out-of-phase RZT (0.17) and less than that at a constant air and RZT of 24C (0.22). RZT affected N accumulation and partitioning of C and N metabolites. Cool roots contained more NO3 and free sugars than warm roots. Leaves had less NO3 in the light than in the dark, and NO3 in leaves of plants with an out-of-phase RZT was depleted in the light. Concentration of free amino acids and protein was greater and the amount of starch was less in leaves of plants with in-phase RZT.
Subirrigation for production of potted ornamental plants reduces the waste of water and fertilizer inherent to conventional overhead watering systems used in greenhouses. Ebb and flow watering systems for flooded floors typically operate slowly so that the substrate takes up water to near effective water-holding capacity during each irrigation event. We used a system that rapidly delivered water to and removed water from the production surface to restrict the water provided to the plants. We examined several parameters that vary between this fast-cycle ebb and flow watering on a flooded floor compared with slow-cycle watering. Water and fertilizer use was reduced by 20% to 30% with fast- compared with slow-cycle watering. Biomass and stem height at bloom were also reduced by 10% to 20% under fast-cycle saturation. This watering method did not affect the rate of flower development or plant nutrient composition. Volumetric water content of the substrate was the only measure that was affected by location on the flooded floor. Despite the fast ebb and flow on pitched floors, none of the aspects of plant growth was affected by location on the floor. This method of watering shows promise as a means to produce uniform crops of container-grown plants while conserving water and fertilizer.
Recycling the nutrient solution used for greenhouse vegetable production can prevent groundwater pollution. Recycling could result in an accumulation or deficiency of elements that would be deleterious to plant growth, product quality, and the dietary value of vegetables. Complex fertilizer systems have been developed to maintain appropriate concentrations of all elements in recycled systems. We compared a much simpler system in which all excess solution drained from the plants was recycled without adjustment or dilution compared with a system with no recycling as a control. Crops of greenhouse tomato (Solanum lycopersicon L.) were grown in two years to compare these systems. Differences in composition of solution drained from the plants developed gradually over more than one month. The transition from vegetative to fruit growth, which coincided with warmer weather, resulted in a decreased demand for nitrate, and other nutrients, and an increase in electrical conductivity (EC) of water drained from the root zone. The composition of the fresh solution supplied to the plants was adjusted accordingly. It took a longer time to re-establish an optimum composition for recycled compared with control watering. EC tended to increase in the recycled system. Recycling decreased total yield and fruit size, but marketable yield was unaffected. The marketable fraction increased in the recycled treatment, primarily as a result of fewer fruit with cracked skin. This effect was consistent across seven cultivars. The cultivars differed in this and other defects, but they did not differ in their response to the two watering systems.
What is the effect of constant compared to diurnal heating of the shoot and root on growth and yield of greenhouse tomato (Lycopersicon esculentum L.)? Seedlings were transplanted on 4 or 25 Mar. 1994 into troughs that were not heated or heated to 21C by buried tubing, either constantly or for 12 h during the day or the night. The greenhouses had either 14/14C or 26/6C day/night minimum air temperatures. After 2 weeks, leaves of the 4 Mar. transplants weighed most with constant root heat and least with no heat. Roots weighed more with 14/14C than 26/6C air heat. With 14/14C air heat, only no root heat reduced leaf weight, whereas with 26/6C air heat, leaf weight was in the order: constant > day > night - no heat. After 2 weeks, leaves of the 25 Mar. transplants weighed least with no heat, and other treatments did not differ. Root heating affected yield. By 1 July, the number of fruit and the number and weight of marketable fruit produced from 4 Mar. transplants was in the order: constant heat > day > night > no heat. The 22/6C air heat increased marketable yield because fewer fruit were small, irregular, or had blossom-end rot. Root heat had no effect on yield of 25 Mar. transplants.