| In constructed wetland paddy fields,chemical fertilizers are used to increase the absorption and utilization of nitrogen and phosphorus nutrients,but also increase the runoff loss of nitrogen and phosphorus,which leads to environmental problems such as eutrophication of external water bodies and groundwater pollution.It is of great significance to study the transformation and loss of nitrogen and phosphorus in constructed wetland paddy fields,and to make a preliminary evaluation of their ecological benefits on this basis.This experiment was carried out at the Jinjing Experimental Station of the Institute of Subtropical Agriculture,Chinese Academy of Sciences.Based on the amount of local conventional nitrogen and phosphate fertilizer application,the settings were 0%chemical fertilizer level(T0),50%chemical fertilizer level(T1),70%chemical fertilizer level(T2),100%chemical fertilizer level(T3)and 150%chemical fertilizer level(T4).Through the experiments of three rice seasons,the effects of different treatments on the risk window period,loss of nitrogen and phosphorus in paddy fields,the absorption and utilization of nitrogen and phosphorus by rice,the balance of nitrogen and phosphorus input and output were explored,and the ecological and economic benefits were evaluated.The main findings are as follows:(1)In the three rice seasons,the total nitrogen loss in the experimental area was 92.31 kg·hm-2,mainly ammonium nitrogen(accounting for 52.85～56.93%);the total phosphorus loss was 2.82 kg·hm-2,mainly particulate phosphorus(accounting for 71.89～76.51%).The loss of nitrogen and phosphorus increases with the increase of fertilization level;9 days after fertilization is the risk window period for nitrogen and phosphorus runoff loss,especially nitrogen loss.The results of the 2019 early rice season showed that the amount of nitrogen loss within 9 days after fertilization accounted for the total nitrogen loss in the entire early rice season was 78.19-89.26%.(2)With the increase of fertilization level,the absorption and utilization rate of nitrogen fertilizer and phosphate fertilizer increased first and then decreased,with T2 treatment being the highest value(38.32～40.05%and 13.26～14.74%respectively);dry matter accumulation,nitrogen and phosphorus content in various parts at maturity and total accumulation of nitrogen and phosphorus,all showed an upward trend;the nitrogen content and phosphorus content of each part of the rice mature period showed the following:grain>stalk>root>stubble.Among them,the total nitrogen and the total phosphorus taken away by straws and grains is 66.00～146.74 kg·hm-2 and 14.07～23.90 kg·hm-2 respectively.Compared with T0 treatment,the nitrogen and phosphorus uptake of plants in the fertilization treatment(average of the three seasons)increased by 39.48～108.40%and 46.13～113.97%respectively.The nitrogen fertilizer absorption and utilization rate of the three seasons was 27.42～40.05%,and the phosphorus fertilizer absorption and utilization rate was 8.63～14.74%.(3)In the estimation of the nitrogen balance of each fertilization treatment:ammonia volatilization loss accounted for 4.70～7.27%,denitrification loss accounted for 12.46～19.26%,runoff loss accounted for 2.28～4.51%,leakage loss accounted for 4.47～8.68%,and harvested nitrogen accounted for 48.64～62.99%.In the estimation of the phosphorus balance of each fertilization treatment:runoff loss accounts for 0.44～0.53%,leakage loss accounts for 0.42～0.95%,and harvested phosphorus accounts for 39.77～60.83%.The surplus of nitrogen and phosphorus showed an upward trend with the increase of fertilization level,and the T4 treatment was the maximum.(4)The comprehensive index of T2 treatment for the three rice seasons is 81.45,74.58,73.19,and the comprehensive evaluation of ecological and economic benefits ranks first.The 70%chemical fertilizer level is a suitable fertilizer amount that takes into account both ecological and economic benefits. |
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