STUDY ON SOIL AND WATER CONSERVATION BENEFITS OF RETURNING BIOCHAR TO SLOPING FARMLAND IN THE SOUTH CHINA KARST AREA

The topography in the South China Karst area is fragmented, while sloping farmland is the most important land use type in this area, and corn is the main crop for sloping farmland, there is no water and soil conservation for a long time, so it causes extremely serious soil loss in the region and becoms the most typical landscape of karst rocky desertification in the world. In order to reduce the impact of corn planting on soil loss in sloping farmland and reveal the impact of biochar returning to the field on runoff and sand production, we set up a biochar returning to field experiment on sloping farmland in the South China Karst area. Based on the measured data of runoff and sediment yield from 36 natural erosive rainfalls, field runoff plot observation method was used to study the soil and water loss characteristics of sloping farmland under five biochar application rates of 0% (CK), 20% (BM1), 40% (BM2), 60% (BM3) and 90% (BM4) during the whole growth period of maize from 2018 to 2019. (1) The total runoff and sediment yield of sloping farmland decreased with the increase of biochar application rate, compared with the control, the total runoff yield of BM1, BM2, BM3 and BM4 decreased by 13.64%, 10.97%, 24.92% and 28.02%, respectively, and the total sediment yield decreased by 6.48%, 12.24%, 21.70% and 36.60%, respectively. (2) BM3 and BM4 could better control soil and water loss on sloping farmland. Under the characteristics of heavy rainfall, high rainfall intensity, their runoff and sediment yield were lower than those of the control, especially in 2019; both runoff yield (11) and sediment yield modulus (M) were significantly positively correlated with rainfall amount (P) and maximum 30 min rainfall intensity (I-30), the correlation between H and P was stronger than that between H and I-30, and the correlation between M and I-30 was stronger than that between M and P, but with the increase of biochar application rates, the correlation was decreased. The H, M and the composite factor PI30 (rainfall amount P and maximum 30 min rainfall intensity I-30) of rainfall characteristics all showed a significant multivariate power function relation (P<0.05). (3) There was an extremely significant positive correlation between M and H (P< 0.01), when no biochar was returned to the field, the relationship between Mand H was more in line with the power function (M=2.8634H(1.7773), R-2= 0.8772), while when the biochar was returned to field, there was a significant linear functional relationship between M and H (M=15.53h-19.97, R-2=0.8013). The results can provide a theoretical basis for the prevention and control of soil and water loss on sloping farmland in the South China Karst area.