Dissipation and transport of clopyralid in soil: effect of application strategies

At present there are no herbicide uses registered for broadleaf weed control in buckwheat. Clopyralid, mixed with desmedipham, was anticipated to provide early-season broadleaf weed suppression with minimal crop injury. However, field trials resulted in limited success, which brought into question the fate and availability of clopyralid for weed control. A 4-year field study was conducted in Lithuania to evaluate the dissipation of clopyralid in Haplic Luvisol sandy loam soil and the influence of application rate, application timing, and coapplication with desmedipham on its degradation and transport. Clopyralid dissipation was rapid; 50% dissipation times, in the surface 5 cm, averaged over the 4 years of the study, were <7 days. Application rate (90 versus 180 g ai ha(-1)), timing (pre-emergence versus postemergence), and coapplication with desmedipham (360 g ai ha(-1)) did not significantly influence clopyralid dissipation. Clopyralid dissipation by leaching was not a significant factor; at 7-21 days after application, <8 μg kg(-1) was found at the 10-20 cm depth. Understanding the dissipation of herbicides and the influence of application strategies on herbicide fate will allow for informed decisions and improved efficacy of weed control. On the basis of the results of this research, weed scientists can now determine whether increased rates of clopyralid would provide sufficient residual chemical for adequate weed control without crop injury.     

Comparison of leaching predictions based on PRZM3.12, LEACHP, and RZWQM98 using standard scenario modeling

Regulatory agencies in the NAFTA region use ground water leaching models to help determine risks to ground water resources. The results of three models for leaching predictions are compared using a standard soil and weather scenario currently used by the New York Department of Environmental Conservation (NYDEC) to simulate the Riverhead soil found on Long Island, New York. The three models, PRZM3.12, LEACHP, and RZWQM98, were configured to simulate the behavior of two example molecules in corn, turfgrass, and bare soil. For the bare soil simulations, LEACHP and RZWQM98 predicted similar peak concentrations and timing of peak concentration. Depending on the dissipation rate of the molecule, PRZM3.12 predicted similar to reduced peak concentrations due to the delayed timing to reach the peak concentration. For the corn and turfgrass simulations, peak concentrations and timing to reach peak concentrations varied between the models due to differences in how each simulates plant growth and evapotranspiration.     

The effect of crop, N-level, soil type and drainage on nitrate leaching from Danish soil

Abstract. Nitrate leaching measurements in Denmark were analysed to examine the effects of husbandry factors. The data comprised weekly measurements of drainage and nitrate concentration from pipe drains in six fields from 1971 to 1991, and weekly measurements of nitrate concentration in soil water, extracted by suction cups at a depth of 1 m, from 16 fields in 1988 to 1993. The soils varied from coarse sand to sandy clay loam.
The model used for analysing the data was: Y = exp (1.136–0.0628 clay + 0.00565N + crop ) D^0.416, with R²= 0.54, where Y is the nitrate leaching (kg N/ha per y), clay is the % clay in 0-25 cm depth (%), N is the average N-application in the rotation (kg/ha/y) and D is drainage (mm/y). The most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17-24 kg/ha/y). Winter cereal following a grass crop, beets, winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36-46 kg/ha/y). High rates of leaching were estimated from winter cereals following rape/peas, bare soil following cereals and from autumn applications of animal manure on bare soil (71-78 kg/ha/y). Estimates of leaching from soil of 5, 12 and 20% clay were 68, 44 and 26 kg/ha/y, respectively. Leaching was estimated to rise significantly with increasing amounts of applied N.
The model is suitable for general calculations of the effects of crop rotation, soil type and N-application on nitrate leaching from sandy soil to sandy clay loarns in a temperate coastal climate.     

Effect of Soil Phosphorus Levels on Phosphorus Runoff Concentrations from Turfgrass

Phosphorus (P) loss from urban areas has been identified as a major contributor to declining surface water quality. The objective of this study was to determine the relationship between extractable soil P, depth of soil sampling, and dissolved reactive P (DP) concentration in runoff from turfgrass areas. At each site, runoff was generated on turfgrass and adjoining areas where turfgrass cover was removed. Across all six locations and the wide range of nutrient management schemes, variation of extractable soil P concentration and saturation ratios of 0–2cm samples accounted for 49–59% (r ² = 0.49–0.59, n = 92) of variation of DP concentration in runoff from bare soil and soil with turfgrass cover. Despite a high degree of soil P stratification, changing sampling depth generally did not improve the relationship between soil test P and runoff DP concentrations. Across the narrower range of soil P levels common to lawns in New York (0–50mg kg^?1 Morgan extractable soil P), none of the soil tests or P saturation levels (for 0–2cm depth) could accurately predict runoff P concentrations from soil with turfgrass cover (r ² = 0.02 to 0.23, n = 72). For bare soil plots, restricting the analysis to the same range (<50mg kg^?1 Morgan extractable P) did not alter the relationship between soil test P and runoff DP concentrations observed for the entire range (0–658mg kg^?1) of soil-test P concentrations. These results suggest soil testing will not be an effective tool to predict runoff from turfgrass areas across the range of soil P levels common to New York State.     

Evaluation of Mobility and Dissipation of Mefenoxam and Pendimethalin by Application of CSTR Model and Field Experiments Using Bare and Tobacco Tilled Soil Columns

The soil mobility and dissipation of two pesticides with different physicochemical properties, namely mefenoxam, a systemic fungicide, and pendimethalin a selective herbicide, were determined in bare and tobacco tilled soil columns, which were installed in field conditions for over 125 days. Soil samples were collected at specific time intervals for a 125-day period and the rate of pesticide dissipation and leaching through the soil column was studied. The dissipation half-lives of mefenoxam from the top soil layer in tilled and bare soil columns were estimated at 10.3 and 13.1 days, respectively, while the corresponding half-lives for pendimethalin were 26.7 and 27.5 days, respectively. The dissipation of mefenoxam and pendimethalin from the top soil in tobacco cultivation was faster in comparison with bare soil; however, 120 days after their application, both pesticide residues were detected in the soil. Maximum concentrations of mefenoxam and pendimethalin were observed on the 15^th and 33^rd day, respectively, in the soil layer of 5–10 cm depth and on the 30^th day and 63^rd day, respectively, in the soil layer of 10–15 cm depth. Higher concentrations were observed in bare soil columns. The leaching of both pesticides was simulated with the continuous stirred tank reactor (CSTR) in series model. The simulated peak concentration and peak time for both pesticides fitted reasonably well to the experimental values.     

Loss of pendimethalin in runoff and leaching from turfgrass land under simulated rainfall

A field study was undertaken to investigate runoff and leaching loss of the herbicide pendimethalin in turfgrass land of loamy sand soil. A series of plots constructed in a golf course fairway were surface-applied with pendimethalin SC formulation at the rate of 2. 25 or 4.50 kg a.i./ha and subjected to simulated rainfall at 2.0 cm/day for 10 consecutive days. Runoff losses of pendimethalin were the highest at the first rainfall and then gradually decreased with time. The first runoff event contained pendimethalin in its highest concentration, and in subsequent runoff samples the concentration decreased exponentially. The ranges of pendimethalin concentration were 80.9-18.2 and 177.4-48.6 microgram/L in the standard and double doses, respectively. Total losses by 20 cm of rainfall for 10 days reached 0.81 and 1.22% of the initial deposits at 2.25 and 4.50 kg a. i./ha, respectively. Pendimethalin concentration in the leachate collected at 30-cm soil depth was quite lower than that in the runoff, and the concentration rapidly decreased from 4.3-4.7 to 0. 2-0.4 microgram/L during the 10 days of rainfall treatment. Soil residue analysis at 45 and 90 days after pendimethalin treatment showed that more than 90% of the residue remained at the top 10 cm of soil depth. Low runoff and leaching confirmed that lateral and downward movement of the herbicide should be limited in turf soil. The half-life of pendimethalin under field conditions was 23-30 days and was not affected by application dose and rainfall treatment, but longer persistence was observed under laboratory conditions. Considering low runoff and leaching, as well as relatively short persistence in soil, it is concluded that little environmental carryover of pendimethalin would be expected in turfgrass land.     

Effects of Compost Sources and Seeding Treatments on Germination and Emergence of Four Turfgrass Species

Greenhouse pot trials were conducted to compare the effects of compost sources and planting treatments on turfgrass germination and emergence. Eight seeding treatments and 4 turfgrass types were factorially combined and replicated four times in a completely randomized block design. The seeding treatments were: 1) seed planted on surface of 2.6 cm compost overlying soil, 2) seed planted on soil surface below 0.65 cm compost, 3) seed planted on soil surface below 1.3 cm compost, 4) seed planted on soil surface below 2.6 cm compost, 5) seed planted on soil surface covered with a 2.6 cm straw mat, 6) seed planted below 1.3 cm soil, 7) seed planted below 1.3 cm of 1:1 compost:soil mix, and 8) seed planted on soil surface. Tall fescue (Festuca arundinacea Schreb.), Kentucky bluegrass (Poa pratensis L.), bermudagrass (Cynodon dactylon L.), and zoysiagrass (Zoysia japonica Steud.) were used as the bioassay crops. The experimental design was repeated over time using composts produced with the following feedstocks: yard waste, food waste, dairy manure, biosolids, and paper mill sludge. Emerged seedlings were counted at 11 days for tall fescue, at 3 weeks for Kentucky bluegrass and at 7 weeks for bermudagrass and zoysiagrass. There were significant (P<0.05) effects of seeding treatment x turfgrass type on germination and emergence for each compost type. All of the composts appeared to be well stabilized using routine compost laboratory testing except the biosolids compost, whose use resulted in the lowest overall germination and emergence rate. The highest rates of germination and emergence occurred in the treatments in which the seeds were planted on the surface, regardless of whether the surface was compost or soil. The lowest rate of germination and emergence occurred where the seed was placed under 2.6 cm compost, regardless of compost maturity.     

控释复合肥对冷季型草坪氨挥发和硝态氮淋洗的影响

通过田间试验,研究了控释复合肥、常规施肥、市售草坪专用肥对冷季型草坪氨挥发和硝态氮淋洗的影响。氨挥发采用通气密闭法收集测定,硝态氮利用土壤溶液提取器收集淋洗液然后进行测定。结果表明,常规施肥处理的氨挥发量为47.7 kg/hm2(占年施氮量的18.3%),显著高于控释复合肥处理(氨挥发损失为2.9 kg/hm2,占年施氮量的1.1%)和市售草坪专用肥处理(氨挥发损失为4.1 kg/hm2,占年施氮量的1.6%)。施氮不同程度增加了淋洗液中硝态氮的浓度,3种氮肥的硝态氮淋洗程度不同。0—50 cm土层,淋洗液的硝态氮浓度范围分别是:控释复合肥处理1.16~.7 mg/L,常规施肥处理1.21~0.1 mg/L,市售草坪专用肥处理1.51~6.7 mg/L;0—100 cm土层,淋洗液的硝态氮浓度范围分别是:控释复合肥处理1.15~.7 mg/L,常规施肥处理1.11~2.5 mg/L,市售草坪专用肥处理1.16~.2 mg/L。综上所述,控释复合肥降低了冷季型草坪氨挥发损失和硝态氮的淋洗,表现出明显的环境效益,是一种有应用前景的新型肥料。     

The dissipation of tebuconazole and propiconazole in boronia (Boronia megastigma Nees)

The broad spectrum, systemic fungicides tebuconazole and propiconazole are used to control rust in boronia (Boronia megastigma Nees). Gas chromatography combined with either a benchtop quadrupole mass spectrometer or a high-resolution mass spectrometer allowed for the monitoring of both pesticides in boronia leaves, flowers, and concrete. Field trials were established at two sites to determine the rate of dissipation of tebuconazole and propiconazole in boronia. At site 1, two application rates of 125 and 250 g active ingredient/hectare (ai/ha) tebuconazole were employed. Treatments were repeated 17 days later. At harvest, 286 days after the final application, tebuconazole was detected at levels of 0.06 +/- 0.05 and 0.5 +/- 0.1 [mg/kg +/- standard error, on a dry matter basis (DMB)] in the leaves collected from plots treated with 125 and 250 g ai/ha of tebuconazole, respectively. The oil produced from the flowers collected at the final harvest had residues of tebuconazole at levels of 0.06 +/- 0.03 and 0.10 +/- 0.08 mg/kg for the 125 and 250 g ai/ha application rates, respectively. Two repeat applications of 125 g ai/ha propiconazole were also used at site 1. Residues of propiconazole were detected at 0.09 +/- 0.03 mg/kg (DMB) 286 days after the final application. At site 2, treatments of 125 g ai/ha of tebuconazole were applied twice. At harvest, 279 days after the final application of tebuconazole, residues were recorded at 0.30 +/- 0.09 mg/kg in the leaves (DMB) while the oil produced had 0.20 +/- 0.07 mg/kg.     

Terrestrial field dissipation of diclosulam at four sites in the United States.

The soil dissipation of diclosulam was studied using 14C-labeled and nonradiolabeled material in Mississippi, North Carolina, Georgia, and Illinois between 1994 and 1997. The test substance was preemergence broadcast applied at target rates of 35 and 37 g ai x ha(-1) for the 14C-labeled and the nonradiolabeled studies, respectively. The degradation of diclosulam was rapid with half-lives ranging from 13 to 43 days at the four sites. Rapid degradation rates and the increasing sorption to soil over time resulted in low persistence and mobility of this compound. Metabolite formation and dissipation in the field reflected observations of photolysis, hydrolysis, and aerobic soil metabolism studies in the laboratory. The rapid field dissipation rates, metabolite formation patterns, and sorption characteristics obtained in these field studies were consistent with the laboratory data generated for diclosulam, and reflect the multiple concurrent degradation mechanisms occurring in the field.     

Method for the analysis of triadimefon and ethofumesate from dislodgeable foliar residues on turfgrass by solid-phase extraction and in-vial elution.

Triadimefon, a fungicide, and ethofumesate, an herbicide, are commonly applied to turfgrass in the Pacific Northwest, resulting in foliar residues. A simple and rapid method was developed to determine triadimefon and ethofumesate concentrations from dislodgeable foliar residues on turfgrass. Turfgrass samples were washed, and wash water containing surfactant (a 0.126% solution) was collected for residue analysis. This analytical method utilizes a 25 mm C(8) Empore disk and in-vial elution to quantitatively determine triadimefon and ethofumesate in 170 mL aqueous samples. The analytes were eluted by placing the disk in a 2 mL autosampler vial with 980 microL of ethyl acetate and 20 microL of 2-chlorolepidine, the internal standard, for analysis by GC/MS. The method quantitation limits are 0.29 microg/L for ethofumesate and 0.59 microg/L for triadimefon. The method detection limits are 0.047 microg/L and 0.29 microg/L for ethofumesate and triadimefon, respectively. Concentrations of triadimefon and ethofumesate from dislodgeable foliar residues from a field study are reported.     

Influence of insecticides on microbial transformation of nitrogen and phosphorus in Typic Orchragualf soil

Four insecticides, viz., BHC, phorate, carbofuran, and fenvalerate, were applied at the rate of 7.5, 1.5, 1.0, and 0.35 kg a.i. ha(-)(1), respectively, to investigate their effects on the growth and activities of N(2)-fixing and phosphate-solubilizing microorganisms in relation to the availability of N and P in laterite (Typic Orchragualf) soil. Insecticides in general, and BHC and phorate in particular, stimulated the proliferation of aerobic nonsymbiotic N(2)-fixing bacteria and phosphate-solubilizing microorganisms and also their biochemical activities, such as nonsymbiotic N(2)-fixing and phosphate-solubilizing capacities, which resulted in greater release of available N (NH(4)(+) and NO(3)(-)) and P in soil. All the insecticides were persistent in soil for a short period of time, and the rate of dissipation was highest for fenvalerate followed by phorate, carbofuran, and BHC, depicting the half-lives (T(1/2)) 8.8, 9.7, 16.9, and 20.6 days, respectively. The insecticides followed first-order reaction kinetics during their dissipation in soil.     

Dissipation of sulfosulfuron in soil and wheat plant under predominant cropping conditions and in a simulated model ecosystem

Environmental fate and dissipation of the sulfonylurea herbicide sulfosulfuron was investigated in soil (inceptisol) and wheat plant under predominant cropping conditions. Studies were conducted in natural field conditions and in a simulated model ecosystem. Thirty days after the wheat seeds had been sown, sulfosulfuron [N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-2-(ethylsulfonyl)imidazo[1,2-a]pyridine-3-sulfonamide] 75% w/w WG formulation was applied once in the field. The dosages were 25 and 50 g of active ingredient (ai)/ha. Studies were conducted in significantly separated individual plots to avoid contamination. In a predetermined interval, soil samples were collected and analyzed for the residues of sulfosulfuron. At harvest, wheat grain, straw, and soil samples were analyzed for the residues. Similar experiments were conducted in a model ecosystem. Apart from this, after harvest, the succeeding crops coriander (Coriandrum sativum) and edible amaranth (Amaranthus mangostanus L.) were raised in the model ecosystem and studied for the residues. No residues were detected in wheat grain, straw, and soil samples collected at harvest from both experiments or in the succeeding crops coriander and edible amaranth in the model ecosystem when tested at the minimum detection level of 0.001 microg/g. The dissipation of sulfosulfuron was found to have first-order kinetics in soil and plant in both studies. The dissipation data of sulfosulfuron in the model ecosystem were compared with those from the natural field conditions.     

Dissipation of propiconazole and tebuconazole in peppermint crops (Mentha piperita (Labiatae)) and their residues in distilled oils

The broad-spectrum, systemic fungicides propiconazole (1) and tebuconazole (2) are used to control rust in peppermint (Mentha piperita L.). An analytical method, using gas chromatography combined with detection by high-resolution mass spectrometry, was developed to allow for the simultaneous monitoring of both pesticides in peppermint leaves and oil. Field trials were established to determine the rate of dissipation of tebuconazole and propiconazole in peppermint crops. Three applications of each fungicide were trialed at two rates (125 and 250 g of active ingredient (ai)/ha). At harvest, 64 days after the final application, propiconazole was detected at levels of 0.06 mg/kg and 0.09 mg/kg of dry weight, and tebuconazole was detected at 0.26 and 0.80 mg/kg dry weight, in identical trials. Rates of dissipation of propiconazole and tebuconazole were lower at a second trial site, where three applications of 125 g/ha ai for each fungicide resulted in residue levels of 0.21 mg/kg for both pesticides, detected 89 days after the last application. Propiconazole and tebuconazole were detected in the distilled oil at levels between 0.02 and 0.05 mg/kg and between 0.011 and 0.041 mg/kg, respectively. Propiconazole had a higher tendency to co-distill with the peppermint oil, with 0.7% of that present in the vegetative material ending up in the oil, compared to 0.09% of tebuconazole.     

Flupyrsulfuron soil dissipation and mobility in winter wheat crops.

Residues of the sulfonylurea herbicide flupyrsulfuron were extracted from cropping soils with 0.1 M NaHCO(3). The soil extracts were cleaned up by partitioning and repeated thin-layer chromatography. Flupyrsulfuron was transformed by diazomethane into N-(4, 6-dimethoxypyrimidine-2-yl)-N-(3-methoxycarbonyl-6-trifluoromet hylpyr idine-2-yl)methylamine (2), which was analyzed by gas-liquid chromatography with electron capture detection, and confirmation for several samples was made by gas chromatography combined with mass spectrometry. The sensitivity limit was 0.5 microg of flupyrsulfuron kg(-)(1) of dry soil. Bioassays using sugar beet as test plant qualitatively confirmed the results of the chemical analyses. Flupyrsulfuron [10 g of active ingredient ha(-)(1)] was applied in autumn on plots in two winter wheat crops on a sandy loam soil, the first crop being made in 1996-1997 and the second one in 1997-1998. In the 0-8 cm surface soil layer of both crops, the flupyrsulfuron soil half-lives were 123 and 92 days, respectively. Flupyrsulfuron was also applied post-emergence in March to other plots in the same crops; the half-lives in the 0-8 cm surface soil layer were similar in both seasons, that is, approximately 58 days. During all crop trials, flupyrsulfuron remained in the 0-8 cm surface soil layer and was not detected in the 8-10, 10-15, and 15-20 cm surface soil layers. The surface-2 cm soil layer contained the greatest flupyrsulfuron soil concentration, but the residues progressively moved down into the 2-4 and 4-6 cm soil layers. At the winter wheat harvest date for each trial, flupyrsulfuron was not detected in any of the soil layers (<0.5 microg kg(-)(1)).     

Compost,Manure and Synthetic Fertilizer Influences Crop Yields,Soil Properties,Nitrate Leaching and Crop Nutrient Content

From 1993 to 2001, a maize-vegetable-wheat rotation was compared using either 1) composts, 2) manure, or 3) synthetic fertilizer for nitrogen nutrient input. From 1993 to 1998, red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) were used as an annual winter legume cover crop prior to maize production. From 1999 to 2001, hairy vetch (Vicia villosa Roth.) served as the legume green manure nitrogen (N) source for maize. In this rotation, wheat depended entirely on residual N that remained in the soil after maize and vegetable (pepper and potato) production. Vegetables received either compost, manure, or fertilizer N inputs. Raw dairy manure stimulated the highest overall maize yields of 7,395 kg/ha (approximately 140 bushels per acre). This exceeded the Berks County mean yield of about 107 bushels per acre from 1994 to 2001. When hairy vetch replaced clover as the winter green manure cover crop, maize yields rose in three of the four treatments (approximately 500-1,300 kg/ha, or 10-24 bu/a). Hairy vetch cover cropping also resulted in a 9-25 % increase in wheat yields in the compost treatments compared to clover cover cropping. Hairy vetch cover crops increased both maize and wheat grain protein contents about 16 to 20% compared to the clover cover crop. Compost was superior to conventional synthetic fertilizer and raw dairy manure in 1) building soil nutrient levels, 2) providing residual nutrient support to wheat production, and 3) reducing nutrient losses to ground and surface waters. After 9 years, soil carbon (C) and soil N remained unchanged or declined slightly in the synthetic fertilizer treatment, but increased with use of compost amendments by 16-27% for C and by 13-16% for N. However, with hairy vetch cover crops, N leaching increased 4 times when compared to clover cover crops. September was the highest month for nitrate leaching, combining high rainfall with a lack of active cash crop or cover crop growth to use residual N. Broiler litter leaf compost (BLLC) showed the lowest nitrate leaching of all the nutrient amendments tested (P= 0.05).     

Analysis of metsulfuron-methyl in soil by liquid chromatography/tandem mass spectrometry. Application to a field dissipation study.

An analytical method is described for the extraction of metsulfuron-methyl from soil at sub-parts per billion levels (LOQ = 0.2 microgram kg(-1)). The herbicide was quantitatively determined and identified by ESI LC/MS/MS. The method has been applied to a field dissipation study in which metsulfuron-methyl was applied to spring barley at three dosage rates: 4, 8, and 16 g of active ingredient ha(-)(1). The results of 2 years are presented. The dissipation rate of metsulfuron-methyl in topsoil was very rapid, with a calculated half-life of 6.5 days. Laboratory mineralization studies with native soils in contrast to autoclaved soils indicated that microbial degradation of (14)C-labeled metsulfuron-methyl and (14)C-labeled 2-amino-4-methoxy-6-methyl-1,3,5-triazine in soil microcosms is an important factor for the complete degradation of metsulfuron-methyl in the field. However, the mineralization rate of the sulfonamide was much higher.     

Ability of Forage Grasses Exposed to Atrazine and Isoxaflutole to Reduce Nutrient Levels in Soils and Shallow Groundwater

Abstract

Successful implementation of vegetative buffers requires inclusion of plant species that facilitate rapid dissipation of deposited contaminants before they have a chance to be transported in surface runoff or to shallow groundwater. Thirty‐six field lysimeters with six different ground covers [bare ground, orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), smooth bromegrass (Bromus inermis Leyss.), timothy (Phleum pratense L.), and switchgrass (Panicum virgatum L.)] were established to evaluate the ability of grasses to reduce nutrient levels in soils and shallow groundwater. Nitrate (NO₃ ^?) and orthophosphate (PO₄ ^3?) were uniformly applied to each lysimeter. In addition, half of the lysimeters received an application of atrazine, and the other half received isoxaflutole (Balance?) at levels indicative of surface runoff from cropland. The leachate from each lysimeter was collected after major rainfall events during a 25‐day period, and soil was collected from each lysimeter at the end of the 25‐day period. Water samples were analyzed for NO₃‐N and PO₄‐P, and soil samples were analyzed for NO₃‐N. Grass treatments reduced NO₃‐N levels in leachate by 74.5 to 99.7% compared to the bare ground control, but timothy was significantly less effective at reducing NO₃‐N leaching than the other grasses. Grass treatments reduced residual soil NO₃‐N levels by 40.9 to 91.2% compared to the control, with tall fescue, smooth bromegrass, and switchgrass having the lowest residual levels. Switchgrass decreased PO₄‐P leaching to the greatest extent, reducing it by 60.0 to 74.2% compared to the control. The ability of the forage grasses to reduce nutrient levels in soil or shallow groundwater were not significant between herbicide treatments. Quantification of microbial NO₃ ^? dissipation rates in soil suggested that denitrification was greatest in switchgrass, smooth bromegrass, and tall fescue treatments. The overall performance of these three grasses indicated that they are the most suitable for use in vegetative buffers because of their superior ability to dissipate soil NO₃ ^? and reduce nutrient transport to shallow groundwater.     

Bypass flow and leaching of nitrogen in a Kenyan Vertisol at the onset of the growing season

Abstract. Bypass flow and concurrent leaching of nitrogen were studied on a Vertisol in south-western Kenya under rangeland and bare, manually tilled cropland. Showers of 30 mm/hr were simulated, causing bypass flow of 47–62% in rangeland topsoils and 19–49% in cropland topsoils. Volumetric water contents after experimentation increased from 28 to 35% and from 24 to 38%, respectively, for the two land-use types.
In rangeland samples up to 3.4 kg N/ha was found in the leachate of unfertilized soil. With a fertilizer application of 50 kg N/ha, up to 5.7 kg N/ha was lost from a pre-wetted soil, and more than 20 kg N/ha from dry soil. In cropland topsoils up to 2.2 kg N/ha was lost from unfertilized soil, and only up to 2.9 kg N/ha from both dry and prewetted fertilized soil. Although Vertisols are often linked with excess water, the phenomenon of bypass flow can cause water stress to crops in their early growth stages. Nitrogen leaching losses were large from dry grassland, but prewetting helped to decrease them. On intensively cultivated cropland there was little nitrogen leaching; the tilled topsoil was able to retain most of the supplied nitrogen.     

太湖地区高产高效措施下水稻氮淋溶和径流损失的研究

在太湖地区,采用田间小区试验,研究了高产高效措施对水稻季氮素淋溶和径流损失的影响。结果发现,水稻季总氮(TN)和可溶性有机氮(DON)淋溶随土壤深度的增加而降低,不同深度下氮淋溶形态不同。60 cm处DON浓度要高于硝氮(NO–3-N)和铵氮(NH4+-N),占TN的40.5%~58.9%;80 cm处NO–3-N的浓度要高于DON和NH4+-N,占TN的52.3%~60.7%。相比当地常规处理,高产高效处理的NO–3-N淋溶减少了51.7%~54.7%,仅占施肥的0.5%~0.9%。在氮的径流损失中,NH4+-N占TN的48.1%~56.4%,而NO–3-N占TN的36%~53%。试验中氮素通过径流途径的损失量很低,仅占施肥的0.34%~0.59%。高产高效处理的氮淋溶和径流损失之和分别为10.59 kg/hm2和10.18 kg/hm2,低于常规处理(13.41 kg/hm2)。除此之外,高产高效措施的作物产量(11.14~12.22 t/hm2)和农学利用率(11.8~12.5 kg/kg)均显著高于当地常规处理。水稻收获后,高产高效处理的土壤TN相比常规处理提高了6.8%~8.1%,有机质含量提高了8.6%~9.2%。综上,高产高效措施不仅有利于作物产量和氮素利用率的提高,还削弱了氮在土-水界面的迁移,是作物增产且环境友好型的有效措施。