ATTRA is the national sustainable agriculture information service operated by the National Centerfor Appropriate Technology, through a grant from the Rural Business-Cooperative Service, U.S.Department of Agriculture. These organizations do not recommend or endorse products, companies,or individuals. NCAT has offices in Fayetteville, Arkansas (P.O. Box 3657, Fayetteville, AR 72702),Butte, Montana, and Davis, California.

By Preston Sullivan, NCAT Agriculture SpecialistIllustrations by Missy GocioUpdated August 2003

AGRONOMY SYSTEMS GUIDE

INTERCROPPING PRINCIPLES

AND PRODUCTION PRACTICES

PrinciplesPrinciplesPrinciplesPrinciplesPrinciples

Sustainable agriculture seeks, at least in prin-ciple, to use nature as the model for designingagricultural systems. Since nature consistentlyintegrates her plants and animals into a diverselandscape, a major tenet of sustainable agricul-ture is to create and maintain diversity. Natureis also efficient. There are no waste products innature. Outputs from one organism become in-puts for another. One organism dies and becomesfood for other organisms. Since we are model-ing nature, let us first look at some of the prin-ciples by which nature functions. By understand-ing these principles we can use them to reduce

Abstract: Intercropping offers farmers the opportunity to engage nature’s principle of diversity on their farms.Spatial arrangements of plants, planting rates, and maturity dates must be considered when planning intercrops.Intercrops can be more productive than growing pure stands. Many different intercrop systems are discussed,including mixed intercropping, strip cropping, and traditional intercropping arrangements. Pest managementbenefits can also be realized from intercropping due to increased diversity. Harvesting options for intercropsinclude hand harvest, machine harvest for on-farm feed, and animal harvest of the standing crop.

costs and increase profitability, while at the sametime sustaining our land resource base.

····· Diversity is nature’s designDiversity is nature’s designDiversity is nature’s designDiversity is nature’s designDiversity is nature’s design

When early humans replaced hunting andgathering of food with domestication of cropsand animals, the landscape changed accordingly.By producing a limited selection of crop plantsand animals, humankind has greatly reduced thelevel of biological diversity over much of theearth. Annual crop monocultures represent a

Table of ContentsPrinciples ............................................ 1

Pursuing Diversity on the Farm ........... 2

Intercropping Concepts ....................... 3

Intercrop Productivity .......................... 4

Managing Intercrops ........................... 5

Examples of Intercrop Systems .......... 6

Escalating Diversity and Stability to aHigher Level ........................................ 7

Escalating Diversity and Stability to anEven Higher Level ............................. 10

Intercropping for Disease Control ..... 11

Adapting Intercropping to Your Farm 11

References ....................................... 12

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 2

classic example. In response to this biologicalsimplification, nature has struggled to restore di-versity to these landscapes—that is her tendency.Our “war” with nature over the tendency to di-versity is what we call “weed control” and “pestmanagement.” Of course we could hardly pro-duce any crops if we simply allowed our fieldsto return to natural vegetation, but we can real-ize some of the benefits of diversity by plantingmixtures of different crops.

····· Cooperation is more apparentCooperation is more apparentCooperation is more apparentCooperation is more apparentCooperation is more apparent

than competitionthan competitionthan competitionthan competitionthan competition

There is far more cooperation in nature thancompetition. Cooperation is typified by mutu-ally beneficial relationships that occur betweenspecies within communities. In The RedesignedForest, ecologist Chris Maser offers a glimpse ofthe cooperation inherent in a northern temperateforest when he describes a relationship that ex-ists among squirrels, fungi, and trees (1). Thesquirrels feed on the fungus, then assist in itsreproduction by dropping fecal pellets contain-ing viable fungal spores onto the forest floor.There new fungal colonies establish. Tree feederroots search out the fungi and form a symbioticassociation that enables the tree roots to increasetheir nutrient uptake. The fungi, in turn, derivefood from the tree roots. Each benefits from theother’s presence or actions.

If we view competition as the driving forcein nature, we fail to see the complex relation-ships and feel compelled to take actions that mayhave unforeseen impacts. The rancher who viewscoyotes as competitors (for calves and lambs) andkills them out may later find the predator helpedkeep rodent populations in check. With thepredator gone, rodent numbers explode andcause more problems than ever before. The sameis true with many insect pests of crops. Whenthe only food for insects is crops, that is whatthey will eat. With no predator or parasite habi-tat present in a pure stand of crop, the pest in-sect could not possibly have it better. If we canshift our view of nature from a theme of compe-tition to one of collaboration, we can act in waysthat yield fewer negative consequences (2).

····· Stability tends to increase withStability tends to increase withStability tends to increase withStability tends to increase withStability tends to increase with

increasing diversityincreasing diversityincreasing diversityincreasing diversityincreasing diversity

If left undisturbed and unplanted, an aban-doned crop field will first be colonized by just afew species of plants, insects, bacteria, and fungi.After several years, a complex community made

up of many wild species develops. Once a wildplant and animal community has reached a highlevel of diversity, it remains stable for many years.

When wild communities are in the earlystages of development, or when they have lostdiversity due to natural catastrophe or humanactions, they are prone to major fluctuations, bothin types of species present and in their numbers.Disease outbreaks in plants and animals occurmore frequently—as do outbreaks of weed, in-sect, bird, or rodent pests. One good example isthe grasshopper plagues that follow regionalweather shifts. Another is the shift in weed spe-cies dominance following a soil disturbance.

The more complex and diverse communitiesbecome, the fewer the fluctuations in numbersof a given species, and the more stable commu-nities tend to be. As the number of species in-creases, so does the web of interdependencies.In both higher and lower rainfall years, there arefewer increases in any one species and fewer fluc-tuations in the community as a whole (2).

Pursuing Diversity on thePursuing Diversity on thePursuing Diversity on thePursuing Diversity on thePursuing Diversity on the

FarmFarmFarmFarmFarm

So, then, how can we begin to model our ag-ricultural pursuits after some of these naturalprinciples? Can we look for patterns in natureand imitate them? Some pioneering farmers havebeen able to utilize nature’s principle of diver-sity to their advantage. Results of their effortsinclude lower cost of production and higher prof-its. Among the practices that promote diversityand stability are:

Enterprise diversificationEnterprise diversificationEnterprise diversificationEnterprise diversificationEnterprise diversification—Risk reductionthrough stability of income and yield are two ofthe reasons people diversify their crop and live-stock systems. Increasing diversity on-farm alsoreduces costs of pest control and fertilizer, be-cause these costs can be spread out over severalcrop or animal enterprises.

CrCrCrCrCrop Rotation op Rotation op Rotation op Rotation op Rotation — Moving from simple mo-noculture to a higher level of diversity begins withviable crop rotations, which break weed and pestlife cycles and provide complementary fertiliza-tion to crops in sequence with each other.

FarmscapingFarmscapingFarmscapingFarmscapingFarmscaping—Diversity can be increased byproviding more habitat for beneficial organisms,habitats such as borders, windbreaks, and spe-cial plantings for natural enemies of pests. Re-quest the ATTRA publication Farmscaping to En-

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 3

hance Biological Control for more information onspecial plantings for beneficial insects.

InterInterInterInterIntercrcrcrcrcroppingoppingoppingoppingopping—Intercropping is the grow-ing of two or more crops in proximity to pro-mote interaction between them. Much of thispublication focuses on the principles and strate-gies of intercropping field crops. A relatedATTRA publication, Companion Planting, providesmore information on intercropping of vegetablecrops.

IntegrationIntegrationIntegrationIntegrationIntegration—On-farm diversity can be car-ried to an even higher level by integrating ani-mals with intercropping. With each increase inthe level of diversity comes an increase in stabil-ity. This publication focuses on intercropping andprovides a section on integrating livestock withcrops.

Intercropping ConceptsIntercropping ConceptsIntercropping ConceptsIntercropping ConceptsIntercropping Concepts

Most grain-crop mixtures with similar ripen-ing times cannot be machine-harvested to pro-duce a marketable commodity since few buyerspurchase mixed grains. Because of limited har-vest options with that type of intercropping, farm-ers are left with the options of hand harvesting,grazing crops in the field with animals, or har-vesting the mixture for on-farm animal feed.However, some intercropping schemes allow forstaggered harvest dates that keep crop speciesseparated. One example would be harvestingwheat that has been interplanted with soybeans,which are harvested later in the season. Anotherexample is planting harvestable strips, also knownas strip cropping.

When two or more crops are growing to-gether, each must have adequate space to maxi-mize cooperation and minimize competition be-tween them. To accom-plish this, four thingsneed to be considered:

1) spatial arrange-ment,

2) plant density,

3) maturity datesof the cropsbeing grown,and

4) plant architec-ture.

SPATIAL ARRANGEMENT

There are at least four basic spatial arrange-ments used in intercropping. Most practical sys-tems are variations of these (3).

· Row intercropping—growing two or morecrops at the same time with at least one cropplanted in rows.

· Strip intercropping—growing two or morecrops together in strips wide enough to per-mit separate crop production using machinesbut close enough for the crops to interact.

· Mixed intercropping—growing two or morecrops together in no distinct row arrange-ment.

· Relay intercropping—planting a second cropinto a standing crop at a time when the stand-ing crop is at its reproductive stage but be-fore harvesting.

PLANT DENSITY

To optimize plant density, the seeding rateof each crop in the mixture is adjusted below itsfull rate. If full rates of each crop were planted,neither would yield well because of intense over-crowding. By reducing the seeding rates of each,the crops have a chance to yield well within themixture. The challenge comes in knowing howmuch to reduce the seeding rates. For example,if you are planning to grow corn and cowpeasand you want mostly peas and only a little corn,it would be easy to achieve this. The corn-seed-ing rate would be drastically cut (by 80% or more)and the pea rate would be near normal. The fieldshould produce near top yields of peas even fromthe lower planting rate and offer the advantageof corn plants for the pea vines to run on. If you

wanted equal yields fromboth peas and corn, then theseeding rates would be ad-justed to produce thoseequal yields.

MATURITY DATES

Planting intercrops thatfeature staggered maturitydates or development peri-ods takes advantage ofvariations in peak resourcedemands for nutrients, wa-ter, and sunlight. Havingstrip cropping

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 4

one crop mature before its companion crop less-ens the competition between the two crops. Anaggressive climbing bean may pull down corn orsorghum growing with it and lower the grainyield. Timing the planting of the aggressive beanmay fix the problem if the corn can be harvestedbefore the bean begins to climb. A common prac-tice in the old southern U.S. cotton culture wasto plant velvet beans or cowpeas into standingcorn at last corn cultivation. The corn was plantedon wide 40-inch rows at a low plant population,allowing enough sunlight to reach the peas orbeans. The corn was close enough to maturitythat the young legumes did not compete. Whenthe corn was mature, the beans or peas had cornstalks to climb on. The end result was corn andbeans that would be hand harvested together inthe fall. Following corn and pea harvest, cattleand hogs would be turned into the field to con-sume the crop fodder.

Selecting crops or varieties with differentmaturity dates can also assist staggered harvest-ing and separation of grain commodities. In thetraditional sorghum/pigeonpea intercrop, com-mon in India, the sorghum dominates the earlystages of growth and matures in about fourmonths. Following harvest of the sorghum, thepigeonpea flowers and ripens. The slow-grow-ing pigeonpea has virtually no effect on the sor-ghum yield (4).

PLANT ARCHITECTURE

Plant architecture is a commonly used strate-gy to allow one member of the mix to capturesunlight that would not otherwise be available tothe others. Widely spaced corn plants growingabove an understory of beans and pumpkins is aclassic example.

Intercrop ProductivityIntercrop ProductivityIntercrop ProductivityIntercrop ProductivityIntercrop Productivity

One of the most important reasons to growtwo or more crops together is the increase in pro-ductivity per unit of land. Researchers have de-signed a method for assessing intercrop perfor-mance as compared to pure stand yields. In re-search trials, they grow mixtures and pure standsin separate plots. Yields from the pure stands,and from each separate crop from within the mix-ture, are measured.

From these yields, an assessment of the landrequirements per unit of yield can be determined.This information tells them the yield advantagethe intercrop has over the pure stand, if any. They

then know how much additional yield is requiredin the pure stand to equal the amount of yieldachieved in the intercrop. The calculated figureis called the Land Equivalency Ratio (LER). Tocalculate an LER, the intercrop yields are dividedby the pure stand yields for each component cropin the intercrop. Then, these two figures are addedtogether. Here’s the equation for a corn/pea in-tercrop where the yields from pure corn, purepeas, and the yields from both corn and peasgrowing together in an intercrop are measured.

(intercrop corn / pure corn) +(intercrop pea / pure pea) = LER

When an LER measures 1.0, it tells us thatthe amount of land required for peas and corngrown together is the same as that for peas andcorn grown in pure stand (i.e., there was no ad-vantage to intercropping over pure stands). LERsabove 1.0 show an advantage to intercropping,while numbers below 1.0 show a disadvantageto intercropping. For example, an LER of 1.25tells us that the yield produced in the total inter-crop would have required 25% more land ifplanted in pure stands. If the LER was 0.75, weknow the intercrop yield was only 75% of that ofthe same amount of land that grew pure stands.

In a South Carolina study, researchers plantedintercrops of southern peas and sweet corn atthree different corn plant densities (5). Theplantings were on raised beds with flat and widecrowns on six-foot centers. In the center of eachbed was a corn row, with two rows of peasplanted 18 inches to either side of the corn row(see Figure 1). The low corn-seeding rate was6,700 plants per acre, medium corn was 9,500per acre, and high was 11,900 plants per acre.Peas were established at a rate of 31,800 plantsper acre in all intercrop plots. In the pure peastand, each bed had two rows of peas spaced 24inches apart. Yields of the intercrops and purestands are shown in Table 1.

In this trial there was a yield advantage fromintercropping over growing the two crops in purestands. Pea yields suffered from the increasedcompetition in the higher densities of corn. Somepractical on-farm guidelines can be drawn toguide seeding-rate choices for a two-crop inter-crop. To test seeding rates, experiment with threesmall plantings of two crops at the following per-centages of their full seeding rates: 1/3 + 2/3,

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 5

1/2 + 1/2, and 2/3 + 1/3. From there, makeadjustments for future plantings based on theresults and your expectations.

Managing IntercropsManaging IntercropsManaging IntercropsManaging IntercropsManaging Intercrops

Many combinations of crops have been grownor experimented with as mixed or relay inter-crops. Some of these include sunflowers grownwith black lentils, wheat with flax, and canolawith flax. Other combinations include cucum-bers, beans, celery, and chives in China; uplandrice, corn, and cassava in Indonesia; and in vari-ous parts of the tropics corn and cassava, cornand peanuts, sorghum and millet, and sorghumand pigeonpeas.

Frequently these cropping combinations in-volve a short and a tall crop both planted at thesame time. In many cases the tall crop is har-vested first. For example, corn grown with ashorter plant would be harvested first, then pea-nut or sweet potato would be harvested later.Another pattern would be planting two tall cropswith different growth rates. In relay intercrops,different planting dates are used so that one crop

might mature sooner. Corn or sorghum, requir-ing three months to mature, can be grown withpigeon pea, requiring 10 months to maturation.

John Bowen and Bernard Kratky, researchersand instructors at the University of Hawaii, tellus that there are five distinct aspects to success-ful multiple cropping. These are:

1) detailed planning,

2) timely planting of each crop,

3) adequate fertilization at the optimaltimes,

4) effective weed and pest control, and

5) efficient harvesting (6).

Before any fieldwork is begun, adequate plan-ning should be done. Planning covers selectionof crop species and appropriate cultivars, wateravailability, plant populations and spacing, laborrequirements throughout the season, tillage re-quirements, and predicted profitability of the in-tercrop. These and other parameters need to beevaluated before spending money on inputs.

With any crop, seed germination and seed-ling establishment are the most critical phases ofthe entire season. A good seedbed is needed toget a good stand. Delayed planting may reduceyield, since crop development may not coincidewith the optimal growth periods.

Planning fertilization for intercrops can bechallenging, as the full needs of both crops mustbe met. Generally, there is little information avail-able on how to go about this. One possibilitywould be to ask for soil test results for each cropseparately, then formulate a recommendation thatwill cover the needs of both crops to be grown.Such recommendations are generally 10% to 30%higher than rates for individual crops.

As with any crop, also accounting for residualor carryover fertility from past crops saves money.Carryover fertility from intercrops may well belower than that of pure stands because of thetwo crops having different root types and feed-ing habits.

Weed and pest controls in intercrops willlikely be different from those in pure stands.Some disease incidence, such as soybean or mungbean rusts, may increase when aggravated withhigh corn populations and overfertilization. Anydisease or pest that prospers in shady conditionscould increase under a taller crop such as corn orsunflowers. In many cases, insect pest popula-tions are lower when two or more crops are

Corn Peas(pounds/ (pounds/

Seed Rates acre) acre) LERFull corn 5600 *** ***

Full peas *** 1200 ***

Low corn 4200 800 1.41

Medium corn 4600 800 1.48

High corn 5000 500 1.30

Table 1. Yields of sweet corn andsouthern peas from intercrops (5)_______________________________________

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Figure 1. Sweetcorn and southern peaplanting pattern

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 6

grown together. More on pest management willbe found later in this publication.

Harvesting of mixed intercrops has been amajor limitation to their adoption in mechanizedfarming. As mentioned earlier, if the crops can-not be harvested by animals, or all together asfeed, you’re left with hand harvesting. Somecrops such as flax and wheat have been harvestedtogether and mechanically separated. Any othermechanized harvest efforts must get one cropwithout damaging the other. One example wouldbe harvesting wheat over the top of a young standof soybeans growing beneath the grain heads. Allintercropping strategies— especially mixed inter-cropping—require advanced planning and keenmanagement. Success will likely be the rewardfor such efforts.

Examples of IntercropExamples of IntercropExamples of IntercropExamples of IntercropExamples of Intercrop

SystemsSystemsSystemsSystemsSystems

TRADITIONAL CORN-BEAN-SQUASH

MIXED INTERCROPS

Farmers throughout Central America tradi-tionally grow an intercrop of corn, beans, andsquash. Grown together, these three crops opti-mize available resources. The corn towers highover the other two crops, and the beans climb upthe corn stalks. The squash plants sprawl alongthe ground, capturing light that filters downthrough the canopy and shading the ground. Theshading discourages weeds from growing.

This mixture was compared to the individualcrops grown separately in a study near Tabasco,Mexico (7). In the study, corn yields were con-siderably higher in the mixture than in a purestand planted at optimum densities. Bean andsquash yields sufferedconsiderable yield reduc-tions when grown in mix-ture. In this example ifcorn were the most impor-tant crop, it was beneficialto grow it in a mixturewith squash and beans.The beans and squashwere just a bonus. TheLER for the whole mixturewas considerably higher(1.6) than any of the purestands. See Table 2 fordetails.

CORN AND SOYBEAN MIXED INTERCROPS

Canadian researchers (8) have worked withseveral corn-soybean intercrop seeding rates todetermine their economic advantages as silage.Pure stands of corn and soybeans were grownfor comparison at 24,000 corn seed per acre and200,000 soybean seed per acre. Results showedthat intercrops were more cost effective than purestands over both years the study was conducted.The study featured five experimental intercropseeding rates with two planting arrangements(alternate and within the row). The researchersconcluded that a planting rate of 16,000 corn seedper acre (67% of the full corn rate) with 135,000soybean seed per acre (67% of the full bean rate)planted within the same rows along with 53 lbs.of N/acre gave the highest economic returns.(Note: the planter was set to drop 151,000 seedsper acre.) This mixture gave an LER of 1.14 overpure stand yields. The crude protein level of theintercrop silage was considerably higher than thatof pure corn silage. A slightly higher yield wasachieved from full stands of both corn and beansin alternate rows (LER=1.23), but the cost of pro-duction was higher, thus offsetting the improvedyields.

CORN AND SORGHUM MIXED INTERCROPS

Frank Cawrse, Jr., of Lebanon, Oregon, inter-crops forage sorghum into his silage corn. Hefirst plants the corn at 28,000 seed per acre, thengoes back over the field with a drill with enoughdrop tubes closed off to plant 8 pounds of sor-ghum on 32-inch rows in between the corn. Healso plants two different maturities of corn, a 95-day and a 75-day, to even out the silage mois-ture content. He harvests a mix of corn in harddent and soft dent, and sorghum in the milk stage

(8).

STRIP CROPPING

CORN/SOYBEANS/SMALL GRAINS

South Dakotafarmer Tod Intermillplants alternatingstrips of corn, soy-beans, and springwheat on his farm (9).The strips are six rowswide in a ridge-tillsystem. All the cropplantings are adapted

Pure Stand Intercrop(pounds/ (pounds/

Crop acre) acre)

Corn 1096 1533

Beans 544 98

Squash 383 71

Table 2. Yields of corn, beans andsquash grown alone or in a mixture(7)_______________________________________

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//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 7

to existing equipment widths. Regular herbicidetreatments can be applied using a ground sprayerof strip width. Even the wheat is drilled on ridges,using a drill with individual depth gauges on eachopener. Intermill orients his rows east and westto minimize the shading effects of taller cropslike corn. The crops are planted in a wheat–corn–soybean pattern, with soybeans on the north sideof the corn (Figure 2). This arrangement reducesthe effect of corn shading often associated with astraight corn-soybean pattern, since the wheat ismature before the corn has a chance to shade it.Corn gains the greatest benefit from the addi-tional sunlight interception on the outside rowsof the corn strip.

Iowa farmer Tom Frantzen strip-crops oats,corn, and soybeans on ridge-till rows. He viewshis strips as a crop rotation in one field. His rowsare oriented generally east and west on the con-tour. His 1989 strip-crop corn yields were 166bushels per acre, compared to 130 for his farmaverage. Stripped soybean yields were two bush-els lower than farm average. His oat yields were109 bushels stripped and 100-bushel farm aver-age. Tom was not surprised at the increase incorn yields. The outer strip rows captured moresunlight. His average corn border row yielded198 bushels per acre next to the soybeans and177 bushels next to oats. The soybean yields were37 bushels, even with the increased shading onthe border rows. This loss was made up in themiddle rows with yields of 44 bushels per acre.Oats showed a 107-bushel yield on the soybeanside, a 103-bushel yield on the corn side, and 99bushels in the middle. Tom says the strip inter-cropping is no more labor intensive thanmonocrop fields. His profits were $76 per acrefor the stripped fields and $55 for the same cropsgrown in monoculture. (11).

Rick Cruse, an Iowa State University agrono-mist, has observed several characteristics that

narrow strips (12 to 30 feet wide) offer. The stripsaccommodate the pest management and soilbuilding advantages of rotations and the yieldboost of border rows. With proper managementthe border effect can pay off; managed improp-erly, it can cost yield. With oat and corn strips,the early-maturing oats are nearly mature beforecorn can pose much of a shade and competitionproblem. The corn can also provide wind pro-tection for the oats. When the oats are harvested,more sunlight is available to the corn. In times oflow moisture, oats may rob the corn border rowsof water. In his field trials, Cruse found a 5%increase in oat yields on their borders, while cornrealized a 12 to 15% increase.

Soybean yields dropped by 10% on their bor-der rows, but the yields in the soybean middlerows were higher than they would be in a solidfield, possibly representing a windbreak effect(10).

Some have experimented with a shorter cornvariety in the border row to minimize shading.One farmer tried planting six rows of corn anddoubling his soybean strips to 12 rows to elimi-nate the impact of corn shading on the beans.This same farmer found that corn strips widerthan eight rows did not provide adequate results.Using a 12-row planter, it’s easy to establish the6-row strips by filling the middle six hoppers withcorn and the outer three hoppers with beans.Some farmers plant higher corn populations andadd higher nitrogen rates in the border rows totake advantage of the extra sunlight exposure.Most farmers agree that strip cropping corn, soy-beans, and oats works best with ridge-till or no-till. When the field is tilled, it’s difficult to gaugewhere the rows should go in order to get thestrips even.

Escalating Diversity andEscalating Diversity andEscalating Diversity andEscalating Diversity andEscalating Diversity and

Stability to a HigherStability to a HigherStability to a HigherStability to a HigherStability to a Higher

LevelLevelLevelLevelLevel

Ecologists tell us that stable natural systemsare typically diverse, containing many differenttypes of plants, arthropods, mammals, birds, andmicroorganisms. In stable systems, serious pestoutbreaks are rare, because natural controls existto automatically bring populations back into bal-ance. Planting crop mixtures, which increasefarmscape biodiversity, can make crop ecosystemsmore stable, and thereby reduce pest problems.

Figure 2. Corn, soybeans, and wheat strip-cropped

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 8

There is overwhelming evidence that plantmixtures support lower numbers of pests thando pure stands (11), and there are two schools ofthought on why this occurs. One suggests thathigher natural enemy populations persist in di-verse mixtures due to more continuous foodsources (nectar, pollen, and prey) and favorablehabitat.

The other thought is that pest insects that feedon only one type of plant have greater opportu-nity to feed, move around in, and breed in purecrop stands because their resources are more con-centrated than they would be in a crop mixture(12). Regardless of which reason you accept, thecrops growing together in the mixture comple-ment one another, resulting in lower pest levels.

Intercropping also aids pest control effortsby reducing the ability of the pest insects to rec-ognize their host plants. For example, thrips andwhite flies are attracted to green plants with abrown (soil) background, ignoring areas wherevegetation cover is complete—including mulchedsoil (13). Some intercrops have a spatial arrange-ment that produces the complete vegetation coverthat would be recognized as unfavorable to thripsand whiteflies. Other insects recognize their hostplants by smell. Onions planted with carrotsmask the smell of carrots from carrot flies. Formore information on companion planting for in-sect management, request the ATTRA publica-tions Farmscaping to Enhance Biological Control andCompanion Planting.

Innovative farmers are paving the way withintercrops and realizing pest management ben-efits as a result. Georgia cotton farmers WayneParramore and sons reduced their insecticide andfertilizer use by growing a lu-pine cover crop ahead of theirspring-planted cotton (14).They started experimentingwith lupines on 100 acres in1993, and by 1995 were grow-ing 1,100 acres of lupines.Ground preparation for cottonplanting is begun about 10days prior to planting by till-ing 14-inch wide strips into thelupines. Herbicides are ap-plied to the strips at that time,and row middles remain un-touched. The remaining lu-pines provide a beneficial in-sect habitat and also serve as a

smother crop to curtail weeds and grasses. Thelupines in the row middles can be tilled in withthe cultivator later in the season to release morelegume nitrogen.

In the Parramores’ system, all the nitrogenneeds of the cotton crop are met with cover cropsexcept for 10 units per acre of starter nitrogenand another 15 units applied while spraying her-bicides. Petiole samples taken every week tomonitor plant nitrogen show that cotton grownwith lupines maintains a normal range of tissuenitrogen throughout the growing season. The ni-trogen level in cotton grown solely with fertilizeris very high initially, then subsequently falls backto a lower level. In one comparative year, thecotton grown following lupine produced 96 morepounds of lint, with only 25 units of commercialnitrogen, compared to a field with 125 units ofnitrogen and no lupines. Additionally, the lu-pine field required less spraying for insects—onlytwice compared to five sprays for the commer-cial nitrogen field. This reduction saved 60% oninsecticides, amounting to $35 per acre. The re-duction in need for pesticides is attributed to thelarge population of beneficial insects generatedand sustained in this system. The lupines pro-vide food for aphids and thrips, which attract la-dybugs, big-eyed bugs, and fire ants as preda-tors. When the cotton gets big enough to shadeout the lupines, the beneficial insects move tothe cotton rather than migrating from the field.The Parramores estimate that improved yields,combined with cost reductions, are netting theman additional $184 per acre with the strip tillagelupine system when compared to the conventionalmanagement system.

Alfalfa is one of thebest crops for attractingand retaining beneficialinsects. This characteris-tic can be enhanced fur-ther. Strip-cutting alfalfa(i.e., cutting only half ofthe crop at any one time,in alternating strips) main-tains two growth stages inthe crop; consequently,some beneficial habitat isavailable at all times. Insome cases alfalfa is mixedwith another legume anda grass. Auburn Univer-sity researcher Mike

lupine

©2003www.clipart.com

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 9

Gayler is just starting research projects using al-falfa as an attractant crop for beneficials. Hespeculates that it will work in the Southeast withproper management. Other main-season stripcrops that research suggests will benefit cottoncrop pest management include cowpeas, sor-ghum, corn, and crotalaria (15).

Dr. Sharad Phatak of the University of Geor-gia has been working with cotton growers inGeorgia testing a strip-cropping method usingannual winter cover crops (16). Planting cottoninto strip-killed crimson clover improves soilhealth, cuts tillage costs, and allows him to growcotton with no insecticides and only 30 poundsof nitrogen fertilizer. Working with Phatak,farmer Benny Johnson reportedly saved at least$120/acre on his 16-acre test plot with the cloversystem. There were no insect problems in thetest plot, while beet armyworms and whiteflieswere infesting nearby cotton and requiring 8 to12 sprayings to control. Cotton intercropped withcrimson clover yielded more than three bales oflint per acre compared to 1.2 bales of lint peracre in the rest of the field (16). Boll counts were30 per plant with crimson clover and 11 withoutit. Phatak identified up to 15 different kinds ofbeneficial insects in these strip-planted plots.

Phatak finds that planting crimson clover seedat 15 pounds per acre in the fall produces around60 pounds of nitrogen per acre by spring. Bylate spring, beneficial insects are active in the clo-ver. At that time, 6- to 12-inch planting strips ofclover are killed with Roundup™ herbicide. Fif-teen to 20 days later the strips are lightly tilledand cotton is planted. The clover in the row-middles is left growing to maintain beneficial in-sect habitat. When the clover is past the bloomstage and less desirable for beneficials, they movereadily onto the cotton. Even early-season thrips,which can be a problem following cover crops,are limited or prevented by beneficial insects inthis system. The timing coincides with a periodwhen cotton is most vulnerable to insect pests.Following cotton defoliation, the beneficials hi-bernate in adjacent non-crop areas.

Phatak points out that switching to a whole-farm focus while reducing off-farm inputs is notsimple. It requires planning, management, andseveral years to implement on a large scale. It isjust as important to increase and maintain organicmatter, which stimulates beneficial soil microor-ganisms. Eventually a “living soil” will keepharmful nematodes and soilborne fungi undercontrol (16). For more information on manage-

ment of soil-borne diseases, request the ATTRApublication Sustainable Management of SoilbornePlant Diseases.

Texas dryland farmer Ron Gobel intercrops8-row strips of sesame and cotton for insect con-trol benefits. The sesame harbors many benefi-cial insects, including high populations of lace-wings, assassin bugs, and lady beetles. Ron’s1995 crop was planted late due to prolongedspring rains. He did not use a Bt cotton variety.Early frost terminated the crop two weeks ear-lier than normal, yet he still produced 0.8 balesper acre under dryland conditions. His sesameproduced 800 pounds per acre. The 1996 cottonrows were planted where the sesame rows werethe previous year, and sesame planted wherecotton was before.

Since Ron sells his cotton for a premium pricein the organic market, he cannot spray any syn-thetic insecticides. Consequently, he must relyon beneficial insects attracted to his fields by cul-tural practices and a handful of natural insecti-cides.

Following the fall harvest, Ron plants annualrye at a low rate of 20 to 40 pounds per acre. Therye is tilled in prior to crop planting in the spring.Ron believes the rye helps with soil moisture re-tention and weed control. During the 1997 cropyear his fields suffered only minimal boll weevildamage. Ron noticed lots of adult bollwormmoths but no worms. The eggs were eaten orparasitized by the beneficials.

Ron’s fields were scouted as part of a bollweevil eradication program. The scouts wereamazed at the lack of worms and the high num-bers of beneficial insects. The cotton crop wassprayed one time with diatomaceous earth im-pregnated with natural pyrethrum, which wasacceptable under the organic standards. The in-sect scouts noticed a 70% reduction in adult bollweevil population three days after the spray.They were so surprised that they placed cages of20 live weevils in the field to see whether thespray was working. The next day, 45% of thoseweevils were dead. The entomologists specu-lated that the weevils were getting enough of thediatomaceous earth on their leg joints to cut theirexoskeletons, allowing the pyrethrum to killthem.

In a scientific study, Mississippi researchersinterplanted 24 rows of cotton with 4 rows ofsesame to study the intercrop’s effects on tobaccobudworms and bollworms (Heliothis spp.).Throughout the growing season, larvae numbers

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 10

were much higher in the sesame than on the cot-ton until late August, indicating the worm’s pref-erence for sesame. Following a large summerrain at a time when the sesame was reachingmaturity, the Heliothis adults became more at-tracted to the cotton. The researchers noted thatsesame’s attractiveness to Heliothis and sesame’sability to harbor high numbers of beneficial in-sects made it useful in a cotton pest managementprogram (17).

Escalating Diversity andEscalating Diversity andEscalating Diversity andEscalating Diversity andEscalating Diversity and

Stability to an EvenStability to an EvenStability to an EvenStability to an EvenStability to an Even

Higher LevelHigher LevelHigher LevelHigher LevelHigher Level

The diversity created by intercropping can beenhanced even further by integrating livestock(single or mixed species) into the cropping planas harvesters. Allowing animals to harvest feedcrops in the field puts gain on animals at the costof crop production—considerably less than thepurchase price of the grain. If you think about it,feed grains cost a lot less when they’re not runthrough a $150,000 combine or hauled 1000 milesacross the country.

Grazing animals and other livestock can bemanaged on croplands to reduce costs, increaseincome, and increase diversity. There are waysof incorporating animals into cropping withoutthe farmer getting into animal husbandry or own-ership directly. Collaboration with neighbors whoown animals will benefit both croppers and live-stock owners. Grazing or hogging-off of cornresidue is one example where a cost can be turnedinto a profit. The animals replace the $6 per acrestalk mowing cost and produce income in ani-mal gains.

Shasta College provides a unique demonstra-tion of integrating livestock with intercrops.Shasta is a two-year community college locatedin Redding, California, that offers associate de-grees in several branches of agriculture. StanGorden (18) heads the college’s holistic resourcelaboratory, where students get hands-on experi-ence with ranching and farming (19). Stan andhis students have taken intercropping to a highlevel of efficiency. They run hogs, sheep, cattle,and chickens together over 42 small paddocks ofvarious forages and crops growing on 100 acresof college-owned land. One paddock is a pump-kin patch, another a garlic and carrot patch. Someare planted in alfalfa or mixes of grasses and clo-

ver. Not all the pastures have water sources forthe animals, so water is moved on a trailer tankwhen necessary. The animals are moved daily ina planned grazing system during rapid plantgrowth and much more slowly, up to five dayson a paddock, during slow plant growth.

Some of the paddocks are planted with mix-tures of either winter or summer forage or graincrops. An intercrop of cereal grain, fava beans,and Canadian field peas is planted for wintergrain, each crop at 1/3 normal seeding rate. Thegrain mixture is combine-harvested to make en-ergy and protein supplement feed as needed.After harvest, the animals are turned into thepaddock to glean what’s left. For summer feed,a mixture of milo planted on 18-inch rows is in-tercropped with a row of black-eyed peas plantedsix inches to either side of each sorghum row,using a drill with partitions in the seedbox. Themilo provides a trellis for the pea vines to run on(Figure 3). The milo/black-eyed mixture requiresno herbicide. Before peas and milo were growntogether, the milo pure stand would be plaguedwith whiteflies and green bugs. Mixing the twocrops together ended the pest problem. Cow-peas have extrafloral nectaries that attract lots ofbeneficial insects.This could ex-plain the absenceof pest insects inthe mixture. Themilo/pea mix-ture is harvestedby setting thecombine to cut atthe height of themilo heads. Thisyields a milo tobean ratio of2:1—ideal forfeed.

The college animal herd consists of 20 sowsthat farrow on pasture, 35 head of cattle, 50 sheep,and 30 laying hens that all range together. Thehens are with the herd during the day and roostin a nearby eggmobile at night. Gorden selectsbreeds and genetics to fit this system, as opposedto selecting breeds for maximum production andadapting a system to match the animal. The ani-mals benefit one another. The sheep learn to stayclose to the middle of the herd to avoid preda-tors, which are fended off by the hogs. The cattlelearn that the hogs know how to break the pump-

Figure 3. Cowpeas andmilo growing together

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 11

kins open, so they stick close and get some too.The hogs eat the cow and sheep droppings andbenefit from the predigestion. The hens scav-enge wasted seeds from the various crops. Thereare three different kinds of hens, each of whichlays eggs of a different color. The eggs are mar-keted as rainbow eggs, with each dozen contain-ing four white, four blue, and four brown eggs.The chickens also scratch apart cattle dung patssearching for insects, thus destroying cattle para-sites.

Gorden says that developing and maintain-ing this high level of diversity has required cre-ativity, selection criteria, constant monitoring, andre-examining traditional beliefs. By challenginglong-held beliefs, Bill and his students discov-ered that hogs do not need standard farrowingcrates and that sheep and cattle are compatiblegrazers. Animals and crops are selected and culledaccording to their ability to adapt to this com-plex system. Shasta College has one of the larg-est heritage hog herds in the country. The hogshave been fitted with humane nose rings to pre-vent rooting. Also, hog breeds are selected thatdon’t root up the ground nor eat the baby lambswhen they are born. The sows farrow on pas-ture with only a single bale of hay for bedding.Hogs are not vaccinated, nor are needle teeth re-moved or other detailing done. Sows generallywean 12 pigs with no supplemental feed. Theonly purchased input is some nitrogen and phos-phorus fertilizer applied to the pastures. Thepigs are only touched twice; once to castrate andonce to wean. As with the hogs, the cattle andsheep are selected to prosper on grass. Preda-tors are not controlled in any way. Any animalthat gets killed by wandering off is naturally se-lected out of the herd.

The sheep/hog/cow mix provides much bet-ter utilization of forage than single species graz-ing. Since the animals do most of the harvesting,less fossil fuel and labor-hours are expended.There are no pens to wash and no manure todeal with. The herd is controlled using an elec-tric fence charged up to 8,000 volts to hold thesheep.

Before the 100-acre crop/animal integrationproject began in 1987, the College’s agricultureresource laboratory was costing $8,000 per year.That was the first year the resource laboratorystarted managing holistically. By 1996, the re-source lab’s income was up $12,000, and expenseswere down $10,000—rendering a $14,000 profit

over the 1987 figure. During that same time thesoil organic matter has increased from 1.7% to3.2 % (18).

Intercropping forIntercropping forIntercropping forIntercropping forIntercropping for

Disease ControlDisease ControlDisease ControlDisease ControlDisease Control

Under direction of an international team ofscientists, farmers in China’s Yunnan provincemade some simple changes in their rice produc-tion methods (20). They changed from plantingtheir typical pure stand of a single rice variety toplanting a mixture of two different rice varieties.Their primary reason for trying this new tech-nique was to reduce the incidence of rice blast,the main disease of rice. The technique was sosuccessful at reducing blast disease that the farm-ers were able to abandon chemical fungicidesthey had been using. The biodiversity effect isapparent here in that if one variety of a crop issusceptible to a disease, the denser the stand,the worse the disease can spread. If susceptibleplants are separated by non-host plants that canact as a physical barrier to the disease, the sus-ceptible variety will suffer less disease infection.Rice blast moves from plant to plant via airbornespores. These spores can be blocked by a row ofa resistant variety. In this on-farm study, therice was harvested by hand. Separating the vari-eties was easily done during harvest, since onevariety towered above the other.

Adapting IntercroppingAdapting IntercroppingAdapting IntercroppingAdapting IntercroppingAdapting Intercropping

to Your Farmto Your Farmto Your Farmto Your Farmto Your Farm

Intercropping has been important in the U.S.and other countries and continues to be an im-portant practice in developing nations. In tradi-tional systems, intercropping evolved throughmany centuries of trial and error. To have per-sisted, intercropping had to have merit biologi-cally, environmentally, economically, and socio-logically. To gain acceptance, any agriculturalpractice must provide advantages over otheravailable options in the eyes of the practitioner .Many of the impediments to adoption of newstrategies or practices of diversification are so-ciological (Will I look foolish to my neighbors?Will I fail?) and financial (What are the risks?What is the profit potential?) rather than techno-logical.

Farmers have generally regarded intercrop-ping as a technique that reduces risks in crop

//INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICESPAGE 12

production; if one member of an intercrop fails,the other survives and compensates in yield tosome extent, allowing the farmer an acceptableharvest. Pest levels are often lowered in inter-crops, as the diversity of plants hampers move-ment of certain pest insects and in some casesencourages beneficial insect populations.

ReferencesReferencesReferencesReferencesReferences

1. Maser, Chris. 1990. The Redesigned Forest.Stoddart, Toronto, Canada. 224 p.

2. Savory, Allan. 1998. Holistic Manage-ment—A New Framework for Decision-Making. 2nd edition. Island Press. Covelo,CA. 550 p.

3. Grossman, Joel, and William Quarles. 1993.Strip intercropping for biological control.IPM Practitioner. April. p. 1–11.

4. Willy, R.W., et al. 1983. Intercroppingstudies with annual crops. In: Better Cropsfor Food, CIBA Foundation Symposium 97.Pitman, London, UK.

5. Francis, R., and D.R. Decoteau. 1993. Devel-oping an effective southernpea and sweetcorn intercrop system. Hort Technology.Vol. 3, No. 2. p. 178–184.

6. Bowen, John F., and Bernard A. Kratky. 1986.Successful multiple cropping requiressuperior management skills. AgribusinessWorldwide. November/December. p. 22–30.

7. Amador, M.F. 1980. Behavior of threespecies (corn, beans, squash) in polyculturein Chontalpa, Tabasco, Mexico. CSAT,Cardenas, Tabasco, Mexico.

8. Martin, Ralph, Don Smith, and HarveyVoldeng. 1987. Intercropping corn andsoybeans. Sustainable Farming. REAPCanada. McGill University, MacdonaldCampus. http://www.eap.mcgill.ca/

9. Anon. 1987. Intercropping bolsters silageyields. Hay and Forage Grower. August. p.29.

10. Tonneson, Lon, and Jim Houtsma. 1991.Adding new wrinkles to alternate strips. TheFarmer. September 7. p. 8–9.

11. Anon. 1990. Strip intercropping offers low-input way to boost yields. Sensible Agricul-ture. May. p. 7–8.

12. Altieri, M.A., and M. Leibman. 1994. Insect,weed, and plant disease management inmultiple cropping systems. In Francis, C.A.

(ed.). Multiple Cropping Systems.Macmillan Company, New York. 383 p.

13. Ecological Agriculture Projects. Mixing CropSpecies. McGill University, MacdonaldCampus. http://www.eap.mcgill.ca/CSI_2.htm

14. Dirnerger, J.M. 1995. The bottom linematters—you can laugh at him on the way tothe bank. National Conservation TillageDigest. October–November. p. 20–23.

15. Rincon-Vitova. No date. Product Informa-tion: Biological Control Solutions for CottonPests. Rincon-Vitova Insectaries, Inc. OakView, CA. 6 p.

16. Yancey, Cecil Jr. 1994. Covers challengecotton chemicals. The New Farm. February.p. 20–23.

17. Laster, M.L., and R.E. Furr. 1972. Heliothispopulations in cotton-sesame interplantings.Journal of Economic Entomology. Vol. 65,No. 5. p. 1524–1525.

18. Stan GordenDepartment of Agriculture and NaturalResourcesShasta CollegePO Box 496006Redding, CA 96049-6006530-225-4687Email: sgorden@shastacollege.eduWeb: http://www.shastacollege.edu

19. Richardson, Pat. 1997. Polyculture makesthe most of biodiversity. HRM of TexasNewsletter. Summer. p. 5, 7.

20. Wolfe, Martin S. 2000. Crop strengththrough diversity. Nature. August. p. 681–682.

By Preston Sullivan, NCAT AgricultureSpecialist

Edited by Paul WilliamsFormatted by Gail Hardy

Updated August 2003

The electronic version of IntercroppingPrinciples and Production Practices islocated at:HTMLhttp://attra.ncat.org/attra-pub/intercrop.htmlPDFhttp://attra.ncat.org/attra-pub/PDF/intercrop.pdf

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