Soil functioning and conservation tillage in the Belgian Loam Belt

One of the most frequently used techniques to combat soil erosion on agricultural fields is conservation agriculture (CA). Conservation tillage techniques (CT), together with residue management and rotation are the pillars of CA. Studies have shown that CT can indeed be very effective in combating soil erosion. While several studies have demonstrated how CT may affect (the distribution of) carbon in the soil and documented compaction risks under CT, much less information is available with respect to the potential effects of CT on within-soil water movement and nutrient status. We therefore investigated the effect of superficial (0.15-0.2 m depth) and deep (0.3-0.4 m depth) CT on soil properties of agricultural silt loam soils in Belgium. From 2008 to 2010, we analyzed the effect of CT on water content, hydraulic conductivity, penetration resistance, bulk density, organic carbon and nitrate content of the soil. At the same time the effect of CT on root growth and crop yield was analyzed. We found that soil structural differences between conventional mouldboard ploughing and deep CT tended to be very small and did not have any effect on root growth and/or crop yield. Furthermore, we were not able to detect any significant difference between the different implements used in CT. The application of superficial CT however, led to an increase in penetration resistance in the upper soil layer hindering vertical soil water movement and root growth on one trial field. Crop yield was not affected due to a sufficient water and nutrient supply. Effects of deep CT on water availability and water movement were very limited and suggest that deep CT may slightly improve water availability only during dry summer periods. Total carbon content was not affected by CT, but its distribution through the plough layer changed whereby the carbon content in the upper few centimetres of soil increased while a decrease was noted at greater depths. The reduction of the nitrate content observed in deeper soil layers indicates that reduced tillage did not lead to increased nitrate leaching and may even help to reduce this problem if adequate catch crops are planted. We conclude that, on the Belgian silt loam soils, deep CT can be practiced whereby good soil functioning can be ensured. As crop yields were also similar, deep CT is a viable alternative that may contribute to soil protection. The use of superficial CT cannot be recommended due to a compaction risk. (c) 2012 Elsevier B.V. All rights reserved.