Soil pH, organic matter, and nutrient content change with the continuous cropping of Cunninghamia lanceolata plantations in South China

Purpose Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China.Consecutive cropping traditionally occurs in Chinese fir plantations(CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs. Materials and methods We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations. Results and discussion In the upper (0–20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation. Conclusions We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed.

研究目的：杉木（Cunninghamia lanceolata (Lamb.) Hook）是我国重要的乡土树种。杉木人工林（Chinese fir plantations, CFPs）传统上普遍采用连作经营模式，但该模式会导致后续轮伐期的林分生产力下降。本研究旨在深入解析连作杉木人工林的土壤性质变化规律。
材料与方法：本研究针对不同林龄、不同轮伐期的杉木人工林，测定了其不同土层及根际土壤（rhizosphere soil, RS）、非根际土壤（non-rhizosphere soil, NRS）的pH值、土壤有机质（soil organic matter, SOM）与养分含量。
结果与讨论：连作成熟杉木人工林的上层（0~20 cm）土壤pH值呈下降趋势，而土壤有机质（SOM）含量则有所升高。上层土壤的全氮（total nitrogen, TN）、速效钾与速效磷含量在不同连作轮伐期间无显著差异。第三轮伐期成熟杉木人工林的根际土壤（RS）pH值显著低于非根际土壤（NRS）。根际与非根际土壤的有机质、全氮（TN）及速效氮含量无显著差异。根际土壤速效磷含量始终低于非根际土壤，且在第三轮伐期时速效磷极度匮乏。
结论：本研究涉及的连作杉木人工林未出现严重的土壤养分退化现象，土壤酸化与磷素缺乏为本次观测到的两大主要问题。