|Allmaras, Ray - USDA-ARS (RETIRED)|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2004
Publication Date: July 1, 2004
Citation: Wilts, A.R., Reicosky, D.C., Allmaras, R.R., Clapp, C.E. 2004. Long-term corn residue effects: Harvest alternatives, soil carbon turnover and root-derived carbon. Soil Science Society of America Journal. 68:1342-1351. Interpretive Summary: Soil carbon (C) sequestration management is important due to an increased carbon dioxide concentration in the atmosphere and potential global warming. The ability to predict C turnover, with estimates of root-derived C, will give scientists, farmers and proponents of ethanol production from corn stover valuable information to consider when developing cropping systems. The cumulative effect of tillage and many cropping rotations has been a 30 to 50% decrease in soil C. Exact and clear data and notes were collected from a 29-yr experiment that included continuous corn with moldboard plow tillage. Treatments included harvest alternatives (stover harvest or return) and fertilization at low or high rates and a control. There are few such experiments with such accurate data to test the values of a changed delta 13 C. The total soil organic C (SOC) and delta 13 C data provided valuable information about the corn-derived C that replaced relic C. Soil organic C declined and delta 13 C increased. Stover yield, SOC and delta 13 C data were applied to a model to estimate unharvestable C (crown, root and exudates) and predict total source C (SC) input from corn. The model estimates greater SC from unharvestable roots compared to most estimates using harvest index and root to shoot ratio. Results showed that stover inputs forced more C turnover than stover removal. Corn harvest alternatives had a greater effect on C turnover than fertility rates. Modelers and crop consultants, in particular, may benefit from this type of information. Their resulting recommendations could increase the efficiency of SOC build up to enable farmers to maintain crop production with minimal impact on the environment.
Technical Abstract: A better understanding of carbon (C) turnover, with estimates of root-derived C, is needed to manage soil C sequestration. Stover and fertilizer treatments (in a 2 X 2 factorial) and a control were imposed on 29 yr of continuous corn (Zea mays L.) with moldboard plow tillage with silage (stover) removal versus grain harvest, each with low (83 kg N ha**1) and high (166 kg N ha**1) fertility, and no added fertilizer with grain harvest. Soil organic carbon (SOC) declined and delta 13 C increased over the 29-yr period ending in May 1995. Field averages of SOC and delta 13 C in the 0 to 30-cm depth were 96.4 Mg ha**1 and -17.3 parts per thousand in 1966; respective values in 1995 were 78.9 Mg ha**1 and -16.6 parts per thousand. Soil organic C loss was greater with corn stover removed or no fertilization; delta 13 C increased for all treatments. Stover yield, SOC and delta 13 C data were applied to a model to estimate unharvestable C (crown, root and exudates) and predict total source C (SC) input from corn. Source C (for 29 yr) totaled 136 to 150 Mg ha**1 when stover was harvested, and 232 to 246 Mg ha**1 when stover was returned. Source C input from unharvestable sources was 1.5 times more than SC from aboveground stover residues when N was added and 0.6 when N was not added. Corn-derived SOC as a function of total SC indicated a 5% retention coefficient due to moldboard tillage. The root:shoot ratio ranged from 0.96 for stover returned to 1.07 for stover harvested and was 0.79 with no N. The model estimates greater SC from unharvestable roots compared to most estimates using harvest index (HI) and the root:shoot ratios. The results clarify the contribution of roots to soil C cycling and sequestration for enhanced soil quality.