by Steve Diver
Appropriate Technology Transfer for Rural Areas — ATTRA
Fayetteville, Arkansas
Last Updated April, 2002
Introduction
No-till systems are gaining increased attention as a practical way to raise vegetables and improve soil quality at the same time. Growing and managing cover crops to provide killed mulches and living mulches is an important component of these production systems. The combination of organic mulches on the soil surface and reduction of tillage have numerous benefits to soil biology, soil structure, and soil health.
In conventional no-till vegetable production, herbicides are commonly used to kill cover crops and create a no-till mulch, and for follow-up post-emergent weed control. Herbicides do a good job of controlling vegetation and they are a major reason no-till agriculture has been so successful.
However, sustainable agriculture has a goal of reducing chemical inputs, instead relying on cultural practices, biological processes, and naturally-derived products. Secondly, herbicides are simply not allowed in certified organic vegetable production. So the question arises, how can farmers get into no-till production without herbicides?
The purpose of this document is to provide resources on no-till vegetable production in general, and secondly, to address non-chemical options for cover crop suppression and weed control. A companion ATTRA publication, Pursuing Conservation Tillage Systems for Organic Crop Production, may be referred to for a more detailed review of the cover crop and tillage techniques described in this publication. It also features a selection of research abstracts that summarize efforts underway in different regions of the United States.
Conservation Tillage
No-till vegetable production is a form of conservation tillage. Conservation tillage is the generic term that describes reduced-tillage cropping systems like no-till, strip-till, mulch-till and ridge-till. In agronomic crop production, for example corn, soybeans, cotton, and peanuts, crop residue management to control soil erosion is the primary goal of conservation tillage. For example, technical specifications for conservation tillage state that crop residues should remain on 30% of the soil surface. These residues protect the soil from erosion and by wind and water.
Conservation tillage also reduces the number of equipment passes (e.g., plow, disc, harrow) required to prepare a seedbed and thus saves fuel and reduces soil disturbance and compaction.The operating principle of conservation tillage is simply to minimize disturbance of the soil.
Maintenance of crop residues, especially killed mulches from cover crops, is key to proper management of these systems. Some benefits of a no-till organic mulch include moisture conservation, weed suppression, erosion control, increased soil organic matter, food and habitat for soil organisms, and, in the case of a legume, biologically fixed nitrogen.
Conservation agriculture is another term used to describe a systems approach to agriculture that focuses on minimal soil disturbance, cover crops, and crop residues.
Source:
Conservation Agriculture: For a Better Environment
European Conservation Agriculture Federation
For background information on the value and importance of conservation tillage on soil health, one book in particular may be viewed as essential reading, Stubble Over the Soil by Carlos Crovetto Lamarca (1). Focusing on the vital role of reduced tillage and plant residues to improve soil quality, Lamarca provides an interesting and practical review of this revolutionary shift in agriculture. His 245-page book is filled with color photos and educational illustrations of no-till agriculture, agricultural implements, cover crops, mulches, crop residues, and soil quality improvements. Larmarca is an agronomist with Chequen farm in Chile, a famous site of no-till agriculture in South America. He has played an instrumental role in no-till agriculture in Venezuela, Columbia, Argentina, Brazil, Uruguay, Bolivia, Mexico, the United Kingdom, and the U.S.
Managing Cover Crops and Weeds Through
Mechanical Suppression
Cover crops are an integral component of conservation tillage cropping systems. A typical system is fall establishment of a winter cover crop, followed by herbicide kill prior to spring planting. The killed residue that results is essentially an organic mulch grown in place.
While herbicides are commonly used to manage cover crops, non-chemical alternatives do exist, though they are less widely known. In keeping with ATTRA’s mandate to transfer technology on low-chemical-input farming methods, and to support the information needs of farmers who want to reduce their use of herbicides or raise certified organic crops, emphasis is placed on non-chemical options to suppress cover crops.
In addition, while the organic mulch that results from cover crops—whether killed by chemical or mechanical means—can provide fairly good weed suppression for the first 30-45 days after kill-down, there will always be additional weeds that sprout through the mulch; therefore, follow-up weed control methods are important.
Non-chemical methods of cover crop suppression that can be integrated with no-till vegetable production include: strip tillage, mowing, rolling and crimping (also known as roll chopping), undercutting, and thermal weed control (flame, steam, infra-red). Based on extensive research and field experience, growers looking into no-till vegetable production can proceed with a high degree of confidence that strip tillage, mowing, roll chopping, and undercutting are solid performers. However, further work is needed to define the commercial viability and affordability of the thermal control techniques in terms of knock-down cover crop suppression.
To handle follow-up weed control for weeds emerging through the killed mulch, supplemental weed control options include: high-residue cultivators, weeder geese, chicken tractors, hand hoeing, and spot-spray steam weed control.
High-residue cultivators are widely used in agronomic no-till crop production, and would be an affordable option on larger-scale no-till vegetable farms raising sweet corn, green beans, and related row crops. Weeder geese, chicken tractors, and hand hoeing also have a proven track record, but are geared to smaller-scale market farming. [See Farmer Profiles] Spot-spray steam weed control is a technique the author feels has good potential as an appropriate technology in association with organic no-till mulch. While commercial steam equipment is available to control vegetation it is extremely expensive and targeted to other market segments (e.g., Aqua Heat for large-scale orchards, Waipuna for municipal parks and non-croplands). Thus, steam needs an infusion of on-farm technology development. Infra-red thermal weeding equipment, on the other hand, looks affordable and practical. Trials in association with organic no-till mulches are needed to ascertain how well it actually works. A companion ATTRA publication, Flame Weeding for Vegetables, provides essential details and equipment suppliers for flame and infra-red weeding systems.
Where is no-till vegetable production taking place, and who are some of the innovative farmers and researchers implementing this technology? What are some examples of non-chemical cover crop suppression? These are the focus of the remaining sections.
A cover crop is any crop grown to provide soil cover, regardless of whether it is later incorporated. In no-till farming, cover crops need to match the growing cycle of the cash crop, be susceptible to chemical or mechanical killing techniques, and provide a reasonably thick mulch.
Common plants raised as cover crops:
Cereal grains: rye, wheat, barley, oats
Grasses: sorghum sudan, millet, annual ryegrass
Forage legumes: clover, vetch, medics
Grain legumes: cow pea, soybean, field peas
Broadleaves: buckwheat, rapeseed, mustard
Resources on Cover Crops:
Managing Cover Crops Profitably, 2nd Edition.
SAN Handbook No. 3
Overview of Cover Crops and Green Manures
ATTRA
Converting the Cover Crop Into an Organic Mulch
Three methods have emerged as non-chemical approaches to knocking down and killing cover crops to create a no-till mulch: mowing, rolling , and undercutting.
Flail mowers are viewed as ideal mow-down equipment, but small-scale farmers are known to employ rotary mowers (commonly known as a "brush hog") and even string weeders (commonly known as a "weed eater") to chop down cover crops. Obviously, the number of acres in production makes a big difference in terms of which piece of equipment is most affordable. For example, the cost of a 4-6 foot wide rotary mower starts at $400-600 while a flail mower starts at about $2,000.
The primary advantage of a high-speeed flail mower is that it can chop cover crops down to about an inch above the ground, shredding the material and leaving the mulch in place. Rotary mowers clip higher and tend to throw the vegetative residue over a wider area. However, a market gardener in Georgia had a local machine shop weld metal strips onto the back end of his rotary mower so that it catches and distributes the cover crop mulch on top of his production beds. Thus, growers are known to make do with what they have and adapt.
Timing is important; hairy vetch should be mowed when it has already begun flowering; mowing of rye should also be delayed until flowering (when the anthers are shedding pollen). When annual cover crops are mowed at the optimum time, the root system senesces and dies. Emphasis is placed on optimum timing because cover crops mowed too early will re-sprout and start to compete with the vegetable crop like a weed. Vetch, for example, is notorious for re-sprouting when it is mowed too early.
Mechanical roller-crimpers and rolling stalk-choppers have evolved as a means to roll down and crimp cover crops -- a technique known as rolling or roll chopping. These are heavy-duty drum rollers with horizontal-welded blunt-steel strips. When they are pulled through the field they crush and crimp the cover crop, which leaves residue lying flat on the soil surface and discourages regrowth.
The rolling stalk chopper is an implement used in field corn production, modified and adapted to no-till vegetable production. Steve Groff, a no-till vegetable farmer in Lancaster County, Pennsylvania, is probably the best known example of a no-till vegetable farmer using a rolling stalk chopper to manage cover crops like rye-vetch.
Mechanical roller crimpers, on the other hand, were specially developed for cover crop management in no-till production. Millions of acres of conservation agriculture in Brazil and Paraguay are managed with these mechanical roller crimpers. Researchers in Alabama showed that rolling down cereal grains like winter rye, wheat, and black oats was most effective during the early milk stage, which occurs after flowering (anthesis) and prior to the soft dough stage (grain formation) (2). Mowing at this stage killed cover crops just as well as herbicides.
The undercutter-roller is a specialized implement developed at OhioStateUniversity, designed to slice through the soil and sever cover crop roots underground. It consists of a V-plow sweep blade mounted on a toolbar, followed by a rolling harrow to crimp and roll the cover crop residue at it falls on the ground.
Undercutting suppressed weeds in trials better than either a flail mower or sicklebar mower (3-4). Whereas mowing cuts the cover crop residue into little pieces and promotes faster breakdown, the undercut mulch is thicker and better able to prevent light penetration to the soil surface, which results in fewer weeds. The residue also remains on the soil surface longer. Materials to build one of these units costs around $800. An schematic diagram of the undercutter toolbar was published in American Journal of Alternative Agriculture (4), and it provides sufficient details to reproduce one of these setups in a local machine shop.
Dr. Nancy Creamer, who led team that developed the undercutter system at OhioState, is now located at North CarolinaStateUniversity. Dr. Creamer continues to work on tillage systems integrated with cover crops in association with vegetable production, and can provide details on modifications since made to the undercutter implement.
Contact: Dr. Nancy Creamer
Organic Farming Systems
Campus Box 7609
North Carolina State University
Raleigh, NC 27695-7609
919-515-9447
919-515-2505 Fax
The USDA Mow-Kill System of No-Till Vegetable Production
USDA researchers in Beltsville, MD demonstrated that no-till tomatoes transplanted into a hairy vetch mulch produce excellent yields (5-6). Since hairy vetch is a winter annual legume, it was planted in the fall on pre-formed beds. A Brillion™ seeder was used to establish the cover crop, ensuring good seed-to-soil contact, germination, and establishment. In the spring the vetch was flail-mowed to about an inch high. Tomatoes were transplanted into the mow-killed mulch immediately following the mowing operation. Transplanting was done with minimal disturbance to the soil.
The researchers compared vetch mulch plots with plastic mulch, paper mulch, and bare ground. Yields from plants grown under the vetch mulch averaged more than 45 tons per acre, trailed by 35 tons for plastic mulch and 34 tons for paper mulch. Control plots managed as bare ground averaged 19 tons per acre.
An important benefit of the vetch mulch was weed control achieved early in the growing season. No pre-plant herbicides were necessary. Weeds emerging later in the growing season were controlled by application of a contact herbicide.
The results of this USDA research are summarized in the USDA Farmers' Bulletin Sustainable Production of Fresh-Market Tomatoes with Organic Mulches. For further information or technical assistance, contact:
Dr. Aref A. Abdul-Baki
USDA-ARS Sustainable Agricultural Systems Laboratory
BLDG 010A, Room 213, BARC-West
Beltsville, MD 20705
301-504-5057
FAX: 301-504-6491
E-mail:
Resource:
Sustainable Production of Fresh-Market Tomatoes with Organic Mulches. 1997. By Aref Abdul-Baki and John R. Teasdale. USDA Farmers' Bulletin No. 2279. 23 p.
Farmer Profiles: Doug Walton and Alex Hitt
In Oklahoma, Doug Walton manages a 1-acre organic market garden and sells fresh produce at the Muskogee Farmers' Market. Walton plants cover crops on top of raised production beds, and uses a string weeder with a plastic head attachment to cut down the cover crops and create a no-till mulch. Hand raking and speading of mulches after weed eating is a necessary chore, but this type of intensive hand labor is a common feature of biointensive market farming and it fits his scale of production. In conjunction with USDA-ARS and OklahomaStateUniversity, Walton is also conducting research on summer cover crops and biculture cover crop mixes, funded through the SARE farmer research grant program.
In North Carolina, Alex Hitt is a well-known organic market gardener who sells fresh produce at the Raleigh Farmers' Market. Following the mow-kill guidelines established by USDA, Hitt uses a flail mower to mechanically kill a rye-vetch cover crop mix and create a no-till mulch for tomatoes. Weeds that emerge through the mulch are simply hand weeded. The mulch does a good job of weed suppression, and the tomatoes grow a thick canopy of leaves that helps shade out weeds, so hand weeding is not too cumbersome.
More on the Rolling Technique: Mechanical Kill of Cover Crop
Prior to the advent of the mechanical roller crimper, USDA researchers in Mississippi set disc coulters at an angle to mechanically kill hairy vetch, referring to this technique as rolling. They learned that the most effective time to do this was in the seed formation growth phase for the legume (mid- to late-April in Mississippi), or when stem lengths along the ground exceeded 15 inches (7). More recently, they have also modified an implement used in Mississippi Delta cotton production known as a "do all." To obtain articles and updates, contact:
Dr. Seth Dabney
USDA-ARS National Sedimentation Laboratory
P.O. Box 1157
Oxford, MS 38655
662-232-2975
Fax: 662-232-2915
E-mail:
Resource:
Managing Cover Crops and Green Manures
Seth Dabney, USDA-ARS National Sedimentation Laboratory