Changes in soil organic matter over 70?years in continuous arable and ley-arable rotations on a sandy loam soil in England.

ABSTRACT: The sequestration in soil of organic carbon (SOC) derived from atmospheric carbon dioxide (CO₂) by replacing arable crops with leys, has been measured over 70?years on a sandy loam soil. The experiment was designed initially to test the effect of leys on the yields of arable crops. A 3-year grazed grass with clover (grass?+?clover) ley in a 5-year rotation with arable crops increased percentage organic carbon (%OC) in the top 25?cm of the soil from 0.98 to 1.23 in 28?years, but with little further increase during the next 40?years with all-grass leys given fertilizer nitrogen (N). In this second period, OC inputs were balanced by losses, suggesting that about 1.3% OC might be near the equilibrium content for this rotation. Including 3-year lucerne (Medicago sativa) leys had little effect on %OC over 28?years, but after changing to grass?+?clover leys, %OC increased to 1.24 during the next 40?years. Eight-year leys (all grass with N or grass?+?clover) in 10-year rotations with arable crops were started in the 1970s, and after three rotations %OC had increased to ca. 1.40 in 2000-2009. Over 70?years, %OC declined from 0.98 to 0.94 in an all-arable rotation with mainly cereals and to 0.82 with more root crops. Applications of 38?t?ha^-1 farmyard manure (FYM) every fifth year increased %OC by 0.13% by the mid-1960s when applications ceased. Soil treated with FYM still contained 0.10% more OC in 2000-2009. Changes in the amount of OC have been modelled with RothC-26.3 and estimated inputs of C for selected rotations. Little of the OC input during the 70?years has been retained; most was retained in the grazed ley rotation, but 9?t?ha^-1 only of a total input of 189?t?ha^-1. In other rotations more than 98% of the total OC input was lost. Despite large losses of C, annual increases in OC of 4‰ are possible on this soil type with the inclusion of grass or grass?+?clover leys or the application of FYM, but only for a limited period. Such increases in SOC might help to limit increases in atmospheric CO₂.

Highlights

Can leys sequester significant amounts of atmospheric CO ₂ in SOM and contribute to the 4‰ initiative?Changes in the percentage and amount of OC were measured and modelled over 70?years and OC losses estimated.Three-year grass or grass?+?clover leys increased %OC, but only to an equilibrium level that was then maintained.Despite large losses, sequestering CO ₂-C at 4‰?year^-1 by growing grass or grass?+?clover leys is possible.

SUBMITTER: Johnston AE 

PROVIDER: S-EPMC5439491 | biostudies-literature | 2017 May

REPOSITORIES: biostudies-literature