Soil qualities and change rules of Eucalyptus grandis × Eucalyptus urophylla plantation with different slash disposals

Slash disposal changes soil quality by affecting soil properties and nutrient cycling, and the appropriate disposal approaches remain controversial. This work aimed to explore the impact of different slash disposal methods on soil qualities. For this purpose, a Eucalyptus grandis × Eucalyptus urophylla plantation that had been cultivated in 2002 and felled for the third time in 2016 was established in Hezhou City, China. Burning forest (BF, for moderate intensity fire) and no-burning forest (NF) were set in the plantation, and the native evergreen broadleaf forest near the plantation was used as the control (CK). Soils were sampled quarterly in 2017, and 27 indicators that represent soil physical, chemical, and biological properties were analyzed and compared through the analysis of the sustainability index (SI), which adopts five indices to calculate soil quality. The obtained data showed that the indicators of BF and NF, except for the total potassium content, were much lower than those of CK. The physical properties (Max-WHC, CWHC, Min-WHC, MMC, CPD, TPD) of NF were significantly better (29.07%, 30.98%, 29.61%, 52.08%, 21.89%, 19.76%) than those of BF, unlike the chemical properties of BF (SOM, TN, ACa, AFe, AMn, ACu, AZn) were significantly better than those of NF (45.61%, 81.33%, 12.78%, 23.18%, 96.13%, 144.30%, 114.04%). The enzymatic activities of NF (URE, APHO) were significantly better (43.33%, 156.58%)than those of BF, except the activities of INV (- 25.21%). Results of SI showed that the soil quality of CK was much better than that of BF, and NF the worst. But it exhibited the most unevenness of CK, followed by NF, and BF the best. The change rules of BF and NF were contrasting, and soil quality reached the same level after half a year. In summary, the soil qualities, either BF or CK, were not comparable to that of CK. BF increased the soil quality fleetly and transiently, and NF was sustainable for the eucalyptus plantation.