| Vegetable land is one of the main land use types in Taihu Lake watershed with high nitrogen and phosphorus output that is responsible for the eutrophication of surface water. It is therefore important to control and prevent N and P transport from vegetable lands to surface water. In this thesis, two vegetable cultivars (Colocasia esculenta L. School Brassica chinensis) were selected to investigate N and P losses to surface water using5fertilization treatments. The treatments included the control without fertilization (CK), medium fertilization (M), organic manure+fertilizer (O+F). high fertilization (H) and control release fertilizer+organic manure (K+O) in the Colocasia esculenta L. School cultivation. Similarly, the5treatments included the control without fertilization (CK2), low fertilization (L2), medium fertilization (M2), high fertilization (H2) and control release fertilizer (K2) in the Brassica chinensis cultivation. Through field leaching and runoff experiments, losses of N and P from the vegetable lands were discussed combined with the lab analysis. The effect of fertilization mode on N and P losses from the vegetable lands was evaluated from the economic, environmental and social aspects. The results were expected to be benefit for the reasonable fertilization in vegetable lands to reduce N and P losses and to prevent surface water eutrophication in Taihu Lake watershed. The main results of this thesis are followed as:1. Compared with the control without treatment all fertilization treatments increased the vegetable yield with the increasing fertilization rate. However, the marginal production effectiveness decreased with the increasing fertilization rate. In consideration of cost and yield, the favorite fertilization mode were O+F and M for the Colocasia esculenta L. Schoot cultivation, while M2and L2for the Brassica chinensis cultivation.2. In the field experiment, nitrate was the main N forms in leaching way in both Colocasia esculenta L. Schoot and Brassica chinensis cultivations. In the Colocasia esculenta L. Schoot cultivation, nitrate leached rate were10.5,21.9,17.1,39.8and28.3kg·hm-2, and the leached ratio were17.0%,13.2%,27.6%and13.1%respectively, with the increase of nitrogen application rate (CK<O+F<K+O<M<H). In the Brassica chinensis cultivation, nitrate leached rate were3.2,13.0,19.6,36.6and28.0kg·hm-2, and the leached ratio were17.0%,13.2%,27.6%and13.1%respectively, with the increase of nitrogen application rate (CK2<L2<M2<K2<H2). These results suggested that various fertilization rate resulted in various nitrate leaching. The effect of similar fertilization rate was different in leaching rate and ratio because of the fertilizer type.3. As obtained by the leaching tube method, the phosphorus leaching was negative in the soil surface layer of0-10cm in the Colocasia esculenta L. Schoot cultivation. In the Brassica chinensis cultivation, the leached rate of P were K21.1kg·hm-2, M24.1kg·hm-2L25.0kg·hm-2and H230.8kg·hm-2respectively, and the leached ratio was M2<L2<H2. These results indicated that the P leaching was related to the application rate. Compared the two cultivations, the leaching tube method was more suitable for the cultivation in the autumn and winter seasons due to a low water table while not suitable with a high water table.4. In the both Colocasia esculenta L. Schoot and Brassica chinensis cultivations, dissolved N as nitrate was the main form in runoff. All fertilization treatments increased the concentrations of nitrate, TDN and TN in runoff, suggesting that it is important to avoid fertilization just after heavy rainfall. The runoff amount and the apparent runoff coefficient of N varied with different fertilization mode and fertilizer application rate. In the Colocasia esculenta L. Schoot cultivation, the amount of TN runoff were0.95,1.81,1.30,1.70and2.27kg·hm-2, and the runoff ratio were1.41%,1.00%,1.18%and1.05%respectively, and the apparent runoff coefficient was in an order as CK<K+O<M<H<O+F, with the increase of nitrogen application rate (CK<O+F<K+O<M<H). As well in the Brassica chinensis cultivation, the amount of TN runoff were0.49,0.54,0.86,0.96and1.18kg·hm-2, and the runoff ratio were0.96%,0.76%,0.84%and0.53%respectively, and the apparent runoff coefficient of TN was in an order as K2>M2>H2>L2, with the increase of nitrogen application rate (CK2<L2<M2<K2<H2).5. The concentrations of TP, TDP and PO43--P in runoff exceeded the critical point of eutrophication by application of P fertilizer during Colocasia esculenta L. Schoot and Brassica chinensis cultivations. Therefore, fertilizers should not be applied before a heavy rainfall in practical production. Particulate phosphorus was the main form of runoff loss during the Colocasia esculenta L. Schoot cultivation, while it was soluble phosphorus during Brassica chinensis cultivation. The amount of PO43--P, TDP and TP loss in runoff were increased and positively related in linear with the phosphorus application rate, but the runoff loss ratio reduced with the increasing of phosphorus fertilizer application, in both vegetable cultivations. In the Colocasia esculenta L. Schoot cultivation, the amount of TP runoff were138.6,169.6,212.4,217.9and233.3g·hm-2, and the runoff loss ratio were0.29%,0.17%,0.12%and0.08%respectively, with the increase of phosphorus application rate (CK<K+0<O+F<M<H). In the Brassica chinensis cultivation, the amount of TP runoff were7.3,10.2and10.3g·hm-2, and the runoff loss ratio were1.3×10-4,0.9×10-4and0.46×10-4respectively, with the increase of phosphorus application rate (L2<M2<H2). The apparent loss coefficient of TP varied with various fertilization modes in an order as CK <H<M<K+O<O+F for Colocasia esculenta L. School cultivation, and H2<L2<M2for Brassica chinensis cultivation. Comparatively, the apparent runoff coefficients of P runoff were lower than those of N. Comprehensively, N and P lost in leaching was the main way in vegetable lands under each fertilization modes.6. The comprehensive effect of various fertilization modes was evaluated using the user-defined system. In the Colocasia esculenta L. School cultivation, the evaluated score had an order as O+F> M> H> K+O. As well in the Brassica chinensis cultivation, it showed as L2> M2> H2> K2. Such a result suggested that the O+F treatment was suitable for Colocasia esculenta L. School cultivation while L2was suitable for the Brassica chinensis cultivation. Therefore, the favorite fertilization mode was recommended in this area for meeting a high yield and low N and P loss to contribute to the eutrophication prevention of Taihu Lake. |
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