[Time series analysis of soil water on sloping land in red soil hilly region]

Based on time series analysis, the correlation between soil water and precipitation on the sloping land in red soil hilly region under two land use modes was studied from March to September, 2002-2004. The results showed that precipitation was not an autocorrelation series, while soil water at the depths of 10, 30, 50, 70 and 90 cm was an autocorrelation series with 30-45 days of time correlation range. Precipitation and land use mode were the main factors affecting the correlation of soil water and precipitation. The effect of precipitation weakened gradually with increasing soil depth. This effect lasted 7-8 days in upper soil layers (0-10 and 0-30 cm) , but no marked regularity was observed in deeper soil layers. 2-3 days after raining, precipitation had the most prominent effect on soil water in 0-100 cm soil layer. The correlation time range was 1-3 days shorter in dry season than in wet season. When it didn' t rain more than 5 days, the water content in topsoil would decrease, and even, lead to seasonal drought. Compared with farmland, tea plantation had a weaker correlation between soil water and precipitation in surface soil, but a stronger and more persistent correlation in soil layers below 50 cm.