Biochar effects on soil aggregate properties under no-till maize

Soil aggregates are useful indicators of soil structure and stability, and the impact on physical and mechanical aggregate properties is critical for the sustainable use of organic amendments in agricultural soil. In this work, we evaluated the short-term soil quality effects of applying biochar (0-10 kg m-2), in combination with swine manure (2.1 and 4.2 kg m-2), to a no-till maize (Zea mays L.) cropping system on a sandy loam soil in Denmark. Topsoil (0-20 cm) aggregates were analyzed for clay dispersibility, aggregate stability, tensile strength (TS), and specific rupture energy (SRE) using end-over-end shaking, a Yoder-type wet-sieving method, and an unconfined compression test in soil samples collected 7 and 19 months after final biochar application. The highest rates of biochar and swine manure application resulted in the highest aggregate stability and lowest clay dispersibility. Applying both amendments systematically increased TS and SRE for large aggregates (4-8 and 8-16 mm) but not for small aggregates (1-2 and 2-4 mm). Increased biochar application also decreased the friability index of soil aggregates. Based on X-ray visualization, it was found that aggregates containing larger amounts of biochar particles had higher TS and SRE probably because of bonding effects. Based on the improved soil aggregate properties, we suggest that biochar can be effective for increasing and sustaining overall soil quality, for example, related to minimizing the soil erosion potential. (C) 2014Wolters Kluwer Health | Lippincott Williams & Wilkins