Progress report for GS21-246
Broccoli is considered a high-value specialty crop that has seen an increase in production in recent years within the southeastern U.S. Considered a cool crop, broccoli is very sensitive to the current scenario of climate change. In the southeastern U.S., the weather variability makes broccoli cultivars yield and time to maturity more difficult to predict, creating challenges to crop management practices for broccoli growers and affecting crop yield. Therefore, the development of a crop model, that would allow growers to predict crop development and yield based on weather conditions, is key to mitigate the challenges caused by climate change. The objective of this project is to develop an accessible agricultural decision tool (i.e., crop model) that will assist broccoli growers on decision making for crop management practices under the environmental conditions of the southeastern U.S. Field experiments will be conducted in 2021 and 2022 at the E.V. Smith Research and Extension Center of Auburn University in Shorter, AL. Field trials will allow for determination of genetic parameters for the most common broccoli cultivars grown in the southeastern U.S. Those parameters are required for the development of the proposed crop model. As a result of this project, the crop model will provide scientifically-based information for researchers and be used as a guide for growers to manage the broccoli industry that is emerging in the southeastern U.S.
The objective of this project is to develop a crop model that simulates broccoli growth and yield for common cultivars grown in the southeastern U.S., and to evaluate the effects of the weather variability of subtropical conditions of southeastern U.S. on broccoli growth and yield by submitting the proposed crop model to different weather scenarios.
The Eastern Broccoli Crop Model
Our research team is proposing to develop an Eastern Broccoli Crop Model (EB-Model) that will account for weather conditions to simulate growth and yield. The EB-model will be developed using the approach proposed by Carranza et al. (2008) and described below:
where W is the increment of the total plant dry biomass (g·m-2); FL = (1-e-k·LAI) is the fraction of light intercepted, k is the extinction coefficient of light, and LAI is the leaf area index; SRAD is the solar radiation (MJ·m-2·d-1); RUE is the radiation use efficiency (g·MJ-1).
Once W is calculated, the broccoli daily biomass accumulation will be estimated as:
Where t is time, Wt is the mass accumulated in time; Δt is 1 (day).
The partitioning of biomass accumulation by plant tissue will be calculated as:
where Wot is the total dry biomass of plant tissues, such as leaves (Wlt), stems (Wst), flowers (Wft) or root (Wrt) on dayt (g·m-2·d-1); Wo (t-1) is the dry biomass of leaves (Wlt-1), stems (Wst-1), flowers (Wft-1), or root (Wrt-1) on dayt-1 (g·m-2·d-1); αo is the leaf distribution coefficient (αl), stems (αs), flowers (αf) or root (αr); αo =1; Wt is the daily growth rate of total dry biomass (g·m-2·d-1); ∆t is the increase over time (1 day).
Field experiments for data collection and model evaluation
Field experiments will be conducted to determine the genetic parameters (i.e., k and RUE) for the most common broccoli cultivars grown in the southeastern U.S. and required by the EB-Model. A one factorial experimental design of 6 broccoli cultivars will be arranged in a complete randomized block design with 4 replications. Broccoli cultivars will be selected using results from the project “Developing and Eastern Broccoli Industry” (USDA/SCRI - award number 2016-51181-25402) coordinated by Dr. Thomas Bjorkman. Trials will be conducted during the fall 2021 and 2022 in the E.V. Smith Research and Extension Center from Auburn University, Shorter, AL. Soil in the experimental area is classified as loamy sandy with low water holding capacity (USDA, 1983). Climate of the region is classified as a subtropical climate according to the Koppen climate classification. Both soil and climate conditions are representative of most broccoli fields of southeastern U.S., while crop management practices will follow the Alabama Cooperative Extension System recommendations, so crop stresses will be controlled as much as possible.
During field experiments daily maximum and minimum air temperature, solar radiation, and rainfall events will be monitored using a weather station installed on-site. Weekly monitoring of crop canopy will be conducted to define broccoli crop development, such as vegetative stage, flowering, head formation, and maturity. Furthermore, plant samples will be collected weekly for evaluation of LAI and biomass accumulation. Each sample will be comprised of two representative plants of each plot. Plants will be split into roots, leaves, stems, and heads. Fresh weight of each plant tissue will be recorded. The LAI will be measured using a Plant Analyzer (LAI-3100C, LI-COR, Inc., Lincoln, NE.). Subsequently, samples will be oven-dried at 150 °F for constant weight, and dry weight recorded. Ultimately, broccoli heads will be harvested at maturity from the two center rows of each plot, and total weight recorded.
Broccoli genetic parameters (i.e., k and RUE) will be determined for each stage of broccoli development during the EB-Model calibration using data collected in year 1 (2021). The initial value tested for all growth stages will be 0.6 for k and 0.23 for the RUE as described by De Wit (1965). Data collected in year 2 (2022) will be used for the EB-Model validation. The entire process will consist of the EB-model evaluation. Once evaluated the EB-Model will be available for growers using different simulation frameworks including a stand-alone version in Excel that will be available for free download via the Alabama Cooperative Extension System – Commercial Horticulture Team.
Accounting the weather variability
An analysis of different environmental scenarios, also known as seasonal analysis, will be performed after the EB-Model evaluation using a historical weather data set from 2011 to 2020 (10 years) in Shorter, AL. Weather data will be collected from the Auburn University Weather Network (MESONET), and five planting dates will be simulated for each cultivar into the EB-Model to account for different weather patterns on broccoli yield. A total of 300 combinations of treatments from the 5 planting dates, 6 cultivars, and 10 harvested years. Simulated broccoli yield will be compared among planting dates in a cumulative probability distribution and the best planting date for broccoli production in the region determined.
Extension and outreach
After the release of the EB-Model, a comprehensive and instructional recorded webinar will be developed and available at the website of the Alabama Cooperative Extension System – Commercial Horticulture Team. The webinar will consist of a step-by-step education on using the EB-Model and will be available continuously available for growers after year 2.
Educational & Outreach Activities
Up to date, field experiments conducted in the fall of 2021 and spring of 2022 evaluated the performance of different broccoli cultivars for the environmental conditions of Alabama. Experiments were conducted in the E.V. Smith Research and Extension Center and a collaborator grower in Madison, AL. Data for the model development was collected and is under analysis. Since the beginning of the project, individual consultations with growers were provided (8), one peer-review article is under development, two on-farm demonstration trials were conducted, one webinar was produced, reaching 115 growers and 22 extension people, and one newsletter was submitted for publication and a second one is under development.
Overall, our field trials were a success. Data has been properly collected and we do not anticipate any problem with deliverables. Ph.D. student Marcos de Barros is in charge of the trials and helping the PI da Silva to conduct extension activities.