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INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES AGRONOMY SYSTEMS GUIDE 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 management benefits can also be realized from intercropping due to increased diversity. Harvesting options for intercrops include hand harvest, machine harvest for on-farm feed, and animal harvest of the standing crop.By Preston Sullivan, NCAT Agriculture SpecialistIllustrations by Missy GocioUpdated August 2003 Table of Contents Principles ............................................ 1 Principles Pursuing Diversity on the Farm ........... 2 Sustainable agriculture seeks, at least in prin- Intercropping Concepts ....................... 3ciple, to use nature as the model for designing Intercrop Productivity .......................... 4agricultural systems. Since nature consistentlyintegrates her plants and animals into a diverse Managing Intercrops ........................... 5landscape, a major tenet of sustainable agricul- Examples of Intercrop Systems .......... 6ture is to create and maintain diversity. Natureis also efficient. There are no waste products in Escalating Diversity and Stability to anature. Outputs from one organism become in- Higher Level ........................................ 7puts for another. One organism dies and becomes Escalating Diversity and Stability to anfood for other organisms. Since we are model- Even Higher Level ............................. 10ing nature, let us first look at some of the prin-ciples by which nature functions. By understand- Intercropping for Disease Control ..... 11ing these principles we can use them to reduce Adapting Intercropping to Your Farm 11 References ....................................... 12 costs and increase profitability, while at the same time sustaining our land resource base. · Diversity is nature’s design When early humans replaced hunting and gathering of food with domestication of crops and animals, the landscape changed accordingly. By producing a limited selection of crop plants and animals, humankind has greatly reduced the level of biological diversity over much of the earth. Annual crop monocultures represent aATTRA 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.
classic example. In response to this biological up of many wild species develops. Once a wildsimplification, nature has struggled to restore di- plant and animal community has reached a highversity to these landscapes—that is her tendency. level of diversity, it remains stable for many years.Our “war” with nature over the tendency to di- When wild communities are in the earlyversity is what we call “weed control” and “pest stages of development, or when they have lostmanagement.” Of course we could hardly pro- diversity due to natural catastrophe or humanduce any crops if we simply allowed our fields actions, they are prone to major fluctuations, bothto return to natural vegetation, but we can real- in types of species present and in their numbers.ize some of the benefits of diversity by planting Disease outbreaks in plants and animals occurmixtures of different crops. more frequently—as do outbreaks of weed, in-· Cooperation is more apparent sect, bird, or rodent pests. One good example is the grasshopper plagues that follow regional than competition weather shifts. Another is the shift in weed spe- There is far more cooperation in nature than cies dominance following a soil disturbance.competition. Cooperation is typified by mutu- The more complex and diverse communitiesally beneficial relationships that occur between become, the fewer the fluctuations in numbersspecies within communities. In The Redesigned of a given species, and the more stable commu-Forest, ecologist Chris Maser offers a glimpse of nities tend to be. As the number of species in-the cooperation inherent in a northern temperate creases, so does the web of interdependencies.forest when he describes a relationship that ex- In both higher and lower rainfall years, there areists among squirrels, fungi, and trees (1). The fewer increases in any one species and fewer fluc-squirrels feed on the fungus, then assist in its tuations in the community as a whole (2).reproduction by dropping fecal pellets contain-ing viable fungal spores onto the forest floor.There new fungal colonies establish. Tree feeder Pursuing Diversity on theroots search out the fungi and form a symbiotic Farmassociation that enables the tree roots to increasetheir nutrient uptake. The fungi, in turn, derive So, then, how can we begin to model our ag-food from the tree roots. Each benefits from the ricultural pursuits after some of these naturalother’s presence or actions. principles? Can we look for patterns in nature If we view competition as the driving force and imitate them? Some pioneering farmers havein nature, we fail to see the complex relation- been able to utilize nature’s principle of diver-ships and feel compelled to take actions that may sity to their advantage. Results of their effortshave unforeseen impacts. The rancher who views include lower cost of production and higher prof-coyotes as competitors (for calves and lambs) and its. Among the practices that promote diversitykills them out may later find the predator helped and stability are:keep rodent populations in check. With the Enterprise diversification—Risk reductionpredator gone, rodent numbers explode and through stability of income and yield are two ofcause more problems than ever before. The same the reasons people diversify their crop and live-is true with many insect pests of crops. When stock systems. Increasing diversity on-farm alsothe only food for insects is crops, that is what reduces costs of pest control and fertilizer, be-they will eat. With no predator or parasite habi- cause these costs can be spread out over severaltat present in a pure stand of crop, the pest in- crop or animal enterprises.sect could not possibly have it better. If we can Crop Crop Rotation — Moving from simple mo-shift our view of nature from a theme of compe- noculture to a higher level of diversity begins withtition to one of collaboration, we can act in ways viable crop rotations, which break weed and pestthat yield fewer negative consequences (2). life cycles and provide complementary fertiliza-· Stability tends to increase with tion to crops in sequence with each other. increasing diversity Farmscaping—Diversity can be increased by If left undisturbed and unplanted, an aban- providing more habitat for beneficial organisms,doned crop field will first be colonized by just a habitats such as borders, windbreaks, and spe-few species of plants, insects, bacteria, and fungi. cial plantings for natural enemies of pests. Re-After several years, a complex community made quest the ATTRA publication Farmscaping to En-PAGE 2 //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES
hance Biological Control for more information on SPATIAL ARRANGEMENTspecial plantings for beneficial insects. There are at least four basic spatial arrange- Intercr cropping Intercropping—Intercropping is the grow- ments used in intercropping. Most practical sys-ing of two or more crops in proximity to pro- tems are variations of these (3).mote interaction between them. Much of thispublication focuses on the principles and strate- · Row intercropping—growing two or moregies of intercropping field crops. A related crops at the same time with at least one cropATTRA publication, Companion Planting, provides planted in rows.more information on intercropping of vegetable · Strip intercropping—growing two or morecrops. crops together in strips wide enough to per- Integration—On-farm diversity can be car- mit separate crop production using machinesried to an even higher level by integrating ani- but close enough for the crops to interact.mals with intercropping. With each increase in · Mixed intercropping—growing two or morethe level of diversity comes an increase in stabil- crops together in no distinct row arrange-ity. This publication focuses on intercropping and ment.provides a section on integrating livestock withcrops. · Relay intercropping—planting a second crop into a standing crop at a time when the stand- Intercropping Concepts ing crop is at its reproductive stage but be- fore harvesting. Most grain-crop mixtures with similar ripen-ing times cannot be machine-harvested to pro- PLANT DENSITYduce a marketable commodity since few buyers To optimize plant density, the seeding ratepurchase mixed grains. Because of limited har- of each crop in the mixture is adjusted below itsvest options with that type of intercropping, farm- full rate. If full rates of each crop were planted,ers are left with the options of hand harvesting, neither would yield well because of intense over-grazing crops in the field with animals, or har- crowding. By reducing the seeding rates of each,vesting the mixture for on-farm animal feed. the crops have a chance to yield well within theHowever, some intercropping schemes allow for mixture. The challenge comes in knowing howstaggered harvest dates that keep crop species much to reduce the seeding rates. For example,separated. One example would be harvesting if you are planning to grow corn and cowpeaswheat that has been interplanted with soybeans, and you want mostly peas and only a little corn,which are harvested later in the season. Another it would be easy to achieve this. The corn-seed-example is planting harvestable strips, also known ing rate would be drastically cut (by 80% or more)as strip cropping. and the pea rate would be near normal. The field When two or more crops are growing to- should produce near top yields of peas even fromgether, each must have adequate space to maxi- the lower planting rate and offer the advantagemize cooperation and minimize competition be- of corn plants for the pea vines to run on. If youtween them. To accom- wanted equal yields fromplish this, four things both peas and corn, then theneed to be considered: seeding rates would be ad- justed to produce those 1) spatial arrange- equal yields. ment, MATURITY DATES 2) plant density, Planting intercrops that 3) maturity dates feature staggered maturity of the crops dates or development peri- being grown, ods takes advantage of and variations in peak resource 4) plant architec- demands for nutrients, wa- strip cropping ter, and sunlight. Having ture. //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 3
one crop mature before its companion crop less- then know how much additional yield is requiredens the competition between the two crops. An in the pure stand to equal the amount of yieldaggressive climbing bean may pull down corn or achieved in the intercrop. The calculated figuresorghum growing with it and lower the grain is called the Land Equivalency Ratio (LER). Toyield. Timing the planting of the aggressive bean calculate an LER, the intercrop yields are dividedmay fix the problem if the corn can be harvested by the pure stand yields for each component cropbefore the bean begins to climb. A common prac- in the intercrop. Then, these two figures are addedtice in the old southern U.S. cotton culture was together. Here’s the equation for a corn/pea in-to plant velvet beans or cowpeas into standing tercrop where the yields from pure corn, purecorn at last corn cultivation. The corn was planted peas, and the yields from both corn and peason wide 40-inch rows at a low plant population, growing together in an intercrop are measured.allowing enough sunlight to reach the peas orbeans. The corn was close enough to maturity (intercrop corn / pure corn) +that the young legumes did not compete. When (intercrop pea / pure pea) = LERthe corn was mature, the beans or peas had cornstalks to climb on. The end result was corn andbeans that would be hand harvested together in When an LER measures 1.0, it tells us thatthe fall. Following corn and pea harvest, cattle the amount of land required for peas and cornand hogs would be turned into the field to con- grown together is the same as that for peas andsume the crop fodder. corn grown in pure stand (i.e., there was no ad- Selecting crops or varieties with different vantage to intercropping over pure stands). LERsmaturity dates can also assist staggered harvest- above 1.0 show an advantage to intercropping,ing and separation of grain commodities. In the while numbers below 1.0 show a disadvantagetraditional sorghum/pigeonpea intercrop, com- to intercropping. For example, an LER of 1.25mon in India, the sorghum dominates the early tells us that the yield produced in the total inter-stages of growth and matures in about four crop would have required 25% more land ifmonths. Following harvest of the sorghum, the planted in pure stands. If the LER was 0.75, wepigeonpea flowers and ripens. The slow-grow- know the intercrop yield was only 75% of that ofing pigeonpea has virtually no effect on the sor- the same amount of land that grew pure stands.ghum yield (4). In a South Carolina study, researchers planted PLANT ARCHITECTURE intercrops of southern peas and sweet corn at three different corn plant densities (5). The Plant architecture is a commonly used strate- plantings were on raised beds with flat and widegy to allow one member of the mix to capture crowns on six-foot centers. In the center of eachsunlight that would not otherwise be available to bed was a corn row, with two rows of peasthe others. Widely spaced corn plants growing planted 18 inches to either side of the corn rowabove an understory of beans and pumpkins is a (see Figure 1). The low corn-seeding rate wasclassic example. 6,700 plants per acre, medium corn was 9,500 Intercrop Productivity per acre, and high was 11,900 plants per acre. Peas were established at a rate of 31,800 plants One of the most important reasons to grow per acre in all intercrop plots. In the pure peatwo or more crops together is the increase in pro- stand, each bed had two rows of peas spaced 24ductivity per unit of land. Researchers have de- inches apart. Yields of the intercrops and puresigned a method for assessing intercrop perfor- stands are shown in Table 1.mance as compared to pure stand yields. In re- In this trial there was a yield advantage fromsearch trials, they grow mixtures and pure stands intercropping over growing the two crops in purein separate plots. Yields from the pure stands, stands. Pea yields suffered from the increasedand from each separate crop from within the mix- competition in the higher densities of corn. Someture, are measured. practical on-farm guidelines can be drawn to From these yields, an assessment of the land guide seeding-rate choices for a two-crop inter-requirements per unit of yield can be determined. crop. To test seeding rates, experiment with threeThis information tells them the yield advantage small plantings of two crops at the following per-the intercrop has over the pure stand, if any. They centages of their full seeding rates: 1/3 + 2/3,PAGE 4 //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES
might mature sooner. Corn or sorghum, requir- Table 1. Yields of sweet corn and ing three months to mature, can be grown with southern peas from intercrops (5) pigeon pea, requiring 10 months to maturation._______________________________________ John Bowen and Bernard Kratky, researchers Corn Peas and instructors at the University of Hawaii, tell (pounds/ (pounds/ us that there are five distinct aspects to success- _Seed_Rates ______________acre)__________ acre) LER___________________________________________ _____ ______ _____ ful multiple cropping. These are: Full corn 5600 *** ***_______________________________________ 1) detailed planning, Full peas *** 1200 ***_______________________________________ 2) timely planting of each crop, Low corn 4200 800 1.41_______________________________________ 3) adequate fertilization at the optimal Medium corn 4600 800 1.48_______________________________________ times, High corn 5000 500 1.30_______________________________________ 4) effective weed and pest control, and 5) efficient harvesting (6).1/2 + 1/2, and 2/3 + 1/3. From there, make Before any fieldwork is begun, adequate plan-adjustments for future plantings based on the ning should be done. Planning covers selectionresults and your expectations. of crop species and appropriate cultivars, water availability, plant populations and spacing, labor Managing Intercrops requirements throughout the season, tillage re- quirements, and predicted profitability of the in- Many combinations of crops have been grown tercrop. These and other parameters need to beor experimented with as mixed or relay inter- evaluated before spending money on inputs.crops. Some of these include sunflowers grown With any crop, seed germination and seed-with black lentils, wheat with flax, and canola ling establishment are the most critical phases ofwith flax. Other combinations include cucum- the entire season. A good seedbed is needed tobers, beans, celery, and chives in China; upland get a good stand. Delayed planting may reducerice, corn, and cassava in Indonesia; and in vari- yield, since crop development may not coincideous parts of the tropics corn and cassava, corn with the optimal growth periods.and peanuts, sorghum and millet, and sorghum Planning fertilization for intercrops can beand pigeonpeas. challenging, as the full needs of both crops must Frequently these cropping combinations in- be met. Generally, there is little information avail-volve a short and a tall crop both planted at the able on how to go about this. One possibilitysame time. In many cases the tall crop is har- would be to ask for soil test results for each cropvested first. For example, corn grown with a separately, then formulate a recommendation thatshorter plant would be harvested first, then pea- will cover the needs of both crops to be grown.nut or sweet potato would be harvested later. Such recommendations are generally 10% to 30%Another pattern would be planting two tall crops higher than rates for individual crops.with different growth rates. In relay intercrops, As with any crop, also accounting for residualdifferent planting dates are used so that one crop or carryover fertility from past crops saves money. Carryover fertility from intercrops may well be lower than that of pure stands because of the two crops having different root types and feed- ing habits. Weed and pest controls in intercrops will likely be different from those in pure stands. Some disease incidence, such as soybean or mung bean rusts, may increase when aggravated with high corn populations and overfertilization. Any disease or pest that prospers in shady conditions could increase under a taller crop such as corn or Figure 1. Sweetcorn and southern pea sunflowers. In many cases, insect pest popula- planting pattern tions are lower when two or more crops are //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 5
grown together. More on pest management will CORN AND SOYBEAN MIXED INTERCROPSbe found later in this publication. Canadian researchers (8) have worked with Harvesting of mixed intercrops has been a several corn-soybean intercrop seeding rates tomajor limitation to their adoption in mechanized determine their economic advantages as silage.farming. As mentioned earlier, if the crops can- Pure stands of corn and soybeans were grownnot be harvested by animals, or all together as for comparison at 24,000 corn seed per acre andfeed, you’re left with hand harvesting. Some 200,000 soybean seed per acre. Results showedcrops such as flax and wheat have been harvested that intercrops were more cost effective than puretogether and mechanically separated. Any other stands over both years the study was conducted.mechanized harvest efforts must get one crop The study featured five experimental intercropwithout damaging the other. One example would seeding rates with two planting arrangementsbe harvesting wheat over the top of a young stand (alternate and within the row). The researchersof soybeans growing beneath the grain heads. All concluded that a planting rate of 16,000 corn seedintercropping strategies— especially mixed inter- per acre (67% of the full corn rate) with 135,000cropping—require advanced planning and keen soybean seed per acre (67% of the full bean rate)management. Success will likely be the reward planted within the same rows along with 53 lbs.for such efforts. of N/acre gave the highest economic returns. Examples of Intercrop (Note: the planter was set to drop 151,000 seeds per acre.) This mixture gave an LER of 1.14 over Systems pure stand yields. The crude protein level of the intercrop silage was considerably higher than that TRADITIONAL CORN-BEAN-SQUASH of pure corn silage. A slightly higher yield was MIXED INTERCROPS achieved from full stands of both corn and beans in alternate rows (LER=1.23), but the cost of pro- Farmers throughout Central America tradi- duction was higher, thus offsetting the improvedtionally grow an intercrop of corn, beans, and yields.squash. Grown together, these three crops opti-mize available resources. The corn towers high CORN AND SORGHUM MIXED INTERCROPSover the other two crops, and the beans climb up Frank Cawrse, Jr., of Lebanon, Oregon, inter-the corn stalks. The squash plants sprawl along crops forage sorghum into his silage corn. Hethe ground, capturing light that filters down first plants the corn at 28,000 seed per acre, thenthrough the canopy and shading the ground. The goes back over the field with a drill with enoughshading discourages weeds from growing. drop tubes closed off to plant 8 pounds of sor- This mixture was compared to the individual ghum on 32-inch rows in between the corn. Hecrops grown separately in a study near Tabasco, also plants two different maturities of corn, a 95-Mexico (7). In the study, corn yields were con- day and a 75-day, to even out the silage mois-siderably higher in the mixture than in a pure ture content. He harvests a mix of corn in hardstand planted at optimum densities. Bean and dent and soft dent, and sorghum in the milk stagesquash yields suffered (8).considerable yield reduc- STRIP CROPPINGtions when grown in mix- Table 2. Yields of corn, beans andture. In this example if squash grown alone or in a mixture CORN/SOYBEANS/ (7)corn were the most impor- _______________________________________ SMALL GRAINStant crop, it was beneficial Pure Stand Intercrop South Dakotato grow it in a mixture (pounds/ (pounds/ farmer Tod Intermillwith squash and beans. ___________________________________________ _Crop ____________________________________ _____ acre) acre) plants alternatingThe beans and squash strips of corn, soy- Corn 1096were just a bonus. The _______________________________________1533 beans, and springLER for the whole mixture Beans 544 98 wheat on his farm (9). _______________________________________was considerably higher The strips are six rows(1.6) than any of the pure Squash 383 71 __________________________________ wide in a ridge-tillstands. See Table 2 for system. All the cropdetails. plantings are adaptedPAGE 6 //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES
to existing equipment widths. Regular herbicide narrow strips (12 to 30 feet wide) offer. The stripstreatments can be applied using a ground sprayer accommodate the pest management and soilof strip width. Even the wheat is drilled on ridges, building advantages of rotations and the yieldusing a drill with individual depth gauges on each boost of border rows. With proper managementopener. Intermill orients his rows east and west the border effect can pay off; managed improp-to minimize the shading effects of taller crops erly, it can cost yield. With oat and corn strips,like corn. The crops are planted in a wheat–corn– the early-maturing oats are nearly mature beforesoybean pattern, with soybeans on the north side corn can pose much of a shade and competitionof the corn (Figure 2). This arrangement reduces problem. The corn can also provide wind pro-the effect of corn shading often associated with a tection for the oats. When the oats are harvested,straight corn-soybean pattern, since the wheat is more sunlight is available to the corn. In times ofmature before the corn has a chance to shade it. low moisture, oats may rob the corn border rowsCorn gains the greatest benefit from the addi- of water. In his field trials, Cruse found a 5%tional sunlight interception on the outside rows increase in oat yields on their borders, while cornof the corn strip. realized a 12 to 15% increase. Soybean yields dropped by 10% on their bor- der rows, but the yields in the soybean middle rows were higher than they would be in a solid field, possibly representing a windbreak effect (10). Some have experimented with a shorter corn variety in the border row to minimize shading. One farmer tried planting six rows of corn and doubling his soybean strips to 12 rows to elimi- nate the impact of corn shading on the beans. Figure 2. Corn, soybeans, and wheat strip- This same farmer found that corn strips wider cropped than eight rows did not provide adequate results. Iowa farmer Tom Frantzen strip-crops oats, Using a 12-row planter, it’s easy to establish thecorn, and soybeans on ridge-till rows. He views 6-row strips by filling the middle six hoppers withhis strips as a crop rotation in one field. His rows corn and the outer three hoppers with beans.are oriented generally east and west on the con- Some farmers plant higher corn populations andtour. His 1989 strip-crop corn yields were 166 add higher nitrogen rates in the border rows tobushels per acre, compared to 130 for his farm take advantage of the extra sunlight exposure.average. Stripped soybean yields were two bush- Most farmers agree that strip cropping corn, soy-els lower than farm average. His oat yields were beans, and oats works best with ridge-till or no-109 bushels stripped and 100-bushel farm aver- till. When the field is tilled, it’s difficult to gaugeage. Tom was not surprised at the increase in where the rows should go in order to get thecorn yields. The outer strip rows captured more strips even.sunlight. His average corn border row yielded198 bushels per acre next to the soybeans and Escalating Diversity and177 bushels next to oats. The soybean yields were37 bushels, even with the increased shading on Stability to a Higherthe border rows. This loss was made up in the Levelmiddle rows with yields of 44 bushels per acre.Oats showed a 107-bushel yield on the soybean Ecologists tell us that stable natural systemsside, a 103-bushel yield on the corn side, and 99 are typically diverse, containing many differentbushels in the middle. Tom says the strip inter- types of plants, arthropods, mammals, birds, andcropping is no more labor intensive than microorganisms. In stable systems, serious pestmonocrop fields. His profits were $76 per acre outbreaks are rare, because natural controls existfor the stripped fields and $55 for the same crops to automatically bring populations back into bal-grown in monoculture. (11). ance. Planting crop mixtures, which increase Rick Cruse, an Iowa State University agrono- farmscape biodiversity, can make crop ecosystemsmist, has observed several characteristics that more stable, and thereby reduce pest problems. //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 7
Gayler is just starting research projects using al- ment of soil-borne diseases, request the ATTRAfalfa as an attractant crop for beneficials. He publication Sustainable Management of Soilbornespeculates that it will work in the Southeast with Plant Diseases.proper management. Other main-season strip Texas dryland farmer Ron Gobel intercropscrops that research suggests will benefit cotton 8-row strips of sesame and cotton for insect con-crop pest management include cowpeas, sor- trol benefits. The sesame harbors many benefi-ghum, corn, and crotalaria (15). cial insects, including high populations of lace- Dr. Sharad Phatak of the University of Geor- wings, assassin bugs, and lady beetles. Ron’sgia has been working with cotton growers in 1995 crop was planted late due to prolongedGeorgia testing a strip-cropping method using spring rains. He did not use a Bt cotton variety.annual winter cover crops (16). Planting cotton Early frost terminated the crop two weeks ear-into strip-killed crimson clover improves soil lier than normal, yet he still produced 0.8 baleshealth, cuts tillage costs, and allows him to grow per acre under dryland conditions. His sesamecotton with no insecticides and only 30 pounds produced 800 pounds per acre. The 1996 cottonof nitrogen fertilizer. Working with Phatak, rows were planted where the sesame rows werefarmer Benny Johnson reportedly saved at least the previous year, and sesame planted where$120/acre on his 16-acre test plot with the clover cotton was before.system. There were no insect problems in the Since Ron sells his cotton for a premium pricetest plot, while beet armyworms and whiteflies in the organic market, he cannot spray any syn-were infesting nearby cotton and requiring 8 to thetic insecticides. Consequently, he must rely12 sprayings to control. Cotton intercropped with on beneficial insects attracted to his fields by cul-crimson clover yielded more than three bales of tural practices and a handful of natural insecti-lint per acre compared to 1.2 bales of lint per cides.acre in the rest of the field (16). Boll counts were Following the fall harvest, Ron plants annual30 per plant with crimson clover and 11 without rye at a low rate of 20 to 40 pounds per acre. Theit. Phatak identified up to 15 different kinds of rye is tilled in prior to crop planting in the spring.beneficial insects in these strip-planted plots. Ron believes the rye helps with soil moisture re- Phatak finds that planting crimson clover seed tention and weed control. During the 1997 cropat 15 pounds per acre in the fall produces around year his fields suffered only minimal boll weevil60 pounds of nitrogen per acre by spring. By damage. Ron noticed lots of adult bollwormlate spring, beneficial insects are active in the clo- moths but no worms. The eggs were eaten orver. At that time, 6- to 12-inch planting strips of parasitized by the beneficials.clover are killed with Roundup™ herbicide. Fif- Ron’s fields were scouted as part of a bollteen to 20 days later the strips are lightly tilled weevil eradication program. The scouts wereand cotton is planted. The clover in the row- amazed at the lack of worms and the high num-middles is left growing to maintain beneficial in- bers of beneficial insects. The cotton crop wassect habitat. When the clover is past the bloom sprayed one time with diatomaceous earth im-stage and less desirable for beneficials, they move pregnated with natural pyrethrum, which wasreadily onto the cotton. Even early-season thrips, acceptable under the organic standards. The in-which can be a problem following cover crops, sect scouts noticed a 70% reduction in adult bollare limited or prevented by beneficial insects in weevil population three days after the spray.this system. The timing coincides with a period They were so surprised that they placed cages ofwhen cotton is most vulnerable to insect pests. 20 live weevils in the field to see whether theFollowing cotton defoliation, the beneficials hi- spray was working. The next day, 45% of thosebernate in adjacent non-crop areas. weevils were dead. The entomologists specu- Phatak points out that switching to a whole- lated that the weevils were getting enough of thefarm focus while reducing off-farm inputs is not diatomaceous earth on their leg joints to cut theirsimple. It requires planning, management, and exoskeletons, allowing the pyrethrum to killseveral years to implement on a large scale. It is them.just as important to increase and maintain organic In a scientific study, Mississippi researchersmatter, which stimulates beneficial soil microor- interplanted 24 rows of cotton with 4 rows ofganisms. Eventually a “living soil” will keep sesame to study the intercrop’s effects on tobaccoharmful nematodes and soilborne fungi under budworms and bollworms (Heliothis spp.).control (16). For more information on manage- Throughout the growing season, larvae numbers //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 9
were much higher in the sesame than on the cot- ver. Not all the pastures have water sources forton until late August, indicating the worm’s pref- the animals, so water is moved on a trailer tankerence for sesame. Following a large summer when necessary. The animals are moved daily inrain at a time when the sesame was reaching a planned grazing system during rapid plantmaturity, the Heliothis adults became more at- growth and much more slowly, up to five daystracted to the cotton. The researchers noted that on a paddock, during slow plant growth.sesame’s attractiveness to Heliothis and sesame’s Some of the paddocks are planted with mix-ability to harbor high numbers of beneficial in- tures of either winter or summer forage or grainsects made it useful in a cotton pest management crops. An intercrop of cereal grain, fava beans,program (17). and Canadian field peas is planted for winter grain, each crop at 1/3 normal seeding rate. The Escalating Diversity and grain mixture is combine-harvested to make en- ergy and protein supplement feed as needed. Stability to an Even After harvest, the animals are turned into the Higher Level paddock to glean what’s left. For summer feed, a mixture of milo planted on 18-inch rows is in- The diversity created by intercropping can be tercropped with a row of black-eyed peas plantedenhanced even further by integrating livestock six inches to either side of each sorghum row,(single or mixed species) into the cropping plan using a drill with partitions in the seedbox. Theas harvesters. Allowing animals to harvest feed milo provides a trellis for the pea vines to run oncrops in the field puts gain on animals at the cost (Figure 3). The milo/black-eyed mixture requiresof crop production—considerably less than the no herbicide. Before peas and milo were grownpurchase price of the grain. If you think about it, together, the milo pure stand would be plaguedfeed grains cost a lot less when they’re not run with whiteflies and green bugs. Mixing the twothrough a $150,000 combine or hauled 1000 miles crops together ended the pest problem. Cow-across the country. peas have extrafloral nectaries that attract lots of Grazing animals and other livestock can be beneficial insects.managed on croplands to reduce costs, increase This could ex-income, and increase diversity. There are ways plain the absenceof incorporating animals into cropping without of pest insects inthe farmer getting into animal husbandry or own- the mixture. Theership directly. Collaboration with neighbors who milo/pea mix-own animals will benefit both croppers and live- ture is harvestedstock owners. Grazing or hogging-off of corn by setting theresidue is one example where a cost can be turned combine to cut atinto a profit. The animals replace the $6 per acre the height of thestalk mowing cost and produce income in ani- milo heads. Thismal gains. yields a milo to Figure 3. Cowpeas and Shasta College provides a unique demonstra- bean ratio of milo growing togethertion of integrating livestock with intercrops. 2:1—ideal forShasta is a two-year community college located feed.in Redding, California, that offers associate de- The college animal herd consists of 20 sowsgrees in several branches of agriculture. Stan that farrow on pasture, 35 head of cattle, 50 sheep,Gorden (18) heads the college’s holistic resource and 30 laying hens that all range together. Thelaboratory, where students get hands-on experi- hens are with the herd during the day and roostence with ranching and farming (19). Stan and in a nearby eggmobile at night. Gorden selectshis students have taken intercropping to a high breeds and genetics to fit this system, as opposedlevel of efficiency. They run hogs, sheep, cattle, to selecting breeds for maximum production andand chickens together over 42 small paddocks of adapting a system to match the animal. The ani-various forages and crops growing on 100 acres mals benefit one another. The sheep learn to stayof college-owned land. One paddock is a pump- close to the middle of the herd to avoid preda-kin patch, another a garlic and carrot patch. Some tors, which are fended off by the hogs. The cattleare planted in alfalfa or mixes of grasses and clo- learn that the hogs know how to break the pump-PAGE 10 //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES
kins open, so they stick close and get some too. over the 1987 figure. During that same time theThe hogs eat the cow and sheep droppings and soil organic matter has increased from 1.7% tobenefit from the predigestion. The hens scav- 3.2 % (18).enge wasted seeds from the various crops. Thereare three different kinds of hens, each of which Intercropping forlays eggs of a different color. The eggs are mar-keted as rainbow eggs, with each dozen contain- Disease Controling four white, four blue, and four brown eggs. Under direction of an international team ofThe chickens also scratch apart cattle dung pats scientists, farmers in China’s Yunnan provincesearching for insects, thus destroying cattle para- made some simple changes in their rice produc-sites. tion methods (20). They changed from planting Gorden says that developing and maintain- their typical pure stand of a single rice variety toing this high level of diversity has required cre- planting a mixture of two different rice varieties.ativity, selection criteria, constant monitoring, and Their primary reason for trying this new tech-re-examining traditional beliefs. By challenging nique was to reduce the incidence of rice blast,long-held beliefs, Bill and his students discov- the main disease of rice. The technique was soered that hogs do not need standard farrowing successful at reducing blast disease that the farm-crates and that sheep and cattle are compatible ers were able to abandon chemical fungicidesgrazers. Animals and crops are selected and culled they had been using. The biodiversity effect isaccording to their ability to adapt to this com- apparent here in that if one variety of a crop isplex system. Shasta College has one of the larg- susceptible to a disease, the denser the stand,est heritage hog herds in the country. The hogs the worse the disease can spread. If susceptiblehave been fitted with humane nose rings to pre- plants are separated by non-host plants that canvent rooting. Also, hog breeds are selected that act as a physical barrier to the disease, the sus-don’t root up the ground nor eat the baby lambs ceptible variety will suffer less disease infection.when they are born. The sows farrow on pas- Rice blast moves from plant to plant via airborneture with only a single bale of hay for bedding. spores. These spores can be blocked by a row ofHogs are not vaccinated, nor are needle teeth re- a resistant variety. In this on-farm study, themoved or other detailing done. Sows generally rice was harvested by hand. Separating the vari-wean 12 pigs with no supplemental feed. The eties was easily done during harvest, since oneonly purchased input is some nitrogen and phos- variety towered above the other.phorus fertilizer applied to the pastures. Thepigs are only touched twice; once to castrate and Adapting Intercroppingonce to wean. As with the hogs, the cattle andsheep are selected to prosper on grass. Preda- to Your Farmtors are not controlled in any way. Any animal Intercropping has been important in the U.S.that gets killed by wandering off is naturally se- and other countries and continues to be an im-lected out of the herd. portant practice in developing nations. In tradi- The sheep/hog/cow mix provides much bet- tional systems, intercropping evolved throughter utilization of forage than single species graz- many centuries of trial and error. To have per-ing. Since the animals do most of the harvesting, sisted, intercropping had to have merit biologi-less fossil fuel and labor-hours are expended. cally, environmentally, economically, and socio-There are no pens to wash and no manure to logically. To gain acceptance, any agriculturaldeal with. The herd is controlled using an elec- practice must provide advantages over othertric fence charged up to 8,000 volts to hold the available options in the eyes of the practitioner .sheep. Many of the impediments to adoption of new Before the 100-acre crop/animal integration strategies or practices of diversification are so-project began in 1987, the College’s agriculture ciological (Will I look foolish to my neighbors?resource laboratory was costing $8,000 per year. Will I fail?) and financial (What are the risks?That was the first year the resource laboratory What is the profit potential?) rather than techno-started managing holistically. By 1996, the re- logical.source lab’s income was up $12,000, and expenses Farmers have generally regarded intercrop-were down $10,000—rendering a $14,000 profit ping as a technique that reduces risks in crop //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES PAGE 11
production; if one member of an intercrop fails, (ed.). Multiple Cropping Systems.the other survives and compensates in yield to Macmillan Company, New York. 383 p.some extent, allowing the farmer an acceptable 13. Ecological Agriculture Projects. Mixing Cropharvest. Pest levels are often lowered in inter- Species. McGill University, Macdonaldcrops, as the diversity of plants hampers move- Campus. http://www.eap.mcgill.ca/ment of certain pest insects and in some cases CSI_2.htmencourages beneficial insect populations. 14. Dirnerger, J.M. 1995. The bottom line matters—you can laugh at him on the way to References the bank. National Conservation Tillage Digest. October–November. p. 20–23.1. Maser, Chris. 1990. The Redesigned Forest. Stoddart, Toronto, Canada. 224 p. 15. Rincon-Vitova. No date. Product Informa- tion: Biological Control Solutions for Cotton2. Savory, Allan. 1998. Holistic Manage- Pests. Rincon-Vitova Insectaries, Inc. Oak ment—A New Framework for Decision- View, CA. 6 p. Making. 2nd edition. Island Press. Covelo, CA. 550 p. 16. Yancey, Cecil Jr. 1994. Covers challenge cotton chemicals. The New Farm. February.3. Grossman, Joel, and William Quarles. 1993. p. 20–23. Strip intercropping for biological control. IPM Practitioner. April. p. 1–11. 17. Laster, M.L., and R.E. Furr. 1972. Heliothis populations in cotton-sesame interplantings.4. Willy, R.W., et al. 1983. Intercropping Journal of Economic Entomology. Vol. 65, studies with annual crops. In: Better Crops No. 5. p. 1524–1525. for Food, CIBA Foundation Symposium 97. Pitman, London, UK. 18. Stan Gorden Department of Agriculture and Natural5. Francis, R., and D.R. Decoteau. 1993. Devel- Resources oping an effective southernpea and sweet Shasta College corn intercrop system. Hort Technology. PO Box 496006 Vol. 3, No. 2. p. 178–184. Redding, CA 96049-60066. Bowen, John F., and Bernard A. Kratky. 1986. 530-225-4687 Successful multiple cropping requires Email: email@example.com superior management skills. Agribusiness Web: http://www.shastacollege.edu Worldwide. November/December. p. 22–30. 19. Richardson, Pat. 1997. Polyculture makes7. Amador, M.F. 1980. Behavior of three the most of biodiversity. HRM of Texas species (corn, beans, squash) in polyculture Newsletter. Summer. p. 5, 7. in Chontalpa, Tabasco, Mexico. CSAT, 20. Wolfe, Martin S. 2000. Crop strength Cardenas, Tabasco, Mexico. through diversity. Nature. August. p. 681–8. Martin, Ralph, Don Smith, and Harvey 682. Voldeng. 1987. Intercropping corn and soybeans. Sustainable Farming. REAP By Preston Sullivan, NCAT Agriculture Canada. McGill University, Macdonald Specialist Campus. http://www.eap.mcgill.ca/9. Anon. 1987. Intercropping bolsters silage Edited by Paul Williams yields. Hay and Forage Grower. August. p. Formatted by Gail Hardy 29. Updated August 200310. Tonneson, Lon, and Jim Houtsma. 1991. IP135/8 Adding new wrinkles to alternate strips. The Farmer. September 7. p. 8–9. The electronic version of Intercropping11. Anon. 1990. Strip intercropping offers low- Principles and Production Practices is input way to boost yields. Sensible Agricul- located at: ture. May. p. 7–8. HTML http://attra.ncat.org/attra-pub/intercrop.html12. Altieri, M.A., and M. Leibman. 1994. Insect, PDF weed, and plant disease management in multiple cropping systems. In Francis, C.A. http://attra.ncat.org/attra-pub/PDF/ intercrop.pdfPAGE 12 //INTERCROPPING PRINCIPLES AND PRODUCTION PRACTICES