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phenolic contents indicate that KPF can work under humid climate conditions and suggest that the use of KPF can improve the quality of the wine grape cultivar Meili. Literature Cited Abbott, N. Coombe, B. Williams, P. 1991 The contribution of hydrolyzed

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Resource Conservation Service have provided an additional incentive for growers to invest and explore the benefits of these protected environment systems. There is a lack of information related to adapting high tunnels to humid, subtropical climates in the

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-filling stage and water demand is at its peak. Thus, irrigation has been proven to markedly enhance pecan production in the region ( Worley, 1982 ). Yet, irrigation scheduling and management of pecans in humid climates is not well established. Daniell (1985

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humid climate with 92–124 cm of rainfall; however, growth was enhanced by irrigation in years 2, 3, and 4. Fereres et al. (1982) suggested that due to the uncertainty of the root zone of newly planted almond [ Prunus dulcis (Mill.) D.A. Webb] trees in

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Temperature differences between tree canopies and air (Tc - Ta) and between leaves and air (T1 - Ta) of apples (Malus domestics Borkh. `Royal Gala') grown in New Zealand were measured with infrared (IR) thermometry. Treatments included three orchard-floor management systems and irrigation withheld (WI) for part of the growing season. Measurements of soil moisture indicated that, under full irrigation (FI), an alfalfa orchard-floor system apparently had higher soil water content than herbicide-strip (H) or plastic-mulch systems, whereas under the drought stress of WI, the H system retained the most water. The Tc - Ta and T1 - Ta of the WI treatment were significantly greater than those of the FI treatment after a soil-moisture differential was established. Linear regression between Tc - Ta, or T1 - Ta, and vapor pressure deficit (VPD) exhibited variable responses among dates. A crop water stress index (CWSI) was calculated from environmental measurements. The calculated CWSIS were not related to soil-moisture measurements. Even 35 days after full irrigation had been reinstated on the WI plots, the Tc - Ta, T1 - Ta, and CWSI of the WI plots were still significantly greater than those of the FI plots. These discrepancies in IR thermometry-based water-stress indices may be due to increased errors in the calculation of minimum CWSI at low VPDS and to fluctuating solar radiation and evapotranspiration, which are prevalent in humid, temperate climates.

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Four decades ago, irrigation in much of the southeastern U.S. was considered not sensible economically because of normal rainfall in excess of 1200 mm in some areas. More-recent research has shown that irrigation makes definite economic sense because it can increase production substantially. This is especially true in Florida citrus, where irrigation can increase yield by up to 60%. Drip and microsprinkler irrigation have become popular, and these methods of partial root-zone coverage affect tree water potential and yield. Growing environmental concerns about possible nitrate and pesticide leaching to the groundwater have led to greater emphasis on irrigation management in an area of highly variable rainfall. Rapidly growing population has brought about increased competition for water and greater restrictions on agricultural water use. Reclaimed water, once considered a disposal problem, is now being promoted as a partial solution for periodic water shortages. Discussion will focus on tree response to different irrigation management systems and how agriculture is dealing with greater irrigation restrictions.

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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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Abstract

Leaf NO3 concentration in ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] and ‘Marsh’ grapefruit (Citrus paradisi Macf.) declined in midsummer when temperature and rainfall were at their maximum. Total N concentration remained steady after declining in the spring. The decrease in NO3-N concentration during the hottest time of the year contrasts with a peak at this time in dry citrus-growing areas.

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The objectives of this 7-year study were to determine the effect of repeated root pruning and irrigation on peach (Prunus persica L. Batsch) tree growth and soil water use. Root pruning began in the year of planting. Peach trees trained to a freestanding “Y” were root-pruned at flowering for 4 years (1985 to 1988) and subsequently at flowering and monthly through July for 3 years (1989 to 1991). Irrigation was withheld or applied the full season or only during stage 3 of fruit growth on root-pruned and non-root-pruned trees. Root pruning limited soil water availability throughout most of the growing season when irrigation was withheld; however, when irrigation was applied, there was no difference in soil water availability. The root length density of peach roots was greatest in the 0 to 30-cm depth, was promoted by irrigation, and was reduced by root pruning in the 0 to 90-cm root zone. Full-season irrigation increased vegetative growth over the nonirrigated treatments. Root pruning had no effect on vegetative growth measured as fresh pruned material. The treatments had no effect on leaf nutrient content, except that root pruning reduced Zn in five consecutive years. Fruit yield was reduced 1 in 5 years by root pruning, and full-season irrigation reduced yield in 3 of 5 years. Repeated root pruning restricted the lateral spread of the root zone and the use of soil resources, yet on the deep soil of this site, restricting the lateral extent of the root zone did not reduce vegetative tree growth.

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