Greenville Sandy Clay Loam Research Articles

Assessment of flumioxazin soil behavior and thermal stability in aqueous solutions

Flumioxazin is a preemergence, N-phenylpththalimide herbicide that can be applied to control a broad spectrum of weeds in a variety of cropping systems. Limited information exists concerning the environmental fate of flumioxazin, therefore the present studies investigated the kinetic behavior of flumioxazin in soil and aqueous solution using field and analytical techniques to establish its degradation properties. Flumioxazin half-life in a Greenville sandy clay loam and Faceville loamy sand was 26.6 d. Flumioxazin was determined to have a groundwater ubiquity score of 1.79, indicating a low leachability potential. There was an inverse correlation between flumioxazin concentration in soil, rainfall, and solar radiation. There was no direct correlation between flumioxazin concentration and soil temperature. Flumioxazin activation energy was 58.4 (±1.2) kJ mol−1 with a Q10 value of 2.2. Even at the lowest amount of solar radiation and soil temperature, the energy from these environmental measures exceeded the activation energy needed for flumioxazin degradation. Flumioxazin stability in solution and field dissipation indicate that, with the input of thermal energy, degradation can be rapid.

Evaluation of Cotton Responses to Fomesafen-Based Treatments Applied Preemergence

AbstractFomesafen provides effective control of glyphosate-resistant Palmer amaranth in cotton. However, cotton seedlings can be injured when fomesafen is applied PRE. Therefore, greenhouse and field experiments were conducted at Athens, GA, and at six locations in Alabama and Georgia in 2013 and 2016 to evaluate cotton growth and yield response to fomesafen applied PRE at 70, 140, 280, 560, 1,120, or 2,240 g ai ha−1, and in combination with pendimethalin, diuron, acetochlor, and fluridone at 1×label rates. Greenhouse bioassays indicated that fomesafen reduced cotton height and dry weight with increasing rate in Cecil sandy loam and Tifton loamy sand but not in Greenville sandy clay loam––possibly as a result of this soil’s higher organic matter (OM) and clay content. Fomesafen applied at 2,240 g ai ha−1reduced cotton stand by as much as 83% compared to the nontreated check (NTC) at all field locations except Alabama’s Macon and Baldwin counties, and 1,120 g ai ha−1reduced cotton stand only at Pulaski County, GA, by 52%. Cotton height was reduced by the two highest rates of fomesafen at all locations except Clarke County, GA, and Baldwin County, AL. Injury data indicated more visual injury followed increasing fomesafen rates, and high-rate treatments produced more injury in sandier soils. Cotton yield was unaffected by herbicide treatments at any location, except for the 1,120 g ai ha−1rate at Pulaski County (49% yield loss compared to NTC), 2,240 g ai ha−1at Pulaski County (72% yield loss), and Tift County (29% yield loss). These data indicated cotton yield should not be negatively affected by fomesafen applied PRE alone within label rates or in combination with pendimethalin, diuron, acetochlor, and fluridone at 1×label rates, although some visual injury, or stand or height reduction may occur early in the growing season.

Fluensulfone sorption and mobility as affected by soil type.

Fluensulfone is a fluoroalkenyl chemical with activity against multiple genera of plant-parasitic nematodes. The adsorption, desorption, and mobility of fluensulfone were evaluated on multiple soils from the USA in laboratory and column experiments. Adsorption data regressed to the logarithmic Freundlich equation resulted in isotherm values of 1.24 to 3.28. Soil adsorption of fluensulfone correlated positively with organic matter (0.67) and clay (0.34), but negatively with sand (-0.54). Fluensulfone soil desorption correlated to pH (0.38) and cation exchange capacity (0.44). Fluensulfone desorption from Arredondo sand soil was 26%, and from other soils ranged from 43 to 70%. In mobility experiments, fluensulfone in the leachate peaked at 3 h, gradually declining and becoming undetectable after 9 h. Recovery from leachate was 45% of the initial fluensulfone applied to the soil surface. In separate experiments, 30-cm-long soil columns were saturated with 1 L of water, and then segregated into three 10-cm sections. Fluensulfone recovery was 41, 34, 29, and 13% in Chualar sandy loam, Arredondo sand, Greenville sandy clay loam, and Tifton loamy sand, respectively, in the top 10-cm section. Data indicated that soil organic matter and clay contents will affect sorption, mobility, and dissipation of fluensulfone. © 2017 Society of Chemical Industry.

Nitrogen mineralization from broiler litter applied to southeastern Coastal Plain soils

A field study was conducted to determine nitrogen (N) mineralization from broiler litter (BL) in two Coastal Plain soils of differing texture, sandy (Tifton loamy sand) or clayey (Greenville sandy clay loam). These soils represented the broad range in surface textures commonly found in soils used for agricultural production in the southeastern Coastal Plain. Published protocols used for the study were designed by the ARS mineralization team. In addition to measuring ammonium (NH₄-N) and nitrate (NO₃-N) in the soil as a measure of N mineralization, both total C and total N were measured to determine the impact of a single BL amendment on C sequestration and N accumulation. Amounts of N in the soil from BL mineralization over 70 days were identical for both soils, 46.4 mg N kg^-1 soil (0.046%), but differences occurred in timing of the mineralization processes. In the sandy Tifton soil, depletion of NH₄-N and nitrification of the NH₄-N to NO₃-N occurred simultaneously. The NH₄-N from the BL was depleted in 21 days while peak NO₃-N concentrations in the soil were found at 28 days. In the clayey Greenville soil, NH₄-N concentrations from BL mineralization increased for 21 days and then decreased until reaching background levels by 70 days. Nitrate concentrations never did increase in the BL amended Greenville soil, indicating both that the nitrification rate was much slower than the ammonification rate, and most likely, that what NO₃-N was produced was lost from the soil by denitrification under wet conditions. The combination of soil textural and microclimate differences along with greater protection of the BL residues in the clayey soil than in the sandy soil are believed responsible for the observed N mineralization differences between the two soils. Previous research has shown that N mineralization rate is positively correlated with sand content and negatively correlated with clay content of soils, and the results of this study concurred with those findings. Measurements of total C and total N in both Coastal Plain soils showed that overall increases were small with a single BL amendment, and it was concluded that long-term studies are needed to investigate C sequestration and N accumulation. It was concluded from the study that there is a high probability that BL mineralization rates will be significantly slower on the more clayey Coastal Plain soils than on very sandy ones, and that farm managers should take these rates into consideration when planning timing and amounts of BL applications.

Nitrogen mineralization from broiler litter applied to southeastern Coastal Plain soils

A field study was conducted to determine nitrogen (N) mineralization from broiler litter (BL) in two Coastal Plain soils of differing texture, sandy (Tifton loamy sand) or clayey (Greenville sandy clay loam). These soils represented the broad range in surface textures commonly found in soils used for agricultural production in the southeastern Coastal Plain. Published protocols used for the study were designed by the ARS mineralization team. In addition to measuring ammonium (NH₄-N) and nitrate (NO₃-N) in the soil as a measure of N mineralization, both total C and total N were measured to determine the impact of a single BL amendment on C sequestration and N accumulation. Amounts of N in the soil from BL mineralization over 70 days were identical for both soils, 46.4 mg N kg^-1 soil (0.046%), but differences occurred in timing of the mineralization processes. In the sandy Tifton soil, depletion of NH₄-N and nitrification of the NH₄-N to NO₃-N occurred simultaneously. The NH₄-N from the BL was depleted in 21 days while peak NO₃-N concentrations in the soil were found at 28 days. In the clayey Greenville soil, NH₄-N concentrations from BL mineralization increased for 21 days and then decreased until reaching background levels by 70 days. Nitrate concentrations never did increase in the BL amended Greenville soil, indicating both that the nitrification rate was much slower than the ammonification rate, and most likely, that what NO₃-N was produced was lost from the soil by denitrification under wet conditions. The combination of soil textural and microclimate differences along with greater protection of the BL residues in the clayey soil than in the sandy soil are believed responsible for the observed N mineralization differences between the two soils. Previous research has shown that N mineralization rate is positively correlated with sand content and negatively correlated with clay content of soils, and the results of this study concurred with those findings. Measurements of total C and total N in both Coastal Plain soils showed that overall increases were small with a single BL amendment, and it was concluded that long-term studies are needed to investigate C sequestration and N accumulation. It was concluded from the study that there is a high probability that BL mineralization rates will be significantly slower on the more clayey Coastal Plain soils than on very sandy ones, and that farm managers should take these rates into consideration when planning timing and amounts of BL applications.

Sorption and desorption of flumioxazin to soil, clay minerals and ion‐exchange resin

Flumioxazin adsorption kinetics were described using a Greenville sandy clay loam soil. Adsorption kinetics experiments showed that 72% of total herbicide was absorbed after 1 h of continuous shaking and continued to increase to 78% after 72 h. Flumioxazin adsorption was then tested on seven agriculturally important soils throughout the southern USA. Adsorption isotherms for all soils had K(f) (Freundlich distribution coefficient) values that ranged from 8.8 to 0.4, with many near 1.5. Soil organic matter content was the parameter most highly correlated with flumioxazin adsorption (r(2) = 0.95, P < 0.001). Sorption to clay minerals had K(f) values ranging from 50 for bentonite to 4.7 for kaolinite. However, normalizing K(f) for sorbent surface area revealed that aluminum hydroxide (gibbsite) possessed the greatest flumioxazin sorption per unit area. Sorption to anionic exchange resin (K(f) 676) was greater than cationic exchange resin (K(f) 42). Molecular model calculations were performed to elucidate why sorption was greater to anionic exchangers. These calculations indicated that a region of dense electronegativity exists on the 3-dione moiety of the molecule. This would lead to greater flumioxazin sorption by positively charged surface sites. Desorption isotherms from soil exhibited no effect of hysteresis. Desorption from clay minerals was very rapid and flumioxazin in solution was undetectable after three desorption steps. From these data it was concluded that flumioxazin can become readily available in soil solution with increase in soil water content.

VARIABLE RAINFALL INTENSITY EFFECTS ON RUNOFF AND INTERRILL EROSION FROM TWO COASTAL PLAIN ULTISOLS IN GEORGIA

Predictions and understanding of runoff and soil loss could be improved if the effect of variable rainfall intensity during a storm were quantified. We quantified and compared effects of constant (Ic) and variable (Iv) rainfall intensity patterns on infiltration, runoff, soil loss, and interrill erodibilities (Ki) from a Tifton loamy sand (Plinthic Kandiudult) and a Greenville sandy clay loam (Rhodic Kandiudult). Each soil was air-dried, sieved (19 mm) and then placed in a 1.5-m2 stainless steel erosion pan (Tifton = 4% slope; Greenville = 7% slope). Simulated rainfall was applied for 70 min at a constant (57 mm h−1) and variable rainfall intensity patterns. The Ic event was determined from the statistical average of the Iv pattern; thus, total rainfall volume applied was the same for both patterns. Values for runoff (R), soil loss (E), splash water (Sw), and splash sediment (Ss) were measured at 5-min intervals throughout each simulation. Rainfall intensity patterns did not affect total runoff or infiltration, but they did influence Rmax values, when runoff occurred, and soil loss from each soil. Runoff curves for Iv events (peaks = 25–28 min) lagged intensity curves (peak = 20 min) by 5–8 min. Rmax values for Iv events were significantly (2 X) greater than those for Ic events and occurred 35–37 min before those for the Ic events. For the Tifton ls, Etot for Ic events was signficantly greater (2 X) than that for Iv events. Conversely, for the Greenville scl, Etot for Iv events was significantly greater (20%) than that for Ic events. For the Greenville scl, Emax for Iv events was significantly greater (3 X) than that for Ic events, whereas time to Emax for both soils was 16 min earlier for Iv events than for Ic events. Runoff and soil loss rates for Ic events increased gradually during the first 35–40 min before reaching steady-state conditions, whereas runoff and soil loss rates for Iv events increased sharply to a maximum at 25–29 min and then gradually declined to quasi-steady-state conditions. As a result, Iv events had about 28% more rainfall run-off and 32% more soil loss during the first 35 min of each event than for Ic events. Conversely, Ic events had about 28% more rainfall run-off and 32% more soil loss during the last 35 min of each event than for Iv events. For Ic events, capacity to transport sediment was limited by the lack of runoff during the first 35–40 min, whereas during the second half of each simulation event, runoff was well established at steady-state rates and able to transport sediment. Soil detachment was maintained or supplied at a constant or increased rate. R70 and E70 values were greater than R35 and E35 values. Greater r2 values were obtained for the R versus E relationship (r2 = 0. 98) than for the Ss versus E relationship (r2 = 0.28) on the Tifton ls, whereas relatively high r2 values were obtained for R versus E (r2 = 0. 99) and Ss versus E (r2 = 0.81) on the Greenville scl. For Iv events, there were detachment- and transport-limiting conditions, especially near the end of each event where capacity to detach soil and transport sediment decreased. R70, E70, and Ss70 values were less than R35, E35, and Ss35 values, and relatively high r2 values were obtained for R versus E (r2 = 0. 94–0. 99) and Ss versus E (r2 = 0.91–0.96). The Greenville scl was 75–97% more erodible than the Tifton ls. Kiq values were 16–30% larger than Kii values. Variable rainfall intensity causes problems, conceptually and mathematically, when calculating Ki. Ki values were not solely a property of the soil, were not constant, and did not increase as soil loss increased. Emax values were up to 13 times greater than steady-state soil loss values, yet Ki values for steady-state conditions were 3–5 times greater than those for maximum loss conditions. If Ki represents the susceptibility of a soil to erosional forces, and since rainfall intensity distributions, runoff, and soil loss within a rainfall event are not constant, then, according to our results, Ki distributions within the same event should not be assumed constant.

Flumioxazin soil persistence and mineralization in laboratory experiments.

Flumioxazin is an herbicide registered for use in soybean and peanut. However, few published papers concerning the soil persistence of flumioxazin are available. Therefore, laboratory studies were initiated to determine the half-life (t(1/2)) of flumioxazin in Greenville sandy clay loam and Tifton loamy sand soils when incubated at 15 and 25 degrees C. Results indicated that temperature had little effect on flumioxazin persistence. The t(1/2) for the Greenville soil was 17.9 and 16.0 days while the Tifton soil was 13.6 and 12.9 days, at 15 and 25 degrees C, respectively. These data correspond to the greater clay content of the Greenville soil (32%) as compared to the Tifton soil (2%). Therefore, the Greenville soil had greater soil adsorption and less flumioxazin was generally available to be degraded by soil microorganisms. In soils that were heat treated to reduce microbe populations, 99% of initial flumioxazin was accounted for after 16 days. Mineralization of flumioxazin, measured as 14CO2 evolution, was also greater in the Tifton soil (2.2% after 64 days) than in the Greenville soil (2.0% after 64 days). From these data, it was concluded that microbes were the most influential factor concerning the degradation of flumioxazin.

Agronomic and Economic Analyses of Cotton Starter Fertilizers

None of the published literature has focused on the response of cotton (Gossypium hirsutum L.) to various starter fertilizer sources. This study was conducted to determine (1) if cotton grown on Coastal Plain soils in South Georgia would respond to different starter fertilizer sources and (2) if use of starter fertilizers would result in an economic gain. Experiments were conducted in 1997 and 1998 at the Coastal Plain Experiment Station in Tifton on a Tifton loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults), the Southeast Georgia Branch Station in Midville on a Dothan loamy sand (fine‐loamy, kaolinitic, thermic Plinthic Kandiudults), and the Southwest Branch Experiment Station in Plains on a Greenville sandy clay loam (fine, kaolinitic, thermic Rhodic Kandiudults). Five starter fertilizer sources were applied 5 cm to the side of and 5 cm below the seed drill at planting in each study. Total shoot N and Ca were increased in two of the six studies with starter fertilizers. Likewise, plant height, leaf area index, and shoot dry weight was increased with starter fertilizers in two of the six studies. With the exception of micronaire, starter fertilizers did not significantly influence the fiber properties investigated. Differences in fiber properties did result in small differences in cotton price premiums or discounts. Lint yields were significantly increased with starter fertilizers at Midville and Plains in 1997, when the crop was exposed to an extended period of cool weather immediately after planting. The most appropriate cotton starter fertilizer appeared to depend on soil type.

Effects of ‘Carpramid’ on nutrient uptake and lint yield of cotton

Growth‐enhancing compounds have become some of the many inputs used in cotton (Gossypium hirsutum L.) production systems across the United States Cotton Belt. Their usefulness, however, in producing high yielding, high quality cotton remains to be resolved. In 1996, a new product emerged on the cotton market that may aid nutrient absorption during reproductive development. Amisorb (polyaspartate), chemical name ‘Carpramid’: copoly‐[(3‐carboxypropionamide)(2‐(carboxymethyl)acetamide)] developed by the Donlar Corporation (Bedford Park, IL) may improve a crops ability to take up nutrients, resulting in improvements in yield and quality. Therefore, the objective of this investigation was to evaluate the effects of ‘Carpramid’ on nutrient uptake and lint yield on cotton. Experiments were conducted in 1996 and 1997 at the Coastal Plain Experiment Station in Tifton on a Tifton loamy sand, the Southeast Georgia Branch Station in Midville on a Dothan loamy sand, and the Southwest Branch Experiment Station in Plains on a Greenville sandy clay loam. ‘Carpramid’ was applied with starter fertilizers 5 cm to the side and 5 cm below the seed drill (2×2) at planting in all experiments. In the two years of this study, ‘Carpramid’ was investigated in four separate studies. ‘Carpramid’ had no positive effects on emergence, main stem nodes, shoot nitrogen (N), phosphorus (P), potassium (K), or sulfur (S), or lint yield in any of these studies. Lint quality was also assessed in the 1997 studies, but was not significantly affected by the treatments imposed. These data do not provide any basis for recommendation of ‘Carpramid’ as a nutrient‐ or yield‐enhancing product.

Long-Term Phosphorus and Potassium Application to Corn on Coastal Plain Soils

The effect of long-term fertilizer applications on soil test levels, yield, and crop removal depends on soil texture and mineralogy. The objectives of this study were to measure the fluctuations in soil P and K in soils of varying texture and to evaluate the usefulness of the Mehlich-1 soil extractant in predicting yield response. A field experiment was conducted for 11 yr on two soils : a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) and a Greenville sandy clay loam (clayey, kaolinitic, thermic Rhodic Kandiudults). Phosphorus treatments were 0, 92, 183, and 275 lb P 2 O 5 lb/acre in the first year followed by annual applications of 0, 37, 73, and 0 lb/acre, respectively. Potassium treatments were 0, 48, 96, and 144 lb K 2 O/acre in the first year followed by annual applications of 0, 48, 96, and 0 lb/acre, respectively. Soil samples (0-6 in.) were collected each year at tasseling of the corn (Zea mays L.) crop, P and K concentrations were determined in soil and grain samples, and yield was measured. Initial application rates influenced initial soil test levels, and annual application rates affected the rate of change of soil test levels with time. All significant yield increases on the Greenville soil were due to P application. Phosphorus moves rapidly from solution into less available forms in the Greenville soil due to the soil's high P fixing capacity. Yield increases on the Tifton soil resulted from K applications, presumably due to greater leaching losses on the sandier textured soil. The Mehlich-1 extractant provides a questionable measure of soil P availability for corn. Particularly in areas where P runoff potential is high, P fertilizer should not be applied to irrigated corn in the Southeast unless the Mehlich-1 extractable soil P concentration ≤ 12 lb/acre. Data from this long-term study show that accounting for soil K below the plow layer may improve the use of mehlich-1 extractant as a measure of K availability for corn.

Provision of mid‐season potassium requirements in cotton with slow release potassium applied pre‐plant

Abstract Mid‐season development of potassium (K) deficiency in cotton is related to the high K demand during flowering and high rainfall, particularly on sandy soils, removing available K prior to peak demand. Slow‐release K sources have potential for supplying mid‐season K requirements of cotton without having to expend additional labor and fuel applying sidedress or foliar K in mid‐season. The objective of this study was to determine the potential for slow‐release K applied preplant in combination with muriate of potash (KCl) for meeting mid‐season K requirements of cotton. Tests were conducted on ‘Georgia King’ cotton grown on three soil types in the Coastal Plain region of Georgia: 1992–1993 on a Greenville sandy clay loam (Rhodic Kandiudults), 1994 on a Tifton sandy loam (Plinthic Kandiudults), and 1993 on a Lakeland sand (Typic Quartzipsamments). Three K rates were applied (0, 55, and 110 kg K2O/ha), and two K sources were utilized, KCl (muriate of potash; 0–0‐60) and Multi‐cote 4 slow‐release ferti...

Response of ‘Tifblue’ and ‘Delite’ Rabbiteye Blueberry Plants to Varying Soil pH

Abstract Plants of ‘Delite’ and ‘Tifblue’ rabbiteye blueberries were planted 3 m × 1.8 m at Plains, Georgia in 1981 in a Greenville sandy clay loam (clayey, kaolimitic, thermic, Rhodic Paleuduit). Total fruit weight, fruit size at the first harvest, and percent marketable yield were recorded. Soil and leaf samples were taken immediately after the last harvest for chemical analysis and ranged in soil water pH from 4.3 to 5.1. Soil pH did not affect soil P, K, or Fe but soil Ca, Mg, Mn, and Cu were highest levels when the soil pH was 6.5. The only effect of soil pH on leaf mineral concentration occurring in 1989 when increasing pH increased leaf Mg. ‘Delite’ yield and plant volume (m3) decreased linearly as the soil pH increased. The percent marketable yield was maximum at soil pH 4.7 to 4.8. Maximum plant growth of ‘Tifblue’ occurred around pH 4.3 to 4.4, then decreased when soil pH increased to 4.8 to 4.9. However, maximum yield and percent marketable yield of ‘Tifblue’ were the highest at soil pH 5.0 to 5.1. Fruit size response of ‘Tifblue’ to soil pH was similar to total yield, but ‘Delite’ fruit were larger on small plants with low yield. ‘Tifblue’ plants were low and spreading in comparison to the taller ‘Delite’ plants. This experiment suggested that these two rabbiteye blueberry cultivars had genetic differences in response to soil water pH.

Zinc toxicity symptom development and partitioning of biomass and zinc in peanut plants1

Abstract High soil zinc (Zn) concentrations can cause Zn toxicity in peanuts (Arachis hypogaea L.), which decreases productivity and can be fatal to the plants. The objectives of this study were 1) to determine the optimal sampling time and plant part for diagnosis of Zn toxicity in peanuts, 2) to relate toxicity symptoms to plant Zn concentrations and calcium:zinc (Ca:Zn) ratios, and 3) to model the distribution of Zn and biomass into plant parts in relation to Zn concentration in the whole plant. A greenhouse study utilized four soils (Lakeland sand, Tifton loamy sand, Greenville sandy clay loam, and Greenville sandy clay) with Zn applications of 0, 10, 20, and 40 mg Zn/kg soil. Plants were sampled for analysis of nutrient concentrations, and Zn toxicity ratings were recorded biweekly. Toxicity symptoms became visible 4–8 weeks after planting, with stunting appearing at four weeks, horizontal leaf growth and leaflet folding at six weeks, and stem splitting at eight weeks. Optimal sampling time for diagn...

Microbial Degradation of Flurtamone in Three Georgia Soils

Degradation of flurtamone in a Greenville sandy clay loam, a Cecil loam, and a Dothan loamy sand with 0, 1, or 2 yr of previous flurtamone field use was evaluated under controlled conditions. Soil sterilization by autoclaving significantly reduced flurtamone dissipation rate in all soils. Enhanced degradation of flurtamone was observed in a Greenville sandy clay loam after 1 yr of previous flurtamone field use and in a Cecil loam after 2 yr of previous flurtamone field use. No enhancement of flurtamone degradation was observed in a Dothan loamy sand. Flurtamone degradation kinetics in these studies was described as a first-order process. Microbial populations in each soil showed no major changes in total bacterial numbers due to preexposure to flurtamone in the field.

Flurtamone Adsorption and Mobility in Three Georgia Soils

Flurtamone and atrazine adsorption to soil was examined using a batch equilibrium method. Flurtamone mobility in packed soil columns under saturated flow conditions was also evaluated. Adsorption was greater for flurtamone than atrazine in the three soils, and the order of adsorption to soil for both herbicides was Greenville sandy clay loam &gt; Cecil loam &gt; Dothan loamy sand. Greater adsorption of each herbicide corresponded to soils with greater organic matter and clay content. The14C–flurtamone movement under saturated flow conditions in 28–cm soil–packed columns was limited to 16 cm, with no flurtamone leaching from any soil column after the addition of two pore volumes of water. Seventy–five percent of the applied14C–flurtamone remained in the 0– to 4–cm soil depth in the Greenville sandy clay loam, with less than 5 percent moving to a depth &gt; 4 cm. Flurtamone movement was greater in the Cecil loam and the Dothan loamy sand, with movement in each soil to a depth of 16 and 12 cm, respectively.

EFFECTS OF PESTICIDE, SOIL, AND RAINFALL CHARACTERISTICS ON POTENTIAL PESTICIDE LOSS BY PERCOLATION -A GLEAMS SIMULATION

ABSTRACT Potential pesticide loss in soil percolate is influenced by pesticide persistence and sorption by soil constituents (organic matter). Pesticide persistence, expressed as half-life (ti/2), changes with soil depth as microbial activity and soil properties change. Little is known, however, how these changes influence potential pesticide transport out of the root zone. Objectives of this study were to investigate relative differences in potential pesticide losses from the root zone by percolation due to 1) different soil surface and subsurface textures and pesticide ti/2 and 2) interactions between pesticide ti/2 and timing of rainfall after pesticide application. The GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model and a 50-year historical rainfall record at Tifton, Georgia, were used to simulate pesticide losses by percolation from three soils ranging in surface texture from sand to sandy clay loam. Hypothetical pesticides had surface ti/2 of 5, 15, 30, and 60 d and a range of subsurface ti/2 (2.5-360 d), and were applied to continuous com {Zea maize, L.) at 2 kg ha~ ^ as surface spray at planting each year on 1 April. Simulated pesticide losses by percolation increased with increased surface and subsuiface t|/2 and decreased with increased KQC (adsorption constant based on soil organic matter) values. Potential pesticide leaching was greatest for Lakeland sand and least for Greenville sandy clay loam. Rainfall timing affected simulated pesticide loss by percolation, especially for nonpersistent pesticides. For short pesticide ti/2 (0-5 d), excessive rainfall events within 1 ti/2 were largely responsible for simulated pesticide loss by percolation. Results indicate that changes in pesticide t|/2 in surface and subsurface horizons of different soils influence potential pesticide leaching from the root zone, and models (i.e., GLEAMS) can be used to provide comparative analysis of soil-pesticide-climate interactions. For example, depending on soil type and pesticide K^^ and surface Xyp^ values, potential leaching losses increased two to seven times as subsurface tiy2 increased six times.

Harvest Management Effects on Alfalfa Yield and Root Carbohydrates in Three Georgia Environments

AbstractAlfalfa (Medicago sativa L.) hay harvest management may need to be modified in the southeastern USA due to the mild winters and hotter summers compared with northern production areas. The objectives of this study were to evaluate the effect of three harvest treatments (10, 50, and 10% bloom until midsummer when one harvest was delayed until 50% bloom‐referred to as “summer rest” management) on herbage yield and seasonal trends of total nonstructural carbohydrates (TNC) in the roots of irrigated semidormant ‘Apollo’ and nondormant ‘Fla‐77’ alfalfa. The experiments were conducted for 2 yr in the Georgia Mountains on Bradson clay loam (Typic Hapludult, clayey, oxidic, mesic), Piedmont on Cecil sandy clay loam (Typic Hapludult, clayey, thermic, kaolinitic), and Coastal Plain on Greenville sandy clay loam (Rhodic Paleudult, clayey, thermic, kaolinitic). Alfalfa at all three locations gave satisfactory yield (12.7 Mg ha−1) when harvested at 10% bloom throughout the growing season including late fall. There was no advantage to either cultivar from harvesting at 50% bloom or allowing a summer rest period. Location effects were minimal. Root TNC concentrations were lowest in midsummer, greatest in late autumn, and decreased during winter. Root TNCs ranged from 200 to 560 g kg−1 for Fla‐77 and 150 to 580 g kg−1 for Apollo. There was no effect of cultivar or harvest management on root TNC concentrations. These results indicate that root TNCs are not a primary limiting factor for alfalfa hay production in the southeastern USA and that harvest can continue throughout the year with no adverse effect on forage yield.

Winter Legume Effects on Soil Properties and Nitrogen Fertilizer Requirements

AbstractWinter legume cover crops have been shown to provide significant amounts of N to subsequent nonleguminous crops, but benefits beyond those directly attributed to N are rarely cited. A 3 yr field study at two Georgia locations utilizing a randomized, complete‐block, split‐plot design with four replications was begun in 1985 to measure the equivalent fertilizer N supplied by winter annual legumes and to monitor changes in soil physical and chemical properties. Corn, Zea mays L. was grown on a Rome gravelly clay loam soil (fine‐loamy, mixed, thermic Typic Hapludult) at the Limestone Valley location, and grain sorghum [Sorghum bicolor (L) Moench] on a Greenville sandy clay loam soil (clayey, kaolinitic, thermic Rhodic Paleudult) in the Coastal Plain. Main plots were cover crops of hairy vetch (Vicia villosa Roth.), crimson clover (Trifolium incarnatum L), berseem clover (Trifolium alexandrinum L), winter pea [Pisum sativum subsp. arvense (L) poir], wheat (Triticum aestivum L), and fallow. Subplots were broadcast NH4NO3 fertilizer of varying rates. Hairy vetch and crimson clover replaced the greatest amount of fertilizer N averaging 123 and 99 kg N ha−1, respectively. More water‐stable aggregates were found following cover crops than fallow in the 0‐ to 0.025‐m depth at the Coastal Plain location. Higher infiltration rates were found following cover crops than fallow at both locations and infiltration rates were greater following hairy vetch than following wheat at the Coastal Plain site. An adapted winter legume cover crop can replace all of the fertilizer N necessary for optimum rain‐fed grain sorghum and up to two‐thirds of that required for corn production, and improve soil physical properties.

Chemical Transport from Coastal Plain Soils Under Simulated Rainfall: L Surface Runoff, Percolation, Nitrate, and Phosphate Movement

ABSTRACT Astudy was conducted to determine amounts and rates of surface runoff, percolation, nitrate and phosphate movement from the upper root zone of three upland Coastal Plain soils. Surface soil samples of Greenville sandy clay loam. Red Bay loamy sand, and Bonifay sand were packed into rectangular stainless steel boxes equipped with surface runoff and percolate collection devices. The soils ranged in clay content from 29.3% to 3.6%, and represented a range of soil textures commonly found in the Coastal Plain. Simulated rainfall was applied to each soil at high (125 mm/hr), medium (75 mm/hr), or low (43 mm/hr) intensities. Surface runoff rates varied from none to about 100 mm/hr depending on soil texture, crusting and sealing, and rainfall intensity. Percolation was found to be the major water-loss pathway on the sandier soils at the lower rainfall intensities. Surface runoff was the major water-loss pathway at the high rainfall intensity on the Bonifay sand (69.8%), and for all three rainfall intensities on the Greenville sandy clay loam. The study showed that percolation is the major pathway for NO3-N movement from the upper root zone of the sandier Coastal Plain soils. Some PO4 moved with percolation on the two sandier soils, but not on the clayey soil. Nitrate and PO4 movement from the clayey soil was primarily in surface runoff. Comparison of NO3-N and PO4 movement predictions made by the GLEAMS model with actual observations showed that the model worked best on the sandier soils. The study indicates that care should be taken to avoid applying NO3-N and PO4 when probability for immediate intense rainfall is great.