Shelterbelts increase crop yields

Crop yield increases in fields adjacent to shelterbelts have been reported in numerous studies. These increases have resulted from reduced wind erosion and wind damage to the crop, improved microclimate and better snow retention.

Studies from Saskatchewan, Manitoba, North and South Dakota have shown an average yield increase of 3.5% for wheat from fields sheltered by mature shelterbelts. This figure included land taken out of production for shelterbelt planting and the competition of the shelterbelt with the crop, two factors which can partially offset gains in yield. Percentage yield increases due to shelterbelts are usually higher in drier regions or in drier years than in conditions of greater moisture. Yield increases can be optimized by the selection of appropriate shelterbelt species, good shelterbelt design and maintenance, and by the use of responsive crops.

The amount of land occupied by mature shelterbelts should be less than 5% of total field area. Land requirements can be minimized by selecting tree species with an upright, narrow growth habit such as green ash. These trees will give the most protection relative to the area of land occupied. If sprawling shelterbelts are already present, the overhanging branches can be pruned to limit land occupation.

Competition from tree roots with adjacent crops can be reduced by avoiding tree species with extensive, shallow root systems. Green ash, caragana, pine and Siberian larch are relatively noncompetitive while Siberian elm is much more competitive. Competition can also be minimized by regularly cutting roots at a distance from the shelterbelt of approximately the height of the tree, to a depth of 60 cm.

Ideally, shelterbelts should trap snow in wide, shallow drifts, reduce soil erosion and create a microclimate which increases crop yield. Unfortunately, very porous shelterbelts are required for even snow trapment while denser belts are necessary for effective reduction of erosion and for better microclimate. Therefore, the primary purpose of the shelterbelt must be determined when shelterbelts are being designed. Generally, tall, long lived trees planted in rows perpendicular to prevailing winds and combined with fields which are as narrow as is practical, can be expected to give the greatest yield increases.

Crops differ in their responsiveness to shelter. Winter wheat, barley, rye, alfalfa and hay are highly responsive to protection, while spring wheat, oats and corn respond to a lesser degree.

By combining proper tree species selection, good shelterbelt maintenance and responsive crops, shelterbelts can be expected to improve yields and increase profits.