What Can Happen With Too Much Rain? Watch that Mulch!!!
Rain is wonderful stuff. If it comes and washes the accumulated salts of the last several years out of the root zones of citrus and avocado, that's a good thing. But what happens if there is a little too much of the good stuff? In the winter of 2005, Venture got over 40” of rain, which is 200% of what is normal. The last time big rains occurred prior to that was in the winter of 1997-98. That year the rains were evenly spaced on almost a weekly basis through the winter and into the late spring and over 50" fell. That year we had major problems with both citrus and avocados collapsing from asphyxiation. The same occurred in 2005, but not so pronounced.
Rain is good, right?
In 2003 we had a lot more rain than we normally see and in Carpinteria it rained 4 inches in July!!!!!! In some young trees with poorly developed root systems, we have seen some collapse from asphyxiation. Avocados tend to be more susceptible than citrus, and some rootstocks more than others. Even big trees collapsed.
Asphyxiation is a physiological problem that may affect certain branches, whole limbs or the entire tree. Leaves wilt and may fall, the fruit withers and drops and the branches die back to a greater or lesser extent. The condition develops so rapidly that it may be regarded as a form of collapse. Usually, the larger stems and branches remain alive, and after a time, vigorous new growth is put out so that the tree tends to recover. Young trees can be harder hit, but sunburn damage from lack of leaves may be more of a problem.
Asphyxiation is related to the air and water conditions of the soil. The trouble appears mainly in fine-textured or shallow soils with impervious sub-soils. In 1997-98, this even occurred on slopes with normally good drainage because the rains were so frequent. When such soils are over-irrigated or wetted by rains, the water displaces the soil oxygen. The smaller roots die when deprived of oxygen. When the stress of water shortage develops, the impaired roots are unable to supply water to the leaves rapidly enough and the tree collapses. The condition is accentuated when rainy weather is followed by winds or warm conditions.
It doesn't take standing water to have asphyxiation occur.
Mulch is good, right?
It can get spread awfully thick
Mulch does lots of good things, like reducing erosion, controlling weeds, improving infiltration, increasing organic matter to control root disease, reducing soil temperatures, reducing evaporation loss and therefore improving soil moisture content. Ah, but that is a problem when there is a lot of rain. It can lead to asphyxiation, just because of that last point. In rainy conditions, there needs to be a period of air entry into the soil and mulch because it reduces evaporative loss can keep the soil TOO wet, leading to asphyxiation.
Asphyxiated tree that has been overmulched and is now recovering after whitewashing.
So what do you do? With a thick layer of mulch when there is too much rain? You pull it away several feet from the base of the tree, so that sun can dry out the soil. It's a lot of work, especially after you have put a lot of work into spreading it.
The roots need to dry out and it can only happen if exposed to light and wind and ambient temperature
On flat ground, your avocados are planted on mounds or berms. And the soil texture is somewhat sandy and well drained. In that case, unless we get rain like 1997-98 when Ojai got nearly 50 inches and it rained just about every week from November through April and it seemed everything was under water, most trees should be all right. But, this last rainfall year I saw cases where unbermed, heavy soil avocado plantings had severe asphyxiation problems. So be forewarned.
In honor of #HealthySoilsWeek2020, our healthy team would like to share background and an update on our healthy soils project @Limoneira in Santa Paula. Our group of researchers and advocates at @VenturaCountyResources Conservation District @UC Cooperative Extension and @Community Environmental Council are studying the climate, water and soil impacts of @Agromin mulch and compost on a new lemon orchard.
Hoping for better days, instead of a field day this year, we hope you enjoy this video to learn more about this project. We are only about halfway through the project, so stay tuned for more results next year!
This project was funded through the Healthy Soils Project at the California Department of Food and Agriculture. CDFA's Healthy Soils Program includes 643 projects totaling more than $42.2 million in grants funds. These projects cover almost 60,000 acres and will sequester more than 112,000 metric tons of CO2e, which is equivalent to removing 24,250 cars from the road each year.
2020 Climate Action and Agriculture Symposium
Information and documents related to the 2020 Climate Action and Agriculture Symposium Webinar featuring information on current climate trends and agricultural impacts, soil health and updates about related projects in San Diego and neighboring counties.
Featured Organizations and Programs:
- San Diego County Farm Bureau
- Spadra Farm, California State Polytechnic University, Pomona
- CDFA-Healthy Soils Program
- Composting Resources, County of San Diego
- Resilient Roots: Climate Smart Agriculture & Food Systems,
Climate Science Alliance
- Carbon Farming, Resource Conservation District of Greater San Diego County
- Solidarity Farm
- San Diego County Food Vision 2030, San Diego Food Systems Alliance
Technical Reports and Resources:
Compost and Mulch Market Study, County of San Diego (PDF Download,2.1 MB)
by the County of San Diego and Hidden Resources
Mulch Resources from Ben Faber, Ph.D., UCCE Farm Advisor (PDF Download,994 KB)
Questions and comments always come up about the use of mulch in orchards. Mulch has its benefits and drawbacks and they need to recognized in order to manage it. It serves to combat erosion and root rot, but it can also burn. Mulch and wood piled up against tree trunks and near trunks can cause damage to those trunks. A Fillmore grower actually goes through the orchard with a blower to move mulch away from trunks when alerted to fire. On the other hand, irrigated orchards have been shown to be effective at suppressing fire encroaching on homes. And mulches can suppress weeds and reduce water use, but it's possible that importing material for mulch can introduce weeds.
So where to read more about fire? Check out some of the blogs from the past.
Mulch and green waste applied to orchards
- Green Waste, Yard Waste, Whatever You Call It- It has Simple Rules for Use
- A Safer Source of Inexpensive Orchard Mulch
- Avocado planting holes
- Cellulase Production by Various Sources of Mulch
- A Caution on Free "Compost/Mulch"
- A Safer Source of Inexpensive Orchard Mulch
- Mulch, Avocados and the Home Garden
- Mature Compost Does NOT Kill Phytophthora
- Use of Mulch in Organic Orchards Called into Question
Mulch and Landscapes
Wandering around a mulched orchard is always an adventure. In the early days of commercial mulching of citrus orchards, it wasn't uncommon to come across golf balls, discarded wallets, and all kinds of things you would not want in your orchard. This can still be a problem when the grower is not watching to make sure the loads are clean.
As the material settled in, over time more commonly, there would be the evidence of the decomposers - the fungi that breakdown the organic mulch into nutrients. It would show up in the fruiting bodies, like those below
The fruiting bodies would show up, but the real activity would be in the mulch itself. The decomposition is done with enzymes that are secreted into the mulch to breakdown the lignin and cellulose that make up plant based materials. When you dig into the mulch, you find the mycelial mats of those fruiting bodies. The fungus part that actually does the enzyme secretion and nutrient absorption. These enzymes also help control disease organisms like Phytophthora.
But sometimes wandering the orchard, you come across odd things, like slime molds
And then you come across what looks like trash. At this stage of commercial mulching, it's hard to find trash in good quality mulch. Recently, I found some what looked like plastic trash in an orchard. This turns out to be a fungus, though. A stinkhorn. Another decomposer good for plants and the soil.
- Author: Kristian Salgado
For more information on the CDFA Healthy Soils Program: Click here
Kristian M. Salgado
Community Education Specialist 2 (CES2)
Climate Smart Agriculture