Subsoiling improves conservation tillage in cereal production of severely degraded Alfisols under Mediterranean climate

Central Chile has a Mediterranean climate with a mean annual precipitation of 695 mm, 80% concentrated in winter. In this context, water erosion and inappropriate agricultural management along hillslopes are the major causes of soil degradation. From 2007 to 2010, different agricultural systems were compared: conservation tillage with stubble retained: no tillage (Nt), Nt + subsoiling (Nt + Sb), Nt + barrier hedges (Nt + Bh) and Nt + contour plowing (Nt + Cp). All the systems were compared to conventional tillage (Ct) without crop stubble on the surface. The runoff plots were 50 m × 20 m on a hillside with 12.5% slope in an oat–wheat crop rotation. Runoff, sediment and nutrient losses measured for every rainfall event, occurred during winter months when rainfall energy was also the highest of the whole year. Conservation tillage systems mitigate water erosion compared to the Ct system. In heavy rains, conservation tillage systems reduced soil loss by more than 72% compared to Ct. In addition, the runoff coefficient during the rainy period was 70% lower in conservation tillage systems when the crop was at the initial tillering stage and 90% lower at final tillering. These results show the importance of conservation tillage and crop stubble to decrease erosion, especially in years when extreme precipitation presented a high potential for soil erosion. Moreover, cereal production showed higher biomass and grain yield in Nt + Sb. It was concluded that no tillage with stubble retained on the surface was the best option to mitigate soil erosion. However, the effects of subsoiling decrease over time, making new subsoiling necessary with the implied costs. Due to the strong fluctuations in the prices of the agricultural products, it is impossible to estimate the balance of costs/benefits of this system. On other hand, the duration of the experiment may have been too short to measure the real impacts of no-tillage practices.

► We compared conventional and No tillage systems in degraded Alfisols.
► Surface runoff, soil and nutrient losses were evaluated under Mediterranean climate.
► No tillage systems mitigate erosion but decrease yield compared to the conventional.
► No tillage with subsoiling improves yield in highly compacted soils.