The purpose of this study was to compare two commonly used runoff experimental methods, which have different scales, on measurements of runoff and associated fenamiphos and metabolite losses over a 2-year period. Methods used were 15 m wide by 43 m long (645 m(2)) mesoplots and 1.8 m wide by 3 in long (5.4 m(2)) microplots, under simulated rainfall (25 mm h(-1) for 2 h) at 1, 14, and 28 d after fenamiphos application. Mesoplots and microplots were established parallel to a 3% slope on a Tifton loamy sand (Plinthic Kandiudult). All plots were planted to corn (Zea mays L.). Target application rate for fenamiphos was 6.7 kg ha(-1). Runoff totals and maximum rates or meso- and microplots were similar with approximately 25% of the rainfall running off mesoplots and approximately 28% running off microplots. Runoff totals and maximum rates from meso- and microplots were each positively correlated (R-2 = 0.89). In both years, fenamiphos lost in runoff decreased with each rainfall event (1, 14, and 28 d after application). The majority of fenamiphos lost in runoff was in the fenamiphos sulfoxide form. Fenamiphos sulfoxide lost over both years from mesoplots ranged from 51% to 93% of the total fenamiphos lost, and loss from microplots ranged from 47% to 100% of the total fenamiphos lost. Runoff from meso- and microplots I d after fenamiphos application, a "reasonable worst-case" event, had the greatest fenamiphos losses among events. Total losses of fenamiphos or this event averaged 1.2% (CV = 26%) of applied amount for mesoplots and 1.3% (CV = 47%) of applied amount for microplots. Maximum (seasonal) fenamiphos losses for meso- and microplots were 1.4% of applied for mesoplots and 2.6% of applied for microplots. A positive correlation was obtained between microplots and mesoplots for total losses of fenamiphos + metabolites (R-2 = 0.88), fenamiphos parent (R-2 = 0.89), and fenamiphos sulfoxide (R-2 = 0.81). Relatively poor agreement was found for relatively small losses of fenamiphos sulfone between plot types (R-2 = 0.34). Microplots and mesoplots yielded statistically similar results in terms of runoff and fenamiphos losses; thus, microplot results can be extrapolated tip to larger mesoplot areas under these conditions. This has implications for field-scale management and watershed assessment in the Coastal Plain region of the southeast U.S. in that microplot and rainfall simulation results could be useful as statistically valid input datasets to estimate runoff and associated fenamiphos losses from larger areas.

High‐intensity storms that occur shortly after chemical application have the greatest potential to cause chemical runoff. We examined how effectively current chemical transport models GLEAMS, Opus, PRZM2β, and PRZM3 could predict water runoff and runoff losses of atrazine [6‐chloro‐ N ‐ethyl‐ N ′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] under such conditions, as compared with observations from a controlled field runoff experiment. The experiment was conducted for 2 yr using simulated rainfall on two 14.6‐ by 42.7‐m plots within a corn ( Zea mays L.) field on Tifton loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults) under conventional tillage practices. For each plot‐year, atrazine was applied as surface spray immediately after planting and followed by a 50‐mm, 2‐h simulated rainfall 24 h later. A similar preapplication rainfall and four subsequent rainfalls during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly tilled soil or under full canopy cover; more runoff occurred when nearly bare soil had crusted. Observed total seasonal atrazine runoff averaged 2.7% of that applied, with the first posttreatment event runoff averaging 89% of the total. GLEAMS, Opus, PRZM2β and PRZM3 adequately predicted water runoff amounts, with normalized root mean square errors of 29, 29, 31, and 31%, respectively. GLEAMS and PRZM3 predicted atrazine concentrations in runoff within a factor of two of observed concentrations. PRZM2β overpredicted atrazine concentrations. Opus adequately predicted atrazine concentrations in runoff when it was run with an equilibrium adsorption submodel, but significantly underestimated atrazine concentrations when it was run with a kinetic sorption submodel.

In an attempt to increase soybean (Glycine max) yield, studies initiated in 1986 and continued until 1996 have resulted in the recommendation that soybean growers in Georgia foliar-apply 0.28 kg boron ha-1 with Dimilin at 0.07 kg active ingredient ha-1 in reproductive stages. Such applications, at the time an insecticide is needed, have resulted in economically important yield responses of soybeans grown using other best management practices. The yield response appears due to both nutrition and protection from foliage-eating insects. Initial experiments were with applications of nitrogen (N) applied by fertigation using center-pivot sprinkler irrigation systems. Such applications increased yield and protein contents of soybeans in many cases. However, fertigation is not an option for most soybeans, therefore research on foliar effects of N applications were undertaken. Foliar nitrogen applications frequently result in leaf burns, but we found that addition of boron (B) afforded some protection from those burns and provided additional increases in yield. Additional experiments indicated that B application was resulting in yield increases similar to those attained with fertigated N at far less cost. Yield increases of up to 400 kg ha-1 for a single application of 0.28 kg B ha-1 have been attained. The major gross physiological effect of B appears to be an increase in bean size. Recent studies have been directed toward applying the boron with insecticides at the time the insecticide is needed. This method of application reduces the cost of B application to the actual cost of the B source (approximately 3 US ha-1). Soluble disodium octaborate tetrahydrate is compatible with insecticides, including Dimilin (diflubenzuron), an insecticide which is very effective against the velvetbean caterpillar (Anticarsia gemmatalis Hubner).

ABSTRACT NITROGEN was applied to small plots at rates from 87 to 336 kg/ha to compare NO3-N concentrations and loads in shallow ground water as related to application rate. Mean nitrate concentrations at 2.1 m for March 1981-March 1982 ranged from 8.8 mg/L under 87 kg/ha N to 23.7 mg/L under 336 kg/ha N. Twenty-year simulations using CREAMS with 336 kg/ha/yr applied N and a predicted root zone leachate to observed mean ground water NO3-N ratio resulted in a predicted mean NO3-N concentration of 20.8 mg/L at 2.1 m. This was comparable to the 20 mg/L NO3-N presently found where intensive multiple cropping systems have been used for 5 years with center pivot irrigation.

Maintaining efficient N nutrition for irrigated corn ( Zea mays L .) grown on deep sands is difficult due to low N supplying capabilities and leaching losses of applied N. Scheduled applications of N by the use of center-pivot irrigation equipped with modern solution injection equipment should reduce leaching and increase N-use efficiency. The objective of this study was to compare the efficiency of scheduled applications of N through sprinkler irrigation with the more conventional side-dress method for maintaining N nutrition and obtaining high yields. Field experiments were conducted for 5 years on a Bonifay sand (loamy, siliceous, thermic, grossarenic, Plinthic Paleudult) using solid-set irrigation systems. Treatments included side-dressing, sprinkler application for 10 to 11 weeks after planting according to anticipated N needs, and combinations of the two methods, as well as, differential N rates ranging from 168 to 350 kg ha -1 . Maximum yields were obtained with approximately 280 kg N ha -1 . Scheduled sprinkler application of N did not provide better N nutrition than conventional side-dressing. In 4 of the 5 years of the study, corn was planted in soil which had near average rainfall during the winter and some leaching rain in the early growing season. In those years, side-dressing was equal or superior to sprinkler application; while a combination of side-dressing young corn followed by later sprinkler applications produced the highest yields. These responses may be the result of the timing of N applications or of an improved N uptake from the banded method (side-dressing) in comparison to a broadcast method (sprinkler application).

Two greenhouse experiments were conducted to determine the relative efficiencies of SCU (sulfur-coated urea) and urea with and without N-Serve [2-chloro-6-(trichloromethyl)pyridine] or S on growth, uptake and subsequent losses of N from sugarcane (a trispecies hybrid of Saccharum) grown on Arredondo fs (a loamy, siliceous, hyperthermic Grossarenic Paleudult). In the first experiment, three SCU products, with initial dissolution rates of 32.5, 29.6, and 26.8% of the total N in water during a 7-day period were compared with urea, urea applied in two application, urea + N-Serve, and urea + powdered S at the equivalent amount of S in SCU. In the second experiment SCU-30 was compared with urea, urea applied in two applications, urea + N-Serve, and urea + powdered S at two irrigation regimes (36 and 48 mm/week). Nitrogen fertilizers were applied at rates of 1.78 g/pot of N. Growth and uptake of N by sugarcane plants were not significantly different among treatments, but there were significant differences in leached and residual N. Nitrogen leaching varied from 6 to 24% of applied N depending on the fertilizer treatment and irrigation level. Leaching of the applied N was mainly in the NO3- form, but when irrigation took place before the N hydrolyzed from urea was completely nitrified, leaching in the NH4+ form was of considerable magnitude. The least N leaching resulted from application of SCU. Inclusion of N-Serve with urea did not improve fertilizer efficiency. Under the conditions of these experiments, SCU was more promising for commercial use than was granular urea mixed with N-Serve. Leaching losses of N from all the sources increased with irrigation but to a varying degree. Eleven to fifteen percent of the applied N was not accounted for by the plant, leachate or soil. These results generally agree with those of a previous field experiment conducted by the authors on the same soil.

are common in the southeast Coastal Plains and south- ern Piedmont. Given the extensive area that is treated High-intensity storms that occur shortly after chemical application with pesticides in this region, particularly during the have the greatest potential to cause chemical runoff. We examined months of March, April, and May, it is likely that a how effectively current chemical transport models GLEAMS, Opus, PRZM2b, and PRZM3 could predict water runoff and runoff losses storm of sufficient magnitude to cause surface water of atrazine (6-chloro-N-ethyl-N9-(1-methylethyl)-1,3,5-triazine-2,4- runoff will occur on some fields that have recently been diamine) under such conditions, as compared with observations from treated with pesticides. a controlled field runoff experiment. The experiment was conducted Field studies of pesticide runoff typically depend on for 2 yr using simulated rainfall on two 14.6- by 42.7-m plots within the occurrence of natural rainfall because simulated a corn (Zea mays L.) field on Tifton loamy sand (fine-loamy, kaolinitic, rainfall cannot be generated at hectare and larger scales. thermic Plinthic Kandiudults) under conventional tillage practices. Micro-scale plots (microplots), typically 5 to 50 m2, are For each plot-year, atrazine was applied as surface spray immediately commonly used with rainfall simulators. While valuable after planting and followed by a 50-mm, 2-h simulated rainfall 24 h in specific pesticide transport studies, microplots are later. A similar preapplication rainfall and four subsequent rainfalls thought to overestimate pesticide runoff as compared during the growing season were also applied. Observed water runoff averaged 20% of the applied rainfall. Less runoff occurred from freshly with typical field studies. This is more likely due to the tilled soil or under full canopy cover; more runoff occurred when severe conditions often used in microplots (Wauchope nearly bare soil had crusted. Observed total seasonal atrazine runoff et al., 1995; Wauchope and Burgoa, 1995). Moreover, averaged 2.7% of that applied, with the first posttreatment event microplots cannot adequately represent typical agricul- runoff averaging 89% of the total. GLEAMS, Opus, PRZM2b and tural management practices and the major characteris- PRZM3 adequately predicted water runoff amounts, with normalized tics of a typical field. In the early 1990s, Coody et al. root mean square errors of 29, 29, 31, and 31%, respectively. GLEAMS (1990, 1994) developed a rainfall simulator for use on and PRZM3 predicted atrazine concentrations in runoff within a intermediate-scale plots, typically 500 m2, sometimes re- factor of two of observed concentrations. PRZM2b overpredicted ferred to as "mesoplots." This equipment made it feasi- atrazine concentrations. Opus adequately predicted atrazine concen-