Preparation of Plant Medium Containing Nitrogen and Phosphorus Polymer Composites

【Objective】A soilless culture substrate with double cross-linking network hydrogel containing fertilizer with controllable pores and substrate integration was developed.【Method】With polyvinyl alcohol (PVA) and sodium alginate (SA) solution as raw materials, the Ca2+-PVA/SA double cross-linking network hydrogel medium with controllable pores was prepared by chemical pore-making method with pore-making agent calcium carbonate (CaCO3) and pore-making agent citric acid (C6H8O7). By adding hydroxymethylurea (MU), calcium dihydrogen phosphate[Ca(H2PO4)2]provided nutrients for plant growth, and a soilless culture substrate of Ca2+-PVA/SA-MU with controllable holes was prepared. The structure of the prepared substrate was characterized by FTIR and TG, and the surface morphology of the substrate was observed by SEM. The effects of ratio of raw materials as well as ratio of SA and Ca2+ on the mechanical properties of the substrate and the density and size of the pores were studied. The effects of different ratios of substrate on fresh weight, dry weight and seedling emergence rate of rapeseed were studied by culture experiment.【Result】The structure characterization result showed that Ca2+-PVA/SA-MU hydrogel had macropore and micropore cross structure. FTIR and TG tests showed that MU was indeed compounded into Ca2+-SA/PVA double cross-linked hydrogel, and MU had hydrogen bonding with PVA. The mechanical properties showed that PVA ∶ SA=20 ∶ 1 substrate had the best compression performance, and the addition of MU slightly affected the mechanical properties of hydrogel. Culture experiments showed that the germination rate of Ca2+-SA/PVA-MU double crosslinking network hydrogel reached the highest at the 3rd day when SA ∶ CaCO3=40 ∶ 1, and reached 100% after 5 days. The germination rate of Ca2+-SA/PVA-MU double crosslinking network hydrogel added with MU was better than that of conventional SA/PVA hydrogel.【Conclusion】PVA and SA are safe and green materials, which are suitable to be selected as soilless culture substrates for plant growth.