| The threat of potential water eutrophication and non-point source pollution in farmland ecosystem has been a hotspot in applied ecology. Understanding the distribution pattern and spatio-temporal variation of nutrient in intensive vegetable production and researching how the vegetable responded to the differentiated-nutrient management is helpful for controlling non-point source pollution and preventing water eutrophication, as well as increasing the nutrient utilization efficiency.In this study, Western celery was under differentiated N management (DNM) which treated as limited N fertilization (LF), non-N fertilization (NF), high N fertilization (HF) and blank control (CK) in two farm types (platform and farmland in plateau basin), in Dianchi basin. This study was carried out in March and July,2009, when it was in the crop growth periods. Soil nutrient, plant nutrient and atmosphere N were analyzed in different growth periods to perform the distribution pattern of N in atmosphere-crop-soil farmland ecosystem, especially soil N content, gaseous N loss and plant N accumulation and its variation in seasons and growth periods under different soil textures. Then the amount of N lost to the watershed was estimated. Meanwhile plant functional traits was measured to understand how the Western celery responding to the differentiated N management, especially its crop and root traits. The results are as follows:(1)In Dianchi basin, lots of N was lost through the volatilization of NH3, nitrogen oxides and N2. There was big difference for the N emission among land use types. The soil temperature, fertilization type and its amount were the key factors to control the N emission. The amount of N emission is higher at plateau basin than that in platforms due to the soil texture and underground water level. The amount of lost N was 12.98 to 44.59 percent of amount of fertilized N. The volatilization amount of NH3 was 0.09～23.44 kg/ha and was 0.06%～2.57% of fertilized N during one whole growth season. The amount of nitrogen oxides was 15.45～183.97 kg/ha and was 11.22%～19.02% of fertilized N, and the soil "dry and humidity effect" and the crop were helpful for the emission of nitrogen oxides. The amount of N2 was 7.7～276.0 kg/ha and was 1.7%～23% of fertilized N. (2) Crop fertilization in a single growth-season had little influence on the intensive vegetation biomass accumulation. The crop biomass was positive with the amount of fertilization. Comparing the management NF with no N fertilization, the crop biomass of LF, HF with N fertilization was higher 7.3%～11.4%. But the accumulated biomass was not positive with the amount of fertilization. Nitrogen nutrient utilization ratio in a single growth-season was between 8.5%～30.4%, which was highest under the LF treatment but lower than the average single season utilization ratio in China (30%～41%).(3)There was an obvious vertical distribution of soil N, which was remarkable different in different depth soils. Due to the soil background with high nutrient content, Fertilized N had on little influence soil N content and caused the surplus of N which raised the risk of water eutrophication. Fertilization caused the variation of amount of NH4+-N in the surface soil. The high groundwater level raised the nitrification effect and caused a decreasing trend of NH4+-N through down the soil, but this tendency was not obvious during the growth season. Fertilization caused the surplus of NO3--N in the surface and subsurface soil and the content was higher in earlier growth period than that of later period. The content of NO2--N was very low and had no obvious vertical distribution.(4) There were no relationship between height, active root volume, active root specific surface, diameter of secondary roots, aboveground biomass and amount of fertilization. The aboveground biomass/underground biomass ratio (BR), the total length of roots, length of main root, diameter of root were positive with the amount of fertilization. The BR was between 14.8and 22.41 and increased through the growth season. Biomass accumulation and growth was inconsistent with Equalized Growth Hypothesis. Root specific surface was between 33.20%～43.06%. The underground biomass was negative with the amount of fertilizationThe diameter of secondary roots changed little and had no significant difference within treatments and high fertilization was harmful for the lateral root growth. Fertilization with nitrogen was the main reason that causing high nitrate content in crop. With reasonable fertilization, the nitrate content would decrease when crop mature, due to biomass accumulation. |
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