Experiment on seedling of compressed substrates with cow dung aerobic composting and earthworm cow dung composting

Abstract: Compared with the traditional substrate for nursery, compressed substrates could provide a good environment for seedlings to grow. The seedling planted in compressed substrates could be transplanted well into the field as a whole, which could protect the root system of seedling and shorten recovering period, and would promote the development of agricultural mechanization in China. In addition, it could reduce the usage of plastic seedling trays and then reduce plastic pollution. This study was aimed to evaluate the feasibility of using the compost material mainly composed of cow dung and rice straw or the earthworm and cow dung compost as compressed substrates for the production of vegetable seedlings, and optimized the formula of compressed substrates for nursery. The aerobic compost and earthworm compost from cow dung were respectively mixed with peat, water absorption resin and wood vinegar as compressed substrates for the cucumber seedling production. The Four-factor three-level orthogonal experiment was carried out: the levels of the aerobic compost and earthworm compost were respectively 3, 4 and 5 L; the levels of peat were 1, 2 and 3 L; the levels of water absorption resin were 27, 54 and 81 mL; the levels of wood vinegar were 30, 60 and 90 mL; the cucumber was the indicator plant. The expansion properties, broken rate and damage rate of compressed substrates, and the survival rate, stem diameter and plant height of the seedlings were determined for comprehensive evaluation. It showed that the expansion properties, broken rate and damage rate in the seedling period for the compressed substrates obtained from cow dung aerobic compost were better than that for the compressed substrates composed of cow dung earthworm compost, and the expansion coefficient would be increasing with the levels of the aerobic compost increasing, but the opposite trend occurred in the broken rate and damage rate. However, the pH value and EC (electrical conductivity) value of the compressed substrates obtained from cow dung aerobic compost were higher, so the survival rate, stem diameter and plant height of the seedlings in the cow dung aerobic compost compressed substrates were worse, and the survival rate, stem diameter and plant height of the seedlings were increased when the usage of earthworm compost increased. The highest comprehensive evaluation index in the formulas of aerobic compost occurred under the T6 treatment (4 L aerobic compost, 3 L peat, 27 mL water absorption resin, and 60 mL wood vinegar), which was 84.89, and that in the formulas of earthworm compost occurred under the TS8 treatment (3 L earthworm compost, 2 L peat, 27 mL water absorption resin, and 90 mL wood vinegar), which was 86.09. In accordance with the comprehensive evaluation index of compressed substrates, a set of suitable formulas were determined: the 2 kinds of main raw materials were mixed with peat at a rough ratio of 57.14%-60.0% by volume; there were 27 mL expansive agent added in the 5-6 L total material, and 60 mL wood vinegar liquid in the 7 L total material in formulas of aerobic composts, but the latter ratio in the earthworm compost was 18 mL:1 L. With these ratios, the broken rates were both under 5%, the damage rate of cow dung compost formula was under 20% and that of earthworm compost was under 40%, the survival rates of those were beyond 40% and 70%, respectively, and the plant dry weights were both beyond 100 mg.