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Abstract. Multiple cropping systems are prevalent in many parts of the world, and alternating strips of corn and soybeans or dry beans ha ve been used by farmers in the temperate region. Strip cropping has the potential to reduce erosion on hilly lands, to allow a crop rotation in the field if strips are changes from one season to the next, and to increase total system yields Results from several experiments in Eastern and Midwest U. S. show considerable variation in production among years and locations. Corn grown in narrow strips has yielded from 10 to 40 percent over sole cropping, while soybeans or dry beans in narrow strips suffer yield reductions of 10 to 30 percent due to light, water and nutrient competition. There has been no definitive research to quantify the relative importance of these factors in the competitive interface between corn and legume rows. With wider strips there is less increase in corn yields and less reduction in legume yields compared to sole cropping Changes in component crop yields also depend on rainfall, and may be influenced by the variety of each component crop and by the width of strips. Rarely does total yield in a strip crop system fall below the average monoculture performance. In years of adequate rainfall, production of strip crops may outyield sole crops by 10 to 20 percent. Potential production of strip cropping systems is reviewed, and projected soil conservation is estimated using the Universal Soil Loss Equation.
Crops have been grown in association with one another for centuries. In fact, crop mixtures probably represent some of the first farming systems (Plucknett and Smith, 1986). Complex crop mixtures have been recognized as being important in the subtropics and temperate zones, primarily in labor intensive cropping systems (King, 1911; Aiyer, 1949). Corn and soybeans were grown together for silage in the early 1900s in the Northeastern U. S. after the introduction of soybeans from China. These two crops were grown together in the same row, in alternating rows, or in strips. Research has been conducted to determine optimum plant densities for the mixture to produce maximum yield, and for contributions of nitrogen to the soil (Brown, 1935; Etheridge and Helm, 1924; Hackleman et al., 1928; Lipman 1912; Morrish, 1934; Thatcher, 1925). Crop mixtures have been abandoned in favor of sole cropping of the two crops with the introduction of inexpensive nitrogen fertilizers and highly responsive hybrid corn. Reviews by Fred et al. (1932) and Kass (1978) provide a useful historical perspective on crop mixtures.
Corn and dry beans are commonly planted together in much of the medium elevation and highlands of Central and South America. These areas are often cultivated by hand on small holdings. Systems often include subsistence crops on which the family diet and income depend. The crops are grown together because of higher system yields and greater biological and economic stability in the system (Francis, 1986). It has been estimated that about 60 percent of the corn and 80 percent of the beans in Latin America are produced in these systems (Francis, 1978). Advantages of multiple crop systems under small farm conditions include reduced risk and more secure supply of food and income. Modified multiple crop systems using regular strip patterns may have potential in temperate zone farming systems in the U.S. Several options for these systems have been described by Crookston (1976) and Brown and Rosenberg (1975). A number of farmers are using strip cropping in the Midwest, and report that this is more productive than sole cropping (Holmberg, 1985). Research results and farmer experience need to be reviewed to better understand the extent to which these systems might be adapted in the U. S. and where they could be effective in improving crop production and maintaining soil productivity.
Strip cropping of corn and soybeans in Illinois in the 1960s showed that the system produced about 10 percent more corn and 10 percent less soybeans compared to sole culture of the respective crops. This research by Pendleton et al. (1963) using 4-row and 6-row alternating strips further explored the effects of the immediate interface environment between neighboring rows of corn and soybeans. Their data are summarized in Figures 1 and 2. Border rows of corn produced 25 to 39 percent more than sole crops, and the second and third rows from the interface were still significantly higher yielding than sole crop. Border rows of soybean were reduced by 28 to 34 percent compared to sole crop, while the inner rows were more similar in yield to sole crop. These changes in yield, especially in the interface rows, were probably due to the success of corn in competing for light, water and nutrients. They concluded that the advantage to strip cropping would depend on relative potential yields and prices of the two crops.
Crookston and Hill (1979) studied the effects of different widths of soybean and corn strips, and also the impact of changing corn density and hybrid in alternating single rows of the two crops.
Reducing corn density to one-half the recommended rate or changing to a short season corn reduced total system yields significantly in three season/location environments in Minnesota. Results of the tests of different strip widths are shown in Table 1. A comparison of sole crop with the alternating single rows shows an increase in corn yields of 26 to 35 percent with the strip cropping method; soybean yields in single rows were reduced by 22 to 35 percent from the sole crop levers. Wider strips of the two crops were intermediate between these extremes.
The Land Laboratory at Parkland College in Champaign, Illinois has included strip cropping of corn and soybeans in its demonstration/research area for the past several years (Wittler, 1982, 1983, 1984, 1985). Several different row patterns were used, including 8:8, 6:6, and 4:4 alternating rows of corn and soybeans. Although Wittler used both East/West and North/South row directions, only the former are reported -they were superior in the two years of testing. Table 2 presents the results of four years of alternating strips of corn and soybeans. Comparing the sole culture of component crops to the best strip crop system, corn yields were increased from 22 to 41 percent and soybean yields were reduced from 18 to 20 percent in the strip crops. The best patterns were 8:8 in 1983, 6:6 in 1984, and 4:4 in 1982 and 1985. All patterns were not included in all years. Despite the fact that we can't be certain which patterns are superior, it is apparent that yearly climatic variations affect the relative success of the several patterns.
In the early 1950s, soybeans and corn were grown in alternating 2-row strips (91 cm row spacing) in Virginia (Alexander and Genter, 1962). In their experiments, corn in strips produced about 30 percent more than corn grown as sole crop, while soybean yields were not different. In Maryland, Beste (1976) reported total system yields from 10 percent longer to 40 percent higher for strip cropping of sweetcorn and soybeans compared to sole culture of these two crops. Cunard (1976) found 20 to 50 percent higher yields for a system of high lysine corn and edible soybeans grown in strips compared to sole culture of the two crops.
Corn and dry beans were planted in several alternating row patterns in Eastern Pennsylvania in 1984 and 1985 (first year's results reported by Francis et al., 1985). The comparisons of 4:4, 2:2 and 1:1 row strips of corn:beans and sole culture of the two crops are shown in Table 3. Over four field environments in the two years, corn yields in strips increased from 10 to 44 percent, while bean yields ranged from a 37 percent reduction to an 8 percent increase. Four row alternating strips appeared to produce the best combination of corn and dry bean yields in three of the four environments.
These system comparisons in the Midwest and Eastern U.S. are of interest, but it would be more useful if yields of the crops could be combined using an index of total productivity. How do we "combine apples and oranges?"
The land equivalent ratio is a measure often used to combine the yields of two or more unlike crops into one index for comparison with sole culture or among intercrop systems. This index starts with the ratio of intercrop (or strip crop) yields to sole crop yields of each component crop -- a measure of productivity of each crop in a complex system compared to its yield when planted alone. Then the ratios of the component crops are summed to give an index of total system performance compared to sole crops. For example, if corn produces 100 qq/ha in sole culture and 140 qq/ha in strip cropping, and if soybeans produce 30 qq/ha in sole culture and 24 qq/ha in the strip crop, the efficiency can be calculated. In one hectare of strip cropping (half corn and half soybean) the corn produces 70 qq or 70% of a full crop and the soybean produces 12 qq or 40% of a full crop due to successful competition of the taller crop for light, water and nutrients. The Land Equivalent Ratio (efficiency) would be:
LER = 70/100 + 12/30 = 0.7 + 0.4
In summary, the strip crop system is 10 percent more efficient than the two sole cultures; in other words, 10 percent more land would be required to produce the same amount of corn and soybeans in sole culture.
Land equivalent ratios have been calculated for different strip crop row combinations for the Illinois, Minnesota, and Pennsylvania data presented in previous tables. They are summarized in Table 4. For corn/soybean strip cropping the ratios range from 0.95 to 1.15. More important, of the 23 strip cropping patterns studied over these 8 environments, 17 were from 0.97 to 1.03; these ratios plus or minus 0.03 from sole culture generally are not consistently different from 1.00 (sole culture). From the risk standpoint, only one pattern was as low as 0.95, while two of the best patterns were 1.10 and 1.15 in Champaign. For corn/ dry bean strip cropping in Pennsylvania the ratios were 1.01 to 1.18 in the experiments reported. These data indicate that strip cropping can be as much as 5 percent less efficient, and up to 18 percent more efficient, compared to sole culture of these crops.
If the different row patterns are compared, there is no consistent advantage of a specific combination of rows. As shown in the yield data (Tables 1, 2, 3), there is a strong compensation between the two crop components. With wider strips there is less increase in corn yield and less reduction in soybean or dry bean yield, compared to sole crops. With narrow strips the corn takes advantage of light and nutrients and produces relatively higher yields, but the soybeans are reduced proportionately. Only where corn yield increases are greater than soybean yield reductions can there be a biological advantage, e.g. higher total yield, to the strip crop patterns.
There are a number of management practices which could be included by the producer to exploit these competition effects and to favor one crop or the other. Changing relative numbers of rows of crops, e.g. narrow corn strips and wider soybean strips, would maximize advantages to corn and minimize disadvantages to soybeans. Setting up rotations where strips are changed from cereal to legume each year could help control weeds and insects, reduce purchased nitrogen requirements for the cereal, and provide soil conservation potential in the system. Altering relative crop densities, time of planting, and changing hybrids or varieties could contribute to greater system yields (Holmberg, 1985). Most of these factors are yet to be researched in detail. Another dimension of this comparison is relative prices of the two crops, and this must be considered in making management decisions.
Although there may be some systems which are biologically better than others, the short-term bottom fine for the producer is economic. The returns from alternative cropping patterns will depend on biological differences among these systems, the costs involved in production and any differences which might exist, and the relative prices of the two commodities. Four years' data from Champaign at the Land Laboratory are summarized in Table 5. These are the best sole crop treatments for each year and the best strip cropping combinations among the different row directions, hybrids and varieties, and row alternatives. Current prices of each commodity were used to calculate returns each year. Different patterns were best in different years, 4:4 strips in 1982 and 1985, 8:8 strips in 1983, and 6:6 strips in 1984. The range was from an economic advantage of $161.45 for strip cropping in 1983 to an advantage of $8.23 for sole cropping in 1985. On the average, however, there was a $83.02 advantage of strip cropping in gross income over the four years studied. If there are no differences in production costs between sole cropping and strip cropping, the data indicate a clear advantage to strip cropping in three of the four years using current prices in each year.
It is difficult to choose a pattern, based on these data, since different row pattern combinations were superior in each year. The producer could begin this type of system with existing equipment, and it appears that four-row, six-row, or eight-row equipment would be feasible for these production patterns. Just as with any new innovation, a farmer would be wise to try these systems in one part of the farm rather than converting a large area to the new system. This would allow the producer to gain experience and to determine whether the management time needed to implement a complex system were justified by the returns. Other long term economic considerations such as preventing erosion on hilly lands may also be a reason for adopting strip cropping production systems.
Another dimension of strip cropping is the use of annual small grains or perennial hay crops in alternating strips with corn or soybeans. In addition, crop rotations, residue management and conservation practices all contribute to the maintenance of productive topsoil on erosive hillsides. Water-induced soil erosion is retarded by introducing small grain or meadow/legume crops as part of alternative farming systems. The relative impacts of these cropping and conservation practices on potential so erosion are illustrated in Table 6.
Maximum potential soil erosion for the Sharpsburg silty clay loam soil in Southeastern Nebraska was estimated as 47.4 ton/acre/year using the Universal Soil Loss Equation (USLE). Constant values of 160 for the rainfall factor and 0.43 for the soil erosivity factor were used in the calculation. The field was assumed to have a 6% slope and 400 ft slope length. Maximum potential erosion occurred with a corn-soybean rotation, no conservation practices (field operations performed up and down the slope) and tillage practices which left no residue on the soil surface. These same practices for continuous corn (mono culture) were associated with erosion levers about 76% of maximum. This difference is accounted for by the increased cover and effectiveness of corn residue to intercept raindrops prior to tillage as compared to soybeans.
Erosion can be reduced by implementing contour farming and contour strip cropping. Contour farming requires that crops be planted perpendicular to instead of up and clown the hillslope. The movement of water downslope is retarded as it reaches each row and furrow. As a result, the speed with which water moves downslope is slowed and less soil is dislodged which can erode off the hill. When contour farming of continuous corn or corn-soybean rotations is combined with alternating strips of small grains or meadow (strip cropping), erosion can be reduced to 40% or less of maximum. Contour strip cropping with meadow is most effective because vegetation covers the soil surface for the greatest period of the year. Ground cover is especially important when heavy rains occur and row crop canopies are not yet fully formed during fate spring. Maintaining crop residue on the soil is another effective way to reduce erosion. When combined with contour strip cropping, erosion may be as little as 6% of maximum. These examples illustrate the potential for combining corn or soybean strips with other crops in conjunction with minimum tillage to reduce soil erosion.
Cropping with alternating corn/soybean or corn/dry bean strips may have promise as a future system in the temperate zone. Results from experiment station trials indicate that year to year climatic variation largely determines which strip widths are most productive, and whether in fact any one practice is more advantageous for the producer. Strip cropping has been shown to produce from 5 percent less up to 18 percent more total system yield as compared to sole cultures of the component crops in the same field. Generally, yields of strip crops in the locations where these trials were conducted are within a few percentage points of the sole crops with a land equivalent ratio more often slightly above unity. Efficiency of the strip crops varied with location, width of strips (8 row: 8 row, 6 row: 6 row, 4 row: 4 row), hybrid and varieties included in the strips, and year. The experimental data show that a range of row combinations may be used, and different patterns may be advantageous in specific locations or years. The strip cropping alternative generally is equal to or better than sole cropping.
In the economic comparisons of best sole crops with best strip cropping systems in Illinois, there was a clear advantage for strip cropping systems in 3 of 4 years. Average gross income advantage was $83/hectare over the 4 years; this would translate into a similar added profit if costs were the same in the two systems. These results from the Land Laboratory confirm reports from producers in the Midwest.
Some farmers are convinced of the value of this practice (Holmberg, 1985). Those interviewed and quoted in Successful Farming have been using strip cropping of corn and soybeans for several years and intend to continue the practice. They claim up to 15 percent improvement in yields for the total system. Farmers also indicate that reduced erosion and an internal corn -- soybean rotation are additional benefits of the system. It has been established that a cereal -- legume rotation of this type can contribute up to 50 kg/ha of nitrogen to the cereal, reducing need for adding purchased fertilizer. A 10 percent increase in yield is expected from rotations, independent of the nitrogen contribution of a legume. These are not arguments for strip cropping, but are some of the reasons presented by farmers for using systems other than monoculture year after year.
The estimates of predicted soil erosion on hillsides which have different management systems provide another reason to consider strip cropping. Practices which reduce erosion include minimum tillage, maintenance of increased levers of residue on the surface, performing field operations on the contour, and providing alternating strips of crops which can slow or stop water and soil movement during heavy rains. Strips of hay or meadow crops, or strips of high population small grains, can drastically reduce erosion and nutrient loss from hilly lands. If alternating corn and soybean strips are used on the contour, and if tillage is minimized so that more than 30% of residues are in place until the next 'spring's planting, similar benefits will accrue in the long term. A legume planted into the maturing cereal or soybean crop would provide additional cover and erosion control, if rainfall were adequate to supply this additional crop.
These options deserve to be tested under farm conditions in the temperate regions where monoculture of corn or soybean has prevailed. Experiment station trials can give some indications of relative efficiencies of systems, but the real test will be on the farm, using current equipment and farmer expertise. Strip cropping is one method which could potentially help cut costs and reduce losses of soil and nutrients. It would have a beneficial effect both on the farm production system and on the total environment beyond the farm boundaries by reducing erosion. Both farmers and researchers are studying new options to make production agriculture more efficient and sustainable, and to make farming activities more compatible with resource conservation and environmental protection.
Acknowledgment. This paper is published as Journal Series Number 8221, Univ. of Nebraska, and as Journal Series Number 15,235 of the Minnesota Experiment Station.
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Citation : Francis Charles, Jones Alice, Crookston Kent, Wittler Kyle, Goodman Sondra 1986, " Strip cropping corn and grain legumes : a review", Vol. 1, No. 4, 1986, pp. 159 -164
Copyright © 1986 Reprinted with permission.
Reprinted with permission.
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