Effects Of Nitrogen Application Level On Soil Nitrogen Composition And Nitrogen Phosphorus And Potassium Accumulation In Maize

Maize is an important food and feed crop in China.In 2022,the maize planting area is 43.07million hectares,and the maize yield is 277.2 million tons.Increasing maize yield is of vital significance for the country’s food security.Nitrogen is an essential nutrient element in maize growth and development,which plays a key role in crop yield and quality formation.Appropriate increase of nitrogen fertilizer application can create a good soil nitrogen supply environment,promote soil nutrient absorption,improve soil nitrogen invertase activity,promote the accumulation and transport of dry matter and nutrients in various nutrient organs of corn,and then increase corn yield.Therefore,it is of great significance to study the effects of nitrogen application level on soil nitrogen composition and nitrogen,phosphorus and potassium accumulation in plants.This experiment was carried out in 2022.Using the located experiment area started from Xiangyang Practice Base of Northeast Agricultural University in 2015,two planting methods of maize-soybean rotation and maize continuous cropping were set.Urea（46%）was used as nitrogen fertilizer.Urea application rates in maize fields were:no nitrogen（0 kg/hm²）,low nitrogen（175kg/hm²）,medium nitrogen（350 kg/hm²）,high nitrogen（525 kg/hm²）,the application amounts of pure nitrogen were 0 kg/hm²,81.67 kg/hm²,163.33 kg/hm²and 245 kg/hm²,respectively.The dosage of ¹⁵N was 0g/plant,0.97g/plant,1.94g/plant,2.92g/plant,respectively.Urea application amounts of soybean fields were:no nitrogen（0 kg/hm²）,low nitrogen（30 kg/hm²）,medium nitrogen（60 kg/hm²）,high nitrogen（90 kg/hm²）,and converted pure nitrogen application amounts were 0 kg/hm²,14 kg/hm²,28 kg/hm²,42 kg/hm²,respectively.The four nitrogen application levels of maize continuous cropping were denoted as:CN₀,CN₁,CN₂,CN₃;the four nitrogen application treatments of soybean and maize rotation are denoted as:RN₀,RN₁,RN₂,RN₃.The effects of nitrogen application level on soil nitrogen component,soil enzyme,maize growth and nutrient accumulation were studied.The test results show that:（1）The content of soil total nitrogen and soil available nitrogen increased with the increase of nitrogen application,and the difference between high nitrogen and medium nitrogen was significant compared with no nitrogen application.Under the same nitrogen application level,soil total nitrogen and soil available nitrogen contents in the upper layer（0～15 cm）were higher than those in the lower layer（15～30 cm）.Under different nitrogen application levels,the total nitrogen content in the upper and lower layers of soybean-maize rotation increased under RN₃,RN₂and RN₁treatments compared with RN₀,respectively 29.60%,12.81%,8.24%and 20.95%,13.53%,8.95%;The total nitrogen content in the upper and lower layers of maize continuous cropping increased in CN₃,CN₂and CN₁treatment compared with CN₀treatment,respectively38.80%,21.17%,9.34%and 40.15%,20.53%,15.09%.The content of ammonium nitrogen in the upper and lower layers of soy-maize rotation was increased by RN₃,RN₂and RN₁treatments compared with RN0,respectively 118.99%,83.65%,23.76%and 158.88%,104.88%,17.75%;The content of ammonium nitrogen in the upper and lower layers of maize continuous cropping increased in CN₃,CN₂and CN₁treatment compared with CN₀treatment,respectively185.91%,53.25%23.24%and160.82%,49.57%,12.17%.The nitrate nitrogen content in the upper and lower layers of soy-maize rotation was increased by RN₃,RN₂and RN₁treatments compared with RN₀,respectively 51.82%,26.22%,10.07%and 46.98%,21.15%,8.03%;The nitrate nitrogen content in the upper and lower layers of maize continuous cropping increased in CN₃,CN₂and CN₁treatment compared with CN₀treatment,respectively 48.68%,31.48%,14.95%and 76.21%,49.52%,42.77%.（2）Except for unknown and non-acidolytic nitrogen,the content of soil nitrogen increased with the increase of nitrogen application rate;the content of total nitrogen and amino acid nitrogen in high nitrogen treatment was significantly higher than that in no nitrogen treatment,and the rule was inconsistent among other treatments.Under the same nitrogen application level,the soil nitrogen content was higher in the upper layer than in the lower layer,and the soil nitrogen content in soybean-maize rotation was higher than that in maize continuous cropping.Under the same nitrogen application level,the order of the content of each component of soil acidolytic nitrogen was as follows:acidolytic ammonia nitrogen>amino acid nitrogen>acidolytic unknown nitrogen>amino sugar nitrogen.（3）The activities of nitrite reductase,leucine aminopeptidase and N-acetyl-β-D-glucosidase in soil increased with the increase of nitrogen application,the activities of urease and nitrate reductase in soybean-miaze rotation soil showed the same change rules,and the activities of urease and nitrate reductase in maize continuous cropping soil increased first and then decreased with the increase of nitrogen application.Except nitrite reductase,soil enzyme activity in nitrogen treatment was significantly higher than that in no nitrogen treatment.Under the same nitrogen application level,soil enzyme activitice in the upper layer was higher than those in the lower layer,and soybean-maize rotation soil enzyme activity was higher than maize continuous cropping.（4）The accumulation of nitrogen,phosphorus and potassium in maize plants increased with the increase of nitrogen application rate.The accumulation of nitrogen,phosphorus and potassium in maize plants under high nitrogen and medium nitrogen treatment was significantly higher than that under no nitrogen application rate.The regularity of low nitrogen treatment and no nitrogen application rate was inconsistent in different organs.In soybean-maize rotation and maize continuous cropping,nitrogen accumulation in root increased under high nitrogen,medium nitrogen and low nitrogen treatments compared with no nitrogen,respectively 404.30%,191.44%,169.72%and 368.11%,192.80%,111.48%,nitrogen accumulation in stems and leaves of plants under high nitrogen,medium nitrogen and low nitrogen treatment was increased compared with no nitrogen treatment,respectively105.74%,80.09%,43.64%and 513.63%,246.63%,220.28%,the nitrogen accumulation of female panicle was increased under high nitrogen,medium nitrogen and low nitrogen treatment compared with no nitrogen treatment 74.20%,40.20%,33.11%and233.17%,204.72%,113.57%;the accumulation of phosphorus in plant roots increased under high nitrogen,medium nitrogen and low nitrogen treatment compared with no nitrogen treatment109.58%,52.74%,45.39%and 84.39%,47.35%,23.88%,The accumulation of phosphorus in stems and leaves of plants under high nitrogen,medium nitrogen and low nitrogen treatments was increased compared with that without nitrogen,respectively 100.17%,50.78%,32.27%and154.28%,67.52%,31.54%,the accumulation of phosphorus in female panicle of plants under high nitrogen,medium nitrogen and low nitrogen treatment was increased than that without nitrogen,respectively86.30%,41.96%,14.67%and 78.13%,75.95%,40.58%;The accumulation of potassium in plant roots increased under high nitrogen,medium nitrogen and low nitrogen treatment compared with no nitrogen treatment 104.55%,44.50%,36.68%and 77.04%,42.76%,17.02%,the accumulation of potassium in stems and leaves of plants under high nitrogen,medium nitrogen and low nitrogen treatment was increased compared with no nitrogen treatment,respectively 84.49%,25.05%,66.55%and 81.07%,42.32%,22.68%,the accumulation of potassium in female panicle was increased under the treatment of high nitrogen,medium nitrogen and low nitrogen,respectively 59.46%,42.50%,14.35%and 94.69%,83.16%,46.19%.（5）The abundance of ¹⁵N decreased gradually with the growth period,but increased with the increase of nitrogen application rate,high nitrogen>medium nitrogen>low nitrogen,only high nitrogen and low nitrogen treatments showed significant differences;Nitrogen use efficiency RN₃and RN₁were significantly higher than RN₂under soy-maize rotation,there was no significant difference among the treatments under continuous cropping.The N efficiency of soybean and maize rotation was higher than that of maize under low N,medium N and high N,respectively21.97%,5.57%,30.03%.（6）The dry weight and yield of maize plants increased with the increase of nitrogen application rate,and the dry weight with high nitrogen was significantly higher than that without nitrogen application.The yield performance was RN₃>RN₂>RN₁>CN₃>RN₀>CN₂>CN₁>CN₀,there was no significant difference between RN₃and RN₂treatments in soybean-maize rotation mode,but significant difference between other treatments,there were significant differences among maize continuous cropping treatments;Compared with maize continuous cropping,soybean maize rotation yield was higher at no nitrogen,low nitrogen,medium nitrogen and high nitrogen levels,respectively79.92%,39.03%,36.67%,25.99%.