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Habib Khemira, T. L. Righetti, David Sugar and A. N. Azarenko

Current N fertilization practices, where high spring applications are utilized, may lead to excessive vegetative growth. However, high rates may not be required to maximize fruit yield and quality. Therefore, alternative strategies to minimize shoot growth while still providing the N needs of the tree were investigated. Mature `Comice' and `Bosc' pear trees were given one of the following treatments: a spring soil (SS) application of NH4NO3 nitrate at 112.5 kg/ha rate, a similar application in the fall after harvest (FS), a fall foliar (FF) spray of a 7.5% urea solution after harvest (FF), or no N (Control). Trees that received a FF application had the same leaf and fruit N content as control trees, but they yielded more fruit The SS application gave more vigorous trees than FF application. Yield, however, was not different.

A 15N enriched urea solution was applied at harvest as either a foliar spray, soil application, or combination of both treatments to mature `Comice' trees. Flower buds from trees that previously received a foliar treatment had 37% of their N derived from the foliar N application. No labeled N was detected in buds from the soil treatment These results indicate that vegetative and reproductive N requirements of fruit trees may be managed separately.

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George J. Hochmuth, Earl E. Albregts and Craig K. Chandler

During the 1992-93 fruiting season, strawberries were fertigated weekly with 0.28, 0.56, 0.84, 1.12, or 1.40 kg N/ha/day from ammonium nitrate. K was applied uniformly at 0.84 kg/ha/day by fertigation. Irrigation maintained soil moisture tension in the beds between -10 and -15 kPa. Fruit yields responded positively to N fertilization with yields maximized at 0.56 kg N/ha/day. Leaf N and petiole sap nitrate N concentrations increased with N rate with leaf-N for the plants receiving 0.28 kg N/ha/day remaining below 25 g·kg-1 most of the season. Sufficiency ranges for petiole sap nitrate-N quick testing were developed.

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Anthony F. Silvernail and Gary R. Cline

The effects of cover crop, tillage, and N fertilization on yields of `Paladin' watermelon (Citrullus lanatus) were analyzed by determining available soil N levels, foliar N content, and relative greenness with a SPAD-502 chlorophyll meter. Analyses from all three analytical procedures identified N deficiencies in watermelon with their respected measurements. Available soil N analyses indicated that soil N levels below 40 mg·kg–1 at vining caused dramatic decreases in yields, while the level needed to ensure maximal yields during the same period was 100 mg·kg–1. Results from foliar and SPAD tests indicated that plants with foliar N levels below 42 g·kg–1 and SPAD readings below 40 SPAD units at anthesis will have suppressed yields. Optimal foliar N levels and SPAD readings required for maximum yields were 50 g·kg –1 and 48 SPAD units, respectively. The main difference among all three N testing procedures was that available soil N analysis was able to detect possible deficiencies two to three weeks before either the foliar or SPAD analysis. Differences in yield between plants from conventionally tilled plots and no-till plots were not significant. However, inorganic N fertilization significantly increased yields in watermelon following both rye (Secale cereale) and mix cover crop treatments. Watermelon yields of plants following the hairy vetch (Vicia villosa) cover crop treatment showed no response to inorganic N fertilization. Of the three cover crop treatments, the addition of N fertilizer had the most effect in the rye treatment.

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Joseph Naraguma and John R. Clark

Applications of N to blackberry plantings are a common practice in Arkansas, but fertilizer recommendations are largely based on those of other states. The need for information on fertility of a new blackberry from the Arkansas breeding program motivated this study. A three-year-old `Arapaho' blackberry planting at the University of Arkansas Fruit Substation was used for this study. Treatments which began in 1994 and continued through 1996 were: 1) control—no N applied, 2) 56 Kg N/ha applied in a single application in early spring, 3) 112 Kg N/ha applied in a single early spring application, and 4) 112 Kg/ha applied in a split application with one-half applied in the early spring and one-half applied immediately after harvest. Fruit was harvested from the plots in June and total yield and average berry weight determined. Foliar samples were collected in August and elemental analysis conducted. Primocanes in each plot were counted at the end of the growing season. Over the three years, there was no significant treatment effect on yield, berry weight, or primocane number. A trend toward higher primocane number where N was applied was seen, however. Foliar levels of N, P, K, Ca, S, and Mn were affected by either N rate or time of application. The foliar N levels were influenced by N rate and the split application gave the highest concentration. Calcium was higher when no N was applied, Mn was greater at higher N rates while the control had the lowest foliar N level in each year.

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Barbara Cohea Pitman, D.C. Sanders and W.H. Swallow

One-year-old crowns of Asparagus officinalis L. cv. Princeville were grown for up to 2 years in pots containing a mineral soil. Nitrogen concentrations ranged from O to 340 kg N/ha. Increasing N fertilizer level resulted in a decrease in total crown fructose concentration and an increase in fern growth, both leveling off at higher N levels. Crown growth was maximized at intermediate N levels. To obtain maximum crown growth and total fructose concentration, while avoiding the excessive fern growth associated with higher N fertilizer levels, ≈57 kg N/ha should be applied to asparagus during the 2nd and 3rd years of growth.

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Baoxin Chang, Benjamin Wherley, Jacqueline Aitkenhead-Peterson, Nadezda Ojeda, Charles Fontanier and Philip Dwyer

Wetting agents have been widely used in the turf industry for ameliorating hydrophobic soil conditions and improving water use efficiency. However, limited information is available regarding potential benefits of wetting agents on fine textured soil lawns where wettable soils are commonly found, because most prior studies have been conducted in sand-based turf systems. This 2-year field study evaluated the potential for wetting agents to improve turf quality, as well as to reduce runoff losses of water and nutrients from st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] lawns. Over two seasons, turfgrass quality, percent green cover, and soil moisture in plots were evaluated in response to wetting agent and fertilizer treatments. During precipitation events, total runoff volumes were measured, as well as total export of nutrients including NO3-N, NH4-N, total dissolved N, dissolved organic N, dissolved organic C, and PO4-P. No runoff was detected from any treatments when precipitation was less than 13 mm. St. augustinegrass turfgrass quality and soil moisture were slightly improved by wetting agent and fertilizer treatments during the study, but no significant effects of either of the treatments were found on runoff volumes or nutrient exports. Although turf was managed under deficit irrigation levels of 0.3 × reference evapotranspiration, irrigation events were not withheld due to rainfall, and thus, little to no drought stress was observed during the study.

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Michael D. McCullough, James E. Motes and Brian A. Kahn

Two problems associated with machine harvesting of peppers (Capsicum annuum L.) are plant lodging during growth and uprooting. Factorial combinations of four bedding treatments and two N rates were compared for effects on lodging, uprooting, and fruit yield of chile and paprika-type peppers in Fort Cobb and Bixby, Okla. Bedding treatments were 1) no bed (T1); 2) no bed with 5 cm of soil hilled to the plant bases (T2); 3) bedded preplant, but bed not sustained (i.e., allowed to erode) during the growing season (T3); and 4) bedded preplant and bed sustained during the growing season (T4). All plots received preplant N at 45 kg·ha–1. In 1992, one-half of the plots were sidedressed with 45 kg N/ha. In 1993, one-half of the plots were sidedressed with N at 45 and 90 kg·ha–1 for paprika and chile, respectively. The higher N rates consistently produced larger and higher-yielding chile plants and generally increased yield and stem and leaf weights of paprika plants. The force required to uproot plants was not significantly affected by N rates. Plant lodging was significantly worse at the higher N rates in only one of five studies. Bedding treatments did not have a consistent influence on fruit yield. The force required to uproot plants was greater with T2 and 4 compared to T1 and 3 in three of four studies. Plant lodging was not influenced by the bedding treatments.

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Fang Xiao, Zaiqiang Yang, Haijing Huang, Fei Yang, Liyun Zhu and Dong Han

indirectly by influencing chlorophyll content ( Berges et al., 1996 ; Rufty et al., 1988 ). Moreover, there is a significant positive correlation between N fertilization contents and photosynthetic rate of plant leaves. Some researchers found that N can

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Mary Ann Rose, John W. White and Mark A. Rose

`Celebrate 2' poinsettias (Euphorbia pulcherrima Willd.) received either a constant application rate of 200 mg N/liter or a variable rate that was linked to the N accumulation pattern of the crop. At final harvest, shoot N content, N concentration, dry weight, leaf area, and quality were similar for the treatments. However, N recovery efficiency of the variable treatment was greater (58% vs. 38%), and 41% less total N was applied compared to the constant-rate treatment. Growth analysis revealed that N accumulation rates for both treatments increased rapidly as side branches developed, reaching a maximum 50 to 60 days after potting, and decreased throughout bract development. The decrease in N accumulation rates after day 60 reflected a shift in N allocation from leaves to bracts, a tissue with a lower N concentration.

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John E. Erickson and Kevin E. Kenworthy

achieved, but they did not find the same relationship at higher temperatures. Higher WUE has been reported for slow-release N fertilizers ( Saha et al., 2005 ). Other studies have shown that N fertilization is positively related to WUE ( Brueck, 2008