Author
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Dao, Thanh |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/7/2001 Publication Date: 2/6/2002 Citation: N/A Interpretive Summary: Large-scale re-vegetation efforts to promote soil conservation and support farm income under the Conservation Reserve program (CRP) may have a beneficial role in the global climate warming phenomenon. The change in land use may help reduce the increasing emission of carbon dioxide to the atmosphere from human activities. However, changes in soil carbon (C) and nitrogen (N) upon seeding perennial grass on highly erodible croplands and the impact of reversion to row crop production in semiarid regions are not well understood. A study was conducted to measure the effects of four post-contract options of grass management and re-cropping on soil C and N storage in two CRP fields in western Oklahoma. We found that soil soluble C increased under CRP tenure, averaging 160 to 360 lbs C a-1 in soils. Generally, soil total C in the 0-4" depth remained unchanged or increased slightly while organic C remained unchanged at both locations. Finite changes in soil total C occurred within the 0-12" depth because a sweep- or disc-tillage operation to destroy the sod and prepare for planting crops caused internal cycling of inorganic carbonate-C to the near surface zone. Shifts to a permanent vegetative cover, N fertilization, direct seeding and avoidance of tillage on highly erodible lands appeared beneficial to their productivity. The length of time required to transform these lands into storage sinks for atmospheric C may be the major limiting factor in a subhumid and semiarid climate. Technical Abstract: Changes in soil carbon (C) and nitrogen (N) upon seeding perennial grass on highly erodible croplands under the Conservation Reserve Program (CRP) and the impact of reversion to crop cultivation in semiarid regions are not well understood. A study was conducted to measure the effects of four post-contract options of grass management and re-cropping on soil C and N storage in two CRP fields in western Oklahoma. The fields were located on Dalhart fine-sandy loam (Aridic Haplustalf) and La Casa-Aspermont clay loams (Typic Paleustoll). Soil cores were collected from the 0-0.05, 0.05-0.1, 0.1-0.2, and 0.2-0.3-m depths. Dissolved C, mineralizable C, carbonate C, organic C (OC), total C (TC) and N, and potential mineralizable N were determined in samples collected at the initiation of re-cropping in 1994 and after the third year of cultivation. Soil mineralizable C increased under CRP tenure, averaging 0.18 to 0.4 Mg C ha-1 and 0.15 to 0.18 Mg C ha-1 in the Dalhart and La Casa-Aspermont soils, respectively. Generally, soil TC in the 0-0.1-m depth appeared unchanged or increased slightly while OC remained unchanged at both locations. Finite shifts in TC within the 0-0.3-m surface indicated internal cycling of carbonate-C to the near surface. Shifts to a permanent vegetative cover, management of excessive aboveground dry matter, N fertilization, and avoidance of tillage on highly erodible lands appeared beneficial to their productivity. The length of time required to transform these lands into sinks of atmospheric C may be the major limiting factor in semiarid regions. |
