含稻秸蔬菜育苗基质块成型工艺参数优化

Parameters optimization for molding of vegetable seedling substrate nursery block with rice straw

为了确定黄瓜育苗块成型的最优工艺参数,以育苗基质和水稻秸秆的混合物为原料,育苗块的抗破坏强度和尺寸稳定性为成型质量检测指标,采用四元二次回归通用旋转组合试验设计结合响应面法,探讨了原料含水率、压力、秸秆长度和秸秆含量对育苗块成型的影响,建立了黄瓜育苗块成型特性参数与各因素之间的回归模型。综合分析表明,各因素对育苗块抗破坏强度的影响主次顺序为:压力>秸秆长度>含水率=秸秆含量,在交互作用中,含水率与秸秆含量、压力与秸秆长度、秸秆长度与秸秆含量对育苗块抗破坏强度的影响显著(P<0.05);各因素对育苗块尺寸稳定性的影响主次顺序为:秸秆含量>含水率>压力>秸秆长度,含水率与秸秆长度的交互作用对育苗块尺寸稳定性的影响较显著(P<0.05)。利用Design-Expert8.0.6软件得出理论最优工艺参数,并考虑试验的可操作性,对理论最优工艺参数进行调整及试验验证,得到最优工艺参数:含水率为21%,压力为4.5 k N,秸秆长度为10 mm,秸秆质量分数为12%,该组合条件下的育苗块抗破坏强度为23.03 N,尺寸稳定性为82.83%。分析表明,优化后育苗块的理化特性符合黄瓜育苗的农艺要求。该研究可为黄瓜育苗块成型机工艺参数优化提供理论和实践依据。

Raising vegetable seedling with growing substrate nursery block is an effective way to utilize agricultural byproduct, reduce use of plastic pot which may pollute the environment and realize the optimal treatment of the growing media favorable for the growth of the seedlings. For the technology, the growing media is compacted and molded into nursery blocks; seeds are planted into the block in greenhouse; and seedlings with blocks are transplanted without the process of removing the plastic pot of traditional seedling raising at transplanting. Breaking strength and dimensional stability of the molded block are critical for the delivery and seedling production process and they affect the mechanical properties of the block as well, such as the density, and the porosity. And the parameters will affect the germination, emergence and growth of the crop seedlings. The compression ratio was determined as 3：1 according to previous studies. A mold was developed and equipped on a WDW-200 type computer-controlled electrical testing machine to compress the block according to horticultural requirement. The tested materials was the mixture of rice straw and growing substrate whose principal components were peat, vermiculite and other nutrients demanded for plant growing, which was produced by Shenyang Fannong Horticultural Materials Co. Ltd. and supervised by Seedling Developing Room of Horticulture College, Shenyang Agricultural University. Quadratic regression general rotary combined experiments of 4 factors were carried out, and by means of surface response methodology, the effects of moisture content, pressure, straw length and straw content on breaking strength and dimensional stability of the manufactured substrate block were investigated, and the regression models were set up. The fitting degree and significance of the regression model were tested through the analysis of variance. The results showed that the significance of the factors for breaking strength of the block was： pressure 〉 straw length 〉 moisture content = straw content; the interactions between moisture content and straw content, between pressure and straw length, and between straw length and straw content on breaking strength of the block were all significant （P〈0.05）; the influence of the factors on dimensional stability of the seedling nursery blocks was： content of straw 〉 moisture content 〉 pressure 〉 straw length; the interaction of moisture content and straw length was significant for dimensional stability of the block （P〈0.05）. The optimal theoretical process parameters were obtained with Design-Expert 8.0.6. The optimal values of the factors were adjusted according to the operability and verification experiment results. The final optimal process parameters were determined as follows： moisture content of 21%, pressure of 4.5 N, straw length of 10 mm and straw content of 12%. The corresponding breaking strength and dimension stability of the block were 23.03 N and 82.83% respectively. The parameters of physical and chemical properties of the optimized seedling block were determined as follows： bulk density of 0.43 g/cm3, total porosity of 73.31%, aeration porosity of 32.6%, EC value of 1.76 mS/cm and pH value of 6.3. The analysis showed that the optimized parameters could meet the demand of physical and chemical requirement of vegetable seedling raising according to the relevant literature. The study may provide theoretical basis for process parameters optimization and machine development of vegetable seedling nursery block molding.