| The yellow soil is the second largest soil type in the dry slope farmland in Sichuan Province,mainly distributed in the eastern part of the Sichuan Basin and the low and middle mountains around it.In the study area,torrential rain and unstable soil structure,as well as unreasonable tillage measure caused soil erosion in slope farmland.Maize is one of the main crops in sloping land of yellow soil,the growth period of maize is the same as rainfall erosion period,maize growth period has the same characteristics as rainfall erosion period.Therefore,this study took the sloping farmland of yellow soil as the research object,adopted the method of combining the field runoff plot location monitoring and indoor analysis.The study was carried out on the nitrogen loss characteristics of maize growth stages farmland under different tillage measures under the natural rainfall conditions.The characteristics of nitrogen loss in runoff and erosion sediment under different tillage measures were revealed,and the main ways of nitrogen loss during the whole growth period of maize under natural rainfall conditions were identified,and the models of nitrogen loss under different conditions were constructed.In order to provide some theoretical basis for soil erosion prevention and nutrient management in slope farmland of mountain yellow soil.The main research results are as follows:(1)The average rainfall in the whole growth period of maize in three years was736.03 mm,and a total of 48 erosive rainfalls were detected,including 14 moderate rain,19 heavy rain,11 rainstorm and 4 downpour.The erosion rainfall was concentrated in mature stage,accounting for 45.59% of the cumulative erosion rainfall.The rainfall intensity causing erosive rainfall was above 1 mm/h.The general trend of surface runoff,soil flow and nitrogen loss were as follows: mature stage > seedling stage > tasseling stage > elongation stage stage.The surface runoff and nitrogen loss were significantly affected by tillage measures in the whole growth period of maize,and the interflow and nitrogen loss in 0-20 cm and 20-40 cm interflow were significantly affected by tillage measures.The surface runoff and nitrogen loss were shown as downslope ridge planting >flat planting > cross ridge planting,while cross ridge planting in 0-20 cm and 20-40 cm interflow and nitrogen loss was significantly higher than the other two tillage measures.(2)Under different tillage measures and rainfall levels,surface runoff was the main way for nitrogen loss in growth periods of maize,and surface runoff and its nitrogen loss ratio reach the maximum when downslope ridge planting,and their maximum values appeared in elongation stage and seedling stage,the total nitrogen loss in 0-20 cm and20-40 cm interflow exceeded the surface runoff nitrogen loss under the conditions of cross ridge planting in the mature stage of maize.The ratio of different forms of nitrogen to total nitrogen in the test area was successively dissolved organic nitrogen > nitrate nitrogen >ammonium nitrogen.Runoff nitrogen loss was 79.60%-87.06% in total dissolved nitrogen.Dissolved organic nitrogen accounted for the largest proportion of flat planting in 0-20 cm and 20-40 cm interflow,and the largest proportion of cross ridge planting in the surface runoff.Nitrate nitrogen was the main component of inorganic nitrogen loss from surface runoff in slope farmland.(3)The general trend of erosion sediment and nitrogen loss was as follows: seedling stage > mature stage > tasseling stage > elongation stage.The erosion sediment and nitrogen loss during the whole growth period of maize were significantly affected by tillage measures and showed as downslope ridge planting > flat planting > cross ridge planting.Compared with downslope ridge planting,the implementation of cross ridge planting could enhance soil structure stability and weaken the surface runoff carrying capacity of sand,but we should also pay attention to the risk of soil loss in cross ridge planting during the maize maturity.Under the influence of ridge breaking,erosion sediment was the main way of nitrogen loss at seedling stage,accounting for 58.02% of the total nitrogen loss.Under the intensity of heavy rain in each growth period of maize,the amount of eroded sediment and nitrogen loss in each component of eroded sediment reached the maximum.In the erosion sediment,68.19%-87.06% of the organic nitrogen was acid-soluble nitrogen,and its nitrogen composition regularity was amino acid nitrogen > non-acid-soluble nitrogen > unknown nitrogen > ammonia nitrogen > amino sugar nitrogen.Except for the seedling stage of maize,the loss of unknown nitrogen was greater than that of non-acid-soluble nitrogen under each tillage.(4)Under the condition of rainfall events,nitrogen loss is positively correlated with rainfall erosion coefficient,and nitrogen loss increased with the increase of rainfall erosion coefficient.The model of nitrogen loss in the study area has some ability to predict the nitrogen loss in rainfall.The average relative error between calculated and measured values nitrogen loss was 38.68%,but the relative error between the calculated value and the measured value is large under the conditions of rainstorm and rainstorm intensity. |
