Advancing sustainable nitrogen management in strawberries through participatory research and education

View the project final report

Commodities

• Fruits: berries (strawberries)

Practices

• Crop Production: application rate management, fertigation, fertilizers, nutrient management
• Education and Training: decision support system, extension, farmer to farmer

 Farm nutrient management is critical for sustainable agriculture systems. Extension advisors on California’s Central Coast have done
extensive research to investigate nutrient requirements of high value specialty crops such as strawberries, and to develop management
recommendations to achieve high quality, sustainable production. Strawberry growers meanwhile have developed management practices
for farm nutrient management based on both research guidance and years of production experience. Extension advisors offer suggestions
for improved nutrient management that address both production and sustainability objectives. However, where growers’ current practices
meet production objectives, they are often slow to adopt new guidance. California strawberry growers are seeking strategies to improve the
efficiency of their fertilizer management, reduce input costs, and reduce losses to the environment while maintaining the viability of their
operations. Yet growers are understandably hesitant to alter their fertilizer application practices (and potentially compromise their yield)
based on a limited number of trials. There is a critical need for grower participatory research to enhance adoption of more sustainable
practices reflecting current knowledge and understanding. This project will provide the data in real world examples needed to spur
adoption and cultural shift amongst strawberry growers towards sustainable nitrogen management.
In a 2010 survey of 30 commercial strawberry fields evaluating fertilizer practices, researchers at UCCE found that growers nearly always
applied controlled release fertilizers (CRF) regardless of pre-plant soil test nutrient levels (Hartz and Bolda 2010). The efficiency of
pre-plant CRF application, however, was questioned. This led UCCE to investigate nutrient uptake patterns for strawberries on 53
commercial fields and evaluate the efficiency of CRF in three commercial fields in 2011. The results indicated that CRF releases nitrogen at a
rate faster than crop uptake, leading to nitrate loss. Reducing pre-plant CRF rate by 50% or more had no effect on fruit yield in 2 out of 3
trials (Hartz et al 2011).
The total nitrogen demand for a strawberry crop in California ranges from 100 lb of N/ac in organic systems to 190 lb N/ac in conventional
high yield systems (Muramoto and Gaskell 2012). Strawberry growers on California’s Central Coast report pre-plant nitrogen fertilizer
applications ranging from 30 to 115 lb of N/ac. However, a number of studies (Bolda, Bottoms et al 2013) have shown that about half of the
nitrogen is released in the first 3 or 4 months after planting, before plants have the opportunity to uptake it.
Applying liquid nitrogen fertilizer through the irrigation system (fertigation) is a better management strategy to match application with
high crop demand periods and minimize nitrogen loss to the environment. Switching from pre-plant CRF applications to “spoon feeding”
fertigation to meet crop demand requires data on in-field nitrogen conditions throughout the growing season to inform decisions on when
and how much to fertigate. A simple yet underutilized tool to assist fertilizer scheduling decisions based on real-time data is the soil
nitrogen quick test that allows growers to quickly estimate the average concentration of nitrates and ammonia directly in the field.
This participatory research and education project addresses the question: If growers reduce Controlled Release Fertilizer application by
50% or more and instead use data driven fertigation practices is yield maintained? Project Partners will address this question through
participatory research in multiple production settings and varying acreages to: a) design and implement field trials to evaluate different
levels of CRF application in commercial fields, and b) interpret and disseminate the results to other growers and professionals. This will
create a new, innovative model for capturing grower’s attention to address an acute need to re-think N management practices in
strawberries.
Education is an integral component of the participatory research process. Growers will be involved at every stage from designing field
trials, to collecting data, to interpreting and disseminating results. The experience of collaboratively designing and implementing research
trials will not only produce new knowledge, but it will help growers gain confidence and ownership of the scientific research process, while
helping researchers better understand barriers to adoption of new management practices. This process will be highly instructive both for
participating growers and researchers. The education and outreach plan will build capacity among participating growers to evaluate the
effectiveness of various cultural practices and to make informed fertilizer management decisions in their operations in the future.
Participating growers will then share their experience and communicate what and how they learned to other growers in a facilitated
informal setting. This will inform and motivate other growers to consider testing this project’s findings in their own farms. The outreach
plan will also leverage existing training forums that are well attended among the strawberry grower community on the Central Coast. The
project team will produce a number of print and electronic materials and will host field meetings to help communicate research results to
other growers, certified crop advisors and technical assistance providers.
The Project Partners include the Resource Conservation District of Santa Cruz County (RCD SCC), University of California Cooperative
Extension (UCCE), the Natural Resources Conservation Service (NRCS), and five strawberry growers in the Pajaro Valley in southern Santa
Cruz and northern Monterey Counties who are currently collaborating with the RCD SCC on USDA Grant funded project to measure
environmental performance on farms. They grow for four different shippers and represent a diversity of production environments that
reflect the diversity of strawberry operations in the region.

 Our long term goal is to improve the sustainability of strawberry production on the California Central Coast through broad scale adoption
of effective nitrogen management practices that both maintain yields and protect water quality.
By the end of the two and a half year project period we will meet the following objectives:
1. Raise producer and professional awareness of the effectiveness and limitations that different levels of CRF application have on
commercial strawberry fields on the California Central Coast, considering their associated impacts in terms of economic viability,
environmental soundness, and social responsibility.
2. Through participatory field trials with 5 strawberry growers, improve producer confidence in research results and recommendations, as
well as their own capacity to evaluate and communicate the effectiveness of nitrogen management practices.
3. Through participatory education and outreach to 30-50 additional strawberry growers on the Central Coast, increase willingness to
reduce CRF applications and try more efficient, data-driven nitrogen management practices on a test plot within their own operations.
Activities and timeline to achieve these objectives:
Task 1. Project Advisory Committee (including growers, RCD SCC, UCCE, NRCS) to finalize field trial methodology and outreach plan and
to interpret results (months 1-3, semi-annually thereafter).
Task 2. Collect and analyze baseline data from five participating growers on existing nitrogen application practices and potential N losses to
the environment (months 1-3)
Task 3. Conduct participatory field trials based on methodology developed by Mark Bolda (UCCE) and the Project Advisory Committee (2
full growing seasons: October 2017-18, October 2018-19). Work with the growers to identify a test block within each ranch. Based on
baseline data, UCCE will provide advice to each grower on alternative fertilizer application rates and timing (replacing CRF application
with regular, reduced fertilizer injections) for each test block. RCDSCC will work with the growers to conduct soil nitrate quick tests prior to
each fertilizer injection to generate data to further inform decisions on when and how much to fertigate. The growers will perform fertilizer
injections on the test blocks and record each application. Growers will also document yield for their test and control blocks. RCDSCC will
calculate the annual nitrogen mass balance ratio for the test block and control with each grower to discuss changes in nitrogen use efficiency
and yield impacts. Following the trials, RCDSCC will survey the growers to document their experiences and the cost-benefits of reducing
CRF applications and instead using fertigation practices driven by data provided by the soil nitrate quick test and technical advisors.
Task 4. Interpret results with participating growers through individual consultations (months 18-30)
Task 5. Education and Outreach (months 1-30 see detailed plan below)
Task 6. Project evaluation (see Producer Adoption section)
Task 7. Project Management and Reporting