Changes in soil quality following poplar short-rotation forestry under different cutting cycles.

In the last decade, the change of energy concept induced by global warming and fossil fuel depletion together with the advances in agriculture towards a multifunctional and a more sustainable use of rural areas promoted the development of biomass crops. In this regard, Populus is largely utilised in short-rotation forestry (SRF), as it is known to be a fast-growing tree, producing large yields and having a high energy potential. Most studies focused on economic-productive and energetic aspects of Populus plantations, whereas their impact on soil quality and health have been poorly investigated. In this study, the main soil chemical parameters, microbial biomass and activity were assessed aiming at evaluating the impact of Populus SRF under one, two and three-year cutting cycles (T1, T2 and T3) in comparison with an intensive food cropping system (wheat-soybean rotation, WS). In addition, arbuscular mycorrhizal (AM) fungal inoculum potential was measured using root colonisation (RC) and number of entry points (EP). In the 0-10 cm soil depth, pH, phosphorus (P), total nitrogen (N) and soil organic carbon (SOC) were significantly affected by the management. In comparison with WS, Populus SRF treatments produced significant pH decreases together with N and SOC increases, these last ones ranging from 11% to 34% and from 21% to 57%, respectively. Under T3 soil pH decreased of 0.25 units, while P, N and SOC increased of 10%, 34% and 57%, respectively, in comparison with WS. Microbial biomass and soil respiration under SRF showed also mean increases of 71% and 17%, respectively. Under SRF treatments, Lolium perenne, commonly observed in all field plots, was more than twofold colonised by AM fungi in comparison with WS, while the number of EP, observed on Lactuca sativa used as a test plant, showed values ranging from 8 to 21 times higher. The present study shows the potential of a Populus SRF to improve soil chemical, biochemical and biological quality parameters in comparison with an intensive food cropping system.