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Sunny day sampling from 9:00 to 10:00. The ground part was removed from the leaves of the cotyledon, roots and root nodules were excavated and rinsed with water. The fresh weight and moisture coefficient of each part were measured and converted to dry weight; the sample was dried at 65° C., dried and crushed for analysis. When the soybean leaves appear yellow, the frame is enclosed by a 1.5 m high transparent gauze and all the leaves are collected. The nitrogen content of the plant was determined using CuSO4 and K2SO4 as catalysts and digested with concentrated H2SO4. The 15N abundance measurement uses a mass spectrometer to acidify and concentrate the titrant that measures the nitrogen content.
Through automatic determination of nitrogen content in the soil, the nitrogen accumulation in soybean plants increased with the growth process, and the proportion of soil nitrogen and fertilizer nitrogen gradually decreased, while the proportion of nitrogen in root nodules gradually increased. There are three sources of nitrogen in soybean: one is soil nitrogen, the other is fertilizer nitrogen, and the third is nodules nitrogen fixation. In this experiment, the nitrogen nutrition of soybean showed a periodic change along with the birth process, the proportion of soil nitrogen and fertilizer nitrogen gradually decreased, and the proportion of root nodule nitrogen gradually increased. In the period of emergence to four compound leaves (VE-V4), soybeans rely entirely on soil and fertilizer nitrogen, which is an inorganic nitrogen vegetative phase; and in the four compound leaves to the initial flowering stage (V4-R1), the ratio of soil and fertilizer nitrogen The decline of root nodules and nitrogen fixation increased rapidly. Nitrogen nutrition was still mainly from soil nitrogen. It was a period of fast rising of nitrogen fixation in root nodules. The period of vegetative and reproductive growth (R1-R5) was mainly from soil nitrogen and nodules nitrogen fixation. The effect is close, and the effect of fertilizer nitrogen is very small. This stage of soybean relies on both soil nitrogen and root nodule nitrogen fixation, which is the period of inorganic nitrogen nutrition and root nodules nitrogen fixation.
It can be found in the results of the automatic nitrogen determination instrument that the basic nitrogen source of soybean and the main nitrogen source of root nodule fixation are derived from soil nitrogen, and the direct contribution of fertilizer nitrogen is relatively small. However, the regulation effect of fertilizer cannot be ignored in the production process. At the right time, fertilizer nitrogen is used to effectively regulate the nitrogen content of the soil so as to promote the growth and development of soybean.
Analysis of soil nitrogen by automatic nitrogen determination instrument is the main source of soybean nitrogen source
One of the most important nutrients in the growth process of soybean is nitrogen. Its source is relatively complex. It has been found through long-term analysis that it mainly consists of three parts: root nitrogen fixation, soil nitrogen, and fertilizer nitrogen. For this reason, research on the source of nitrogen for soybean cultivation needs to be conducted rigorously. In this experiment,15N isotope tracer technology was used to select the different types of cultivars for the main producing areas of spring soybean in northeast China. A systematic study was conducted on the nitrogen sources of spring soybeans to understand the sources and changes of nitrogen sources of soybeans and enrich the nitrogen metabolism of soybeans. The research content provides theoretical guidance and basis for the rational application of nitrogen fertilizer. For the nitrogen content in the soil, automatic determination of nitrogen is generally used.