Intercropping

Intercropping is a sophisticated method of multiple cropping. It involves growing two or more different crops at the same time on a single field. This practice is a form of polyculture, which means growing many different species together. The primary objective is to achieve a higher yield on a specific piece of land. Farmers do this by utilizing ecological processes or resources that a single crop would not use alone.

To succeed, farmers must carefully manage the spatial and temporal overlap of the plants. Spatial overlap refers to how the plants are arranged in the physical space. Temporal overlap refers to how their growing seasons align.

There are several distinct methods used to organize these crops. Mixed intercropping involves freely mixing multiple crops within the available space. This practice has existed for thousands of years in various cultures. For example, medieval English farmers mixed oat and barley to create livestock feed called dredge. In France, peasants ground wheat and rye together to make a bread known as pain de méteil. Another method uses row crops, which are planted in lines. These rows are wide enough for specialized agricultural machinery to pass through. This method of growing row crops originated in Ancient China during the 6th century BC.

Timing is another essential factor in intercropping strategies. Temporal intercropping combines a fast-growing crop with a slow-growing one. The fast crop is harvested before the slow crop reaches maturity. This can result in a higher total yield than growing either crop by itself. A similar technique is relay cropping. In this system, the second crop is sown while the first crop is still growing. This often happens near the onset of the first crop's reproductive development or fruiting. The first crop is then harvested to provide space for the second crop to develop fully.

Alley cropping is a specialized form of intercropping that uses rows of trees or hedges. These tree strips alternate with strips of crops. Usually, the trees are pruned before the crops are planted. The cut leafy material is then spread over the crops to act as mulch. This provides essential nutrients to the soil. The hedges also serve as windbreaks and help reduce soil erosion. In tropical North and South America, farmers use various Inga species for this purpose.

This method is a sustainable alternative to slash-and-burn cultivation.

One notable example is Inga alley cropping, which was developed in Costa Rica. Tropical ecologist Mike Hands trialed this technique in the late 1980s and early 1990s. Inga trees are leguminous, meaning they fix nitrogen into the soil. This nitrogen is a vital nutrient that plants use to grow. The leaves from these trees form a thick mulch. This layer protects both the roots and the soil from the sun and rain. Additionally, the thick canopy of the trees blocks light from reaching the ground. This naturally suppresses the growth of weeds.

Intercropping relies on the concept of resource partitioning. This requires careful planning regarding soil, climate, and crop varieties. Farmers must ensure that crops do not compete for sunlight, water, nutrients, or physical space. For instance, one might plant a deep-rooted crop alongside a shallow-rooted one. Or, a tall crop might be paired with a shorter one that needs partial shade. This can also create mutualism, where plants help each other. Climbing plants, such as black pepper, can use a companion crop for structural support. This helps prevent plants from tipping over during heavy rain or wind.

Diversity in the field also aids in pest management. Increasing the number of plant species can limit pest outbreaks by increasing predator biodiversity. Some farmers use trap cropping, which involves planting a crop that is more attractive to pests than the main production crop. Other farmers use repellent intercrops. These plants mask the smell of the production crop to keep pests away. A more complex system is push-pull cropping. This combines both attractant and repellent methods to manage insects.

Despite these benefits, intercropping has certain limitations. It can be difficult to implement successfully at a large commercial scale. A 2006 review of 100 trap cropping examples found that only 10 were successful commercially. In those successful cases, farmers had to use extra management to stop insects from moving back to the main crop. Furthermore, crop diversification does not always increase the number of pest predators. A 2008 systematic review found that predators increased in only 53 percent of studies. Additionally, diversification led to increased yields in only 32 percent of the studies examined.