Submitted to: Biology and Fertility of Soils
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2003
Publication Date: 3/5/2003
Citation: Bell, J.M., Smith, J.L., Bailey, V.L., Bolton Jr., H.. 2003. Priming effect and C storage in semi-arid no-till spring crop rotations. Biology and Fertility of Soils 37:237-244. Interpretive Summary: Reducing tillage on agricultural land can have many benefits such as reduced water and wind erosion and improved streamwater quality. Moreover, reduced tillage may decrease the carbon dioxide in the atmosphere by retaining more carbon in the soil. We found that more C is retained in soil under reduced tillage and this retention was not affected by crop rotation. We also found that the frequent addition of crop residue can stimulate carbon loss through microorganism metabolism and that the loss may be greater than the loss from tillage. In developing cropping strategies for dryland conditions we hope to reduce soil erosion and increase the carbon in the soil. These results demonstrate that we need not be concerned with a crop rotation difference in meeting these objectives. In addition, limiting the frequency of residue inputs may help build carbon in the soil.
Technical Abstract: Adoption of less invasive management practices, such as no-till (NT) and continuous cropping, could reduce CO2 emissions from agricultural soils. We hypothesized that C storage increases as cropping intensity increases and tillage decreases. We also hypothesized that pulsed addition of C increases the mineralization of native SOM. We evaluated C storage at the 0-5 cm depth in soils from four crop rotations: winter wheat-fallow, spring wheat-chemical fallow, continuous hard red spring wheat,and spring wheat-spring barley. In two incubation studies using 14C-labeled wheat straw, we traced the decomposition of added residue as influenced by (i) cropping frequency, (ii) tillage, and (iii) pulsed additions of C. Differences in 14C mineralization did not exist among the four rotations at any time throughout the incubations. However differences in total CO2 production between the continuous wheat rotations and the fallow rotations point to a priming of native SOM, the degree of which appears to be related to the relative contributions of fungi and bacteria to the decomposition of added residue. Addition of non-labeled wheat straw to select samples in the second incubation resulted in a flush of 14C-CO2 not seen in the controls. This priming effect suggests C inputs have a greater effect on mineralization of residual C compared to disturbance and endogenous metabolism appears to be the source of primed C, with priming becoming more pronounced as the fungal:bacterial (F:B) ratio in the soil increases.