Assessing the effect of soil crack dynamics on hydraulic properties of agricultural soil from reduced tillage and conventional tillage fields, Wallonia-Belgium

Crack formation and development have been a general concern in agricultural science. Cracks contribute to soil aeration, aggregate formation, and easy root penetration. However, cracks facilitated water evaporation, accelerated soil desiccation, allowed deep infiltration of pesticides/pollutants through preferential flow, and polluted the shallow water-table in Belgium.  From many years, farmers reported the presence of cracks in their field; however, few studies investigated cracks formation from agricultural soil under different cultural practices. This research investigated the effect of cultural practices (conventional and reduced tillage) on crack formation and on soil hydraulic properties.

 

Soils were collected right from the agricultural field and processed (in laboratory) under evaporation experiment on a small drying chamber. Ceramic-IR-emitter heated the chamber while sensors (PT1000, DHT22) measured the temperature and relative humidity. Digital camera took photos of the soil surface at 30min interval. Balance and tensiometer commanded by a datalogger (CR800), recorded the soil hydraulic properties (water suction, water retention, evaporation rate etc.). Cracks were monitored and extracted using image analysis performed by ImageJ and PCAS software. The soil water retention curve (SWRC) was fitted with the bimodal models of Durner (1994) and Seki (2007). The output data were analysed statistically using appropriate software. Three treatments were considered including: disturbed soil, conventional tillage and reduced tillage.  

 

The results showed higher cracks formation on disturbed soil > reduced-tillage > conventional-tillage due to loose of soil cohesion, soil organic content, soil aggregation, biological activities, and soil porosity. Crack formed at low matrix suction for reduce tillage, but higher tension for conventional tillage and disturbed soil. The soil evaporation rate was also greater in reduced-tillage > conventional tillage > disturbed soil. The effect of cracks affected the SWRC for reduced tillage and disturbed soil. The result suspected the presence of pre-installing (or micro)cracks in the reduced-tillage samples. Future study is needed to assess the presence of pre-(micro)-cracks in soil using X-ray microtomography.