|Lerch, Robert - Bob|
Submitted to: Transactions of the ASABE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2013
Publication Date: 12/1/2013
Citation: Lerch, R.N., Harbourt, C.M., Broz, R.R., Thevary, T.J. 2013. Atrazine incorporation and soil erosion: balancing competing water quality concerns for claypan soils. Transactions of the ASABE. 56(6):1305-1316. DOI:10.13031/trans.56.10272. Interpretive Summary: Atrazine is a commonly used weed killer in corn production in the Midwest U.S. Research has shown that the claypan soils of northeastern Missouri are the most vulnerable within the Corn Belt to transport of atrazine by surface runoff. In addition to the high vulnerability to atrazine transport, claypan soils are also highly erosive. Thus, a major challenge for claypan soils is the development of cropping systems that allow for incorporation of soil-applied herbicides to reduce their transport in surface runoff, while maintaining sufficient crop residue cover to control soil erosion. These two goals often conflict since effective erosion control measures, such as no-till, preclude the incorporation of herbicides. The overall objective of this research was to compare the use of a rotary harrow tillage implement, the Phillips harrow which can incorporate atrazine to a depth of about 5 cm (2 in.), to a no-till system without incorporation and a minimum-till system with incorporation to a depth of about 10 cm (4 in.) using a field cultivator. The primary objective was to compare atrazine and sediment losses in surface runoff between these three tillage treatments for a claypan soil. A secondary objective was to compare residue cover, weed control, and corn grain yield between the tillage treatments. The rotary harrow treatment had lower erosion than the minimum-till treatment, but it did not significantly increase erosion compared to no-till. In addition, the rotary harrow reduced atrazine losses compared to no-till, but did not significantly increase atrazine transport compared to minimum-till. The rotary harrow treatment also resulted in comparable or better yields and weed control than the other treatments. The rotary harrow was able to manage the trade-off between soil erosion and atrazine transport in surface runoff for a claypan soil. It is also a practical tillage implement that can easily be integrated with existing farming practices in the region. Although additional studies at other sites need to be conducted to determine the efficacy of rotary harrows under a broader range of conditions, this study strongly supports the conclusion that they can be used as a best management practice (BMP) for claypan and poorly drained soils. The benefits of this research are that the widespread adoption of rotary harrows as a BMP for reducing soil and herbicide transport in runoff has the potential to greatly improve the region’s two most persistent water quality problems, improve the sustainability of crop production, and increase or maintain farmer profitability.
Technical Abstract: In the U.S. Corn Belt, claypan soils are vulnerable to both erosion and transport of unincorporated herbicides. Thus, there is a need to identify tillage practices that can achieve a balance between herbicide transport and soil erosion for these soils. The objectives of this research were to compare the effect of three tillage systems on sediment and atrazine transport in surface runoff for a claypan soil and to compare their agronomic utility. Tillage treatments were: 1) rotary harrow – atrazine incorporated to ~5cm (RH); 2) no-till without incorporation (NT); and 3) minimum-till - incorporated atrazine to approximate 10 cm (MT). Three main tillage plots were established for each of the treatments, and two sets of runoff sub-plots, with three replicates each, were established within the main plots. Runoff was generated with a rainfall simulator at an average rate of 27 mm/ h. Runoff samples were collected at unequal time intervals from 1 to 90 min after runoff initiation, and analyzed for total suspended sediment (TSS) and dissolved-phase atrazine concentrations. The RH treatment had significantly lower TSS concentrations and loads than MT, but it did not significantly increase erosion compared to NT. The RH treatment also had significantly lower atrazine concentrations and relative loads than NT, but not significantly greater atrazine transport than MT. Atrazine relative loads, as a percent of applied, were: NT, 22.2 percent; RH, 10.6 percent; and MT, 6.4 percent. The RH treatment also resulted in comparable or better yields and weed control than the other treatments. The RH treatment successfully managed the trade-off between erosion and atrazine transport for a claypan soil and can be used as a best management practice for claypan and related restrictive layer soils.