Answer: Alleycropping involves growing crops (e.g., grains, forages, and vegetables) between trees planted in rows. The spacing between the rows is designed to accommodate the mature size of the trees while leaving room for the planned alley crops. When such sun-loving plants as corn or some herbs are alleycropped, the alleyways need to be wide enough to let in plenty of light even when the trees have matured.
Alternatively, the cropping sequence can be planned to change as the trees’ growth decreases the available light. For example, soybeans or corn could be grown when the trees are very small. Then as the tree canopy closes, forages could be harvested for hay. And finally, when the trees are fully grown and the ground is more shaded, grazing livestock or shade-tolerant crops such as mushrooms or ornamental ferns could occupy the alleyways.
Like all integrated systems, alleycropping requires skillful management and careful planning. Both the crop and the trees have requirements that sometimes necessitate trade-offs between them. The design must allow sufficient room for the equipment needed to service each enterprise, for example. If either crop requires chemical herbicides or insecticides, the other must be tolerant of these treatments. In the case of livestock, there may be periods during and after the use of chemicals when animals must be withdrawn from the area. Animal manure is a problem when fruit or nuts are harvested from the alleyway floor. Also, livestock can cause damage even when the trees are fully grown; roots injured by hooves are susceptible to disease. And soil compaction is a danger during wet weather. These examples demonstrate how crucial planning is to the ultimate success of an agroforestry system.
Trees are planted in straight rows in many alleycropping systems, sometimes with no regard for slope or contour. There are, however, advantages to planting the trees on the contour to slow surface-water movement and reduce soil erosion. The trees can be planted in single rows or in blocks of multiple rows between alleys. The first row in a block is planted on the contour line; subsequent rows are planted below the original line according to the slope of the land. The final row of trees in one block is planted parallel to the contour line on which the next block of trees will begin. The width of the tree blocks varies, but the cropping alleyways between them have parallel edges. This design avoids creating point rows within the alleys, thus simplifying the way equipment can be maneuvered among the crops. The width of the alleys is determined by the size of the equipment that will be used.
If planting on the contour is impractical, another option is to plant trees in curved zigzags so that water running downhill is captured, or at least slowed. Islands of trees can offer some of the same advantages if they don’t interfere with cropping operations
To ensure that the crop trees develop upright, unbranched trunks, fast-growing hardwoods or pines can be interplanted as trainers. Alternatively, the crop trees can be planted close together in the rows and thinned and pruned several times as they grow. Although the trees that are harvested early may have little market value, their presence during the first years of growth increases the main crop’s value. In order to maximize the profit from the final harvest, the goal is to produce long, straight sawlogs with few lower branches. Regardless of the planting design, trees on the outside edge of a group may grow more side branches, or even a lopsided trunk, resulting in lower-value sawlogs.
More information is available in the ATTRA publication Agroforestry: An Overview. This publication presents an overview of common agroforestry practices, evaluating and planning considerations, marketing opportunities, several case studies, and an extensive list of further resources.
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