Submitted to: Biology and Fertility of Soils
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2003
Publication Date: 6/20/2003
Citation: Bell, J., Smith, J.L., Bailey, V.L., Bolton, H., Jr. Residue C dynamics and C storage in Semi-Arid no-till spring crop rotations. Biology and Fertility of Soils. 2003. v. 37. p. 237-244. Interpretive Summary: Combustion of fossil fuels to power industries and transportation systems results in the release of carbon dioxide, a principal greenhouse gas, into the atmosphere. Increasing the storage of carbon in agricultural soils has potential to balance or offset this release. We hypothesized that carbon storage in the soil can be increased by decreasing tillage and increasing the number of crops grown in a given number of years. Crop producers would receive increased economic returns if they could be paid for the crop and also for extra carbon stored in their soils. Recently a field size project was started to investigate a change in farm management from tillage-based wheat-fallow to no-till continuous spring cropping on soils in the dryland areas of Eastern Washington. After 6 years of no-till continuous spring cropping we investigated the soil carbon changes of all the rotations. There was more carbon stored in the continuous no-till spring cropping rotation compared to the wheat-fallow system. In addition there were biological changes in the soil that reflected differences in tillage and rotation. We also found that the frequency of residue inputs from the crop was important with respect to total carbon storage. This research will help growers and companies interested in buying carbon credits (i.e. carbon stored in soils) verify that more carbon is actually stored in the soil. It is also important to scientists because it explains why carbon can be increased in a soil due to different crop rotations.
Technical Abstract: Increasing carbon storage in agricultural soils has promising potential in mitigating the release of CO2, a principle greenhouse gas, into the atmosphere. Adoption of less invasive management practices, such as no-till (NT) and continuous cropping, could reduce CO2 emissions from agricultural soils by retaining soil organic matter (SOM). We hypothesized that C storage increases as cropping intensity increases and tillage decreases. In addition we hypothesized that pulsed addition of C increases the mineralization of residual SOM. We evaluated C storage at the 0-5 cm depth in soils from four crop rotations: winter wheat-fallow (WW-F), spring wheat-chemical fallow (SW-CF), continuous hard red spring wheat (HRSW), and spring wheat-spring barley (SW-SB) on a Ritzville silt loam (Calcidic Haploxeroll). In two incubation studies using 14C-labeled wheat straw, we traced the decomposition of added residue as influenced by (i) increased cropping frequency, (ii) decreased tillage, and (iii) pulsed additions of non-labeled wheat straw. In both incubations, peak emission of 14C-CO2 occurred on day 5 then steadily decreased until day 17 at which time 14C-CO2 production leveled off. There were no differences in 14C utilization among the four rotations at any time throughout the incubation. However differences in total CO2 production between the continuous wheat rotations and the fallow rotations by the end of the first incubation point to a priming of residual 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 lasting approximately one day, not seen in the stirred-only samples. This priming effect suggests C inputs have a greater effect on mineralization of residual 14C compared to disturbance and the endogenous metabolism appears to be the source of primed C, with this effect becoming more pronounced as the F:B ratio increases.