1326 Table 1 - Test substrates and compounding ratios Substrate No. Fine-grained gangue Tailing coal slime Soil Plant powder Microbial fertilizer R1 22.3% 44.7% 20% 10% 3% R2 33.5% 33.5% 20% 10% 3% R3 44.7% 22.3% 20% 10% 3% R4 21.7% 43.3% 20% 10% 5% R5 32.5% 32.5% 20% 10% 5% R6 43.3% 21.7% 20% 10% 5% R7 20% 40% 20% 10% 10% R8 30% 30% 20% 10% 10% R9 40% 20% 20% 10% 10% CK 100% The pre-planting soil property indicators of different substrates are presented in Table 2. Table 2 - Pre-planting soil property indicators of different substrates Substrate No. pH Organic matter (g/kg) Rapidly available phosphorus (mg/kg) Available nitrogen (mg/kg) Rapidly available potassium (mg/kg) R1 8.52 59.06 5.57 55 120 R2 8.37 52.05 5.61 58 126 R3 8.41 45.05 5.59 57 131 R4 8.36 57.04 7.17 62 138 R5 8.20 50.49 7.32 65 143 R6 8.27 43.94 7.09 63 140 R7 8.02 52.53 9.41 70 158 R8 7.67 46.93 9.82 76 171 R9 7.73 41.33 9.75 72 166 CK 6.97 30.00 15.00 65 125 4. EXPERIMENTAL RESULTS AND ANALYSIS 4.1 Influence of Different Substrates on Crop Growth 4.1.1 Influence on emergence rate The pot-based cultivation experiment was initiated in early April 2024 within a greenhouse. The experiment utilized planting boxes measuring 50 cm (L) × 40 cm (W) × 28 cm (H). Pak choi seeds were procured from Tangshan Academy of Agricultural Sciences. During the growth period, the plants were regularly watered and managed under uniform cultivation conditions. Pak choi sprouts 3 to 4 days after sowing, and the emergence rate reaches its highest level in 6 to 7 days. The emergence rates of pak choi in different substrates are shown in Figure 1.Figure 1 indicates that pak choi is able to germinate in any substrate, with an average emergence rate of over 85% and equivalent to that of the CK. The emergence rate of R2, R5, and R8 is higher than that of the CK; the emergence rate of R1, R4, and R7 is slightly lower than that of the CK; the emergence rate of R3, R6, and R9 is close to that of the CK. This indicates that after adding a certain ratio of microbial fertilizer, the ratio of fine-grained gangue and tailing coal slime is different, and the overall trend in emergence rate follows R2 > R3 > R1, R5 > R6 > R4, and R8 > R9 > R7. This suggests that the substrates exhibit optimal water retention and aeration properties when the fine-grained gangue is mixed with tailing coal slime in a 1:1 ratio. A high ratio of fine-grained gangue results in a weak water retention capacity, adversely affecting seed root development. A high ratio of tailing coal slime reduces substrate aeration, consequently decreasing the emergence rate.
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