Data from: Soil carbon change in intensive agriculture after 25 years of conservation management

Changes in soil organic carbon (SOC) and nitrogen (SON) are strongly
affected by land management, but few long-term comparative studies have
surveyed changes throughout the whole soil profile. We quantified 25-year
SOC and SON changes to 1 m in 10 replicate ecosystems at an Upper Midwest,
USA site. We compared four annual cropping systems in maize (Zea
mays)-soybean (Glycine max)-winter wheat (Triticum aestivum)
rotations, each managed differently (Conventional, No-till, Reduced input,
and Biologically based); in three managed perennial systems (hybrid Poplar
(Populus × euramericana), Alfalfa (Medicago sativa), and
Conifer (Pinus spp.); and in three successional systems (Early,
Mid- and Late succession undergoing a gradual change in species
composition and structure over time). Both Reduced input and Biologically
based systems included winter cover crops. Neither SOC nor SON changed
significantly in the Conventional or Late successional systems over 25
years. All other systems gained SOC and SON to different degrees. SOC
accrual was fastest in the Early successional system
(0.8 ± 0.1 Mg C ha−1 y−1) followed by
Alfalfa and Conifer (avg. 0.7 ± 0.1 Mg C
ha−1 y−1), Poplar, Reduced input, and Biologically based systems
(avg. 0.4 ± 0.1 Mg C ha−1 y−1), and
Mid-successional and No-till systems (0.3 and 0.2 Mg C
ha−1 y−1, respectively). Over the most recent 12 years, rates of
SOC accrual slowed in all systems except Reduced input and
Mid-successional. There was no evidence of SOC loss at depth in any
system, including No-till. Rates of SON accrual ranged from 64.7 to
0.8 kg N ha−1 y−1 in the order
Alfalfa ≥ Early
successional > Reduced input and Biologically
based ≥ Poplar > No-till and
Conifer > Mid-successional systems. Pyrogenic C
levels in the Conventional, Early, and Late successional systems were
similar despite 17 years of annual burning in the Early successional
system (∼ 15 % of SOC to 50 cm, on average, and
∼40 % of SOC from 50 to 100 cm). Results underscore the
importance of cover crops, perennial crops, and no-till options for
sequestering whole profile C in intensively managed croplands.