To explore the responses of soil and water loss to the development of karst fissures

the effects of two different karst fissures structures: fissures exposed rock-soil (XL) and fissures buried rock-soil (XM) on subsurface runoff and nitrogen leaching were studied through rainfall simulation experiments

in which soil experimental micro-plots (QT) were selected as control. The results showed that the responses time of subsurface runoff under different karst fissures structures listed in the order of XL＜XM＜QT

the responses time of subsurface runoff to the rainfall were 29

77

and 139 min

respectively

and responses time of subsurface runoff of XL and XM reduced by 79.14% and 44.60% compared to QT

respectively. The rainfall thresholds were 20.64

55.06

and 94.90 mm

respectively

and rainfall threshold of XL and XM reduced by 78.25% and 41.98% compared to QT

respectively. The times of the stability of subsurface runoff rate were 59

107

and 169 min

and the stability of subsurface runoff rates were 42.09

42.36

and 38.24 mm/h

respectively. The nitrate nitrogen and nitrogen concentration were the highest in XL

which could reach 11.64

10.45 mg/L

respectively. The nutrient concentration in subsurface runoff reached a stable value in XL and QT prior to runoff stopped. The total nitrogen amount under different karst fissures structures followed the order of XL＞XM＞QT

nitrate nitrogen leaching listed in the order of XM＞XL＞QT. Under different karst fissures structures

nitrate nitrogen was the main component of nitrogen leaching

which accounted for 82.32%～90.12% in total nitrogen leaching amount

however

the proportion of ammonia nitrogen was less than 2%. The existence of the fissures

especially the existence of the XL

could enhance both the subsurface runoff rate and the leaching of nitrogen for per unit area soil

the soil which at the bottom of the experimental micro-plot. Because of the widely developed fissures in karst area

the infiltration of water was promoted

moreover

the leaching of nitrogen was intensified too. The relevant results can provide scientific basis for explore the mechanisms of soil and water loss as well as construction material migration model in karst regions.