an introduction to intercropping

Intercropping is a growing method rooted in ecological diversity. In intercropped systems, two or more component crops are grown together for a given growing period. There are currently four common intercropping patterns:

1. Strip: crops are grown simultaneously in independent rows within the same field
2. Row: crops are grown together simultaneously and a minimum of one crop is planted in a row
3. Mixed: there is no specific order to the crops
4. Relay: the growing system is dependent on the lifecycle stage of the intercropped plants. Typically, the second crop in the intercropping schedule is planted after the first crop reaches the reproductive stage and before it reaches peak maturity

Regardless of the intercropping pattern selected, the plants grown together should be complementary in nature in that they have different “rooting abilities, canopy structure, height and nutrient requirements” which produce a yield advantage. This occurs when resources that could not be utilized by a single crop are utilized by an additional crop growing in the same space.  

One of the best-known examples of intercropping is the three sisters method developed by Native Americans in the United States, where Maize, pole beans and winter squash are grown together. The Maize provides a form for the beans to climb and shades the squash. The beans stabilize and fix nitrogen for the Maize plants. The squash provides ground cover, effectively maintaining moisture levels and suppressing weeds.

To develop an advantageous intercropped system, five fundamental principles must be adhered to:  

1. A detailed plan must be developed, including an understanding of the characteristics of the component crops
2. Crops must be timely sown
3. Adequate fertilizer must be applied at the appropriate time
4. A weed and pest strategy must be in place
5. Harvesting must be efficient

If the wrong types of plants are grown together or the spacing is incorrect, the output will decrease.  

The most common way to measure the efficacy of an intercropped system is with the land equivalent ratio [LER] is typically used, where:  

(INTERCROP 1 / PURE YIELD 1) / (INTERCROP 2 / PURE YIELD 2).

Results > 1.0 indicate an advantageous pairing.

Results < 1.0 indicate a disadvantageous pairing.

sources:

• Lithourgidis, A., Dordas, C., Damalas, C. A., Vlachostergios, D.N. (2011) Annual intercrops: An alternative pathway for sustainable agriculture. Australian Journal of Crop Science, 5(4). 
• Mousavi, S. R.; Eskandari, H. (2011, January). A General Overview on Intercropping and Its Advantages in Sustainable Agriculture. Applied Environmental Biological Sciences. 1(11). 
• Sullivan, P. (1998, November). Intercropping Principles and Production Practices. Agronomy Systems Guide. 
• Wiley, R.W. and Rao, R.M. (1980, April) A Competitive Ratio for Quantifying Competition Between Intercrops. Experimental Agriculture, 16(02). 
• Zeman, F. (2012) Metropolitan sustainability: understanding and improving the urban environment. Oxford, Cambridge, Philadelphia, Delhi: Woodhead Publishing Limited.