ARS | Publication request: Fall conservation deep tillage stabilizes maize residues into soil organic matter

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 25, 2012
Publication Date: N/A

Interpretive Summary: Storage of carbon in soil benefits the soil and atmosphere in many ways, including improved soil fertility. One management option to store carbon in agricultural soils is to reduce the frequency of field tillage, including plowing and other forms of land preparation. In situations where tillage is preferred, a second option might be to place crop straw and roots deep into the soil through deep tillage. But little information exists on whether this approach is effective. Working in a Nebraska field that was rotated each year between corn and soybean, we found that the introduction of deep tillage after 14 years of no tillage caused a rapid loss of soil carbon. But during the next three years, placement of crop straw and roots deep into the soil caused the deep levels of soil carbon to increase, compensating for the initial loss of carbon when tillage was begun. These results indicate that continued deep placement of crop straw and roots in future years might lead to significant storage of carbon in lower soil depths. This knowledge is beneficial for farmers who seek to promote storage of carbon in their fields. It is also useful to researchers who study soil carbon storage and availability.

Technical Abstract: Efforts for increasing soil organic matter (SOM) content under agricultural systems have primarily focused on management practices that reduce exposure of SOM to decomposition via minimum tillage. We assess an alternative approach, termed ‘fall conservation deep tillage’ (FCDT), to SOM stabilization through fall incorporation of crop residues into the soil profile together with nitrogen (N) fertilizer. In an eastern Nebraska field under irrigated continuous maize (Zea mays L.), we measured total soil carbon (C) and N stocks on an equal soil mass basis (0-30 cm depth) and the composition of four SOM fractions after 14 years of previous no-till management and one, two and three years after conversion to FCDT. After three years of tillage, redistribution of soil C, N and soil organic matter fractions occurred within the soil profile; however, total soil C and N stocks remained unchanged. An increase in the soil-crop residue interface through FCDT increased free light fraction by 170% in deeper strata in the soil profile. Change from no-till to FCDT led to initial reduction of C and N stocks as mobile and calcium bound humic acid fractions after one year of tillage, suggesting enhanced decomposition and/or condensation. By the second and third years of FCDT, stabilization of crop residues into these humified fractions was significant. The trends observed after three years of FCDT at field-scale match prior plot-scale experiments from the same region, and suggest that a positive balance of soil C and N accrual and losses may be achieved by enhancing the soil-residue interface in these soils.