Development and Demonstration of a New Method of Physical Weed Control

Project Overview

Project Type: Research and Education
Funds awarded in 2010: $174,603.00
Projected End Date: 12/31/2013
Region: North Central
State: South Dakota
Project Coordinator:

Annual Reports

Information Products


  • Agronomic: corn, soybeans
  • Fruits: berries (brambles)


  • Education and Training: demonstration, on-farm/ranch research
  • Pest Management: physical control
  • Production Systems: organic agriculture

    Proposal abstract:

    Because weed control is the most challenging agronomic aspect of organic cropping systems, many growers believe that new and more efficacious tactics for weed control are needed. In response to this need, a single-nozzle abrasive grit applicator was developed and tested in greenhouse and small field trials using pulverized corn cobs as grit. This proof-of-concept showed promise in controlling weeds with minimal crop (field corn) injury. As follow-up, we propose to build and test a demonstration-model abrasive grit applicator configured with eight nozzles for postemergence weed control in four crop rows simultaneously. Senior students in the SDSU Engineering Manufacturing program will build the initial applicator and nozzles for their Senior Research Design course with input from organic growers and guidance from professional engineers. A post-doctoral agricultural engineer will oversee testing of the applicator in row crops like corn, sweet corn, and soybean in eastern SD and MN to determine weed control efficacy, application timing and frequency, crop injury and yields, grit types and use rates, costs, and other specific parameters that will help to make best use of the technology. Once tested and refined on-station, the technology will be evaluated further and demonstrated on-farm and at field days. Local engineering companies and shops are involved with the project and will have first “right-of-refusal” for developing commercially viable implements and component parts.

    Project objectives from proposal:

    The project has two phases, an engineering phase and an agronomic phase. The two phases are intimately related, and each has multiple components. Research on some components from each phase can be performed simultaneously. However, some components of the engineering phase must be executed before those of the agronomic phase and, likewise, some aspects of the agronomic phase must precede some from the engineering phase. We ask the indulgence of reviewers while reading the following paragraphs, as descriptions of categories (phase components) and chronologies (work schedules) may be confusing. Additionally, we recognize that the engineering phase of the research is not hypothesis-driven in the classical sense, yet it is an essential precursor to the more hypothesis-driven agronomic research.

    Engineering approaches involve (i) harnessing a tractor’s energy to compress air for (ii) propelling crop-derived grit in a directed fashion through nozzles at speeds that abrade small weed seedlings selectively within crop rows, (iii) adapting nozzles for optimum patterns of grit application, and (iv) attaching multiple pairs of nozzles onto a tractor-mounted toolbar for simultaneous multiple-row weed control.

    (i) We plan to use a dedicated tractor for the engineering research. The tractor’s minimum size will be 100 hp. The minimum size is required to operate an add-on air compressor, such as the HKL-series of hydraulic-powered compressors from Dynaset Corporation or belt-driven VANAIR 130CFM. The exact compressor to be used will be determined by the engineering students at SDSU in consultation with professional engineers based upon known mechanical specifications and anticipated power needs. (ii) Manifolds will be devised to split the compressed air into eight regulated lines, each tipped by a nozzle. (iii) Nozzles will be designed to provide specific patterns (e.g., flat fan) of grit deposition. Currently available nozzles are characterized by solid cone-type deposition patterns. Nozzle types that work maximally for shredding weeds are not yet known and form part of the agronomic research described below. For experimental purposes, nozzle orifice areas will remain constant, but their shapes will be modified to provide desired delivery patterns of grit. A malleable metal, like copper, can be used to fashion prototype nozzles, but permanent nozzles will be contructed from more resistant materials. (iv) Swivels will be used that allow adjustments regarding the distance of the nozzles from the soil surface, angle of the nozzle relative to the soil surface, and angle of the nozzle relative to the crop row. Optimum distances and angles are not yet known. Components i and ii, above, are interrelated and are expected to represent Senior Design projects for a team of two students. Components iii and iv also are related, but they are simpler technically and represent a combined Senior Design project for a single student. The post doctoral agricultural engineer will be responsible for integrating the components into a functional system, always in consultation with professional engineers.

    Agronomic field research entails testing (i) the timing and frequency of application passes, (ii) air pressure or grit air speed requirements, (iii) grit type, size and hardness to affect season-long control of weeds without crop injury in common annual and high-value perennial row crops, (iv) applicator ground speed, and (v) on-farm comparisons and demonstrations.

    (i) Factorial experiments with replicated treatments will test for the best times to abrade weed seedlings in terms of crop stages (corn stages V0 through V6) and the frequency of abrasions (1 to 4) needed for season-long weed control. The hypothesis being that multiple abrasion events at critical crop growth stages will control early- as well as late-emerging weed seedlings more effectively than a single event. Although corn will be emphasized in all experiments, supplementary experiments will include soybean and a perennial horticultural crop, possibly brambles.

    (ii) Grit air speed probably is the defining variable for injuring small weed seedlings, and this variable can be regulated in part by air pressure and nozzle type and distance to the soil surface. Replicated experiments will test these factors independently in field settings after minimum and maximum boundaries are determined in greenhouse situations.

    (iii) Agriculturally-derived grit is available in different forms and mesh sizes. All preliminary experiments employed 20-40 mesh grit, but other sizes may be better suited for weed control. Nozzle orifice diameters determine, in part, appropriately-sized grits. Furthermore, grit is available in differing textures, e.g., hard (walnut) vs. soft (corn cob).

    Because almost any material that flows freely can be used as grit, our grower-advisors suggested that pelletized organic manures and other soil amendments be examined for efficacy in weed control with the grit applicator. This intriguing suggestion would affect two agronomic issues simultaneously, namely weeds and soil fertility (soil chemistry). Besides weed control, soil fertility status could be enhanced with materials such as ‘Cluck’ chicken manure and alfalfa meal, and soil pH can be modified with limestone (decreases soil acidity) and cotton seed meal (increases soil acidity). All of these materials are pelletized and amendable to use as grit. We will test and compare grit types, sizes and textures in replicated greenhouse and field experiments. Appropriate experimental designs will be chosen to fit the need of the specific experiment. Weedy and hand-weeded checks will be included where appropriate. Furthermore, in field experiments, we will keep track of grit use rates, tractor fuel consumption and crop yields to calculate costs and cost-effectiveness of using the proposed techniques for weed control.

    An especially interesting type of grit may be corn gluten meal. CGM normally is used as a preemergence herbicide (and N source). Use rates of CGM range from 400 lbs/acre in established turf to 2400 lbs/acre in bare soil (with per acre costs of $100 to $600). Its benefit to weed control may increase if it could be used first to control the initial flush of small weed seedlings via an abrasive grit applicator and, subsequently, to control late-emerging seedlings through its normal preemergence mode of action.

    (iv) Tractor/implement speed will affect grit application rate. Simple factorial experiments will examine the interaction between tractor speeds and air pressure for weed control, application rate, and costs. For costs, grit and time will be measured directly, whereas fuel use will be estimated based upon rpm and fuel consumption relationships for specific tractors.

    The post doctoral researcher is expected to oversee the agronomic experiments. This individual will be assisted ably by two technical staff members at the USDA-ARS Soils Lab who are permanently assigned to the lab’s weed research program.

    (v) Once the prototype field-scale implement is designed and built by our team in 2010-2011, we will test it on-station first. In 2012, at least one organic grower in both SD and MN will be asked to participate in on-farm trials. Several organic growers already have volunteered for this activity. Unfortunately, by 2012 only a single farm-scale implement likely will be available for use. Thus, transportation and timeliness issues are expected if too many on-farm trials are attempted. The implement first will be demonstrated to the growers on their properties, and immediately afterwards the growers will be asked to use the implement on small strip plots within one of their own fields. Their buy-in to the new implement will be critical for generating interest among implement manufacturers as well as other growers. Approximately one to two weeks after on-farm testing, weed control in test strips will be compared to adjacent strips that underwent standard practices as well as small weedy check areas. After assessments are made, the weedy check areas will be hand-weeded.

    At this early stage of development of the concept for a new form of weed control, we will not ask growers to dedicate large acreages for testing and, therefore, we have no plans at this time to allocate NC-SARE funds to growers except as land rental fees. Indeed, most organic growers we know are happy to participate without compensation. The reward, in their minds, is knowing that USDA/university-led research is occurring along the lines that they have advocated repeatedly.

    Organic growers are intimately involved with the planning and execution of the two annually-held organic field days (Lamberton MN and Yankton SD). Our intention is to garner ideas from growers at such field days in 2010 and 2011 for the types of demonstrations they would like to see in 2012, as well as to solicit additional input regarding implement specifications that would make a prototype implement more useful and acceptable on their farms. Information will also be provided at other field days at other field experiment station locations such as SE Farm, NE Farm, Brookings, and FarmFest in Mitchell, SD and USD-ARS Field Days in Morris.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.