Objective  To utilize spent of Chinese herbal medicine materials after extraction, feasibility of the application as a soilless substrate for watermelon cultivation in a greenhouse was studied.

  Methods  The herbal residues were fully fermented and decomposed prior to mixing with cow dung, mushroom discards, and other waste materials in varied proportions for the experiment. Effects of the substrates on the plant growth and yield and quality of watermelon in a greenhouse were analyzed.

  Results  Increasing amount of the spent material raised the porosity, aeration pores, ratio of pore sizes as well as the pH and EC, but lowered the bulk density and water holding pores of the substrates. As the plants grew, the SPAD and net photosynthetic rate (Pn) of the leaves rose at first to peak in the flowering and fruit setting stages and declined afterward. Meanwhile, the intercellular CO₂ concentration (Ci) continuously increased to reach a maximum at maturity. For the various formulations, Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V=3 ∶ 4 ∶ 3 produced plants with 33.15% increase on the dried weight of aboveground parts, 34.29% on the fresh weight of aboveground parts, 35.36% on the dried weight of underground parts, 30.26% on the fresh weight of underground parts, and 37.33% on the main root length over control. During flowering and fruit setting, the leaf SPAD, Pn, stomatal conductance (Gs), and transpiration rate (Tr) were significantly higher than those of control by 12.24%, 8.47%, 93.94%, and 9.85%, respectively, but Ci significantly lower by 8.65%. The leaf water use efficiency (WUE) of the plants grown on Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V=3 ∶ 3 ∶ 4 was significantly greater than that of control by 70.25%. On fruit yield, the plants under Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V= 3 ∶ 4 ∶ 3 were the highest with a significant increase over control by 21.23%. In contrast, Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =3 ∶ 3 ∶ 4 and Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =3 ∶ 1 ∶ 1 cultivations resulted in significantly reduced yields by 12.49% and 36.47%, respectively, while the other formulations exerted no significant differences in comparison to control (P＜0.05). The melons harvested from Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =4 ∶ 3 ∶ 3 and Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =3 ∶ 4 ∶ 3 treatments had significantly higher soluble solid contents than control, but those from Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =3 ∶ 3 ∶ 4 and Chinese medicine residue V ∶ cow dung V ∶ mushroom residue V =3 ∶ 1 ∶ 1 significantly lower by 8.63% and 12.66%, respectively. No significant effects by other treatments were observed.

  Conclusion  It seemed feasible to use the traditional Chinese medicine spent for watermelon cultivation. An inclusion of the material with cow dung and mushroom discards in the ratio of 3 ∶ 4 ∶ 3 in the soilless substrate was considered optimal for melon cultivation, and at the same time, for effective cost reduction on production and waste disposal.