Over the course of the past year, many of the goals set forth in the original research proposal have been met and steps have been taken toward achieving others. Work over the last year has included sample collection, chemical analyses, and data collation and analysis. In addition to the scheduled tasks, we have completed a manuscript examining the influence of grassland management on C sequestration (Ecological Applications), a manuscript, and presentation, evaluating the potential for C sequestration in pasture soils in the southeastern US with changes in pasture management (more info), and have begun a manuscript evaluating the influence of overgrazing on soil C (in prep).
Thirty demonstration farms have been funded in Mississippi, many of which had limited early success but failed to generate persistent management improvement. Some of the farms, however, have had great success and in early spring 1999, we visited 12 of these farms in Mississippi to identify site suitability for comparative soil sample collection. Walter Jackson (NRCS Jackson) arranged visits to these farms accompanied by the landowners and local soil scientists. Pastures in this region are widespread and under substantially different levels of management. Unfortunately, many of the improvements implemented through the demonstration project were not continued or did not appear likely to continue on some of the farms. Other owners, however, had enthusiastically adopted changes and appeared likely to maintain improved pasture management as suggested by NRCS.
Of the farms we visited, seven contained management treatments that were either immediately comparable or presented interesting sites to be resampled in the future. Soil samples were collected in late spring 1999. One group of farms, in Hinds county, had many different types of management, including cultivated fields, pastures that had been converted from cultivation for various periods of time, ungrazed grasslands, and recently planted pines. Comparisons in other areas included conversions from cultivation to pasture of various ages and fertilized versus unfertilized fields. Much of the pasture land (and cultivated land) in Mississippi is being converted to pine trees for economic reasons. Two relocateable sites were established in fields recently planted with pines. Locations of microsites were established with a differential GPS and a relocatable marker ball was installed at each microsite so that the exact locations of the soil cores can be revisited in the future. Soil cores comprising more than 1T of soil were returned to NREL and sample preparation and analysis began in December.
Plans are underway to visit Tennessee (3/21/00-3/23/00), to review the demonstration farm program, and Kentucky (3/24/00) to sample fields at the University of Kentucky agricultural research station. Our original plans to sample in Georgia were changed after talking with the State NRCS demonstration farm coordinator since projects there focus mainly on hay storage techniques. We will be working with Greg Brann, the Tennessee NRCS demonstration farm coordinator and Jimmie Henning of the University of Kentucky. We plan another visit to collect soil samples and establish microsites in late Spring 2000.
We evaluated the potential for C sequestration in Southeastern pasture due to changes in land use and land management. We used the 1982 and 1992 NRI land use data to quantify changes from cropland into pasture for each state. Using county-scale climate data, we tied this information to C sequestration rates based on data from the literature. We estimated that conversion from cropland to pasture sequestered 0.22 tg C yr-1 between 1982 and 1992. We used a similar approach to evaluate the effect of land management on C sequestration. We polled knowledgeable people in each state (usually NRCS forage specialists) on adoption of improved management (intensive grazing management, fertilization, and active sowing of legumes). We used these data to extrapolate for the entire region based on data from the literature. We estimate that 0.99 tg C yr-1 and 0.75 tg C yr-1 are sequestered annually due to fertilization and sowing legumes, respectively. We extrapolated based on historic trends and determined that 14 tg C will be sequestered between now and 2020 if current land use change trends continue. Further, higher adoption rates of fertilization and sowing legumes can potentially lead to as much as 2 tg C yr-1 more sequestration than low adoption rates. These results were presented at the ‘Agricultural practices and policies for carbon sequestration in soil' meeting (July 1999) and results will be published as a book chapter. Slides from the presentation can be viewed here.
| 1998 | 1998 | 1998 | 1999 | 1999 | 1999 | 1999 | 2000 | 2000 | 2000 | 2000 | 2001 | |
| Research task | Su | A | W | Sp | Su | A | W | Sp | Su | A | W | Sp |
| Task 1 - Landuse/Recon. | VA | VA | VA/MS | VA/MS | TN/KY | |||||||
| Task 2 - Field comparisons | VA | MS | TN/KY | |||||||||
| Task 3 - Microsites | VA | MS | TN/KY | |||||||||
| Task 4 - Modeling | VA/MS | MS | MS/TN | TN/KY |
Preliminary analyses on soil samples from the Wayson farm in Virginia have been completed. Results indicate that soil C decreased significantly (P<0.05) following conversion from forest to pasture (Fig. 1). However, over the course of the chronosequence (~45 years) soil C levels rose eventually becoming equivalent to forest C content. Similarly, although substantial C was likely lost during long-term conversion on some fields, soil C content in fields that were converted from cultivation to pasture 45 years ago were equivalent to those in both forest and long-term pasture soils. Soil N tended to increase over time following forest to pasture conversion, likely due to accumulation of added N. Preliminary analysis indicates that our sampling scheme could detect changes of the magnitude observed elsewhere over short time periods (~5 years). Minimum detectible differences were 5.6 tC ha-1 and 401 kg N ha-1.
We have completed the tasks scheduled for the second year of the project and have implemented plans to begin tasks scheduled for the third year (i.e. TN/KY field visits, sample analysis, and modeling). Presentations were given at the Ecological Society of America annual meeting (poster, August 1999) and at a special C sequestration meeting at Tri-State Power Company (February 2000). Presentations describing research results are scheduled for the Ecological Society of America annual meeting (poster, August 2000), the 2000 Bioenergy and Carbon Sequestration Conference (poster, August 2000), the Soil Science Society of America annual meeting (November 2000), and the NACD grazing lands conference (December 2000). A manuscript describing grassland management and soil C is complete and has been submitted to Ecological Applications. As mentioned above, a book chapter reporting results of a study on SE land use and pasture management on soil C sequestration has been submitted. A series of manuscripts describing inter-comparison of land use and soil datasets, and model sensitivity to input data, are in various states of completion (prelim. results). Also, a manuscript describing the effects of overgrazing on soil C, and implications for C sequestration, will be submitted soon. In cooperation with Walter Jackson (NRCS, Jackson) and George Bates (Alcorn State University), we developed a proposal (to be submitted to USDA SARE) to study the influence of intensive grazing management on primary production at the Alcorn State Experimental Farm. We also received funding from the Environmental Resources Trust to increase soil sampling intensity (more samples) and extensively (more sites) in Tennessee.