PURPOSE: Nontoxic cinnamaldehyde or its derivative is combined with the manure and applied to crops to control injurious microorganisms in soil, protect crops and overcome troubles in repeated cultivation without any adverse effect on manure-decomposing microorganisms.

CONSTITUTION: Cinnamaldehyde or its derivative such as brominated cinnamaldehyde is applied to crops together with manure where in case of soil manure which is absorbed from roots, the aldehyde is adsorbed in a dried powder or granules of porous clay, which is combined with the manure, by about 200ppm based onthe total amount of the manure and the clay or in case of liquid manure, a diluent high compatible in the liquid manure such as ethyl acetate is used so that the amount of the aldehyde becomes 200ppm in maximum based on the manure and diluent.

EFFECT: It shows no adverse effect on useful bacteria at all, with high residual and durative effects. Huge costs to be required in soil disinfection can be saved.