Characteristics of Nutrient Loss from Sloping Farmland in Karst Region as A Function of Rainfall Intensity

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National Key Research and Development Plan of China (No.2016YFC0502604), the First-class Subject Construction Project of Guizhou Province (No.GNYL[2017]007), the Important Science&Technology Specific Project of Guizhou Province (No.[2016]3022)

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    【Objective】As the multi-media environment in the karst region is so peculiar, few case-specific research methods are available, making it hard to carry out researches in this region of how soil nutrients are lost from slope farmlands. Although some have been done, outcomes vary sharply and are far from complete, adequate or systematic to exposit rules of nutrient loss from slope farmlands in the karst region, let alone mechanisms of underground soil nutrient lost. Therefore, this study was unfolded to explore characteristics and mechanisms of soil nutrient loss from slope farmlands in the karst region as a function of rainfall intensity, in an attempt to provide certain theoretical reference for control of nutrient loss and non-point source pollution from slope farmlands in the karst region. 【Method】An in-lab experiment was carried out with soil packed in a steel trough to s imulate bare slope farmland in morphological structure, 20% in bedrock outcropping rate, 20° in slope gradient, and 3% in porosity. Besides, the experiment was designed to have five levels of rainfall intensity, i.e. 15 mm∙h-1, 30 mm∙h-1, 50 mm∙h-1, 70 mm∙h-1and 90 mm∙h-1, to scour the aritificial slope farmland. Before the experiment began, the soil was made saturated in moisture with a light rainfall event, and effluent was collected for 30 minutes after the slope began to yield runoff. 【Result】(1) The rainfall intensity critical for runoff and sediment yield to transit from underground to surface varied in the range of 30 mm∙h-1~50 mm∙h-1 and runoff and sediment yield increased with rising rainfall intensity, and occurred mainly on the surface. (2) Under light rainfalls, 15 mm∙h-1 or 30 mm∙h-1 in intensity, loss of TN, TP and TK occurred mainly with underground runoff, while under heavy rainfalls, ≥ 50 mm∙h-1 in intensity, the loss of nutrients with surface runoff gained in proportion to the total loss and reached three times as much as that with underground runoff. The runoff loss of TP increased in both volume and concentration with rising rainfall intensity, but the loss of TK and TN did not change so significantly. (3) The nutrient loss with sediment occurred mainly on the surface, reaching about 5.03 times higher than that underground, and nutrients in the sediment were higher in concentration than those in the runoff. Nutrient enrichment rate of the surface sediment was on the whole higher than that of underground leaching. The totals of nutrient losses with surface and underground sediments and their moduli all increased with rising rainfall intensity. And (4) Significantly positive relationships were found of the total volume of runoff with nutrients (TP & TK) in runoff and nutrients (TN, TP & TK) in sediment (P< 0. 05), and with TN in runoff, too (P < 0. 01). 【Conclusion】The losses of TN, TP and TK occur mainly with runoff in slope farmlands in the karst region, and partly with sediment. Under rainfalls light in intensity (15 mm∙h-1 ~ 30 mm∙h-1), attention should be paid mainly to control of nutrient loss with underground runoff. The impact of rainfall intensity is significant on TP loss with runoff in volume and concentration, as well as on totals of nutrients lost with surface and underground sediments and their nutrient loss moduli. The total volume of runoff is significantly related to the losses of nutrients with runoff and sediment.

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GAO Ruxue, DAI Quanhou, GAN Yixian, YAN Youjin, PENG Xudong. Characteristics of Nutrient Loss from Sloping Farmland in Karst Region as A Function of Rainfall Intensity[J]. Acta Pedologica Sinica,2019,56(5):1072-1084.

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  • Received:May 07,2018
  • Revised:October 27,2018
  • Adopted:November 19,2018
  • Online: April 30,2019
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