Effects Of Application Of Organic And Inorganic Fertilizers On Vegetable δ¹⁵N And Soil Microbial Properties

Organic farming has been developping faster and faster around the world since1990s.How to identify organic products is a key problem to promote organic agriculturedevelopment. Under the same application ratio of nitrogen, cauliflower and spinach fieldexperiment were conducted to study the effects of application of organic fertilizer or inorganicfertilizer or combined application of organic and inorganic fertilizers on vegetable and soilδ¹⁵N value (natural¹⁵N abundance), soil biochemistry characteristic and crop growth, yieldand quality, the possibility of using vegetable δ¹⁵N, quality indicators and soil microbialproperties to indentify the form of nitrogen fertilizer was discussed. The main results were asfollowed:1. Compared with the control, pure organic fertilizer significantly increased δ¹⁵N valuesof cauliflower root and every part of spinach, and pure inorganic fertilizer significantlydecreased δ¹⁵N values of spinach and cauliflower root, leaf and flowers （P<0.05）. There wasno signifiant difference on δ¹⁵N values of cauliflower stem in different treaments. δ¹⁵N valuesof different parts of cauliflower performanced as: flowers≥leaf> stem> root （P<0.05）except pure inorganic fertilizer treatment; the above-ground components of spinach hadhigher δ¹⁵N values than under-ground components. Under the same fertilizing amount ofnitrogen, δ¹⁵N values of the soil increased as the application rate of organic fertilizerincreased, but the differences of soil δ¹⁵N values in different treaments were not so obvious asplant δ¹⁵N values.2. The correlation of δ¹⁵N between cauliflower components and fertilizer, spinachcomponents and fertilizer were significant at the0.01level; the correlation of δ¹⁵N valuesbetween different components of the same crop was significant at the0.01level. Thecorrelation of δ¹⁵N between cauliflower root and soil was significant at the0.05level andbetween each components of spinach and soil was significant at the0.01level. The δ¹⁵N valueof soil changed with the application of fertilizers, but the correlation of δ¹⁵N between soil andfertilizer was not as significant as that between plant and fertilizer.3. Compared cauliflower and spinach, the main¹⁵N-source of cauliflower in all the fivetreaments was soil, but¹⁵N-source of spinach mainly depended on the application of fertilizer, which meaned that using δ¹⁵N to indentify organic spinach was more effective than toindentify cauliflower. There was a cross of plant δ¹⁵N between application of organic fertilizeror inorganic fertilizer and combined application of organic and inorganic fertilizers. Therefore,it may be difficult to use δ¹⁵N values as the only indicator of organic products. We shouldcombine δ¹⁵N with other managing measures and set up a process-tracking quality controlsystem of organic products.4. Compared with CK, application of fertilizers increased soil microbial biomassC（SMBC）, N（SMBN） and P（SMBP）, and organic fertilizer was better than inorganic ones. Inthis study, the increasing effectiveness of organic fertilizer combined with inorganic fertilizerat the ratio of3:1in SMBC and SMBN was better than pure organic fertilizer or pureinorganic fertilizer. SMBP increased as the application of organic fertilizer increased, showingas organic fertilizer> organic fertilizer combined with inorganic fertilizer at the ratio of3:1>organic fertilizer combined with inorganic fertilizer at the ratio of1:3> inorganic fertilizer.5. The activities of urease, catalase decreased for the application of inorganic fertilizeronly, but neutral phosphatase activity tended to increase. The effect of organic fertilizer onsoil invertase activity was not apparent. The application of organic fertilizer only may haveinhibiting effect on phosphatase activity. Soil catalase activity decreased as the applicationratio of inorganic fertilizer increased and SMBP increased as the application ratio of organicfertilizer increased, meaning these two could be used as the secondary indicators to indentifyorganic products.6. In this study, plant growth condition was better and yield, N/P/K content were higheras the application ratio of inorganic fertilizer increased, while the content of NO3-N increasedand Vitamine C decreased. Applying inorganic fertilizer in large doses decresed crop qualityand caused lots of problems such as soil acidification and the content of organic matterreducing. Vegatable quality indicators such as the content of NO3-N and Vitamine C couldeffectively distinguish the conventional production applied chemical fertilizer only andorganic production applied organic fertilizer only.