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Suat Irmak and Dorota Z. Haman

Evaporation pans continue to be used extensively throughout the world to measure free-surface water evaporation (Epan) and to estimate evapotranspiration for irrigation scheduling and water management for agronomic and horticultural crops. Epan is also being used extensively to estimate evaporation rates from lakes, wetlands, rivers, reservoirs, and other water bodies for management of wildlife and ecological habitat. A reliable method is needed to estimate missing daily Epan data. Determination of a reliable method for the estimation of Epan would also be useful in modeling of crop growth, and hydrological and ecological systems. Five methods [Penman (Penman, 1948), Kohler-Nordenson-Fox (KNF) (Kohler et al., 1955), Christiansen (Christiansen, 1968), Priestley-Taylor (PT) (Priestley and Taylor, 1972), and Linacre (Linacre, 1977)] for estimating Epan were compared with the historical (23-year) measured daily values to determine the suc- cess of accurate and consistent Epan estimations under humid climatic conditions in Florida. The root mean square error (RMSE) was used as the criteria to judge the accuracy and reliability of a given method. An RMSE value of <0.5 mm·d-1 (0.02 inches/d) between the measured and estimated Epan was considered as an acceptable error for daily estimations. The standard deviation (sd) values, and percent error (%E) between the estimated and measured values were also considered in the performance evaluations. Performance evaluations of the Epan estimates of the methods were made on a daily, monthly, and annual basis. Results indicated that the KNF method provided the best Epan estimations. The Linacre method yielded the poorest estimates. The second, third, and fourth best methods were the Penman, PT, and Christiansen, respectively. The RMSE and sd of Epan estimates were lowest when using KNF method. The mean value of the %E of daily, monthly, and annual estimations were 27%, 27%, and 26% for Christiansen; 6%, 6%, and 4% for KNF; 33%, 32%, and 26% for Linacre; 24%, 24%, and 21% for PT; and 19%, 17%, and 11% for Penman methods, respectively. The weekly, monthly, and annual total of Epan estimates from KNF method were also compared to the measured values of the two selected years of data (1981 and 1983). The annual rainfall totals were significantly lower than the 23-year mean in 1981, and higher in 1983. The %Es of weekly, monthly, and annual total Epan estimates were 9%, 9%, and -1% in 1981; and 11%, 5%, and 4% in 1983, respectively. The KNF method underestimated Epan in 1981 (dry year) and the underestimations were higher in summer months. The underestimations in a dry year, especially in summer months, might be due to the fact that the sensible heat advection is not effectively accounted for in the KNF equation causing underestimations of Epan. Overall results indicated that the KNF method should be the first choice, among the methods tested, for estimating daily Epan for irrigation scheduling and for estimating the missing Epan data in humid areas.

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Suat Irmak, Dorota Z. Haman, Ayse Irmak, James W. Jones, Kenneth L. Campbell and Thomas L. Crisman

Two colors (white and black) of a recently introduced irrigation-plant production system [multi-pot box system (MPBS)] for container-grown nurseries were researched and results were compared with those obtained from the sprinkler-irrigated conventional (control) system (CS). Experiments were carried out in summer and fall of 2001 in Gainesville, Fla. Plant growth [growth index (GI), growth rate (GR), and dry matter] and stress parameters [stomatal resistance (rs), crop water stress index (CWSI), plant water potential (PWP), and substrate temperature (ST)] were measured and analyzed for Viburnum odoratissimum (Ker-gawl). In both seasons, plants grown in the white MPBS had significantly higher GI and GR as compared to the plants in the black MPBS and CS. In summer, plants in the white MPBS reached marketable size about 17 days and 86 days earlier than those in the black MPBS and CS, respectively. In fall, they reached marketable size about 25 and 115 days earlier than those plants in the black MPBS and CS, respectively. Plants in the white and black MPBSs showed exponential growth rate in summer with plants in the white MPBS having significantly higher growth rate (greater slope) than the other two treatments. In both seasons, plants in the white MPBS produced the highest amount of dry matter. In general, plants in the white MPBS had lower rs values to vapor transport compared to the other two treatments, and the black MPBS treatment had lower rs values than the CS in both seasons. The CWSI values of the plants in both white and black MPBSs were significantly lower than the CS. In both seasons, ST in the black MPBS and CS exceeded the critical value of 40 °C several times. The ST of >40 °C is often reported to significantly reduce the plant growth and cause root death and/or injury for container-grown plants. Overall, the white MPBS provided a better environment for root development and plant growth under these experimental conditions. Results strongly suggest that there is a potential opportunity of using MPBS for irrigation and production of nursery plants. These important findings suggest that, in practice, producing nursery plants in a shorter period of time by using white MPBS will result in significant savings of energy, water, chemicals, and other inputs and thereby reducing the costs and increasing profits.

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Elio Jovicich, Daniel J. Cantliffe, Peter J. Stoffella and Dorota Z. Haman

Frequent fertigation of soilless-grown bell pepper (Capsicum annuum L.) can increase fruit production, but development of fruit disorders may offset the increase in yield of first-quality (blemish-free) fruit in greenhouses with minimal environmental control. Fruit yield and quality were studied as affected by water volumes and nutrient concentration levels, delivered with irrigation events initiated after determined cumulative solar radiation levels, in ‘HA3378’ bell pepper from October to May in north–central Florida. Irrigation events occurred after solar radiation integral levels (SRI; ±SD) 1.7 ± 0.42, 3.7 ± 0.42, 5.7 ± 0.42, 7.7 ± 0.42, and 9.7 ± 0.42 kW·min−1·m−2, which led to mean number of daily irrigation events of 61 ± 31, 26 ± 12, 17 ± 8, 12 ± 5, and 10 ± 4 respectively. In peat mix, perlite, and pine bark media, volume per irrigation event and concentration levels of the nutrient solution were, in the first experiment, 74 mL standard (74-s), and in a second concurrent experiment, 74 mL half-standard (74-½s) or 3) 37 mL standard (37-s). In both studies, combined marketable fruit yields of first quality and second quality (minor cracking patterns and yellow spots) increased linearly with decreasing SRI (increased events per day). First-quality fruit weight with 74-s was unaffected by media and, in a quadratic response to SRI, reached 5.4 kg·m−2 at 5.7 kW·min−1·m−2. First-quality weight with 74-½s and 37-s did not differ. Weight was unaffected by SRI in peat mix and perlite, and a quadratic response was recorded in pine bark, with yields of ≤3.6 kg·m−2. Fruit cracking incidence decreased with increased SRI, and was generally greater in pine bark. Incidence of yellow spots doubled with 74-½s compared with 37-s, and decreased linearly with increased SRI; the disorder was minor with 74-s. Compared with 37-s, 74-½s decreased fruit with blossom-end rot by 14%, increased marketable fruit weight by 10% in media with the lowest water-holding capacity (perlite, pine bark), and increased nutrient use efficiency. With any media used, the SRI set point of 5.7 kW·min−1·m−2 (daily mean of 17 irrigation events) and 74 mL, at standard nutrient concentration levels, appeared to produce greater blemish-free fruit yield than delivering 37 mL/event or half-concentrated 74 mL/event within the range of SRI means of 1.7 to 9.7 kW·min−1·m−2 (61–10 irrigation events/day). Disorder-tolerant pepper cultivars, better temperature control, and August plantings are additional suggestions for irrigation management to increase first-quality fruit yield.

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Jeffrey G. Williamson, Luis Mejia, Bradley Ferguson, Paul Miller and Dorota Z. Haman

Nonweighing drainage lysimeters were used to measure seasonal water use of mature ‘Emerald’ southern highbush blueberry (SHB; Vaccinium corymbosum interspecific hybrid) plants grown in pine bark beds and in pine bark amended soil in north central Florida. In the absence of rain, irrigation was applied daily with microsprinklers at ≈120% to 175% of reference evapotranspiration as either single or split applications. Leachate was collected and its volume determined from each lysimeter at 6- to 10-day intervals throughout the study. Water use, expressed as L/plant, was calculated as the difference between the amount of irrigation/rain added to lysimeters and the amount of leachate collected from lysimeters during each measurement period. Average daily water use was calculated for monthly intervals beginning in Apr. 2010 and ending in Sept. 2012. Water use increased rapidly during spring through the final stages of fruit ripening and harvest (May) with peak water use occurring during mid to late summer (July, August, and September). Plants grown in pine bark beds used more water than plants in pine bark amended soil during Apr., May, and Dec. 2010, Feb. 2011, and Mar. 2012, but there were no differences during the periods of highest water use. No differences in water use were observed between single or split-application irrigation treatments. Monthly averages for daily water use during the 30-month period ranged from ≈1.75 L/plant in January to ≈8.0 L/plant in mid to late summer. Mean monthly crop coefficient values during the 30-month period ranged from 0.44 in February to 0.86 in September. Canopy volume, yield, and mean berry weight were unaffected by soil or irrigation treatments.