Impact of three and seven years of no-tillage on the soil water storage, in the plant root zone, under a dry subhumid Tunisian climate

Conservation agriculture based on no-tillage (CA/NT) becomes a current tendency to enhance crop productivity by improving: (i) soil quality, (ii) water management and (iii) organic supply. In Tunisia, the applicability of CA was poorly documented. This study was carried out to evaluate changes in soil organic matter (SOM) and water properties generated by seven (NT7) and three (NT3) years of applying NT as compared to conventional tillage (CT). On three adjacent large plots, a field experiment was established since the growing season 2000/01 under rain-fed conditions on a clay loam soil in a dry subhumid zone of North Tunisia. In NT3 plot, a cultivation of wheat/fava bean sequence was investigated and residues biomass of 500 kg ha−1 and 450 kg ha−1 were left on the soil surface for wheat and fava bean, respectively. In NT7 plot, a cultivation of wheat/sulla sequence was investigated and residues biomass of 500 kg ha−1 and 700 kg ha−1 were left on the soil surface for wheat and sulla, respectively. However for the CT plot, a moldboard plowing at approximately 20 cm depth was managed for continuous wheat production. The selected key parameters evaluated for a 0–30 cm soil profile were SOM, bulk density (BD), total porosity (TP), macro-porosity (MP), micro-porosity (mP), soil water retention at field capacity (FC) and at permanent wilting point (PWP), available water content (AWC) and soil moisture content (SMC). ve increased significantly (p < 0.05) levels of SOM at the top 30 cm soil layer, which in turn enhanced BD and TP of soil as compared to CT. However, improvement of these parameters was restricted to 0–10 cm layer with NT3. Both NT3 and NT7 have increased considerably (p < 0.05) mP at 0–30 cm thereby increasing soil water content at FC and PWP, whereas MP was remarkably reduced by NT treatments as compared to CT but reduction was less important in NT7 plot. AWC was significantly (p < 0.05) higher in NT7 across the 30 cm profile while NT3 and CT have similar effect to each other. SMC was improved at different soil depths by NT system during the whole agricultural season and the highest content was found with NT3. Soil moisture values increased with increasing soil depth in both NT3 and NT7 indicating a good water infiltration induced by these treatments. Hence, water storage properties in rooting zone could be enhanced by NT7 and NT3 but water availability for plants was more important with NT7.