Experimental Study On Soil Nutrients Loss From Typicl Hillslope Farmland In Karst Region

Soil nutrient loss in karst slope is not only the research core content of soil erosion and non-point source pollution but also the common concern focus for soil science, hydrology and environmental science and other subjects. Serious water and soil and nutrient loss in karst region not only did cause land productivity reduced but also made regional ecological environment damaged.Taking typical karst sloping farmland as research object, lime soil as test soil, through the steel tank which slope gradient and underground pore fissure degree was adjustable combined with field survey data, the characteristics of surface and underground nutrient loss in karst slope farmland was clarified using artificial rainfall experiments under different rainfall intensity, slope gradient and underground pore fissure degrees. The main impact factors of soil nutrient loss was also analyzed, and put forward the corresponding nutrient loss prediction model. Rerults from the present study could provide a theoretical basis for nutrient loss control and non-point source pollution management, evaluation and adjustment in karst areas. The main conclusions are as follows:(1) Rainfall intensity effect on nutrient concentration of surface runoff loss was not obvious, but that of underground runoff loss was generally increased with rainfall intensity increasing; nutrient loss of surface runoff increased with rainfall intensity increasing, however, that of underground runoff had not obvious variations. Nutrient concentration of surface sediment loss increased with rainfall intensity increasing, but that of underground sediment loss had no obviousvariations; Nutrient loss of surface sediment increased with rainfall intensity increasing, while that of underground sediment decreased had no significant changes with the increase of rainfall intensity. For nutrient ratio coefficient of surface runoff sediment, it increased with the increase of rainfall intensity, and there was no significant correlation between soil nutrient enrichment ratio and rainfall intensity.(2) TN concentration in surface runoff had no obvious variation with slope gradient generally, but that in underground runoff decreased with slope gradient increasing. TP loss amount in surface runoff increased with slope gradient increasing generally, but that in underground runoff had no obvious variation. TK loss amount in surface runoff increased with slope gradient increaseing, however, that in underground runoff had no obvious variation with increase of slope gradient, which mainly showed that loss amount of steep slope was higher than that of gentle slope. Each nutrient loss amount of surface sediment yield under different slope gradient increased with slope gradient increasing; as for the nutrient loss of underground sediment yield, each nutrient loss amount had no significant variation with slope gradient increasing. The Nitrogen enrichment ratio of sediment yield was greater than 1 generally; the TK enrichment ratio of sediment yield was more than 1 at the slope gradient of 20° and 25°, correspondingly the others were less than 1. The TP enrichment ratio of sediment yield on slope had no obvious differences between all slope gradient conditions, slope gradient had no obvious influence on TP enrichment ratio.(3) TN, TP and TK loss in surface runoff had no obvious relations to underground pore fissure degree; TN loss amont of underground runoff in general increased with underground pore fissure degree increasing, in which the total amount of TN reached the maximum(4028.38 mg) at 4% of underground pore fissure degree; TP and TK loss showed no obvious changing with underground pore fissure degree increasing, which changed between 44.92 and 225.76 mg. The loss amount of each nutrient of surface sediment had no obvious variations with underground pore fissure degree, the nutrients except for TP and available phosphorus presented obvious enrichment phenomenon. There was no significant variation between underground pore fissure degree and concentrations of each nutrient in sediment, however, available potassium, TN and alkali-hydrolyzable nitrogen increased and then decreased with underground pore fissure degree increasing, nevertheless, TK, TP and available phosphorus did not change significantly.(4) Both TN and TK loss amout in surface runoff was significantly correlated(p <0.05) with rainfall intensity, correlation coefficient r were 0.867 and 0.956, respectively, and TP loss amout was significantly correlated(p <0.01) with rainfall intensity, r was 0.984. Both TP and TK loss in surface runoff was significantly correlated(p <0.05) to slope, r were 0.945 and 0.931, respectively, however, the correlation between loss mount of TN and slope was not significant(p?0.05). Correlation between slope and loss amount of each nutrient in underground runoff did not reach significant levels(p?0.05). Correlation between underground pore fissure degree and loss amount of each nutrient in surface and underground runoff were not significant(p?0.05).(5) Individual pollutant modulus of TN, TP and TK in surface runoff were significant or extremely significant correlated with rainfall intensity, and was significant correlated with slope while was not correlated with underground pore fissure degree. Individual pollutant modulus of each nutrient in underground runoff was not correlated with rainfall intensity, slope and underground pore fissure. Surface sediment was extremely significant correlated with rainfall intensity, and was significantly correlated with underground pore fissure degree. However, underground sediment was not correlated with rainfall intensity, slope and underground pore fissure degree.