| It has been confirmed that nutrient loss from cropland has potential risk towards eutrophication.Greenhouse vegetables become the rapid development of profitable agriculture in our country for their higher multiple cropping index,shorter growth period and faster increase benefits.Otherwise,they are prone to lager nitrogen(N)and phosphorus(P)losses caused by the intensive fertilization and flooding irrigation.Considering the potential capacity of paddy field which could purify the inflow,this thesis attempted to build greenhouse vegetables-paddy field coupled mode from the point of coupling between different cropping patterns.Based on the study of the rules of N and P losses from the greenhouse vegetables and the dynamic changes of N and P in paddy field surface water,the feasibility of N and P interception,rice fertilizer reduction under the coupled mode were explored through field experiments,thus providing a simple and effective measure to control N and P losses from greenhouse vegetables and reduce the risk of eutrophication.The main conclusions of this thesis were as follows:(1)Fertilization affected N leakage and ammonia volatilization significantly,while it had little impact on the distribution of the concentration and forms of P in soil profile.P mainly concentrated in the surface of soil due to its weaker filtration ability.It was shown that the outflow of greenhouse vegetables almost occurred during the irrigation period of planting,the average drainage rate was 43.39%,and the average losses of N and P in a single crop season were 4.97 kg·hm-2 and 0.42 kg·hm-2 respectively.Meanwhile,the major loss form of P was particulate phosphorus(PP)and the loss form of N varied with the period of the outflow:nitrate nitrogen(NO3--N)wasthe main loss form in the period of sowing while during the fertigation,ammonia nitrogen(NH4+-N)was the main loss form.(2)The variations of N and P concentration in the surface water were not affected by greenhouse vegetables-paddy field coupled mode.The peak values of TN and NH4+-N occurred on the 1st and 2nd day after fertilization,and gradually descended to a low level and became stable within 7 days.The concentration of NO3--N in the surface water reached the maximum during the 3rd day to 5th day and approached to a relatively stable background level 9 days later.The concentration of TP and DP in surface water showed similar variation trends,reaching the highest on the 1st day after application of phosphate fertilizer,and getting stable within 10 days.The main forms of N and P in surface water were NH4+-N and DP,respectively.(3)Compared with uncoupled mode,the greenhouse vegetables-paddy field coupled mode not only could reduce the risk of N and P losses,but also ensure the rice yields under the conventional fertilization level,and mitigate the emissions of total nitrogen(TN)and total phosphorus(TP)by 32.66%and 37.72%respectively when the area ratio was 1:3.(4)The findings indicated that assuring the production of rice yields,the greenhouse vegetables-paddy field coupled mode appeared to be an effective measure for the control of N and P losses under conventional fertilization and 80%of conventional fertilization.When the paddy field was treated with 80%of conventional fertilization,the coupled mode could achieve better N and P reduction(30.04%for TN,38.13%for TP)and higher yield with less fertilizer. |
