Tomer M D, Meek D W, Kramer L A
National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011, USA.
J Environ Qual. 2005 Aug 9;34(5):1547-58. doi: 10.2134/jeq2004.0199. Print 2005 Sep-Oct.
Agricultural tillage influences runoff and infiltration, but consequent effects on watershed hydrology are poorly documented. This study evaluated 25 yr (1971-1995) hydrologic records from four first-order watersheds in Iowa's loess hills. Two watersheds were under conventional tillage and two were under conservation (ridge) tillage, one of which was terraced. All four watersheds grew corn (Zea mays L.) every year. Flow-frequency statistics and autoregressive modeling were used to determine how conservation treatments influenced stream hydrology. The autoregressive modeling characterized variations in discharge, baseflow, and runoff at multi-year, annual, and shorter time scales. The ridge-tilled watershed (nonterraced) had 47% less runoff and 36% more baseflow than the conventional watershed of similar landform and slope. Recovery of baseflow after drought was quicker in the conservation watersheds, as evidenced by 365-d moving average plots, and 67% greater baseflow during the driest 2 yr. The two conventional watersheds were similar, except the steeper watershed discharged more runoff and baseflow during short (<30 d), wet periods. Significant multi-year and annual cycles occurred in all variables. Under ridge-till, seasonal (annual-cycle) variations in baseflow had greater amplitude, showing the seasonality of subsurface contaminant movement could increase under conservation practices. However, deviations from the modeled cycles of baseflow were also more persistent under conservation practices, indicating baseflow was more stable. Indeed, flow-frequency curves showed wet-weather discharge decreased and dry-weather discharge increased under conservation practices. Although mean discharge increased in the conservation watersheds, variance and skewness of daily values were smaller. Ridge tillage with or without terraces increased stream discharge but reduced its variability.
农业耕作会影响径流和入渗，但对流域水文的后续影响却鲜有文献记载。本研究评估了爱荷华州黄土丘陵区四个一级流域25年（1971 - 1995年）的水文记录。其中两个流域采用传统耕作方式，另外两个采用保护性（垄作）耕作方式，其中一个还进行了梯田化处理。所有四个流域每年都种植玉米（Zea mays L.）。采用流量频率统计和自回归模型来确定保护性耕作措施如何影响河流水文。自回归模型刻画了多年、年度以及更短时间尺度下流量、基流和径流的变化。与地形和坡度相似的传统流域相比，垄作流域（非梯田化）的径流减少了47%，基流增加了36%。保护性耕作流域干旱后基流的恢复更快，365天移动平均线图证明了这一点，在最干旱的两年里基流比传统流域大67%。两个传统流域情况相似，但较陡的流域在短（<30天）湿润期的径流和基流排放更多。所有变量都出现了显著的多年和年度周期。在垄作条件下，基流的季节性（年度周期）变化幅度更大，表明在保护性耕作措施下，地下污染物运动的季节性可能会增强。然而，在保护性耕作措施下，基流偏离模型周期的情况也更持久，这表明基流更稳定。实际上，流量频率曲线显示，在保护性耕作措施下，湿润天气流量减少，干燥天气流量增加。尽管保护性耕作流域的平均流量增加了，但日流量值的方差和偏度较小。有或没有梯田的垄作增加了河流流量，但降低了其变异性。
