Changes in soil carbon under long-term maize in monoculture and legume-based rotation

Abstract

. 2001. Changes in soil carbon under long-term maize in monoculture and legume-based rotation. Can. J. Soil Sci. 81: 21-31. Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13 C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13 C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha -1 . The effects of fertilization on soil C were small (~6 Mg C ha -1 ), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha -1 in the fertilized and 14 Mg ha -1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha -1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legumebased...

Decomposition of residues and loss of the δ-endotoxin from transgenic (Bt) corn (Zea mays L.) in soil

“…It was used for the decomposition experiment because it had never received residues from any Bt crop. Data from a previously published (Gregorich and Ellert 1994) field investigation on corn residue decomposition in a North Gower loam soil at Winchester, Ontario were also used for comparison.…”

“…To relate the loss of C during the laboratory incubation to decomposition in the field, we contrasted the C loss during incubation with the curve of mass loss from litter bags buried at Winchester, Ontario (Gregorich and Ellert 1994) against Cumulative Days × maximum daily temperature in Degrees Celsius above 0°C air temperature (cumulative degree days above zero, referred to as "CDD > 0").…”

“…Corn production leads to large quantities of residues returned to the soil, with between 3 and 5 Mg C ha -1 being typical in eastern Canada (Gregorich et al 2001). This is approximately equivalent to the grain yields on a dry matter basis (Gregorich et al 2001), and it contributes to organic matter replenishment and return of nutrients.…”

“…This is approximately equivalent to the grain yields on a dry matter basis (Gregorich et al 2001), and it contributes to organic matter replenishment and return of nutrients. However, residues from Bt-corn will also carry the δ-endotoxin into soil, and it is, therefore, ecologically relevant to examine the distribution and dynamics of the δ-endotoxin from corn residues under field conditions.…”

Legume, cropping intensity, and N-fertilization effects on soil attributes and processes from an eight-year-old semiarid wheat system

“…Reduced SOM losses have been attributed to both N fertilizer additions that increased crop residues Paustian et al 1997;Varvel et al 2002) and to legume inclusion (Drinkwater et al 1998;Gregorich et al 2001;Fortuna et al 2008). Recent meta-analyses also highlight, however, that N fertilizer can be inconsistent in mitigating SOM losses, and may even exacerbate SOM losses in some cases (Khan et al 2007;Mulvaney et al 2009;Russell et al 2009).…”