Corn stover harvest increases herbicide movement to subsurface drains - Root Zone Water Quality Model simulations.

BACKGROUND: Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid (OXA). RESULTS: The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal. CONCLUSION: The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Comparative losses of glyphosate and selected residual herbicides in surface runoff from conservation-tilled watersheds planted with corn or soybean.

Residual herbicides regularly used in conjunction with conservation tillage to produce corn ( L.) and soybean [ (L.) Merr] are often detected in surface water at concentrations that exceed their U.S. maximum contaminant levels (MCL) and ecological standards. These risks might be reduced by planting glyphosate-tolerant varieties of these crops and totally or partially replacing the residual herbicides alachlor, atrazine, linuron, and metribuzin with glyphosate, a contact herbicide that has a short half-life and is strongly sorbed to soil. Therefore, we applied both herbicide types at typical rates and times to two chisel-plowed and two no-till watersheds in a 2-yr corn/soybean rotation and at half rates to three disked watersheds in a 3-yr corn/soybean/wheat-red clover ( L.- L.) rotation and monitored herbicide losses in surface runoff for three crop years. Average dissolved glyphosate loss for all tillage practices, as a percentage of the amount applied, was significantly less ( ≤ 0.05) than the losses of atrazine (21.4x), alachlor (3.5x), and linuron (8.7x) in corn-crop years. Annual, flow-weighted, concentration of atrazine was as high as 41.3 µg L, much greater than its 3 µg L MCL. Likewise, annual, flow-weighted alachlor concentration (MCL = 2 µg L) was as high as 11.2 and 4.9 µg L in corn- and soybean-crop years, respectively. In only one runoff event during the 18 watershed-years it was applied did glyphosate concentration exceed its 700 µg L MCL and the highest, annual, flow-weighted concentration was 3.9 µg L. Planting glyphosate-tolerant corn and soybean and using glyphosate in lieu of some residual herbicides should reduce the impact of the production of these crops on surface water quality.

Impact of grassed waterways and compost filter socks on the quality of surface runoff from corn fields.

Surface runoff from cropland frequently has high concentrations of nutrients and herbicides, particularly in the first few events after application. Grassed waterways can control erosion while transmitting this runoff offsite, but are generally ineffective in removing dissolved agrochemicals. In this study, we routed runoff from one tilled (0.67 ha) and one no-till watershed (0.79 ha) planted to corn (Zea mays L.) into parallel, 30-m-long grassed waterways. Two 46-cm-diam. filter socks filled with composted bark and wood chips were placed 7.5 m apart in the upper half of one waterway and in the lower half of the other waterway to determine if they decreased concentrations of sediment and dissolved chemicals. Automated samplers were used to obtain samples above and below the treated segments of the waterways for two crop years. The filter socks had no significant effect (P

Effect of tillage and rainfall on transport of manure-applied Cryptosporidium parvum oocysts through soil.

Most waterborne outbreaks of cryptosporidiosis have been attributed to agricultural sources due to the high prevalence of Cryptosporidium oocysts in animal wastes and manure spreading on farmlands. No-till, an effective conservation practice, often results in soil having higher water infiltration and percolation rates than conventional tillage. We treated six undisturbed no-till and six tilled soil blocks (30 by 30 by 30 cm) with 1 L liquid dairy manure containing 10(5) C. parvum oocysts per milliliter to test the effect of tillage and rainfall on oocyst transport. The blocks were subjected to rainfall treatments consisting of 5 mm or 30 mm in 30 min. Leachate was collected from the base of the blocks in 35-mL increments using a 64-cell grid lysimeter. Even before any rain was applied, approximately 300 mL of water from the liquid manure (30% of that applied) was transported through the no-till soil, but none through the tilled blocks. After rain was applied, a greater number and percentage of first leachate samples from the no-till soil blocks compared to the tilled blocks tested positive for Cryptosporidium oocysts. In contrast to leachate, greater numbers of oocysts were recovered from the tilled soil, itself, than from the no-till soil. Although tillage was the most important factor affecting oocyst transport, rainfall timing and intensity were also important. To minimize transport of Cryptosporidium in no-till fields, manure should be applied at least 48 h before heavy rainfall is anticipated or methods of disrupting the direct linkage of surface soil to drains, via macropores, need to be used.

Impact of using paper mill sludge for surface-mine reclamation on runoff water quality and plant growth.

Paper mills generate large amounts of solid waste consisting of fibrous cellulose, clay, and lime. Paper mill sludge (PMS) can improve reclamation of surface-coal mines where low pH and organic-carbon levels in the spoil cover material can inhibit revegetation. When applied at high rates, however, PMS may adversely impact the quality of surface runoff. Therefore, we applied PMS at 0, 224, and 672 dry Mg ha(-)(1) to 22.1 x 4.6-m plots at a recently mined site and monitored runoff for a total of 13 mo. The zero-rate plots served as controls and received standard reclamation consisting of mulching with hay and fertilization at planting. Compared to the control plots, PMS reduced runoff fourfold to sixfold and decreased erosion from 47 Mg ha(-1) to <1 Mg ha(-1). Most of the reduction occurred in the 2.5 mo before the plots were planted. Flow-weighted average dissolved oxygen concentrations in runoff from plots at the 224 and 672 Mg ha(-1) rates, however, were much lower (

Impact of glyphosate-tolerant soybean and glufosinate-tolerant corn production on herbicide losses in surface runoff.

Residual herbicides used in the production of soybean [Glycine max (L.) Merr] and corn (Zea mays L.) are often detected in surface runoff at concentrations exceeding their maximum contaminant levels (MCL) or health advisory levels (HAL). With the advent of transgenic, glyphosate-tolerant soybean and glufosinate-tolerant corn this concern might be reduced by replacing some of the residual herbicides with short half-life, strongly sorbed, contact herbicides. We applied both herbicide types to two chiseled and two no-till watersheds in a 2-yr corn-soybean rotation and at half rates to three disked watersheds in a 3-yr corn/soybean/wheat (Triticum aestivum L.)-red clover (Trifolium pratense L.) rotation and monitored herbicide losses in runoff water for four crop years. In soybean years, average glyphosate loss (0.07%) was approximately 1/7 that of metribuzin (0.48%) and about one-half that of alachlor (0.12%), residual herbicides it can replace. Maximum, annual, flow-weighted concentration of glyphosate (9.2 microg L(-1)) was well below its 700 microg L(-1) MCL and metribuzin (9.5 microg L(-1)) was well below its 200 microg L(-1) HAL, whereas alachlor (44.5 microg L(-1)) was well above its 2 microg L(-1) MCL. In corn years, average glufosinate loss (0.10%) was similar to losses of alachlor (0.07%) and linuron (0.15%), but about one-fourth that of atrazine (0.37%). Maximum, annual, flow-weighted concentration of glufosinate (no MCL) was 3.5 microg L(-1), whereas atrazine (31.5 microg L(-1)) and alachlor (9.8 microg L(-1)) substantially exceeded their MCLs of 3 and 2 microg L(-1), respectively. Regardless of tillage system, flow-weighted atrazine and alachlor concentrations exceeded their MCLs in at least one crop year. Replacing these herbicides with glyphosate and glufosinate can reduce the occurrence of dissolved herbicide concentrations in runoff exceeding drinking water standards.

Tillage system, application rate, and extreme event effects on herbicide losses in surface runoff.

Conservation tillage can reduce soil loss; however, the residual herbicides normally used to control weeds are often detected in surface runoff at high levels, particularly if runoff-producing storms occur shortly after application. Therefore, we measured losses of alachlor, atrazine, linuron, and metribuzin from seven small (0.45-0.79-ha) watersheds for 9 yr (1993-2001) to investigate whether a reduced-input system for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production with light disking, cultivation, and half-rate herbicide applications could reduce losses compared with chisel and no-till. As a percentage of application, annual losses were highest for all herbicides for no-till and similar for chisel and reduced-input. Atrazine was the most frequently detected herbicide and yearly flow-weighted concentrations exceeded the drinking water standard of 3 microg L(-1) in 20 out of 27 watershed years that it was applied. Averaged for 9 corn yr, yearly flow-weighted atrazine concentrations were 26.3, 9.6, and 8.3 microg L(-1) for no-till, chisel, and reduced-input, respectively. Similarly, flow-weighted concentrations of alachlor exceeded the drinking water standard of 2 microg L(-1) in 23 out of 54 application years and in all treatments. Thus, while banding and half-rate applications as part of a reduced-input management practice reduced herbicide loss, concentrations of some herbicides may still be a concern. For all watersheds, 60 to 99% of herbicide loss was due to the five largest transport events during the 9-yr period. Thus, regardless of tillage practice, a small number of runoff events, usually shortly after herbicide application, dominated herbicide transport.

Herbicide leaching as affected by macropore flow and within-storm rainfall intensity variation: a RZWQM simulation.

Within-event variability in rainfall intensity may affect pesticide leaching rates in soil, but most laboratory studies of pesticide leaching use a rainfall simulator operating at constant rainfall intensity, or cover the soil with ponded water. This is especially true in experiments where macropores are present--macroporous soils present experimental complexities enough without the added complexity of variable rainfall intensity. One way to get around this difficulty is to use a suitable pesticide transport model, calibrate it to describe accurately a fixed-intensity experiment, and then explore the affects of within-event rainfall intensity variation on pesticide leaching through macropores. We used the Root Zone Water Quality Model (RZWQM) to investigate the effect of variable rainfall intensity on alachlor and atrazine transport through macropores. Data were used from an experiment in which atrazine and alachlor were surface-applied to 30 x 30 x 30 cm undisturbed blocks of two macroporous silt loam soils from glacial till regions. One hour later the blocks were subjected to 30-mm simulated rain with constant intensity for 0.5 h. Percolate was collected and analyzed from 64 square cells at the base of the blocks. RZWQM was calibrated to describe accurately the atrazine and alachlor leaching data, and then a median Mid-west variable-intensity storm, in which the initial intensity was high, was simulated. The variable-intensity storm more than quadrupled alachlor losses and almost doubled atrazine losses in one soil over the constant-intensity storm of the same total depth. Also rainfall intensity may affect percolate-producing macroporosity and consequently pesticide transport through macropores. For example, under variable rainfall intensity RZWQM predicted the alachlor concentration to be 2.7 microg ml(-1) with an effective macroporosity of 2.2 E(-4) cm(3) cm(-3) and 1.4 microg ml(-1) with an effective macroporosity of 4.6 E(-4) cm(3) cm(-3). Percolate-producing macroporosity and herbicide leaching under different rainfall intensity patterns, however, are not well understood. Clearly, further investigation of rainfall intensity variation on pesticide leaching through macropores is needed.

Earthworm additions affect leachate production and nitrogen losses in typical midwestern agroecosystems.

Earthworms affect soil structure and the movement of agrochemicals. Yet, there have been few field-scale studies that quantify the effect of earthworms on dissolved nitrogen fluxes in agroecosystems. We investigated the influence of semi-annual earthworm additions on leachate production and quality in different row crop agroecosystems. Chisel-till corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation (CT) and ridge-till corn-soybean-wheat (Triticum aestivum L.) rotation (RT) plots were arranged in a complete randomized block design (n = 3) with earthworm treatments (addition and ambient) as subplots where zero-tension lysimeters were placed 45 cm below ground. We assessed earthworm populations semi-annually and collected leachate biweekly over a three-year period and determined leachate volume and concentrations of total inorganic nitrogen (TIN) and dissolved organic nitrogen (DON). Abundance of deep-burrowing earthworms was increased in addition treatments over ambient and for both agroecosystems. Leachate loss was similar among agroecosystems, but earthworm additions increased leachate production in the range of 4.5 to 45.2% above ambient in CT cropping. Although leachate TIN and DON concentrations were generally similar between agroecosystems or earthworm treatments, transport of TIN was significantly increased in addition treatments over ambient in CT cropping due to increased leachate volume. Losses of total nitrogen in leachate loadings were up to approximately 10% of agroecosystem N inputs. The coincidence of (i) soluble N production and availability and (ii) preferential leaching pathways formed by deep-burrowing earthworms thereby increased N losses from the CT agroecosystem at the 45-cm depth. Processing of N compounds and transport in soil water from RT cropping were more affected by management phase and largely independent of earthworm activity.

Atrazine, deethylatrazine, and deisopropylatrazine in surface runoff from conservation tilled watersheds.

Atrazine and two of its metabolites, deethylatrazine (DEA) and deisopropylatrazine (DIA), are frequently detected in surface runoff. Although their health and environmental effects may be similar to that of atrazine and ratios of their concentrations are useful in delineating sources of contamination, there have been few long-term studies of the factors affecting their losses in runoff. Therefore, losses of atrazine, DEA, and DIA were monitored for six years in runoff from seven small (0.45-0.79 ha) watersheds under three tillage practices. Weather year and the timing of runoff-producing rainfall had a greater effect on atrazine, DEA, and DIA concentrations and losses than did tillage practice. DEA was the most frequently detected metabolite with an average concentration in the year of atrazine application, of 2.5 microg L(-1) compared to 0.7 microg L(-1) for DIA. Atrazine exceeded its 3 /g L(-1) maximum contaminant level (MCL) up to 100 days after application. DEA and DIA exceeded the atrazine MCL up to 50 days after atrazine application; thus, failure to monitor their presence may result in underestimation of the environmental impact of atrazine usage. The molar concentration ratio of DEA to atrazine (DAR) was affected by tillage treatment, weather year, and possibly soil type. These factors may need to be taken into account when DAR is used as an index of atrazine movement. The ratio of DIA to DEA (D2R) was fairly constant and should be useful in determining the parent compounds contributing DIA to surface waters.