Irrigation method for vegetable seedling using cow dung compressed substrates

Abstract: Compressed substrates had certain mechanical strength, which were produced by application of mechanical pressure to the seedling substrates, such as peats and earthworm compost. In this case, during seedling production the plastic plug was not used, which was helpful for saving resources and protecting environment. More importantly, it would not harm seedlings when transplanting the seedlings, since the compressed substrates and seedling were combined together. Compressed substrate was more suitable for seedlings than incompact substrates, however, the method of irrigation for compressed substrate was different from the traditional irrigation and there was hardly any research on it. So it was interesting to optimize the irrigation of vegetable seedling compressed substrates and improve the growth of vegetable seedling. The experiment was carried out inside a greenhouse at Huazhong Agricultural University (Wuhan City, Hubei Province) for 26 days in March 2017. The cow dung aerobic compost and cow dung earthworm compost were respectively as the main material of compressed substrates for the aims above in 2 groups. There were 6 treatments of irrigation in each group. In aerobic compost group, there were treatments of T1 (2500 mL), T2 (350 mL), T3 (700 mL), T4 (1050 mL), T5 (1400 mL) and T6 (1750 mL). In earthworm compost group, there were treatments of TS1 (3500 mL), TS2 (700 mL), TS3 (1050 mL), TS4 (1400 mL), TS5 (1750 mL) and TS6 (2100 mL). Among them, T1 and TS1 were irrigated in soak irrigation, and the others were irrigated in different gradients of micro spray irrigation. And the migration of TN (total nitrogen), TP (total phosphorus) and TK (total potassium) in different irrigation conditions in compressed substrates for vegetable seedling production was discussed. Results showed that 2 kinds of compressed substrates could be irrigated sufficiently and washed, and the desalt effect of compressed substrates was relatively small under soak irrigation (T1 or TS1). Although the desalt effect and nutrient loss of compressed substrates under the minimum gradient of micro spray irrigation (T2 or TS2) were both smaller than that under soak irrigation (T1 or TS1), these compressed substrates could not be irrigated sufficiently which would hinder the growth of seedlings. With the T3-T6 or TS3-TS6 of micro spray irrigation, the loss of TN, TP and TK in compressed substrates was higher than that in compressed substrates under soak irrigation (T1 or TS1), and then it went gradually higher with the increase of gradient in micro spray irrigation. Based on the results above, for the cow dung aerobic compost, the electric conductivity of compressed substrates is not normal until compressed substrates have been irrigated by 6 times, so compressed substrates in aerobic compost group ought to be irrigated using T4 for 6 times, and then the micro spray irrigation should be transferred to soak irrigation until the end of the seedling stage, which can not only promote the growth of seedlings but also save the irrigating water and decrease the loss of TN, TP and TK in compressed substrate. Under TS1 treatment, the maximum values of thick stems, plant height, dry weight of seedling above-ground and dry weight of root were 6.23 mm, 138.09 mm, 758.85 mg and 147.92 mg on the 26th day after seeding, respectively. And the irrigation water use efficiency of cucumber seedling was 2.79±0.33 g/kg. Compressed substrates ought to be irrigated with soak irrigation in earthworm compost group.