| There are about 40,000,000 hm2 of slope land in China, and most of them locate in the west. They are an important part of the arable land resource, and relate to national ecological environment construction and food security. But, a long term of unreasonable production activity by human and natural factors caused serious soil and water losses, which not only led to thinner layer, coarser texture, lower fertility, low and unstable productivity of soil, but also resulted in environmental pollution and sedimentation in water bodies that maybe destroy their function. So soil and water losses control on slope land always was of great concern by government and local people. This paper took slope lands on loess plateau north of Weihe River as research object, using combined methods of located monitoring, survey, and indoor analysis, investigated the mechanism of soil degradation and approaches of recovery by human. Some main conclusions were found:1. The main reason for soil degradation of slope lands was soil and water losses. The frequency of soil and water losses within one year was increased with times of erosive rainfall events. The frequency of losses in wet years was higher than in drought years. As slope gradient increased, the amount and intensity of losses both increased. During the observation period, total soil and water losses amounts from slope with gradients of 5°, 10°and 15°were 321 t/a?km2 and 13303 m3/a?km2, 1865 t/a?km2, 43289 m3/a?km2 and 3536 t/a?km2和53373 m3/a?km2, respectively. The results of losses were higher bulk density, lower porosity, worse water holding capacity. At the same time, lots of available nutrients were carried away. Measurements showed that concentration of organic matter, total nitrogen, nitrate, ammonium, and available potassium in sediment was much higher than that in soil at top arable layer, which means there was an enrichment phenomenon.2. Crop cover could effectively reduce soil and water losses to a certain extent depended on the treatments. During the observation period, runoff and sediment yields from monoculture corn and alfalfa fields reduced by 17.7% and 27.3%, 70.2% and 84.2% respectively, compared to bare soil treatment, meanwhile, runoff and sediment yields from strip intercropping fields of corn and alfalfa reduced by 61.8% and 79.9%. Amount of soil and water losses influenced crop yield and biomass to a certain extent. Experiments proved that crop yield and biomass reduced 8.7% and 22.8% by average as increasing of slope gradient and soil and water losses amount. Under the treatment of no fertilizer, every 1 cm erosion of soil of arable layer would cause yield of corn decreased by 2.2% to 2.0%, biomass of corn decreased by 1.1% to 2.0%.3. Increasing the depth of arable layer and fertilizer amount, and implementation of soil and water conservation were main approaches of promoting the productivity of soil. Experiments proved that, under the treatment of no fertilizer, when the depth of arable layer increased from 0 cm to 40 cm, crop yield and biomass of corn increased by 128.5% and 207.6% respectively; when the fertilizer amount increased from 0 kg/hm2 to 600 N kg/hm2, 300 P2O5 kg/hm2,300 K2Okg/hm2, crop yield and biomass increased by 95.2% and 82.6% respectively;when slope land was terraced, the average yield was 4.9%,9.9%,14.2% higher than slope lands with 5°,10°and 15°gradient,respectively; the average biomass was 18.2%,30.4%,42.5% higher than slope lands with 5°,10°and 15°gradient,respectively.4. The evaluation of productivity index proved that the index of fields with strip tillage treatment was obviously higher that of bare soil, and appeared a decreasing trend as slope gradient increased. With the increasing of fertilizer amount, the productivity index also increased. Trend of corn yield approximately agreed with the productivity index, and there was a positive relationship between them. |
