Information – Crop Management – Production
Corn, Bean, Squash Intercrop Experiment, 2002-03
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Background
Beans, Maize and Squash are frequently planted together as part of an intercropping system in the highland subtropics of Central America. This apparently has several advantages, particularly for the maize, which performs as well as or better than it does alone.
Choice of varieties is very important for this type of experiment. In Mexico where this practice was established the combination is between specific varieties of corn beans and squash.
Results from a famous experiment near Tabasco in Mexico are presented in Table 1 below
TABLE 1: Yields and Total Biomass of Maize, Beans, and Squash (kg/ha) in Polyculture as Compared with Several Densities (plants/ha) of each crop in monoculture (from Gliessman l998)
|
Crop |
Monoculture |
Polyculture |
|||
| Maize | |||||
|
Density |
33,000 | 40,000 | 66,600 | 100,000 |
50,000 |
|
Yield |
990 | 1,150 | 1,230 | 1,170 |
1,720 |
|
Biomass |
2,823 | 3,119 | 4,487 | 4,871 |
5,927 |
| Beans | |||||
|
Density |
56,800 | 64,000 | 100,000 | 133,200 |
40,000 |
|
Yield |
425 | 740 | 610 | 695 |
110 |
|
Biomass |
853 | 895 | 843 | 1,390 |
253 |
| Squash | |||||
|
Density |
1,200 | 1,875 | 7500 | 30,000 |
3,330 |
|
Yield |
15 | 215 | 430 | 225 |
80 |
|
Biomass |
241 | 841 | 1,254 | 802 |
478 |
| Total polyculture yield |
1,910 |
||||
| Total polyculture biomass |
6,659 |
||||
There are several approaches to analysing the relationships and relative yield within these intercropping systems. Here we will look at the treatments outlined in the table below;
| Maize | 100% | (flour) | Blue Hopi | 1 |
| Beans | 100% | (dry) | Pinto | 2 |
| Squash | 100% | (non running) | Sweet Mama | 3 |
| Maize bean squash | 100% | 4 | ||
| Maize bean squash | 75% | 5 | ||
| Maize bean squash | 50% | 6 |
Three replicates were made of each of the six treatments
|
|
100% |
75% |
50% |
||||||
| Inrow | Interow | Density(plants/m2) | Inrow | Interow | Density(plants/m2) | Inrow | Interow | Density(plants/m2) | |
| corn | 0.3 | 0.45 | 7.41 | 0.4 | 0.45 | 5.56 | 0.6 | 0.45 | 3.70 |
| beans | 0.15 | 0.45 | 14.8 | 0.2 | 0.45 | 11.1 | 0.3 | 0.45 | 7.41 |
| squash | 0.45 | 0.45 | 4.94 | 0.6 | 0.45 | 3.70 | 0.9 | 0.45 | 2.47 |
Crops were planted on a grid where the rows of corn, beans and squash were 0.15m offset from each other to minimise early competition between species.
Due to season length and low germination considerations the maize corn was grown as cell transplants, while the squash and beans being short season plants were direct seeded. None of the plots were weeded so the yield effects of weed suppression could be expressed.
Results
Unfortunately each of the treatments was highly variable between reps. This meant little opportunity to separate the means but also gave the polycultures a greater opportunity to compensate where one crop did poorly.
Direct relative yield results are illustrated in the table below.
| Cropping System | Squash | Bean | Corn | % relative yield | |
| Monocrop Maize | 100% | 100% | b | ||
| Monocrop Beans | 100% | 100% | b | ||
| Monocrop Squash | 100% | 100% | b | ||
| Polyculture 100% | 61% | 19% | 90% | 170% | a |
| Polyculture 75% | 59% | 19% | 94% | 172% | a |
| Polyculture 50% | 57% | 21% | 70% | 148% | a |
The Mexican experience had a cumulative relative yield or land efficiency ratio (LER) of 1.73 for this cropping combination when compared to optimal planting densities. Other subsistence farming intercrop combinations have shown results of up to 2.82 with recently designed combinations (Altieri 2002)
|
BHU |
monoculture |
polyculture |
||
| Maize |
100% |
100% |
75% |
50% |
| Density |
74074 |
74074 |
55556 |
37037 |
| Yield |
4389 |
3963 |
4111 |
3062 |
| %CV |
31% |
|||
| Beans | ||||
| Density |
148148 |
148148 |
111111 |
74074 |
| Yield |
3498 |
1244 |
1279 |
1399 |
| %CV |
32% |
|||
| Squash | ||||
| Density |
49383 |
49383 |
37037 |
24691 |
| Yield |
36214 |
22016 |
21193 |
20576 |
| %CV |
23% |
|||
| Total polyculture yield |
27223 |
26583 |
25037 |
|
| %CV |
15% |
5% |
20% |
|
Yield stability was higher with the polycultures as opposed to the monocultures as can be seen by the coefficient of variation (%CV). A lower %CV means less variation relative to the yield, so polyculture crops had a LER that varied by 5 – 20% while monoculture crops varied by 23 – 32%.
Similar intercrops have been used on European organic farms to produce cereal legume stock feed mixes e.g. oats and peas (Lampkin 1990). There is potential for the use of this type of system to produce food directly for humans as well.
One of the additional advantages of the corn-bean-squash intercrop system is the additional biomass produced (Gliessman, 1998). The additional biomass produced has the potential for stock food or for ‘feeding’ the soil. Unfortunately, biomass production was not examined in this experiment.
Conclusion
Polycultures have the potential to increase yields and sustainability in many parts of the world. This type of system could be designed to fit the New Zealand context.
References
Alteri, M. A. 2002.
Gliessman, S.R. 1998. Agroecology: ecological process in sustainable agriculture. Ann Arbor Press, Michigan.
Lampkin N, 1990. Organic Farming. Farming Press Books, Ipswich.