Assisting Vegetable Growers in Florida with Soil Health Evaluation Associated with Cover Cropping/Green Manure Practice During Summer

Final report for OS18-114

Project Type: On-Farm Research
Funds awarded in 2018: $15,000.00
Projected End Date: 03/14/2020
Grant Recipient: University of Florida
Region: Southern
State: Florida
Principal Investigator:
Jehangir Bhadha
University of Florida, Institute of Food and Agricultural Sciences Everglades Research and Education Center
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Project Information

Abstract:

Cover crops are proving to be vital in the development of soil health. Growing cover crops is perhaps the most valuable strategy we can adopt to feed our soil, build up its fertility, and improve its structure with each passing season. Green manure is a cover crop used primarily as a soil amendment and a nutrient source for subsequent crops. In most production environments, lack of nitrogen limits plant growth more than any other nutrient. Legumes, however, possess a symbiotic relationship with rhizobial bacteria capable of transforming atmospheric N2 into plant usable form and may accumulate large amounts of N via this pathway. Legumes utilized as green manure therefore represent a potentially renewable source of on-farm, biologically fixed N. Unlike chemical N fertilizers, legumes may also fix and add large amounts of carbon to a cropping system. Green manure approaches may also drive long-term increases of soil organic matter and microbial biomass, further improving nutrient retention and N-uptake efficiency. When used in place of fallow, well-chosen green manures may reduce erosion and suppress weeds and specific crop pests. Green manures may also offer habitat or resources for beneficial organisms. All of these processes are quintessential for improving soil quality.

We propose evaluating sunn hemp (Crotalaria juncea) and cowpeas (Vigna unguiculata) as two green manure options that would perform well in Florida during summer.

 

Project Objectives:

The research approach comprises of the following four tasks:

  • Identification and commitment from cooperative growers;
  • Study design;
  • Soil testing and analyses;
  • Assisting growers adopt cover cropping practice

Cooperators

Click linked name(s) to expand
  • Stewart Swanson (Educator and Researcher)
  • Jay Capasso (Educator and Researcher)
  • Nan Xu (Researcher)
  • Kevin Korus (Educator and Researcher)
  • Christian Miller (Educator and Researcher)

Research

Materials and methods:

 

The purpose of this project was to identify growers within Florida that practiced cover cropping during the fallow period. Due to the climatic variability within the state from North to South, in south Florida the fallow period is usually summer month, while in north Florida winter months are usually fallow. As part of this study we were able to identify 8 collaborative growers across the state, representing 9 unique farming programs. The common denominator being that they all cover crop during the fallow period.  

Once we had identified the growers, we wanted to shadow their practice and collect soil samples before and after their cover cropping program, to evaluate the change in soil health properties as a function of cover cropping. 

Locations of various collaborative growers that participated in this study.
Study plan logic model

 

Research results and discussion:

Summary of changes in soil health indicators based observed on 9 field sites across Florida and 8 growers, all of them practicing cover cropping during the fallow period.

+ indicates increase in soil property

- indicates a decrease in soil property 

 

Participation Summary
8 Farmers participating in research

Educational & Outreach Activities

20 Consultations
1 Curricula, factsheets or educational tools
1 Online trainings
3 Webinars / talks / presentations
2 Other educational activities: Each year my program organizes a booth at two annual events (i) South Florida Fair, (ii) Fall Scarecrow Festival. These events attracts general public along with local growers, farmers and ranchers. The South Florida Fair is an annual winter event that lasts for 17 days and attracts nearly 15,000 people each day. We displayed information related to soil health and sustainability within the region, and the importance of cover cropping to improve soil quality.

Participation Summary:

40 Farmers
29 Ag professionals participated
Education/outreach description:

As part of our Education and Outreach program, we have had at least 20 consultations with our collaborative farmers. These consultations typically are held at their farms and last about an hour. The educational tool that was developed in the last year was a six-module In-service training (IST) comprising of presentations and hands-on demonstrations on the topic of soil health and sustainability. Two such training was provided to the agricultural professionals, particularly extension agents and extension specialists. The topics covered included subjects like soil health principles, soil microbiology, soil health indicators, benefits of cover cropping etc. This IST is now also available online for agricultural professionals to take remotely. In 2018, we compiled a Soil Health and Sustainability Handbook, that will be distributed to all our project collaborators.   

Our future planned activity includes conducting a training in 2019 for the growers on the topic of soil health and sustainability and also publish an extension article on the topic of cover cropping during fallow period.

Learning Outcomes

6 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • Soil fertility/nutrient status

  • Cation exchange capacity of the soil

  • Water holding capacity of the soil

  • Organic matter content

  • Soil health indicators

Project Outcomes

3 Farmers changed or adopted a practice
1 Grant received that built upon this project
8 New working collaborations
Project outcomes:

As part of the first year of this project we had six collaborative growers on whose farms we were able to get both pre and post cover cropping soil samples. We were also able to identify one new Extension agent, and two additional growers (3 sites) that wish to participate in this study during year two. Results indicate that 2/6 farms showed a reduction in bulk density (BD), 3/6 showed an increase in BD, whereas 1/6 farm showed no change in BD. Soil pH reduced in 4/6 farms, whereas 2/6 farms showed an increase in soil pH. 5/6 farms showed an increase in maximum water holding capacity (MWHC) of the soil, whereas only 1/6 farm showed a decrease in MWHC. 4/6 farms showed an increase in organic matter (OM), whereas 2/6 farms showed a decrease in OM content. All 6/6 farms showed a reduction in Active carbon content. Cation exchange capacity (CEC) appeared to increase in 3/6 farms, whereas remaining 3/6 farms showed a decrease in CEC. 3/6 farms showed a increase in total Kjeldahl nitrogen (TKN), whereas the remaining 3/6 farms showed a decrease in TKN content. Total phosphorus (TP) increased in 3/6 farms, whereas the remaining 3/6 farms showed a decrease in TP. 4/6 farms showed an increase in Mehlich-3 P (M3P) content, whereas 2/6 farms showed a decrease in M3P. All 6/6 farms showed a reduction in Mehlich-3 potassium (M3K) content. Soil protein increased in 5/6 farms, while 1/6 farm did not show an increase in soil protein. 

As part of the second year of this study we had two additional growers involved with this study. Which meant that in total we had 8 collaborating growers and 9 field sites. At the end of two years we compiled the data from all 9 sites. What we found was that 2/9 sites showed a reduction in soil bulk density, 5/9 sites showed an increase in maximum water holding capacity, 7/9 sites showed a reduction in soil pH, 5/9 sites showed an increase in soil organic matter content, 3/9 sites showed an increase in active carbon, 4/9 sites showed an increase in cation exchange capacity, 3/9 farm sites showed an increase in total Kjeldahl nitrogen (TKN), 5/9 sites showed an increase in soil total phosphorus (TP), 6/9 sites showed an increase in Mehlich-3 P (M3P) content, 1/9 sites showed an increase in soil Mehlich-3 potassium (M3K) content, and 6/9 sites showed an increase in soil protein content.

Recommendations:

Based on this two-year field study working with 8 collaborative growers, on 9 different field sites what we found was that there was a lot of enthusiasm from the growers to learn how their soils behaved when they practiced cover cropping during the fallow period. Based on our observations, we found that in general the soil organic matter content does increase, and that reflects in an increase in soil maximum water holding capacity. From a nutrient perspective 6/9 farms showed an increase in Mehlich-3 phosphorus, which would be a positive feature for subsequent cash crops that are being planted. However, all but one farm showed an increase in soil Mehlich-3 potassium, which would suggest that growers may want to supplement their soils with a potassium prior to planting subsequent cash crop. 

Information Products

  • Soil-health benefits of cover cropping during summer (Conference/Presentation Material)
  • Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.