Cultivating crops—such as wheat, barley and rye—alongside rows of trees is a system of agroforestry that is known as "alley-cropping." It serves many functions: in addition to enhancing ecosystems and biodiversity, it can also counteract the negative effects of growing crops in treeless open land. The advantages of alley-cropping come from the interaction between trees and crops, resulting in improved soil quality, reduced wind erosion, enhanced nutrient cycling, and climate change mitigation through increased carbon capture.
However, rows of trees can create competition for resources such as water, sunlight and nutrients, which negatively affects crop yield. A research team led by the University of Göttingen has now shown that, in systems with rows of fast-growing poplar trees, choosing between winter and spring crops based on the age of the trees can cancel out competition, creating opportunities for farmers to optimize their harvests. The results were published in the journal Agronomy for Sustainable Development.
The study was conducted over six years at four different areas in Germany. Crop yields were measured at various distances from the tree rows. The trees were managed as "short-rotation coppice"—meaning trees are planted and cut down to near ground level every three to nine years before being allowed to regrow.
The results showed that spring crops in agroforestry had between 10% and 35% lower yields compared to treeless open farmland when the trees were 5 years or older. The greatest reduction in yield occurred in crops growing within four meters (13 feet) of the tree rows and was primarily due to limited light caused by the shade from the trees. However, this effect was not observed in winter crops, where researchers found similar yields to those in treeless open land across the nine years of tree growth. In addition, annual wood production was three times higher after the second tree harvest compared to the first two tree harvests.
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