The use of pre-plant controlled release fertilizers (CRF) -regardless of pre-plant soil nitrogen levels- has been a common practice for years among strawberry producers on the central coast. UCCE research has questioned the efficiency and the value of CRF use, by showing that CRF releases nitrogen at a faster rate than crop uptake (leading to nitrate loss) and that reducing pre-plant CRF application by 50% or more has no effect on fruit yield. This project engages partnering professionals and strawberry producers in a collaborative research and education effort seeking to build confidence in research findings, and increase adoption of more sustainable nitrogen fertilizer use practices reflecting current knowledge and understanding. The 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 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. 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.
By the end of the two and a half year project period we expect to meet the following objectives:
- Improve understanding among partnering professionals and producers about the effectiveness and limitations of different levels of controlled release fertilizer (CRF) application on commercial strawberry fields on the California Central Coast, considering their associated impacts in terms of crop yield and potential water quality impairment.
- 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.
- 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.
In each ranch the grower selected an experimental block where the the rate of application of pre-plant nitrogen fertilizer was reduced by an amount ranging from 40% to 100% (i.e. no pre-plant nitrogen applied).
In the blocks where pre-plant nitrogen was reduced, Nitrogen will be applied starting in March
Educational & Outreach Activities
Four ranches joined the project, with experimental blocks ranging from 1400 ft2 to 1 acre, and reductions of pre-plant applied nitrogen ranging from 40% to 100%.
Soil nitrate monitoring started in Sep-Oct 2017 when a baseline soil nitrate test was collected for all ranches, before the application of pre-plant fertilizer. Additional soil nitrate tests were collected on Nov 15th 2017 and Dec 8th 2017 in all ranches both in the experimental and in the control block.
Figure 1. Collecting soil samples from the experimental blocks
Figure 2. Results of the nitrate test
Preliminary results indicate slow release and mineralization of nitrate in the first foot of soil and high variability on nitrate in the second foot of soil, presumably caused by the leaching effect of winter rains.
Figure 3. Nitrate concentration of the soil samples collected at the experimental and control blocks for depths 0 to 12 inches and 12 to 24 inches.