The California Department of Food and Agriculture (CDFA) Fertilizer Research and Education Program (FREP) and Western Plant Health Association (WPHA) presented their annual Nutrient Management Conference as a webinar October 28-29. This series of five blog posts links to each conference session and highlights the most common questions asked by the conference audience and presenters’ responses during the Q&A sessions.
Presentation: Improving Nitrate and Salinity Management Strategies for Almonds
Presenter: Daniela Reineke, Soils and Biogeochemistry Graduate Group, University of California, Davis (Presentation link)
Most almond growers currently provide nitrogen (N) fertilization in liquid form through micro-irrigation systems (drip and micro-spray) and increasingly growers are utilizing groundwater that is saline to some degree. While micro-irrigation (MI) methods are effective in boosting productivity and improving water/nutrient use efficiency, micro-irrigation does result in a smaller rooting zone and in a highly non-uniform salt deposition (toward the edge of wetting pattern) in the active rooting zone. This has negative consequences for nitrate management since nitrate that is pushed into the high salt regions at the periphery of the wetted zone will not be available to plant roots and hence is vulnerable to leaching. A large-scale experiment is being conducted with 48 five-year old almond trees growing in-field in very large growing tanks (22 feet x 8 feet x 4 feet) that allows for accurate monitoring or tree performance, soil salinity and nitrate movement and root distribution patterns under highly controlled irrigation and fertigation strategies. The goal is to develop fertigation management strategies that satisfy the dual goal of minimizing root zone salinity while simultaneously minimizing nitrate leaching.
Q: Could Daniela specify what type of N fertilizer is being applied as that could have a huge effect on N distribution in the drip zone?
A: We are using calcium nitrate because that was the easiest way to monitor it rather than urea. Since urea must be transformed first to nitrate, adding another layer of complication, we decided to use calcium nitrate to keep it simple from a scientific standpoint.
Q: What is the influence of soil organic matter and soil physical properties on water uptake and salt tolerance?
A: There are definitely interactions between soil organic matter, soil texture, physical properties and water uptake; especially soil texture that influences root growth, but we did not look at that in this study.
Q: According to your results when an anion leaches it must be accompanied by a cation. Are we losing potassium or other essential plant nutrients when we remove salinity in the soil?
A: I think there is a potential to lose cations; however, potassium is not considered that mobile in the soil and if we fertigate with potassium it will not move that quickly because it will take part in the cation exchange capacity, but other cations might leach in turn.
Q: Any advice on how to manage salts and N during the winter rain season when the irrigation system is turned off?
A: The most important thing to do is to match N application with crop demands to prevent large amount of nitrate left in the soil in the beginning of the winter and thus decrease risk of leaching. If there is large amount of winter rain, then there shouldn’t be any concern about salinity for the next season, but our research shows that if there is insufficient rainfall, the salinity might be carried over to the next season.
Presentation: Importance of a Good Distribution Uniformity
Presenter: Brian Hockett, District Manager, North West Kern Resource Conservation District (Presentation link)
This presentation covered the advantages of micro irrigation systems, how to conduct an irrigation system evaluation and how to calculate Distribution Uniformity (DU). The presentation also included some of the problems Brian has found working in the field the past 30 years along with common maintenance that should be undertaken.
Q: What percentage difference should we see in pressure before and after the filter station? And what pressure differences should we see throughout a single block?
A: At the filter stations, if there is a 5 PSI differential before and after the filter or less than that then that’s a good range. Once it starts getting over 5 PSI, depending on how much the difference is, I might have the grower adjust the cycle. If the difference is 10 PSI or more and the psi doesn’t come down after adjustment, then they might want to do a hard flush of the system. In the field, depending on the topography and pressure loss, especially in drip lines, you might lose a pound or two of pressure from the inlet down to the hose. You might lose another pound or two down to the manifold if everything is clean. So, you can have a system to be designed so that your pressure be 40 at the pump and mid to low 30s at the end of the line in the hose. That is reasonable and achievable.
Q: Is it practical and realistic to design irrigation systems to deliver water according to changes in soil texture, within and across a field?
A: Sure, if you want to put the money into it and have someone design it for you. Typically, the design is on the grid, everything is laid out and there is no difference in application rate. In my 30 years of experience, I have only seen two systems that had taken the soil texture into account. It might be hard to do the test, but it is very practical considering the soil texture differences in different parts of the field. Those systems were shown to be very efficient and practical.
Q: You mentioned using acid and chlorine to clean out the system. Where would one to go to get advice on how much is needed, when to apply and how to manage those chemicals?
A: Everyone uses a fertilizer company for their chemicals and fertilizers, so I refer growers to their Pest Control Advisors (PCAs) on what to use and questions about ratios. Some growers prefer to use different types of line cleaners if they have plugging problems; it might be sulfuric acid, or another available combination can be used, but I personally do not have a preference.
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For more than 25 years, FREP has presented its pioneering fertilizer research at annual conferences. Since 2007, FREP has collaborated with the Western Plant Health Association (WPHA) to create a conference that balances technical research with discussion on practical application. Presenters from academia, industry, and agricultural consulting provide general and technical information, current research and data, and practical applications addressing statewide and regional nutrient management issues. Visit the Annual FREP/WPHA Conference webpage for links to all the 2020 conference sessions and the 2020 Conference Proceedings booklet.