A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 551 ABSTRACT To improve site-specifi c N recommendations a more complete understanding of the mechanisms responsible for synergistic relationships between N and water is needed. Th e objective of this research was to determine the infl uence of soil water regime on the ability of corn (Zea mays L.) to use N derived from fertilizer and soil. A randomized split-block experiment was conducted in 2002, 2003, and 2004. Soil at the site was a Brandt silty clay loam (fi ne-silty, mixed, superactive frigid Calcic Hapludoll). Blocks were split into moderate (natural rainfall) and high (natural + supplemental irrigation) water regimes. Nitrogen rates were 0, 56, 112, and 168 kg urea-N ha -1 that was surface applied. Water, soil N, and N fertilizer use effi ciencies were determined. Plant utilization of soil N was determined by mass balance in the unfertilized control plots and by using the δ 15 N approach in fertilized plots. Findings showed that: (i) plants responded to N and water simultaneously; (ii) N fertilizer increased water use effi ciency (170 kg vs. 223 kg grain cm -1 in 0 and 112 kg N ha -1 treatments, respectively); and (iii) water increased the ability of corn to use N derived from soil (67.7 and 61.6% effi cient in high and moderate water regimes, respectively, P = 0.002) and fertilizer (48 and 44% effi cient in high and moderate water regimes, respectively, P = 0.10). Higher N use effi ciency in the high water regime was attributed to two interrelated factors. First, total growth and evapotranspiration (ET) were higher in the high than the moderate water regime. Second, N transport to the root increased with water transpired. For precision farming, results indicate that: (i) the amount of N fertilizer needed to produce a kg of grain is related to the yield loss due to water stress; and (ii) the rate constant used in yield goal equations can be replaced with a variable.

Interactions between water and N may impact remote-sensingbased N recommendations. The objectives of this study were to determine the influence of water and N stress on reflectance from a corn (Zea mays L.) crop, and to evaluate the impacts of implementing a remote-sensing-based model on N recommendations. A replicated N and water treatment factorial experiment was conducted in 2002, 2003, and 2004. Yield losses due to water (YLWS) and N (YLNS) stress were determined using the 13 C discrimination (D) approach. Reflectance data (400-1800 nm) collected at three growth stages (V8-V9, V11-VT, and R1-R2) were used to calculate six different remote sensing indices (normalized difference vegetation index [NDVI], green normalized vegetation index, normalized difference water index [NDWI], N reflectance index, and chorophyll green and red edge indices). At the V8-V9 growth stage, increasing the N rate from 0 to 112 kg N ha 21 decreased reflectance in the blue (485 nm), green (586 nm), and red (661 nm) bands. Nitrogen had an opposite effect in the near-infrared (NIR, 840 nm) band. At the V11-VT growth stage, reflectance in the blue, green, and red bands were lower in fertilized than unfertilized treatments. At the R1-R2 growth stage, YLWS was highly correlated (r 5 0.58, P 5 0.01) with red reflectance and NDVI (r 5 20.61, P 5 0.01), while YLNS was correlated with all of the indices except NDVI. A remote sensing model based on YLNS was more accurate at predicting N requirements than models based on yield or yield plus YLWS. These results were attributed to N and water having an additive effect on yield, and similar optimum N rates (100-120 kg N ha 21 ) for both moisture regimes.

BACKGROUND:Green manure and graminaceousmanure crops have several benefits, such as improving soil physical and chemical propertiesand utilizing excessive greenhouse nutrients that they have a potential to be a water pollutant source. METHODS AND RESULTS:The objective of this study was to investigate nitrogen (N) supplying capabilities of green manure and graminaceous manure cropsfor lettuce (Lactuca sativa L.) and Chinese cabbage (Brassica campestris L.) grown under greenhouse conditions. For this two leguminous manures (Crotalaria juncea (Cr.) and Sesbaniaexaltata (Se.)) and two graminaceous manures (Sorghum bicolor; Haussolgo(Ha.) and Sudangrass (Sg.)) in the greenhouse were grown, cut, and incorporated into the greenhouse soil before planting. Chemical nitrogen (N) fertilizer rate was estimated based on N recommendation for lettuce and Chinese cabbage. 100% of the N recommended rates (1N) were 70 kg N ha -1 for lettuce and 60 kg N ha -1 for Chinese cabbage and 50% of the N recommendation rates (0.5N) were 35 kg N ha -1 for lettuce and 30 kg N ha -1 for Chinese cabbage. Nitrogen treatments were control (0N), Cr., Se.,

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The use of subsurface drip fertigation using slurry composting bio-filtration (SCB) as nitrogen (N) fertilizer source can be beneficial to improve fertilizer management decision. The objective of this study was to evaluate effects of SCB liquid fertilizer by subsurface drip fertigation on cucumber (Cucumis sativus L.) yield and soil nitrogen (

Zeolite may help crop growth, yield increase, and salt removal. Field experiment under greenhouse cultivation was conducted to study the effect of zeolite application on growth and yield of Chinese cabbage (Brassica campestris L.) and soil. Soil was classified as Gyuam series (coarse silty, mixed, nonacid, mesic family of Aquic Fluvaquentic Eutrudepts). Six zeolite rates were 0, 3, 5, 10, 20 and 40 Mg ha -1. Experimental design was a completely randomized design. Chinese cabbage was grown three times consecutively. Established plant number of plant and yield as fresh weight (F.W.) were measured and soil samples were taken before and after harvesting. Chinese cabbage yield was 76.9 Mg ha -1 at a rate of 20 Mg zeolite ha , and 51.3 Mg ha -1 at control (no zeolite), respectively. Second order regression analysis using zeolite rate and yield showed that optimum zeolite application rate was between 24 and 26 Mg ha -1. The regression equation explained about 88% of the yield variability. The electrical conductivity (EC) decreased from 3.2 to 1.0 dS m -1 for all treatments so that salt accumulation was not a concern. Based on the results, we recommend that optimum zeolite application rate is between 20 and 24 Mg ha -1 for Chinese cabbage under greenhouse cultivation.

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In this study, we monitored 4 volatile organic compounds (VOCs) such as chloroform, dichloromethane, 1,2-dichloroethane, and tetrachloromethane in groundwater samples to determine the detection frequency and their concentrations and evaluated the health risk level considering ingestion, inhalation, and skin contact. 75 groundwater wells were selected. 24 wells were from monitoring background groundwater quality level and 51 wells were from monitoring groundwater quality level in industrial or contamination source area. In the results, the detection frequency for chloroform, dichloromethane, 1,2-dichloroethane, and tetrachloromethane was 42.3%, 8.1%, 6.0%, and 3.4%, respectively. The average concentrations of VOCs were high in the order of chloroform (1.7 µg L ). Chloroform had the highest detection frequency and average detection concentration. In the contaminated groundwater, the detection frequency of VOCs was high in the order of chloroform, dichloromethane, 1,2-dchloroethane, and tetrachloromethane. The average concentrations for chloroform, dichloromethane, 1,2-dichloroethane, and tetrachloromethane were 2.23 µg L , respectively. All the 4 compounds were detected at industrial complex and storage tank area. The maximum concentration of chloroform, dichloromethane, and 1,2-dichloroethane was detected at industrial complex area. Especially, the maximum concentration of chloroform and dichloromethane was detected at a chemical factory area. In the uncontaminated groundwater, the detection frequency of VOCs was high in the order of chloroform, dichloromethane, and 1,2-dchloroethane and tetrachloromethane was not detected. The average concentrations for chloroform, dichloromethane, and 1,2-dichloroethane were 0.57 µg L , respectively. Although chloroform in the uncontaminated groundwater was detected the most, the concentration of chloroform was not exceeding water quality standards. By land use, the maximum detection frequency of 1,2-dichloroethane was found near a traffic area. For human risk assessment, the cancer risk for the 4 VOCs was 10, while the non-cancer risk (HQ value) for the 4 VOCs is 10