Performing Department
Crop and Soil Sciences
Non Technical Summary
The soils we have chosen in this study represent 1.2 million ha of class prime farmland spanning the entire Coastal Plain region of the southeast. The agricultural landscape found on these soils is diverse, however there is a unifying feature that all farmers are challenged with in this region, low soil C and low soil health. Transition to organic management is challenging due to short-term limitations in soil health and productivity before longer-term agroecosystem benefits can be realized. This challenge is exacerbated by the sandy soils and warm climate of the southeastern Coastal Plain. When managed conventionally, these soils have very low (<1%) concentrations of organic matter. Yet, preliminary data from the soil survey show that reforested sites have significantly increased SOC (45-200%), therefore there is clearly potential for these soils to retain more C. By most soil health metrics, which are strongly correlated to soil organic carbon (SOC) content, these soils are considered unhealthy and may remain in a poor state of soil health for a substantial period after transition. Determining the potential of southeastern Coastal Plain soils to accrue C, defining possible rates of sequestration, and identifying practices that can accelerate short-term gains can help guide the transition to organic management. Therefore, the goal of this integrated research, extension and education initiative is to develop an understanding of soil carbon and soil health accrual over time in organically managed fields in the characteristically low-C soils of the coastal plain region of the Southeast. Our two-pronged approach will use on-farm sampling and controlled field experiments to understand soil C and soil health dynamics from the onset of transition to organic into the long-term (15+ years). Field and on-farm experiments will address the following four objectives: 1) determine a baseline soil carbon accrual rate in the region by comparing paired conventional agriculture and afforested sites; 2) assess soil carbon and soil health indicators on 20 organically managed fields along a chronosequence from 1 to 20+ yrs from transition to organic; 3) establish a field experiment at two sites, evaluating different carbon input strategies to jump start soil C accrual and soil health metrics for comparison to the baseline and sampled chronosequence of organic farms; and 4) educate researchers, farmers, students and extension agents through an integrated outreach program, highlighting long-term outcomes and short-term strategies for accelerated soil health improvement during transition. Our results will provide key insights on soil C stocks in organic farms within this region and help determine which C input strategies could improve soil health rapidly during the challenging transition period to organic.?
Animal Health Component
0%
Research Effort Categories
Basic
20%
Applied
60%
Developmental
20%
Goals / Objectives
The major goal of this research project is to create a framework and protocol to understand the lower and upper boundaries of soil health and soil carbon sequestration potentials based on transition from organic farming. Traditionally this would require long-term field experiments, however theapproach in this studyavoids the need for long-term experimentation by sampling organic farms that have been in organic management over a range of years to create a Chrono sequence. In this study we have constrained this analysis on the coastal plain region of North Carolina, a region characterized by low soil carbon and poor soil health. The carbon and soil health accrual rate determination developed will be used to compliment the research station field experiments. The second goal of this study is to determine how rapidly soil health and carbon can be improved through intensive management during the 3-yr transition period from conventional to organic through the use of organic amendments and cover crops in a representative crop rotation found in this region. Specific objectives are as follows:1) Establish baselines of mean soil C stocks for conventional agricultural fields and mature secondary growth forest stands on the Atlantic Coastal Plain.2) Evaluate the long-term effects of organic agriculture (>15 years) on soil C and related soil health metrics using Chronosequence methods.3) Evaluate carbon (composts, bio char, cover crop biomass) input strategies during a 3-year transition period in a high disturbance crop rotation on soil organic carbon, soil health indicators and crop yields.
Project Methods
Chronosequence On-Farm Study We will utilize paired site methods to evaluate a minimum of 10 plots representing SOC pools under conventional agriculture and maximum expected SOC pools under mature (>50 years) forest. The 10 paired plots will be used to derive a mean/median baseline between initial and projected maximum SOC for the Goldsboro/Norfolk soil series. We will utilize fixed incremental sampling at 0-5, 5-10, 10-20, 20-30, 30-50, 50-75, and 75-100 cm for statistical comparisons by depth among study sites. Soil measurements will include bulk density, particle size distribution, and total C/N concentration. Soil C concentrations will be converted to landscape pools and compared between conventional farm fields and mature secondary growth forest. These data will be used as the minimum-maximum boundaries between which organic systems can be compared to detect short and long-term changes in soil C accrual.We will select a minimum of 15 and maximum of 20 organic farm fields mapped as Goldsboro or Norfolk series to be sampled by stratified age groups. We will define age since transition groups as recent since transition (1-5 years in organic agriculture), mid since transition (5-10 years in organic agriculture), and late since transition (10+ years in organic agriculture). In the first field season we will replicate soil measurements in a single soil map unit at representative sites from each of the three defined age groups to understand within-site variability in soil properties. The data will be used to construct a regional chronosequence for SOC and associated soil health metrics. Effort: This chronosequence will be used both to identify the trajectory of organic management system soil health over time after transition and as a metric to evaluate C input strategies during transition as described the research station project.Soil metrics will include core method bulk density and soil texture via hydrometer. Saturated hydraulic conductivity and water holding capacity will be obtained from cores. Aggregate stability as mean weight diameter will be assessed via wet sieving. Soil pH will be measured using 1:1 soil:DI water and 1:2 soil:CaCl2, and soil electrical conductivity will be measured using 1:2 soil:DI water. Cation exchange capacity (CEC) and base saturation will be quantified for the upper sandy horizons and at the transition to the clayey subsoil using NH4 OAc, pH 7 extractions. Total soil C and N concentrations will be quantified via thermal combustion. Carbon and N mineralization potential will be measured via incubation, and labile C will be quantified as permanganate-oxidizable C. Enzymes: â-glucosidase, â-glucosaminidase, phosphatase and arylsulfatase will be assayed as indicators for nutrient cycling. Lastly, soil protein will be measured as an indicator of bioavailable N.Effort: Regression techniques will be utilized to create soil pedotransfer functions between SOC and other soil health indicators to quantitatively establish the connections between organic agriculture and soil health in the Atlantic Coastal Plain. In addition, a principle component analysis (PCA) will be conducted on the measured soil health indicators. Evaluation: Utilizing a previously used scoring scheme as a baseline, we will then identify indicators that account for the majority of the cumulative variability and will use a weighted mean to develop a more regionally representative soil health report. In this study, length of time from transition will be the metric of comparison.Research Station 3-yr Transition ExperimentWe propose a field experiment designed to evaluate the impact of using increasingly recalcitrant C material on SOC and soil health indicators during the transition period from conventional to organic. The most labile C input will be the inclusion of grass and legume cover crops within the rotation, followed by a compost, a compost and biochar mix, and lastly biochar alone. In addition, we evaluate the potential benefit of applying a single large application of amendment as compared to annual application over the 3-year transition period. By creating a 3x2x2 factorial design we will be able to determine the efficacy of individual C input strategies (timing, source) and the potential synergistic effect of combining inputs with the presence of cover crops on SOC and soil health. In addition, a no amendment treatment will serve as a control. Deep core samples (1 m) taken at the end of the 3-yr since transition will be identical to the samples taken in the chronosequence.The underlying croping rotation used in this study will be a corn-sweet potato-soybean rotation, a second cropping rotation incorporates winter cover crops, with the same summer crops ((Crimson Clover) - Corn - (Crimson Clover) - Sweet Potato - (Rye) -Soybean)). The field sites will enter organic management in the fall with planting of crimson clover. The organic amendments include: a yard waste certified compost, a pine based biochar, and a 50/50 mix of compost and biochar. The composted material will be applied at 75 t ha-1 in a single application or 25 t ha-1 per year for 3 years. The compost/biochar treatment will be mixed (50% Compost/50% Biochar) based on C concentration. The biochar treatment will be applied at the same C rate as the compost, and annual application treatments will again be split evenly between three years.The certified organic compost will be composed of predominantly yard waste feedstock, with woodchips as a bulking agent sourced from a commercial composting operation. Chemical composition of the composts will be analyzed every year for Total CHN and submitted to the NCDA&CS laboratory for a standard waste analysis. The biochar material will be sourced from a pine feedstock. The biochar will be characterized following the ASTM D1862-84 Standard Test Method for Chemical Analysis of Wood Charcoal.Background soil samples will be taken at the same depth increments as in the chronosequence sampling within each block (n=4 per site) prior to study initiation. These samples will be analyzed for total C and N and the same soil health parameters outlined in the chronosequence. Surface soil samples will be taken (0-15 cm) and submitted for routine soil fertility analysis. At planting, surface soil samples will be collected (0-15 cm) and analyzed for potentially mineralizable N (PMN) via incubation. The PMN values will allow an estimate of in-season N release to the crop. At harvest in Yr. 1 and Yr. 2, surface soil samples will be collected (0-15 cm) an analyzed for the suite of soil health metrics a with the exception of total C and N. Evaluation: After harvest of the soybean in Yr. 3, deep soil cores will be collected from all experimental units and analyzed for all soil health indicators as well as total C and N and compared to values of varying aged organic farms to determine the success or failure of this approach to rapid soil health improvement.All soil health parameters, SOC, above ground biomass, harvestable yield will be analyzed using generalized linear mixed models. Soil health results derived from the field study will be compared to those from the chronosequence by plotting results on the regional chronosequence graphs after 3 years and via one-way ANOVA of aggregated sites by age. Using PCA we will determine weighted soil health indicators, as described in the chronosequence methods and create a minimum dataset to remove highly correlated parameters. Effort: Correlation and multiple linear regressions between crop yields and the minimum dataset soil health indicators will be completed. We will also compare the PCA and weighting estimates with the long-term on-farm sampling and assess the similarity or difference of the rapidly changed soil health indicators compared to the long-term. Evaluation: The goal is to improve correlations so regionally important soil health indicators have a more meaningful connection with yield.