Effect of hedgerow patterns controlling nitrogen loss of slope farmland in purple soil area

Abstract: Agricultural non-point source nitrogen is one of the major sources for surface water eutrophication in the world. Hedgerows have been widely used as a measure of controlling soil, water and nutrient losses. However, there are few studies on nitrogen concentration loading and composition in runoff under long period hedgerow patterns in purple soil area of southwest China. Field experiments were carried out for three years to examine effects of 13-year hedgerow intercropping patterns for controlling nitrogen loss. There were six treatments: contour cropping (T1), Amorpha hedgerow plus contour cropping (T2), and Vetiver hedgerow plus contour cropping (T3) on 20° slope land, and contour cropping (T4), alfalfa hedgerow plus contour cropping (T5) and Eulaliopsis binata hedgerow plus contour cropping (T6) on 13° slope land. Results showed that in general, hedgerow patterns can reduce total nitrogen concentration and different forms of nitrogen in runoff. In terms of total N, compared with T1, average total nitrogen concentration in runoff decreased by 36.0%, 33.0% for T2 and T3 on the 20o slope farmland, respectively. Compared with T4, average total nitrogen concentration in runoff decreased by 5.9% for T5, and it had no significant decrease for T6 (P>0.05) on the 13o slope farmland. Enrichment rate of sediment nitrogen for hedgerow patterns was higher (P<0.05) than that of the contour cropping treatment. This indicated that hedgerow patterns can effectively control sediment nitrogen loss. Hedgerow patterns reduced total nitrogen and different form of nitrogen loss from slope farmland. In terms of total nitrogen, compared with T1, annual average total nitrogen loss under T2 and T3 was respectively reduced by 32.86 and 31.99 kg/hm2 accounting for 92.4% and 90.0% nitrogen loss reduction on the 20o slope farmland. Compared with T4, annual average total nitrogen loss under T5 and T6 was respectively reduced by 27.55 and 26.04 kg/hm2 accounting for 88.7% and 83.9% in nitrogen loss reduction on the 13o slope farmland. Therefore, Amorpha, Vetiver, alfalfa and Eulaliopsis binata hedgerow patterns can be used for controlling agricultural non-point pollution in purple soil area. Effects of different hedgerow patterns on controlling nitrogen loss were difference. On same slope, effects of Amorpha patterns controlling nitrogen loss was better than that of Vetiver, and effects of Alfalfa patterns controlling nitrogen loss was better than that of Eulaliopsis Binata. Effects of hedgerow patterns in controlling nitrogen loss increased with the increase in slope degree. Overall, shrub hedgerow patterns can be used to control nitrogen loss in runoff under 20o slope farmland. More research is still needed when slope is larger than 20o slope.