The Accumulation And Migera And Fate Of Soil Nitrogen In Drylands Under Plastic Film Mulching On Loess Plateau

The ridge and furrow system with plastic film mulching increased crop yield significantly and has been widely used in the Loess Plateau.However,the low utilization rate of nitrogen fertilizer in this area restricts the sustainable development of agriculture.Meanwhile,the nitrogen transport and transformation processes may change under plastic film mulching,due to the improved soil water and temperature conditions.Therefore,it is important to study the accumulation,transport and fate of fertilizer nitrogen under the film mulching to improve the nitrogen use efficiency.This study was conducted during 2015-2017by comparing the differences between a mulching system（a ridge and furrow system with plastic film mulching）and a control system（a flat system without plastic film mulching）,to 1)investigate the N accumulation and distribution characteristics in soil profile under mulching;2)analyze the fate of fertilizer nitrogen and the differences between ridge and furrow in mulching system by urea-¹⁵N microplot experiment;3)prove the N transport combined with vertical and lateral movement in mulching system by ¹⁵N isotope tracing;and 4)investigate the N mineralization process under mulching.（1）The accumulation of mineral nitrogen in mulching system was 5.9 times higher than that in non-mulching soil,and it mainly occurred in 0-30 cm soil layer.During the maize growing period of 80-110 days,the content of soil mineral nitrogen at surface layer increased explosively in mulching system-ridge.（2）The plant N uptake derived from urea-fertilizer（Ndff）was 85.2 and 49.8 kg hm^-2 in mulching system and control system,respectively,which mulching system was 72.5%higher than control system.The amount of residual ¹⁵N in soil was 110.9 and 69.8 kg hm^-2respectively,which mulching system was 58.8%higher than control system.The N losses was63.9 and 139.7 kg hm^-2 for the two system,and mulching decreased the N loss by 54.5%,compared with control system.（3）In mulching system,96.5%of total plant ¹⁵N uptake derived from ridge,and only 3.5%derived from furrow;while 78.6%of the N losses were from furrow.The results indicated that ridge was the main source for plant uptake nitrogen,and furrow was the main source for nitrogen loss.The fertilizer ¹⁵N moved from furrow to ridge（furrow?ridge）and from ridge to furrow（ridge?furrow）,which were 12.2 and 6.0 kg ha^-1,respectively.The lateral movement of nitrogen occurred in the 0-40 cm soil layer.（4）During maize growing period,nitrogen mineralization was found in mulching system-ridge and the mineral nitrogen content in surface soil increased obviously,but decreased to background value at the end of growing period.By analyzing the changes of organic nitrogen（total nitrogen）and mineral nitrogen in the mineralization device under mulching system,reverse trends were found between them,indicating that the total nitrogen and mineral nitrogen in the soil had a mutual transformation relationship.In maize growing period,mineralization process controlled in the period with high temperature and more rainfall,and the immobilization controlled in the period with low temperature and less rainfall.