Progress report for GS23-284
Project Information
The Everglades Agricultural Area (EAA) located in South Florida is approximately 283,000 ha in size, comprising of highly organic soils (Histosols). However, this fertile “muck” soil has been experiencing soil loss via microbial organic matter (OM) oxidation, locally referred to as “soil subsidence” which is known to decrease soil health and agricultural sustainability within the region. Increasing concern about the long-term sustainability of agricultural production within the EAA has emphasized the need for developing C-farming practices including (i) crop rotation (flooded rice with sugarcane), (ii) flooded-fallow instead of fallow fields, and (iii) growing cover crops that can enhance C input and reduce rate of microbial OM oxidation particularly during the hot dry periods. However, long-term quantitative studies evaluating the effects of these C-farming practices on soil subsidence are lacking. Therefore, the overall objective of this study is to identify C-farming practices among these existing farming practices that can address soil subsidence within EAA. The specific objective of this study is to investigate the impact of these existing farming practices on (i) C input, (ii) soil enzymatic activity associated with mineralizing soil C to CO2, and (iii) active carbon, which is a portion of OM susceptible to be mineralized to CO2 by soil enzymes. Knowledge of C input, soil enzymatic activities and active carbon will help growers, and land managers in decision-making when selecting C-farming practices that could potentially mitigate soil subsidence, thus, improving and sustaining soil for food production while lowering C losses to the atmosphere within EAA.
The overarching objective of this study is to test a subset of a four-year long PhD project, specifically focusing on the impact of currently applied BMPs on C input, and changes in (i) soil C stock, (ii) enzymatic activities controlling soil C stock due to their role in oxidizing soil C to CO2, (iii) soil environmental factors influencing enzymatic activities, and (iv) active carbon, which is a portion of OM susceptible to be oxidized by microbial activity in Histosols, the purpose being to identify C-farming among existing BMPs that has potential to mitigate soil subsidence. We hypothesize that the proposed C-farming practices will increase soil C pool via atmospheric CO2 sequestration and reduce soil loss via reducing enzymatic activities playing role in OM oxidation. To test this hypothesis, three separate field studies will be conducted on commercial farms within the EAA in collaboration with our local stakeholders (Florida Crystals, Sugar Cane Growers Co-Operative of Florida, Roth Farms, Veg Pro International, and Roth Farms).
Study 1 (Crop rotation [sugarcane and flooded rice])
The objective of this study is to quantify the above and below-ground biomass C input and evaluate changes in soil C stock, active carbon, microbial activity measured by extracellular enzymatic activities, and soil environmental factors under flooded rice as summer crop rotation compared to sugarcane farming practice.
Study 2 (Flooded- fallow versus fallow)
The objective of this study is to determine the effect of flooded fallow on soil C stock, active carbon, microbial activity measured by extracellular enzymatic activities, and soil environmental factors versus fallow fields within the EAA.
Study 3 (growing cover crops)
The objective of this study is to quantify the above and below-ground biomass C input and assess changes in soil C stock, active carbon, microbial activity measured by extracellular enzymatic activities, and soil environmental factors under different cover crops, the purpose being to determine the feasibility of growing cover crops during fallow period and identify suitable varieties that can be adopted by the growers during summer fallow period.
Research
Study 1 (Crop rotation [sugarcane and rice])
Experimental design
This study will be carried out on 16-ha sized sugarcane farm managed by the University of Florida, which is located at the Everglades Research and Education Center (EREC) in the EAA. Sugarcane field will be compared with a similar sized flooded rice field during summer period. Due to variability in soil properties across the farm caused by soil subsidence particularly soil depths and OM, six distant locations will be randomly selected within experimental field, and each location will be considered as one replication, totaling six replications. Before establishing sugarcane experiment, pre-soil samples will be collected at two soil depths (0-0.15 m and 0.15-0.30 m) by travelling in a zigzag pattern at each location to form one composite soil sample, totaling 12 composite samples. Based on our personal survey, it is not possible to get soil deeper than 0.30 m depth in some locations within study area, leading us to set 0.30 m as maximum sampling depth. Sugarcane will be planted. Soil and tissue samples will be collected from each location every three-months until harvesting stage using destructive method combined with linear sampling methods (Verwijst and Telenius, 1999). In this method, one row will be randomly selected near each location, and 2 m length will be measured. All above (stalks+leaves) and belowground (roots) live biomasses of sugarcane found within 2 m length will be gently pulled from the soil and then transported to the Lab for processing. Soil samples will be collected at the same time as tissue sampling whereby soil samples will be collected at 5 different points randomly selected within the sampling row to form one composite soil sample. Study1-flooded rice (diamond variety) experiment will be established after sugarcane study following the same methods used for study 1-sugarcane experiment. Soil temperature, moisture content, dissolved oxygen, redox potential and pH as soil environmental factors will be measured in-situ for all experiments (Study 1, 2, and 3) using electronic sensors connected to dataloggers as detailed in the study of (Unger et al., 2009). Soil sensors will be installed in the field at 0-20 cm depth for monitoring fluctuations in soil environmental factors.
Analytical Procedure
Soil analysis
Fresh soil samples collected from study1 will be air dried at 50 ⁰C for 72-hrs and sieved (2 mm) prior to analyses. Soil will be analyzed for total C (TC, %) by dry combustion method (Nelson and Sommers, 1982), active carbon by potassium permanganate method (Schindelbeck et al., 2016), and bulk density (Bd, Mg m–3) will be calculated by dividing soil mass in a fixed core volume. Soil C stock will be calculated according to the following equation:
Soil C stock (metric tons/ha) = TC × Bd× V,
whereby V is the volume of the soil layer in m3. V=D × A with D is soil depth (m) and A is the study area in m2. Changes in soil C stock will be the difference between soil C stock at each sampling time and initial soil C stock.
Soil enzymatic activities will be analyzed using air dried samples sieved at 2mm-sieve. Four enzymatic activities: β-1,4-glucosidase (BG), β-1,4-N-acetyl-glucosaminidase (BNAG), alkaline phosphatase and aryl sulphatase activities will be analyzed by colorimetric method (Tabatabai, 1994). Data of soil environmental factors will be collected every three months for sugarcane and one month for flooded rice experiment.
Plant biomass analyses
The above and belowground biomass will be rinsed with DI water, separated from each other using a scissor, and then put in oven dry at 70 oC to estimate dry biomasses. Dry biomass will be calculated using the following equation:
Dry biomass (kg/ha)= (kg dry biomass per 1 m x L x N)/A , where L: total row length; N: number of rows within experimental field; A: study area (ha). After weighing dry biomass, a subsample of dry biomasses will separately hammer-milled to analyze C content using dry combustion method (Nelson and Sommers, 1982). The plant C content will be multiplied with dry biomass to get below- and aboveground biomass C input.
Study 2 (Flooded fallow versus fallow)
Experimental design
Every summer growers in the EAA can potentially flood their fields as a practice known as flooded fallow and leave the field uncultivated as practice known fallow for conserving soil loss. After harvesting sugarcane in spring, a field study will be established on 16 ha sized sugarcane farm managed by Sugarcane Growers Cooperative of Florida (SCGC). Two treatment plots consisting of fallow and flooded fallow will be set up. Soil samples will be collected twice, (i) prior to leaving fields under fallow and flooded-fallow conditions (pre- soil samples), and (ii) at the end of summer when the fields are either drained (in case of flooded) or cultivated (in case of fallow), approximately 4 months (post soil samples). For each plot, 6 distant locations will be randomly picked. Soil samples will be collected at 0-0.15 m and 0.15-0.30 m depth following similar methods described in study 1.
Analytical Procedure
Soil samples from both fallow and flooded-fallow plots will be processed and analyzed following the parallel methods delineated in study 1.
Study 3 (Growing cover crops)
Experimental design and data collection
Cover crop experiment will be established on multiple 16 ha commercial farm managed by Roth Farms and Veg Pro International within the EAA. The study will be comprised of 3 treatments, comprising of cowpea (Vigna unguiculata), sunn hemp (Crotalaria juncea L.) and sorghum- sudangrass (Sorghum × drummondii) as a cover crop. The treatments will be compared to an equally sized fallow field. For each treatment, soil samples will be collected twice at two different depths (0-0.15 m and 0.15-0.30 m) (i) prior to sowing cover crop seeds [pre-soil samples], and (ii) after harvest [post-soil samples]. Tissue samples will be collected once for each treatment at the end of growing season. Soil and tissue sampling will follow similar procedure described in study 1.
Analytical procedure
Soil and plant biomass analyses will follow the same procedures described in study 1.
Project report from September 2023-February 2024
September-November 2023, we met with collaborative growers and selected field site for study 1-sugarcane experiment. Field site for study 1 is located at the University of Florida- Everglades Research and Education Center. After selecting field site, baseline soil samples (0-12, and 15-30 cm depth) were collected prior to planting sugarcane. Collected soil, and tissue samples were taken to Soil, Water, & Nutrient Management Lab (EREC)where they were processed for lab analyses.
December 5th, 2023, sugarcane was planted Figure 1, and first soil samples, and tissue samples were collected on February 5th, 2024 Figure 2. Collected soil and tissue samples were transported to Soil, Water, & Nutrient Management Lab (EREC), where they are being processed for Lab analysis. Soil, and plant tissue data will be provided once they are available.
Educational & Outreach Activities
Participation Summary:
Jan 13 to 29th, 2024, We conducted an outreach activities at the South Florida Fair 2024 where we had Posters, and Scientific Demonstrations as well as workshops on educating the public about the role of cover crops, and rotational crops (Cultivation flooded rice in rotation with sugarcane) play in sustaining organic soils of Everglades Agricultural Area. Prior to initiating the project, we visited six commercial farmers, and six Ag professionals that are engaged in Sugarcane plantation to finalize the study area. In addition, We also consulted 6 consultants regarding sugarcane varieties, and field operations. November 10-13, 2024, we plan to attend 2024 ASA, CSSA, SSSA International Annual Meeting, SAN ANTONIO, TEXAS, where we will be presenting the findings of our study.