Soil-Profile Distribution of Particulate Organic Matter, Carbon and Aggregate Stability under Long-Term Tillage and Cover Crops.

Enhancing soil organic matter components and soil structural properties are essential to maintain or sustain soil productivity and environmental quality. A better understanding of the long-term tillage and crop management effects on soil properties is thus needed. The objectives of this study were to evaluate the impacts of 33-yr no-till (NT), NT-cultivated, single disk, double disk (DD), chisel (CH), and plow tillage (PT) under corn-soybean rotation on particulate organic matter (POM), soil organic C (SOC), and wet aggregate stability to 1 m soil depth on two experimental fields on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) in eastern NE. In 2007, seven years prior to this study, blend of cereal rye (Secale cereal L.) and winter peas (Pisum sativum L.) cover crops were added to the NT-cultivated (NTCC) and DD (DDCC) treatments, while single disk was changed to DD. Results showed that, NT and NTCC had 1.25 times greater SOC concentration than PT, while DD, DDCC and CH had 1.21 times greater SOC concentration than PT at the 0 to 10 cm depth in one of the two fields. Also, NT and NTCC increased mean weight diameter of wet aggregates (MWD) by 3.2-fold compared with PT, while DD, DDCC and CH increased MWD by 2.3-fold compared with PT. At both fields, NT had 3 times higher total POM concentration than PT and 2 times greater total POM than reduced tillage systems (DD, DDCC, and CH) at the 0 to 10 cm. However, at the 10-20 cm, PT had significantly higher POM compared with all tillage systems in both fields, suggesting that residue mixing with plowing possibly contributed to POM accumulation at the bottom of plow layer. Addition of CC for seven years to long-term NT and DD systems did not affect soil properties. Overall, these results indicate that NT and reduced tillage systems improved POM, SOC and soil aggregate stability only near the soil surface and inclusion of cover crops had no significant effects.