Tillage management to mitigate herbicide loss in runoff under simulated rainfall conditions

A meta-analysis of pesticide loss in runoff under conventional tillage and no-till management

Global agricultural intensification has led to increased pesticide use (37-fold from 1960 to 2005) and soil erosion (14% since 2000). Conservation tillage, including no-till (NT), has been proposed as an alternative to conventional plow till (PT) to mitigate soil erosion, but past studies have reported mixed results on the effect of conservation tillage on pesticide loss. To explore the underlying factors of these differences, a meta-analysis was conducted using published data on pesticide concentration and load in agricultural runoff from NT and PT fields. Peer-reviewed articles (1985-2016) were compiled to build a database for analysis. Contrary to expectations, results showed greater concentration of atrazine, cyanazine, dicamba, and simazine in runoff from NT than PT fields. Further, we observed greater load of dicamba and metribuzin, but reduced load of alachlor from NT fields. Overall, the concentration and the load of pesticides were greater in runoff from NT fields, especially pesticides with high solubility and low affinity for solids. Thus, NT farming affects soil properties that control pesticide retention and interactions with soils, and ultimately their mobility in the environment. Future research is needed for a more complete understanding of pesticide-soil interactions in NT systems. This research could inform the selection of pesticides by farmers and improve the predictive power of pesticide transport models.

Herbicide transport in surface runoff from conventional and zero-tillage fields

During the past four decades of crop production in the prairie region of Canada, there has been a dramatic shift from conventional management (CM) to conservation tillage management in which one or more tillage operations has been replaced by herbicide application. To determine whether this management shift has affected the quality of snowmelt runoff, field-scale side-by-side runoff watersheds were used in a 6-yr study. Herbicide concentrations and fluxes in snowmelt runoff water from CM and zero-till management (ZTM) systems were compared relative to an organic production system used as the control. Snowmelt runoff volume from the ZTM watershed exceeded that from the CM watershed in 5 yr of the 6-yr study. Frequencies of detection, concentrations and mass loss (mg ha) of the fall-applied herbicides were generally higher in snowmelt runoff relative to those of the spring-applied herbicides. On days when multiple consecutive samples were collected, herbicide concentrations generally decreased as runoff flow increased. Incorporation of trifluralin and triallate reduced their losses in snowmelt runoff by approximately 5 and 8 times, respectively. Regarding the amount of herbicide applied during the 6-yr study, percent loss varied from 0.002% for trifluralin to 0.15% for 2,4-D. Edge-of-field concentrations of 2,4-D, trifluralin, and triallate in snowmelt runoff frequently exceeded Canadian aquatic life water quality guidelines. The adoption of conservation tillage strategies for crop production resulted in increased (∼20%) herbicide use and an increased amount (∼25%) of herbicide transported in snowmelt runoff (8.6 versus 6.9 g ha).

Estimating catchment vulnerability to diffuse herbicide losses from hydrograph statistics

The prediction of diffuse herbicide losses to surface waters using process-based models is data and time demanding. There is a need for simpler and more efficient catchment screening tools. We developed and tested a new proxy for screening catchments for their vulnerability to diffuse herbicide losses relying on widely available river flow data only. The proxy combines the fast flow index (FFI) (i.e., the long-term average proportion of fast flow to total discharge) and the fast flow volume (FFVs) (i.e., the stormflow component of the hydrograph during the spring flush period). We tested the proxy and the underlying hypotheses by regression analyses of existing high-frequency, multiannual monitoring datasets of atrazine, metolachlor, alachlor, and acetochlor concentrations from six US and European catchments. The percentages of applied amounts of three of the four herbicides lost to surface water were positively correlated with the FFV, and the slope of the correlation was positively correlated with the FFI. Based on the empirical data, we derived quantitative proxies to estimate atrazine and metolachlor losses based on the measured FFI and FFV values. The application to 65 European catchments revealed that many of them had a lower vulnerability than the six test catchments. The observed FFI dependency of the slope seems reasonable because with increasing FFI less rain is needed to trigger fast flow and more herbicide is available in the topsoil. The proposed FFI-FFVs proxy can guide researchers and authorities in selecting monitoring areas, setting monitoring results into context, and prioritizing mitigation strategies according to catchment vulnerability.

Dissipation and evaluation of hexaflumuron residues in chinese cabbage grown in open fields

The dissipation and residue behavior of hexaflumuron in Chinese cabbage ( Brassica pekinensis ) under different treatments were investigated at two main cabbage-growing areas in China. The dissipation rates of hexaflumuron in cabbages and soils fit a first-order decay process very well. The dissipation times for 50% of the hexaflumuron in cabbage and soil were 3.37 and 3.01 days from Hunan province and 5.58 and 3.68 days in Tianjin, respectively, when Chinese cabbage was treated with 180 g of active ingredient (ai)/ha. Hexaflumuron residual times in cabbage and soil were influenced strongly by the application rate and frequency. The application regimen of hexaflumuron in the cabbage field, a rate of 120 g of ai/ha with two applications at a 7 day interval and a 21 day preharvest interval, was recommended from the point of view of ensuring food safety. The residual levels of hexaflumuron in cabbages were lower than the standards of the "Positive List System for Agricultural Chemical Residues in Foods" based on the recommended application regimen.

Interactions of tillage and cover crop on water, sediment, and pre-emergence herbicide loss in glyphosate-resistant cotton: implications for the control of glyphosate-resistant weed biotypes

The need to control glyphosate [N-(phosphonomethyl)glycine]-resistant weed biotypes with tillage and preemergence herbicides in glyphosate-resistant crops (GRCs) is causing a reduction in no-tillage hectarage thereby threatening the advances made in water quality over the past decade. Consequently, if environmental gains afforded by GRCs are to be maintained, then an in-field best management practice (BMP) compatible with tillage is required for hectarage infested with glyphosate-resistant weed biotypes. Thus, 1 d after a preemergent application of fluometuron [N,N-dimethyl-N'-(3-(trifluoromethyl)phenyl)urea] (1.02 kg ha(-1)) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] (1.18 kg ha(-1)) to a Dundee silt loam (fine-silty, mixed, active, thermic Typic Endoaqualf), simulated rainfall (60 mm h(-1)) was applied to 0.0002-ha microplots for approximately 1.25 h to elucidate tillage (no tillage [NT] and reduced tillage [RT])and cover crop (no cover [NC] and rye cover [RC]) effects on water, sediment, and herbicide loss in surface runoff. Regardless of tillage, RC delayed time-to-runoff 1.3-fold, reduced cumulative runoff volume 1.4-fold, and decreased cumulative sediment loss 4.7-fold. Cumulative fluometuron loss was not affected by tillage or cover crop. Conversely, total metolachlor loss was 1.3-fold lower in NT than RT and 1.4-fold lower in RC than NC. These data indicate that RC can be established in hectarage requiring tillage and potentially curtail water, sediment, and preemergence herbicide losses in the spring to levels equivalent to or better than that of NT, thereby protecting environmental gains provided by GRCs.