Characteristics Of Nitrogen Transfer And Transformation In Farmland-shelterbelt Slope System In Black Soil Area

The black soil area is an important grain production base in China.The input of a large amount of fertilizer causes a great risk of non-point source pollution in this area.In order to investigate the horizontal transport characterization of inorganic nitrogen through farmland-shelterbelt slope system in black soil region,and evaluate the positive effect of shelterbelt on slowing down non-point source pollution on sloping farmland.Based on soils from typical sloping field(farmland),shelterbelt located on the field boundary of down slope(shelterbelt),and the transition zone between farmland and shelterbelt(transitional zone)soil,the method of self?designed soil column was used to simulate inorganic nitrogen(nitrate nitrogen and ammonium nitrogen)migration process from different depths' soil of the farmland-shelterbelt system.Furthermore,the difference of migration processes and their influence factors were compared and analyzed.Isothermal kinetic method was used to determine the adsorption and desorption strength and fit relevant equations to explore the adsorption capacity of the farmland-shelterbelt system soil to ammonium nitrogen.Constant temperature and humidity culture method was adaped to determine the potential of soil nitrification,denitrification and ammoniation.Results showed that:1)The speed of water-nitrogen transport decreased with increasing migration distance and soil depth.In soil of 0?40 cm,the water?nitrogen transport speed of shelterbelt and transitional zone was greater than which of farmland;the water?nitrogen transport speed in 40?80 cm was all lower than 1 cm·min-1 and presented a consequence order as shelterbelt<farmland and transitional zone.Farmland,transitional zone,shelterbelt showed a strong interception effect on ammonium nitrogen,as the concentration of ammonium nitrogen decreased rapidly with the increase of water-nitrogen migration distance,and the highest initial content of ammonium nitrogen in shelterbelt was found in 0?10 cm soil layer(438.07 mg·kg-1);concentration of ammonium nitrogen of transitional zone(666.81 mg·kg-1)and farmland(420.04 mg·kg-1)in 40?60 cm soil layer was the both highest.Nitrate nitrogen in 0?20 cm from farmland and in 40?80 cm from transitional zone both transported with wetting front moving forward and obviously accumulated in the wetting front;however,soil nitrate nitrogen from shelterbelt did not migrate with the migration of wetting front and showed an interception effect on soil nitrate nitrogen particularly in 0?20 an.2)The adsorption amount of ammonium nitrogen from three diferent land use types all reached a high level at the initial stage of reaction,except for the soil layer of 40?60cm.Transitional zone in the 0?10 cm soil layer showed a stronger adsorption capacity of ammonium nitrogen than shelterbelt and farmland.The desorption capacity of shelterbelt to ammonium nitrogen was obviously lower than that of farmland land and transitional zone,and the adsorption capacity of shelterbelt to ammonium nitrogen was the strongest.3)S0il nitrification activity increased with the increase of culture time,and showed a law of transitional zone>farmland>shelterbelt;however,the nitrification rate first decreased,then increased slightly and then decreased with the increase of culture time.Soil denitrification activiy and rate did not showed a manifested change trend with culture time increasing and difference of landuse type.The ammonification activity and rate of soil in the shelter forest belt were stronger than that in the farmland and the transitional zone,but with the increase of reaction time,the ammoniation activity and rate of shelterbelt were lower than that in the farmland and the transition zone,which was more conducive to the retention of nitrogen in the soil from a long-term perspective.In conclusion,in the farmland-shelterbelt system,shelterbelt could not only increase transportation of nitrogen-water in soil and consequently reduce surface runoff,but also absorb and retard the movement of inorganic nitrogen,especially in 0-20 cm soil layer.Shelterbelt soil has lower nitrification activity than that in farmland land and transitional zone,which is more beneficial to the preservation of nitrogen in soil.In addition,soil organic matter plays an important role in retaining inorganic nitrogen on sloping farmland of black soil region.