Effect of organic microbe fertilizer application on watermelon growth and soil microorganisms under continuous mono-cropping

Plot and field experiments were carried out to investigate the effect of organic microbe fertilizer (OMF) application on the bio-properties of watermelon and soil microorganisms under continuous mono-cropping. The field of the experiment was already continuously mono-cropped for three consecutive years with watermelon. Four treatments were arrayed — watermelon seedling was cultured in healthy vegetable garden soil (T1, control), T1 + application of 25 g per plant of OMF at transplanting period (T2), water- melon seedling was cultured in healthy vegetable garden soil with 2% OMF; T4: T3 + application of 25 g per plant of OMF at transplanting period. Results showed that compared with the control, application of OMF significantly increased (P < 0.05) plant height, leaf number, chlorophyll content, total uptakes of N, P and K, and quality and yield of watermelon. After high-quality carbon and microbe OMF application, the numbers of bacteria of the treatments T2 and T4 increased by 24.9%~51.0% and 35.7~55.8%, actinomycetes by 18%~41% and 15%~35% and fungi by 7.4%~21.9% and 4.9%~31.9%, respectively over the control. Conversely, the number of fusarium oxysporum (a witling disease causing fungi) significantly decreased. The number of actinomycetes, fungi was increased. The control rate of wilt was more than 83%. The results suggested that OMF application (especially at seedling and transplanting stages) significantly promoted watermelon growth, stimulated soil microbial activity and limited the adverse effects of continuously cropping on watermelon.