No-Till Vegetable Production Non-Chemical Methods of Cover Crop Suppression and Weed Control

No-Till Vegetable Production: Non-Chemical Methods of Cover Crop Suppressionand Weed Control by Steve Diver Appropriate Technology Transfer for Rural Areas — ATTRA Fayetteville, Arkansa

No-Till Vegetable Production: Non-Chemical Methods of Cover Crop Suppression

and Weed Control

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 Systemsfor 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, 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

mulch-conservation tillage For example, technical specifications for mulch-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

Conservation agriculture refers to several practices which permit the management of the soil for agrarian uses, altering its composition, structure and natural biodiversity

as little as possible and defending it from degradation processes (e.g soil erosion and compaction) Direct sowing (non-tillage), reduced tillage (minimum tillage), non- or surface-incorporation of crop residues and establishment of cover crops in perennial woody crops (of spontaneous vegetation or by sowing appropriate species)

or in between successive annual crops, are some of the techniques which constitute conservation agriculture Generally, conservation agriculture includes any practice which reduces, changes or eliminates soil tillage and avoids residue burning to

maintain enough surface residue throughout the year

Source:

Conservation Agriculture: For a Better Environment

European Conservation Agriculture Federation

http://www.ecaf.org/English/englis.htm

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, Waipunafor 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

Focus on Cover Crops

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

http://www.sare.org/handbook/mccp2/index.htm

Overview of Cover Crops and Green Manures

ATTRA

http://attra.ncat.org/attra-pub/covercrop.html

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 Ohio State University,

designed to slice through the soil and sever cover crop roots underground It consists of aV-plow sweep blade mounted on a toolbar, followed by a rolling harrow to crimp and rollthe 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 onthe 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 Ohio State, isnow located at North Carolina State University Dr Creamer continues to work on tillagesystems 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

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 peracre, 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

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

http://www.ars.usda.gov/is/np/tomatoes.html

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 Oklahoma State University, 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:

Resource:

Managing Cover Crops and Green Manures

Seth Dabney, USDA-ARS National Sedimentation Laboratory

http://www.sedlab.olemiss.edu/uep_unit/projects/cover_crops/index.html

Researchers with USDA and Virginia Polytechnic Institute demonstrated the feasibility

of planting vegetables (broccoli and cabbage) into a soybean cover crop that is cut or

“rolled” down to provide a no-till mulch ‘Devine’, a forage soybean variety, was bred as

a hay crop and therefore produces lush growth More biomass is desirable because it translates to higher nitrogen fixation and a thicker mulch The thick thatch that results helps keep down weeds, holds moisture, protects the soil from fall rains, and enriches the soil with organic matter In addition, as the soybean mulch decays, it releases nitrogen which feeds the vegetable crop

In research trials, yields from no-till plots were comparable to those from conventional plots where vegetables were planted into bare soil To ensure uniform plant stand

establishment, the researchers started with vegetable transplants and set them out with a multi-row no-till transplanter

Soybeans take about 60 days to grow and start flowering, a period which coincides with optimum plowdown as a cover crop Thus, spring-planted (April 15-May 15) “hay beans” would be available as a summer mulch (June 15-July 15) Summer-planted (July 1-August 1) “hay beans” would be available as a fall mulch (September 1-October 1)

More recently, Dr Aref A Abdul-Baki has grown fond of “Iron and Clay” cowpeas as a summer cover crop In the 1997 growing season, which featured one of the worst

droughts Maryland experienced in years, ‘Iron and Clay’ cowpeas withstood drouthy conditions better than ‘Devine’ soybeans

For further information and details, contact:

Dr Aref A Abdul-Baki

USDA-ARS Sustainable Agricultural Systems Laboratory

BLDG 010A, Room 213, BARC-West

The result is a field with narrow strips of exposed soil that vegetables are planted into, and broader strips of cover crop vegetation that remain as a living mulch between the rows Depending on the specific cropping system, the cover crops in the alleyway are eventually killed (usually with herbicides) to avoid competition, or left undisturbed as a living mulch However, living mulch left in the field may require additional vegetative suppression to avoid competition with the main vegetable crop For example, partial tillage has been shown to work well with white clover

Dr Sharad Phatak, a researcher at the University of Georgia, has pioneered innovative methods of strip-tillage vegetable production in association with cover crops in the southeastern United States To obtain articles and updates, contact:

Dr Greg Hoyt

North Carolina State University

Mountain Horticultural Crops Research & Extension Center

Northwest The strip tillage reports on their web page at Oregon State provides details oncover cropping systems, equipment, and related cultural practices This is an excellent website on strip-tillage vegetable production, including field trials with cover crops See:

Strip Tillage Vegetable Production Systems

http://ifs.orst.edu/strptil.html

High Residue Cultivators

The aim of conservation tillage is to maintain sufficient crop residues to cover at least 30% of the soil surface after planting Since the action of post-plant cultivation

incorporates crop residues and reduces surface protection, herbicides are preferred over mechanical cultivation to obtain adequate weed control In the instance where

mechanical cultivation is still desirable as a form of weed control—such as in reduced or zero-use herbicide cropping systems, or under dry conditions when herbicides are not effective—high-residue cultivators are an option

Conservation tillage cultivators look much like conventional cultivators However, instead of three to five shovels per row, high-residue cultivators usually bear a single shank that supports a wide sweep or horizontal disk A coulter is mounted in front of the shank to cut through residue Whereas regular cultivators cut weeds and “throw” soil andcrop residues, a conservation tillage sweep is designed to cut weeds and allow soil and residues to “float” over the sweep as it passes through the soil

In vegetable production, high-residue cultivation may be appropriate for direct-seeded row crops like sweet corn, green beans, and potatoes

Resource:

Cultivators for No-till and Ridge-till

Iowa State University

http://www.ae.iastate.edu/tillage/AE-3055.txt

Thermal Vegetation Control: Flame, Steam, Infra-Red

Several sources have reported that flamers—especially hooded flamers— are used in Europe as a method to kill and suppress cover crops prior to planting

Since there is little experience with flamers in the U.S as a means of cover crop

suppression, it should be viewed as a potentially useful but experimental method Ron Jones of Thermal Weed Control Systems, Inc in Neillsville, WI, a manufacturer of hooded flamers, reports they are being used by vegetable growers in the U.S to fry lettuce residues between sequential crops, thereby reducing incidence of disease

Flamers are a common non-chemical weed control technique in organic vegetable

production, mainly as a stale seedbed technique to control the first flush of weeds in the spring (i.e., beds are flamed prior to planting the vegetables) Flaming can also be used

as a post-emergence treatment in certain vegetable crops like sweet corn, potatoes, and onions

Thus, while flaming equipment is available and experience supports its use to control and post-emerge weeds, trials are necessary to determine how well a flaming treatment will, for example, suppress cover crops in a vegetative stage of growth It is quite

pre-possible that flaming will suppress certain cover crops and not others

Flaming the dried residues of a killed winter cover crop mulch may result in a fire

hazard Thus, flaming is suggested as a means to kill cover crops, but not as a method forpost-emergent weed control in association with no-till organic mulches

Steam is an old form of thermal weed control that is regaining popularity after several decades of little use Steam is very effective as a non-chemical means of vegetation control, and can be used to kill live stands of cover crops and turfgrass sod Aqua Heat and Waipuna are the two main companies supplying steam weeding equipment, and both offer patented technology that improves steam's performance

However, steam equipment is expensive and bulky and has not been developed with row crop farming mind The Aqua Heat equipment is geared to large-scale orchards and vineyards, and the Waipuna equipment is geared to municipal and institutional use in non-cropland areas such as pavements and fence rows Innovative farmers may find a way to devise a portable steamer Such a device seems an ideal match to no-till organic vegetable production, and could be used as a knock-down treatment to create a no-till mulch or as a spot-spray treatment for post-emergent weeds

Infra-red weeders have been used in Europe for several years, and in 2001 a North American distributor started carrying this equipment An infra-red weeder consists of a propane flamer that heats a ceramic tile; these are mounted on a frame with wheels, similar to a wheel hoe; radiant heat from the ceramic tile, rather than flame itself, sears the weeds Thus, an infra-red weeder could be an ideal tool to enable post-emergent weed control in organic no-till Field trials are needed Two resources on thermal weed control are provided below

Flame Weeding Resource List: Literature, Web Links, Videos, Equipment and Supplies

ATTRA

http://ncatark.uark.edu/~steved/flame-weeding-RL.doc

FOREVERGREEN™ Chemical Free Weed Control

http://www.chemfree-weedcontrol.com/

Matching Cover Crops to No-Till Vegetable Production

Timing is a critical factor in vegetable production Vegetable farmers like to plant as soon as possible in the Spring with an aim to harvest early and sell into market windows that yield a premium price In addition, farmers that live in hot, dry regions plant early totake advantage of spring rains and cooler temperatures

On the other hand, no-till production relies on cover crop maturation to occur prior to mechanical disturbance by mowing or roll chopping Therefore, matching a cover crop

to the growing cycle of the vegetable crop is very important For example, in the South (Arkansas-Oklahoma region where the author lives) the flowering cycle of crimsonclover corresponds fairly reliably to the average frost-free date, which is April 15th Thus, crimson clover would be a good selection for warm-season transplant crops like tomatoes, peppers, and summer squash, or it could be direct-seeded to sweet corn, green beans, or watermelon On the other hand, hairy vetch blooms 30 days later than crimson clover Thus, vetch is better suited to hot-loving crops like eggplant and okra, as well as second-round plantings of tomatoes and peppers Bigflower vetch is a desirable species because it flowers about two weeks earlier than hairy vetch

Winter Annual Cover Crops + Warm-Season Vegetables:

*Crimson clover, Hairy vetch, Winter wheat, Rye

*Establish cover crops in September-October

*Rapid cover crop growth in April-May, flowering begins

*Mow or crimp cover crops in April-May

*Plant tomatoes, peppers, summer squash, green beans into no-till mulch in

April-May

Summer Annual Cover Crops + Cool-Season Vegetables:

*Forage soybeans, Forage cowpeas, millet, buckwheat

*Establish cover crops in June-July

*Rapid cover crop growth in August-September, flowering begins

*Mow or crimp cover crops in August-September

*Plant broccoli, cauliflower, cabbage into no-till mulch in August,

September

General Observations about Vetch as a No-Till Mulch

The United States is a large country with lots of different growing climates and soil types These differences in climatic growing conditions affect the way cover crops perform in different regions In light of these differences, it may be helpful to mention a few universal points about hairy vetch as a no-till mulch

First, to obtain a no-till legume mulch for spring-planted vegetables, vetch is treated as a winter annual legume, meaning it is planted in the fall and matures in the following