Objectives Applying small molecule organic sylvite is one of the measures to promote rice growth and production. This study investigated the effects of three small molecule organic sylvites on rice seed germination and seedling growth at different concentrations.

Methods Germination and hydroponic experiments were conducted using rice cultivar Lindao 21 as tested material. Three small molecular organic sylvites of potassium formate (OSA), potassium acetate (OSB) and potassium propionate (OSC) were used as treatments and potassium sulfate (IOS) as control. The concentrations of K⁺ in the nutrient solution were 0.25 mmol/L and 0.50 mmol/L. Rice seeds were loaded on paper, which was soaked in treatment solutions, for germinating at 25℃. Rice seedlings at 2-leaves-one-sprout stage were transformed into treatment solutions and cultured at 25℃ and 12 h light/12 h dark. At 4-leaves-one-sprout stage, the seedlings were harvested for the measurement of growth, root morphology and photosynthetic characteristics.

Results Small molecule organic sylvite promoted the early germination of rice seeds. At 48 h, the germination rates of OSA and OSB were respectively 35.6% and 37.8% higher than that of IOS in the K⁺ concentration of 0.25 mmol/L, and 34.0% and 27.7% higher in the concentration of 0.50 mmol/L. Compared with IOS, OSA at 0.25 and 0.50 mmol/L, and OSB at 0.25 mmol/L significantly increased the leaf width and fresh weight of rice seedling, and significantly increased the root weight, total root length, root surface area and root volume of rice seedling. Compared with IOS, OSC increased the chlorophyll content in leaves, while OSA and OSB significantly increased the net photosynthetic efficiency, stomatal conductance and transpiration rate of rice seedling leaves. The small molecule organic sylvite could improve the root activity of rice seedlings, and promote the absorption of potassium in rice seedlings. At 0.50 mmol/L of K⁺ treatment concentration, the total plant K contents in OSA and OSB were significantly increased by 19.6% and 28.3% compared with IOS.

Conclusions Compared with potassium sulfate, potassium formate, potassium acetate and potassium propionate could promote the early germination of rice seeds, the growth of rice seedlings, the photosynthetic efficiency and the absorption of K, and the best effect is from 0.25 mmol/L potassium formate.