ARS | Publication request: Stratification ratios in a rainfed Mediterranean Vertisol in wheat under different tillage, rotation and N fertilization rates

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2011
Publication Date: March 1, 2012
Citation: Melero, S., Lopez-Bellido, R.J., Lopez-Bellido, L., Munoz-Romero, V., Moreno, F., Murillo, J.M., Franzluebbers, A.J. 2012. Stratification ratios in a rainfed Mediterranean Vertisol in wheat under different tillage, rotation and N fertilization rates. Soil and Tillage Research. 119:7-12.

Interpretive Summary: Assessing soil quality of a diversity of soils around the world is complicated due to unique characteristics that pose challenges when using standard analytical techniques. Collaboration among scientists at the Spanish National Research Council (IRNAS-CSIC), University of Cordoba, and USDA Agricultural Research Service in Watkinsville Georgia was undertaken to evaluate long-term changes in soil quality of a Vertisol in Spain using a relatively new concept of stratification ratio of soil organic matter fractions. Soil organic matter fractions were enhanced in the surface layer under no tillage, more so than in the surface layer under conventional tillage. Stratification ratio of ß-glucosidase activity was the most sensitive soil property to long-term effects of management. Low stratification ratios were observed relative to ratios from other soils around the world, which may have been due to the self-tilling properties of the high-clay content soil. Tillage and crop rotation were more important than N fertilizer rate in affecting stratification ratio. These results have important implications for determining (1) soil quality in a diversity of soils around the world and (2) the impacts of crop and tillage management on soil quality.

Technical Abstract: Semiarid Mediterranean climatic conditions and intensive tillage systems accelerate soil organic matter losses. Therefore, assessing agricultural practices that enhance storage of soil organic matter is needed. Stratification of soil properties with soil depth, expressed as a ratio, could indicate soil quality under different soil management. We measured soil depth stratification ratio (0-5 / 10-30 cm and 0-5 / 30-50 cm) of soil organic C (SOC), total nitrogen (TN), chemically labile carbon (CLC), water soluble carbon (WSC), and soil enzymatic activities [dehydrogenase activity (DHA) and ß-glucosidase activity (BGA)] of a Typic Haploxerert in southern Spain. The experimental design consisted of a split-split plot design with three replications and soil properties evaluated at the end of 22 years. Tillage systems included conventional tillage (CT) and no tillage (NT). Dryland, 2-year crop rotations were wheat-fallow (WF), wheat-chickpea (WC), wheat-faba bean (WFb), wheat-sunflower (WS), and continuous wheat (WW). Nitrogen fertilizer rates were 0, 50 and 150 kg N/ha. Stratification ratio of CLC, WSC, DHA, and BGA was most responsive to tillage system; NT greater than CT. Stratification ratio of SOC and TN was most responsive to crop rotation; WFb and WW greater than WF, WC, and WS. Nitrogen fertilizer rate did not influence stratification ratio of any organic matter fraction. Stratification ratio was greater when calculated as 0-5 / 30-50 cm depth than as 0-5 / 10-30 cm depth. However all stratification ratios were relatively low, perhaps due to the large shrinking and swelling of soil with high smectitic clay content. Stratification ratio of BGA was greater than of all other organic matter fractions, suggesting that it might be a good indicator of soil quality under different soil management conditions of this Mediterranean Vertisol. This study indicated the value of stratification ratio to detect improvement in soil organic matter fractions with adoption of long-term NT and high organic matter input.