Effects Of Fertilization On Cabbage And Nitrate Content In Soil

The nitrogen is the crucial factor for plant growth. The increase of nitrogen fertilizer application has been broadly accepted as an important way of increasing crops yield. Whereas, in this process, nitrate and nitrite concentration in soil and crops are also been risen rapidly. Therefore concerns about excessive nitrate and nitrite threatening food security and harming ecological environment are raised.Based on cabbage, this paper discusses the impacts of variable nitrogen fertilizer concentration levels and nitrogen supply approaches on cabbage growth, accumulation of nitrate and soil composition, hence provides theoretical evidence about reasonable fertilization and nitrate pollution control for healthy cabbage production. The research results are indicated as:(1) When nitrogen fertilization supply are150kg/hm2、300kg/hm2 and 450kg/hm2, Both of them will decline as the growth of cabbage plants, the nitrite content is in the qualified range, but the nitrate content cannot satisfy the raw vegetables standard before harvest. When nitrogen fertilization supply are 600 kg/hm2 and 750kg/hm2, nitrate supply will considerably increase nitrate and nitrite concentration in cabbage plants.The nitrate and nitrite content are not in the qualified range.The cabbages are edible.Furthermore, the nitrate level changes in cabbage growth stage, and it is vastly higher in earlier growing stage than mature period.(2) There is noticeably positive correlation between nitrogen fertilizers and nitrate in soil. Nitrate in 80～100cm soil layer appears to accumulate when nitrogen fertilization supply are 600kg/hm2 and 750kg/hm2, but ammonium nitrogen concentration will not been boosted in deep layer soil although it increases as the addition of nitrogen fertilizers in surface soil. Thus, the optimum nitrogen fertilization is measured as 450 kg/hm2 pure nitrogen in experimental conditions under the holistic consideration that the cabbage yield will not decline while cabbage nitrate is limited to the lowest standard referring to variable factors mentioned, such as nitrate, nitrite, nitrate in soil and ammonium nitrogen.(3) Extended nitrogen supply duration will neither influence soil nitrate/ammonium nitrogen content nor improve cabbage output significantly. It is considered that nitrogen fertilizers supplement discontinues 15 days before harvest for best result in regard to cabbage growth and nitrate concentration.(4) Nitrate test stripes-re flcctometer is the method applied in measuring nitrate amount in plant due to the accurate and stable outcomes after pretreatments by GB method.