Abstract
In order to prepare sustained-release organic liquid fertilizer, alginate and amide nitrogen urea were used as materials to study the release of alginate from urea and its application in soilless cultivation. The interactions between alginate and urea in aqueous solutions were investigated based on particle size, zeta-potential, scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) measurements. We used ultrafiltration centrifuge tubes to separate the alginate, binary complex of alginate and urea, and free urea. The sustained-release action of alginate was characterized by measuring the content of free urea. XRD and FTIR results revealed that a binary complex between alginate and urea was successfully generated because of non-covalent interaction forces, hydrogen bonds and hydrophobic effects. The release efficiency of alginate was 54.58% with urea. These results indicate that alginate is suitable for the slow release of urea in aqueous solutions, which is advantageous for the preparation of soilless algal organic fertilizers. In soilless cultivation experiments, the urea release by alginate was slower, resulting a fresh weight, dry weight, protein content, and soluble sugar content retention after the end of the growth of 23.93, 51.16, 23.76, and 16.32%, respectively. These values were higher than those of the control (P <0.05), increasing the growth and N uptake by the crop plants. This trend increased with time, emphasizing the significant role of alginate in urea retention in soilless cultures. The results demonstrated the potential for soilless culture agriculture and the effectiveness of slow-release alginate.
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