An in vitro methodology to estimate the effects of root-growth promotion of soils treated with organic matter and microbial inoculants, in crops, under integrated nutrient management (INM), was developed and validated against data from previous experiments. A soil was prepared with two treatments: a) Control with application of deionized water, and b) INM, comprising the application of humic substances and microbial inoculant. Treated soils were incubated for 72 hours and extracted using five soil to water extraction ratios: 0, 0.05, 0.1, 0.2, and 0.5. Extracts were analyzed for pH and electrical conductivity (EC). Radish and wheat seeds were germinated and irrigated with each solution. Analysis of Variance, Regression and Correlation analyses were performed. Treatment and extraction ratio significantly affected pH and EC of the soil extracts. The application of extracts from soils under INM significantly affected the growth of radish radicles. The growth of radicle and coleoptile of wheat seeds increased when increasing soil proportion in the extract. Maximum growth was obtained with ratios between 1:5 and 2:5. In validation experiments wheat seed growth significantly correlated with soil organic matter content and enzymatic activity, confirming that this method is sensitive to estimate growth-promoting effects.