新垦红壤坡地土壤水分有效性研究

针对南方红壤地区降雨时空分布不均的特点，以未开垦的自然植被为对照，对桂西北环境移民示范区不同季节(早季和雨季)一次性降雨前1d及降雨后4h、2d、4d、6d及8d新垦蔗地(中坡、下坡、谷地）0-20cm，20—40cm、40—60cm3个土层的土壤水分含量进行了测定．结果表明，雨后谷地蔗地的土壤有效水分增量几乎与降雨量相同，而中坡蔗地与未开垦的自然植被土壤有效水分增量仅相当于降雨量于80％．雨季雨后0—60cm土壤层次中土壤有效水分分布均匀，早季主要集中在表层．雨季一次性降雨后各哩理及各土层土壤有效水分饱和度均有显著差异；而早季3个新垦蔗地间无明显差异，3个土层以表层土壤有效水分饱和度最高，亚表层与心土层差异不明显．无论雨季还是旱季，0—60cm土层土壤有效水分的消耗速率都以自然植被处理为最低，由于雨季正是作物生长旺季，其0—60cm土层土壤有效水分的消耗速率比旱季快，按照早季雨后8d土壤有效水分的平均消耗速率，15d内0—60cm土层的有效水分将消耗殆尽。

Soil water availability in new-cultivated hillside land

The dynamics of water content in three soil layers (0-20 cm, 20-40 cm and 40-60 cm) were determined at three geographic locations (mesoslope, downgrade, valley) of new-cultivated sugarcane field and uncultivated hillside land at one day before rain, 4 hours, 2, 4, 6 and 8 days after rain during rainy season and dry season in 1998 at environmental immigrants settlement area of northwest Guangxi. The result showed that the increment of available soil water content in valley sugarcane field after rain was equal to precipitation, but that in mesoslope sugarcane field and uncultivated hillside land was 80% of precipitation. The distribution of available soil water content in 0-60 cm soil horizons was uniform after rain during rainy season; however it was concentrated in surface horizon after rain during dry season. The differences of available soil moisture saturation degree between treatments and between soil horizons were significant during rainy season; nevertheless, those of dry season were not significant. The consumption rate of available soil water content in 0-60 cm soil horizons of uncultivated hillside land was the least among all treatments. Although the consumption rate of available soil water content during dry season was less than that of rainy season, the available soil water content during dry season would be exhausted in 15 days after rain.