Effect of biogas waste applications on soil moisture characteristic curve and assessment of the predictive accuracy of the Van Genuchten model

Abstract

Biogas production has recently become an important issue in countries where alternative energy sources are gaining importance. The study investigates the use of waste, the final product of production, as a soil conditioner and fertilizer for sustainable soil management. The study examines the effects of different amounts of biogas waste [0 (B0), 1 (B1), 2 (B2), 3 (B3) and 4 (B4) ton da-1] on some soil properties and soil moisture characteristic curve (pF). In addition, the van Genuchten model, which has been long and widely used in many studies for the prediction of hydraulic properties, was compared with the pF curves that were obtained using the predicted and real values obtained from the applications. The results of the study showed that although biogas waste applications were more effective in the wet region of the moisture characteristic curve, B3 was the most effective dose that improved the physical properties of the soil. The B4 application had a decrease of about 16% in the penetration resistance and an increase of about 21% in the wilting point compared with those of the control group. The decrease in the macro pore volume due to biogas waste applications was not statistically significant, while biogas waste applications caused a statistically significant increase in the micro pore volume (P <0.05). Among the van Genuchten model parameters, the moisture content in saturation (θS) and residual water (θr) had realistic results in all biogas waste applications. Moreover, the air entry value (1 / α) was estimated to be 41.667 cm in the B0 application and 55.556 cm in the B4 application. In conclusion, high-accuracy estimates were obtained using the van Genuchten model with a R2 value of 0.901 and root mean square error (RMSE) value of 0.061 cm3 cm-3 in the moisture characteristic curve of the control (B0) soil.