Effects of molybdenum on yield and NPK absorption of muskmelon cultivated on substrate with B. methylotrophicus

Objectives B. methylotrophicus are often inoculated in the growth substrate to deal with soil-borne diseases in the production of melons. As the sensitivity of B. methylotrophicus activity to micronutrient contents, we studied the proper concentration of Mo in order to provide theoretical basis for preparation of high-quality growth substrate in the production of melons.

Methods The experiment was conducted in Yangling Agricultural Demonstration Zone, Shaanxi Province from May to August in 2019. The thin-skin melon variety ‘Qianyu No.6’ was used as the material, and three levels of ammonium molybdate tetrahydrate (NH₄)₂MoO₄·4H₂O at 0, 0.02 and 0.04 mg/L were set. The accumulation and contribution of dry matter and total NPK to fruit were measured at the early, middle and late fruiting stages, and the fruit quality and yield were investigated.

Results The total Mo content of melon fruits increased with the increase of Mo level, while the free amino acid content, nitrate nitrogen content, single fruit weight and yield were the highest at the level of (NH₄)₂MoO₄·4H₂O 0.02 mg /L, and the soluble protein content was the highest at the level of no Mo application. Except for the dry matter content of melon stems in the early and middle stages of the fruiting, the accumulation and transfer of dry matter, total dry matter, total N, total P and total K in melon organs were all higher at 0.02 mg/L (NH₄)₂MoO₄·4H₂O. Mean while, 0.02 mg/L (NH₄)₂MoO₄·4H₂O treatment increased fruit yield by promoting the accumulation and transport of dry matter and nutrients (N, P, K) and other organs^, contribution to fruit nutrients, and also improved nutrient use efficiency by increasing plant absorption and accumulation of nutrients. And compared with the 0.02 mg/L ammonium molybdate tetrahydrate treatment, the 0 mg/L and 0.04 mg/L of Mo treatment reduced the yield, N, P and K nutrient utilization rate by 48.63% and 17.50%, 16.58% and 22.44%, 2.39% and 13.84%, 27.34% and 25.28%, respectively.

Conclusions The application of Mo has significant effect on increasing the accumulation and transportation of dry matter and nutrients, and enhancing the fruit yield and quality of melon grown in substrate contain B. methylotrophicus. The addition concentration 0.02 mg/L of ammonium molybdate tetrahydrate performs well.