Giant reed (Arundo donax L.) is one of the most well-studied perennial biomass crops because of its high productivity and potential to store carbon. Yet, little information on controlling weeds in giant reed plantations and their influences on the soil ecosystem is available. In the present study, three different weed control methods, i.e., intercropping (living mulch) with sweet clover (Melilotus officinalis L.), herbicide (glyphosate), and hoeing, were investigated in a 2-year giant reed farm. The intercropping presented significantly higher values (on average) of all the tested soil properties than herbicide and hoeing, except for the catalase activity and pH. The dehydrogenase, phosphatase, and urease activities in the soil under intercropping were higher than the herbicide by 75%, 65%, and 80% (on average), respectively. Also, the soil under intercropping had higher soil organic matter (SOM) and soil respiration than the herbicide by 20% and 25%, respectively. Intercropping also increased the content of N pools, i.e., NO3--N, NH4+-N, Org-N, and Total-N by 517%, 356%, 38%, and 137%, respectively, compared to herbicide. These findings illustrated that controlling weeds in biomass plantations through legume intercropping brings benefits not only to soil properties but also to biomass productivity.
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