Abstract: Background and Objective: Information concerning moisture properties of soil on account of their direct relation with changes of soil matrix can be obtained by evaluating the Atterberg limits of the soil. The study was carried out to evaluate the influence of five annual applications of poultry manure and spent mushroom substrates on plastic limit and susceptibility of the soil to deformation during cultivation. Materials and Methods: The study was conducted in an experimental plots where different rates of poultry manure and spent mushroom substrates have been applied for 5 years. The treatments were: Control, 5 t ha–1 poultry manure (PM5), 10 t ha–1 poultry manure (PM10), 5 t ha–1 spent mushroom substrate (SMS5), 10 t ha–1 spent mushroom substrate (SMS10) and 5 t ha–1 poultry manure+5 t ha–1 spent mushroom substrate (PM5+SMS5). Results: Results showed that plastic limit, liquid limit and plasticity index varied significantly (p<0.05) due to treatments. Plastic limit was highest (16.65%) in SMS5, followed by PM10 with mean value of 12.48%. Liquid limit showed the highest value of 30.0% in PM10 soil. Saturation water content was significantly (p<0.05) higher in Pm5+SMS5 with corresponding increase in mean weight diameter of aggregates and total porosity. Conclusion: Results revealed that spent mushroom substrate increased optimum cultivation water content while poultry manure increased the susceptibility of soil to deformation during cultivation. Combination of poultry manure and spent mushroom substrates increase stability of aggregates and reduced plastic index.