Experimental study on molding technology for making seedling block based on maize stovers

Seedling blocks contained maize stovers as the main component, added cow manure, inorganic complex, polyacrylate sodium, ferrous sulfate, and other auxiliary materials ground as the substrate for growing seedlings, the seed once pressed molding in the substrate, also could be planted in the planting hole. First of all, the production process for making seedling block based on maize stovers were discussed in this study, regarded the crushed maize stovers mixed with cow dung as premixed materials, polyacrylate sodium and other supplementary material dissolved as premixed liquid to soak of strovers and cow dung, ground into a viscous paste together as matrix material, using homemade compression mold, hot pepper seeds and substrate material compressed into a block together, the final drying to facilitate storage and transportation. The matrix conductivity in the process of the test was no more than 800 µs/cm, or else reduce the concentration of the pre-mixed solution to ensure the seed normal germination. The material characteristics of substrate and nutrition were tested or laboratory analyzed, the determination of substrate materials, pH value of 6.4 was suitable to the vegetation, the unit weight of 0.4 g/cm3, the total porosity of 65.82%, the aeration porosity of 19.16%, the water-holding porosity of 56.66%, in addition to the phosphorus and potassium levels slightly higher, nitrogen, iron, magnesium, and other nutritional elements were in suitable range. In this study, the pressed seedling block was put on the test platform of the WDW-200 compression testing machine, and the stress at the deformation degree of 20% was taken as the destructive strength. Soak the blocks water for more than 2 hours or spray for more than 3 hours, until the mass after absorption was no longer changed, with the mass after absorption minus the mass before absorption divided by the mass after absorption determined the water absorption. According to the test method of seedling block water absorption, the measurement of the expansion rate is the volume difference after and before water absorption divided by the volume without water absorption. By using the Design-Expert 8.06 software and according to the general rotating combination design method, the three-factors quadratic orthogonal rotating combination experiment was selected. The test results showed that the destructive strength of block was significantly higher when the water content was between 15.99% and 22.03% and decreased when it exceeded 30%. The larger compression ratio and the greater destructive strength of block led to the lower water absorption. When the compression ratio was 2.25, the maximum expansion rate was 4.60%, and then gradually decreased with the increase of the compression ratio to a minimum of 2.80%. The compression speed had a certain influence on the destructive strength of blocks, but it was not obvious. The influence on the water absorption conformed to the logarithmic function, and the influence on the expansion rate conformed to the quadratic function. The Orthogonal rotation combination test of the ternary quadratic was carried out to establish the mathematical model between the parameters of water content, compression ratio, compression speed, and water absorption, anti-destruction strength, and expansion rate. The optimized parameter of each index was obtained as follows: water content was 22%, the compression ratio was 2.9, and the compression speed was 90 mm/min. The results of the verification test showed that the seedling blocks met the requirements of seedling raising with good water absorption, destructive strength, and lower expansion rate. Seedling blocks compressed with hot pepper soaked for 2 hours and then micro-sprayed for 7 days, the germination rate reached 95%. The study provided a theoretical basis for the stovers seedling blocks molding process, the design, and optimization of molding machinery.