| The mulched drip irrigation technology combines the temperature-enhancement and moisture-preserving effects of the film mulch and the advantage of the accuracy control of water and fertilizer in drip irrigation.It has been widely used in northwest and northeast China.However,at present,the study on the characteristics of nitrogen distribution and the transformation process in the soil under mulching film cannot considering the drip irrigation and other irrigation techniques,then there is a lack of understanding of nitrogen dynamics,transformation and absorption processes,the mechanism of nitrogen affected by the different mulching methods and fertigation technology parameters lacks in-depth research and fails to provide scientific basis for water and fertilizer management under mulched drip irrigation.In addition,the hazards of agricultural residual film have become increasingly apparent in recent years.The ecological environment of mulched drip irrigation technology is increasingly valued.The use of a biodegradable membrane with a suitable degradation time is the trend of the development of mulched drip irrigation technology in the future.For this reason,it is urgent to carry out research on the appropriate film removing time and fertilization system optimization for mulched drip irrigation.Maize was chose as the research object,and studied nitrogen distribution,conversion and absorption with mulched drip irrigation by experiment and model.The film uncovering time and fertilizer amount were set as the main factor in the experiment,there were 3 levels of uncovering film at the seedling stage,uncovering film at the heading date,and covering film in the whole process,and the bare soil was set as a control.Each level included 2 treatments of fertilization and no fertilization.Soil moisture content,soil nitrate nitrogen,soil ammonium soil redox potential value,soil urease activity and soil asparagine activity were measured at the each growth period of maize,soil temperature was observed daily,plant height,leaf area index,above-ground dry matter weight and nitrogen uptake were measured periodically,and yeild was measured at the end of period of maize.The DNDC model was used to optimize the fertilizing schedule for mulched drip irrigation.The main conclusions were as follows:(1)Comparing with bare treatment,the treatments of uncovering film at the seedling stage,uncovering film at the heading stage,and covering film at whole period of maize with fertilizer could increase the soil moisture content of 12.2%,13.6%,and 10.6%in the 0-20cm soil layer,respectively.The water content in the 20-90cm soil layer was not different in this three treatments.In the unfertilizing condition,the moisture content of each layer of the soil was increased in three film uncovering treatments,they could increased Soil moisture content of 9.6%7.9%and 9.4%in the 0-90cm soil layer,Compared with the bare soil treatment.The plastic film could increase the surface soil temperature during the growth period of maize,and highest temperature increase appeared at the seedling stage of maize,and the lowest temperature increase occurred at the heading stage of maize;the uncovering film at the seedling stage,uncovering film at the heading stage,and covering film at whole period of maize treatment can increase soil effective accumulated temperature during the maize growth period by 9.2%,12.8%and 18.1%,respectively.(2)The film uncovering treatments could increase the nitrate nitrogen content in the 0-90cm soil layer at the seedling,jointing and heading stages of maize,while the bare soil treatment and the covering film treatment in the whole growth period can increase the nitrate nitrogen content in 90cm soil layer at maize filling and maturation period;In unfertilizing condition,each film uncovering treatment could increase the ammonium nitrogen content in 0-20cm soil layer,and under the condition of fertilizing,each film uncovering treatment could increase the ammonium nitrogen content in 20-50cm soil layer;Treatment of uncovered film during the whole growing season could increase the soil organic nitrogen mineralization,treatment of removing the film at the seedling stage and treatment of removing the film at the heading stage would reduce the soil organic nitrogen mineralization.(3)The Eh of bare soil treatment in the 0-30cm soil layer was 3.08-57.08mV higher than that of the uncovered film treatments.The increase value at the early growth stage of maize was largest,the lowest increase value appeared at the late growth stage of maize,to the end of the growth period,there was no difference in all treatments;Variance test results showed that the all removing film treatments had no significant effect on the Eh,it can be seen that the film mulching did not significantly affect the soil aeration.The film mulching could significantly reduce the urease activity in all layers of soil.Treatments of removing the film at the seedling stage and the heading stage of maize did not increase soil urease activity.Correlation analysis showed that soil urease activity was significantly negatively correlated with ammonium nitrogen in the soil.The increase of soil ammonium nitrogen after film mulching reduced soil urease activity;Film mulching had no significant effect on soil asparaginase activity,but it was positively correlated with nitrogen uptake in maize,their correlation coefficient under plastic film and fertilizer condition is 0.891.(4)Film-covering treatment can significantly increase plant height,leaf area index,dry matter weight and nitrogen uptake in maize seedling stage,and the difference between uncovered film treatments is not significant;treatment of film mulching at whole period of maize could significantly improve the number of double ears and 100-grain weight of maize in no fertilization condition,which resulted in the highest yield.Under the fertilization conditions,the treatment of removing film at seedling stage could significantly increase the number of double ears in maize and harvest the highest corn yield.Considering the effects of temperature increase of film mulching,conversion and absorption of nitrogen and crop yield,it is appropriate to adopt the treatment of removing film at the seedling stage of maize for mulched drip irrigation in the Northeast China.(5)Optimization of fertigation schedule using DNDC model under mulched drip irrigation showed that when the initial inorganic nitrogen content in soil is about 60 mgy/kg,the suitable nitrogen application amount for maize is 150-200 kg/hm2 in the semi-humid zone of northeastern China,and a ratio of 1:3 during the heading stage and the grain-filling period could reduce nitrogen leaching losses with obtaining higher maize yield. |
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