The Relations Of Chinese Fir Plantation Soil Moisture And Environmental Factors

Soil moisture is one of the most important part of soil, and is one of the main source of plant water uptake and water cycle. Soil moisture’s spatial variability is the combined result of soil physical properties, land use (vegetation), and the factors of the environment (rainfall, temperature and humidity) at multiple scales, but the role of these factors vary by seasons, so the measurement of the soil moisture dynamic changes and the monitoring of various environmental factors are the most important ways to study soil moisture. As the main tree species of southern China, Fir Plantations takes about1/4of the distribution of national total plantation area, which also has triple functions of timber forest、water conservation forest and scenic forest. The research of soil moisture dynamics of Chinese fir plantation and the relationship between environmental factors and soil moisture provide theoretical foundation in water conservation, forest recovery, ecological environment improvement, and has a very important practical significance.The study makes the Chinese fir plantation in Hunan Huitong as the target, using the observational data of the Ⅱ catchment of the National Key Field Research Station-the fir forest ecology station in Huitong. The include soil moisture, temperature, soil temperature, relative humidity, total radiation, net radiation, and other ecological factors sentinel observations (observation period:January-December of2012) to analyze the relationship between soil moisture and ecological factors, and attempts to analyze the impact. Study achieves the following results:(1) Soil moisture variationThe Day average variation of soil moisture is:from midnight to early morning, the soil moisture gradually increased, the maximum peak appears between9:00am to10:30, then rapidly decline to the minimum between18:00to19:30in the evening, after experiencd a steady upward trend during the night. Annual changes of soil moisture were low in summer and the high trend showed in winter.(2) The relationship of rainfall and soil moistureThe monthly rainfall changes fluctuation presented a multi-peak variation. The highest average monthly rainfall appeared in May (241.42mm), and the lowest was in Feb.(11.71mm). There was no significant correlation between the rainfall and the soil moisture by data and the correlation analysis. Rainfall was not the most significant ecological factor that affects the soil moisture.(3) The relationship of temperature and soil moistureThe temperature had obvious seasonal variation in the year and the annual variation of the temperature was big. The average daily temperature appears in July (28.1℃) and the minimum appears in January (minus1.6℃).By data analysis and correlation, air temperature and soil moisture had significantly negative correlation. Higher the air temperature was, lower the soil moisture went, and vice versa. Similarly, soil temperature and air temperature showed obvious seasonal fluctuations: the lowest soil daily average temperature showed in January (3.0℃), while the highest was in August (27.6℃). Soil temperature and soil moisture also presented a significant negative correlation.(4) The relationship of relative humidity and soil moistureJudging from the year as a whole, the relative humidity of the year is always in a relatively stable state. In the winter months, the relative humidity variations was relatively large, compared to the soil moisture at a high level; six months in the summer, the relative humidity variations were relatively small, and the soil moisture were at a low level; For the full year, the relative humidity and soil moisture showed a significant positive correlation, but the soil moisture showed a certain lag in the change.(5) The relationship of wind speed and soil moistureThe wind speed average variation in typical seasonal month showed an inverted "U" single peak. And the change of wind speed during the day was significantly higher than the night. From January to April, the wind speed had a big variations while the soil moisture variations was not obvious; from June to September, the wind speed variation was flated and the soil moisture showed a downward trend. Through data and correlation analysis, wind speed and soil moisture showed a positive correlation, but the wind speed had little effect on changes in soil moisture.(6) The relationship of radiation and soil moistureThe daily variation of total radiation and net radiation in typical month was an inverted "U" shaped curve; the total radiation was peaking at noon, and it reached closly to0at midnight, while the net radiation values were shown as negative in nighttime. Take the annual change as the point of view, both the fluctuation frequency of the total radiation and net radiation were relatively large. The analysis drawed the conclusion that the total radiation and the net radiation showed a significant negative correlation to the soil moisture.