Daniel H. Willits

Effects of irrigation frequency and scheduling on fruit production and radial fruit cracking in greenhouse tomatoes in soil beds and in a soil-less medium in bags

Abstract The effects on yield and radial fruit cracking of 2 media (soil in beds and soil-less medium in bags) and 2 drip-irrigation frequencies (once and 4 times daily) were determined for 4 greenhouse tomato (Lycopersicum esculentum L. Mill.) cultivars. For plants grown in soil-less medium, 2 tensiometer-controlled, drip-irrigation scheduling methods were compared. ‘Michigan’—‘Ohio’ hybrid fruit cracked significantly more than the 3 remaining cultivars, but did not differ in production of total and No. 1 fruit. The amount and severity of fruit cracking was least from the soil-less, bag-cultured plants. Total mean fruit weight was greatest from soil-grown plants. Although no differences in cracking occurred in the fruit from soil-less, bag-cultured plants, those whose irrigation was based on soil-less medium tensiometer readings produced lower total mean fruit weight than those whose irrigation was based on soil tensiometer readings. Number and weight of defective fruit was lowest from plants grown in soil-less medium and whose irrigation was based on soil tensiometer readings, and greatest from soil-grown plants. Fruit cracking was reduced by increasing the irrigation frequency from 1 to 4 times daily.

The effect of night temperature on chrysanthemum flowering: heat-tolerant versus heat-sensitive cultivars

Abstract The effect of night temperature on the flowering of heat-tolerant and heat-sensitive cultivars of potted chrysanthemum (Chrysanthemum xgrandiflorum) was examined in four experiments over a period of 4 years. Temperature reductions were imposed only while the plants were under black cloth using a combination of air-conditioning and under-cloth ventilation. The two heat-sensitive cultivars tested were ‘Yellow Mandalay’ and ‘Coral Charm’ and the two heat-tolerant cultivars were ‘Iridon’ and ‘Dark Bronze Charm’. Differences in time-to-flower (TTF) between heat tolerance classifications were less than anticipated. TTF was affected the most in ‘Iridon’, a heat-tolerant cultivar, decreasing by an average of 4.2 days/°C as mean diurnal temperatures (MT) decreased from about 26°C to about 23°C. TTF was affected the least in ‘Coral Charm’, a heat-sensitive cultivar, decreasing by an average of 2.8 days/°C over the same range. Inflorescence diameter, on the other hand, increased by as much as 9% in the two heat-sensitive cultivars but by only about 4% in the heat-tolerant cultivars. The results suggest that the heat-tolerant cultivars tested here may have been classified based on consistency of flower quality rather than TTF.

CO2 enrichment of greenhouse tomatoes using a closed-loop heat storage: Effects of cultivar and nitrogen

Abstract Spring crops of soil-grown greenhouse tomatoes (Lycopersion Lycopersicum (L.) Karst ex. Farw cultivars MO and TR-VE 23) were provided with three levels of nitrogen addition with and without added CO2. Using a closed-loop solar collection/storage system, crops could be CO2-enriched for 76–77% of the daylight hours. CO2 enrichment increased No. 1 grade fruit weight by 14 and 27% and by 4 and 18% for both cultivars in 1981 and 1982, respectively. Although the method and amount of nitrogen application differed between 1981 and 1982, a trend was seen in both years for low nitrogen treatments to produce a greater response to CO2 enrichment than high nitrogen treatments. A trend was also seen in both years for low nitrogen treatment to depress yield and quality in the non-enriched house, but to have no effect in the enriched house. This trend was particularly apparent in the cultivar with lower vegetative vigor, which also responded more overall to CO2 enrichment than the cultivar with greater vegetative vigor.

Pot soil air composition in conditions of high soil moisture and its influence on chrysanthemum growth

Abstract Chrysanthemums were grown in 15.2 cm standard pots in a heavy mix of clay loam soil+sphagnum peat moss (2:1). A fine texture mix was used to accentuate undesirable gas profiles in the soil. Soil air was analyzed at five depths in the soil profile. In one set of tests, water was applied to the top of the pot at a matrix potential in the center of the soil profile of −5 kPa. The average gas concentrations in soil air in the top and bottom fifths of soil were for O 2 —20.0 and 14.5%, for CO 2 —0.8 and 2.4%, and for C 2 H 4 —0 and 0.08 μ l dm −3 . Smooth concentration gradients of each gas occurred from top to bottom of the soil profile. The composition of soil air changed greatly during the drying cycle. At soil moisture tensions of −0.7, −2.5, and −5 kPa in the center of the soil profile, the gas concentrations in the lowest fifth of soil were for O 2 —9.6, 15.3, and 20.3%, and for CO 2 —4.5, 3.5, and 0.6%, respectively. Thus, soil atmospheric conditions for plant growth were poorest immediately after watering and continuously improved up to the time of watering. When pots of chrysanthemum were watered by capillary action from mats, the average concentration of gases in soil air in the lowest fifth of soil were 5.8% O 2 , 3.6% CO 2 , and 0.38 μ l dm −3 C 2 H 4 . This gas profile was less desirable for growth than the profile found in top-watered pots. Unlike the situation in top-watered pots, the gas concentrations in mat-watered pots were stable. Roots in top-watered pots were restricted to the upper two thirds of the soil ball, and were distributed evenly in the inner part of the soil and at the periphery. Roots of mat-watered plants developed further down the vertical periphery of the pot than roots of top-watered plants, but they did not grow inside the ball. Chrysanthemum plants were grown through a hole in the side wall of each of five 3.9 cm tall by 15.2 cm diameter plastic rings stacked vertically and separated by stainless steel screens that allowed for passage of water but not roots. Water was applied to the top of these cylinder stacks. The largest plants developed in the top ring with progressively smaller plants at lower depths. Plants in the lower two rings developed interveinal chlorosis and did not reach commercial size.