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Catherine S. Fleming, Mark S. Reiter, Joshua H. Freeman and Rory Maguire

Chesapeake Bay and tributaries leading to the bay, nitrate leaching and runoff are of great concern. Drip irrigation combined with polyethylene mulch is a common practice for commercially grown fresh market tomato in the mid-Atlantic United States. Drip

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Giuseppe Colla, Carolina María Cardona Suárez, Mariateresa Cardarelli and Youssef Rouphael

nitrate leaching in tile-drained midwestern soils Agron. J. 94 153 171 Dong, H.H. Niu, Y.H. Li, W.J. Zhang, D.M. 2008 Effects of cotton rootstock on endogenous cytokinins and abscisic acid in xylem

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A.K. Alva

Nitrate pollution of surfacial aquifer is fairly widespread in deep sandy soil areas of Central Florida. Since citrus is a predominant crop in this area, despite lack of conclusive evidence suggesting citrus fertilization as the source of nitrate pollution, investigations are in progress to develop Best Management Practice (BMP) recommendations for N fertilization of citrus in an effort to improve N use by the trees and to minimize potential nitrate leaching. Our ongoing studies on both young and mature trees have demonstrated that the use of improved fertilizer formulations and programmed application schedules have facilitated to decrease the rate of N application considerably without any adverse impact on tree growth and/or fruit production while minimizing nitrate leaching below the rootzone. Our approach involves developing BMP recommendations on the basis of iudicious irrigation management and generating database on N removal by the fruits, annual N contribution to the trees by mineralization of organic N, and N losses including leaching, denitrification, etc.

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T.L. Schultz and U.K. Schuch

Nitrate nitrogen is becoming a major pollutant in much of our nation's water supply. High levels of nitrate runoff are commonly found to occur from intense agricultural areas such as container nurseries. The objective of this study was to investigate combinations of liquid fertilizer (LF) plus controlled-release fertilizer (CRF) that would both minimize nitrate runoff and provide nutrient levels for optimum growth of Ilex verticillata L. The experiment was established in 1998 at the Iowa State Univ. Horticulture Research Station, Ames. Six fertilizer treatments were arranged in a randomized block design with eight replications. Treatment combinations of liquid fertilizer (LF) and controlled-release fertilizer (CRF) were [LF (mg/L)/CRF (g)]: 90/0, 90/8.5, 90/17, 180/0, 180/8.5, 180/17 (Peter's Excel 21-5-20 and Osmocote 18-6-12, 9-month release, respectively). Analysis of nitrate leaching showed that in 12 out of 16 weeks, the 180 mg/L LF treatments resulted in twice the amount of nitrate leached compared to the 90 mg/L LF. In 3 out of 16 weeks, treatments containing 0 g CRF leached significantly less nitrate than those containing 17 g CRF. None of the treatments produced a difference in total dry weight or caliper of Ilex verticlillata L. This data suggests that plant growth remains similar over a range of fertilizer input and higher rates of applied LF result in higher nitrate leaching.

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Steven A. Weinbaum, Wesley Asai, David Goldhamer and Franz J.A. Niederholzer

A project to study the interrelationships between leaf N conc., relative tree yield (RTY), nitrate leaching and fertilizer N recovery was established in 1990. Collection of pretreatment baseline data was followed by differential rates of N fertilization. Significant differences in leaf N conc. and RTY were obtained in 1992 and 1993, respectively. RTY is defined as tree yield in 1993 expressed as a percentage of pretreatment (1990) yield. 15N-depleted (NH4)2SO4 was applied postharvest in 1993 to 17 trees differing in RTY and leaf N conc., and recovery of labelled N in the blossoms of these trees (March, 1994) will be discussed.

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L. Gene Albrigo and James P. Syvertsen

In order to evaluate possible reduced nitrate leaching while maintaining yield, `Hamlin' orange and `Flame' grapefruit trees on `Carrizo' or `Swingle Citrumelo' rootstocks were grown from planting using only foliar urea or soil-applied nitrate or ammonium N. An intermediate treatment of foliar and ground N was included also. From the 4th year, yields were recorded for 3 years. As previously reported, canopy growth was greater for the foliar urea treatment for the first 3 years. For 2 of the next 3 bearing years, the grapefruit trees in the foliar urea N treatment produced significantly less yield than the soil-applied treatment and the intermediate treatment was intermediate. The orange trees in the foliar urea treatment produced significantly less fruit than the soil N treatment in only 1 of 3 years, but the yields were numerically less every year. Results for fruit quality and nitrate leaching will be reported also. Foliar urea application alone was more costly and less productive than a soil N program.

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Mark D. Hamilton, Frank J. Cruz and James McConnell

The performance and leaching behavior of six nitrogen fertilizers on bermuda grass were studied under humid tropical conditions. The grass was established in 20 × 36 cm pots filled with 8 cm pea gravel and 28 cm of silica sand. Ammonium nitrate was applied to the turf at monthly rates between 0.25 and 6 lb/1000ft2. Performance was gauged by clipping dry weights, image analysis for greeness, and visual ratings. Leachates were checked for nitrate levels. A rate of 2 lbs/1000ft2 produced quality turf while yielding a minimum of nitrate leaching. Rates of 6 and 4 lb./1000ft2/mo. resulted in the highest readings without an increase in quality. Rates less than 2lb/1000ft2 had leachate nitrate less than 9 ppm but produced turf of unacceptable quality.

Nutralene, Nitroform, sulfur coated urea, IBDU, and AN were applied at a rate of 2 lb./1000ft/mo. The slow-release forms were applied as a 3 month dose. Performance was determined as above and nitrate leaching was monitored by weekly collections. Nutralene, SCU and Nitroform had peak nitrate levels 2 weeks after application, IBDU had peak nitrate levels after 4 weeks. Turf quality diminished at 6 weeks.

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Carl J. Rosen and Mohamed Errebhi

Applying appropriate rates of nitrogen fertilizer during the growing season for potatoes on irrigated sandy soils is an important concern from both a production and environmental standpoint. Although potatoes on sandy soils are responsive to nitrogen fertilizer, high rates of nitrogen applied early in the growing season have been associated with nitrate leaching due to unpredictable rainfall. Use of lower nitrogen rates applied more frequently through the season is one strategy to minimize nitrate losses and improve nitrogen use efficiency. Portable nitrate electrodes were used to measure nitrate concentrations in petiole sap. Diagnostic criteria based on final yield and nitrate sap concentrations at various growth stages were developed over a three year period. This rapid test can now be used to make an immediate assessment of nitrogen status of the plant and a prediction for whether supplemental nitrogen will be needed. On-farm trials are currently being carried out to demonstrate the use of the saptest as a best management practice.

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Peter Bierman and Tom Wall

Inadequate N can reduce growth and yield, but excess N can be uneconomical and environmentally harmful. Our objective was to investigate the potential for using fertigation and on-farm plant-nutrient monitoring to improve the efficiency of N fertilizer use by bell peppers (Capsicum annuum L.). Two N fertilizer treatments were compared: 1) all N applied preplant and 2) one-third of the N applied preplant and the remainder injected into the drip-irrigation lines throughout the growing season. Total application rates were N at 118 kg·ha–1 for both treatments. Data were collected for total yield, marketable yield, and fruit size. Leaf and petiole samples were collected every 2 weeks and were used to monitor plant N status throughout the growing season. A Horiba/Cardy nitrate meter was used to measure nitrate concentrations in freshly-pressed petiole sap. A SPAD chlorophyll meter was used to measure leaf chlorophyll content and give an indirect measure of leaf N concentrations. Subsamples of leaves and petioles also were saved for conventional laboratory analyses. Whole (aboveground) plant samples were collected every 2 weeks, analyzed, and used to calculate differences in N accumulation. Suction cup samplers were installed at the 24-in soil depth and water samples collected every 1 to 2 weeks for nitrate analysis. Except for early in the growing season, petiole sap nitrate and leaf chlorophyll were higher in the fertigation treatment. Plant dry matter and total N accumulation also were much larger, but fertigation did not increase yield. Nitrate leaching was greater early in the season with 100% preplant N, but later in the season it was greater with fertigation. Data suggested that adequate plant N, reduced nitrate leaching, and equivalent yields are possible with fertigation at reduced N-rates compared to 100% preplant fertilizer applications.

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Clint C. Shock, Erik B. G. Feibert and Monty Saunders

Seven potato cultivars were grown in an adequately irrigated check (100% of crop evapotranspiration replaced at -60 kPa) and three deficit irrigation regimes in order to evaluate varietal response to water stress and to evaluate nitrate leaching below the crop root zone in relation to the irrigation management. Potatoes were grown with sprinkler irrigation on silt loam in 1882 and 1993. Water stress treatments were achieved by partial or complete crop evapotranspiration replacement when soil water potential reached -60 or -80 kPa. In 1992, over all varieties, tuber yield and grade were significantly reduced by the two higher levels of water stress. In 1993, a relatively cool year, yield was reduced by water stress, but grade was not. Tuber internal quality was affected more by variety than by deficit irrigation both years. A comparison of pre-plant and post-harvest soil nitrate and ammonium shows that a small amount of nitrate moved from the top two feet of soil to the third and fourth foot in the check plots. Soil nitrogen accounting for the season showed large surpluses, indicating the importance of natural sources of available nitrogen.