Spring Root-flush

 

Spring Root-flush

Winter dormancy is an important development stage in the tree growth cycle. During this time period crops rest and recharge for the upcoming growing season. Both cold air and soil temperatures are required to supply much needed “chill hours” for resting trees. “Chill hours” are a lot like REM sleep to you and me. REM sleep is the nightly deep-sleep that is vital for keeping us healthy and well rested upon awakening. Simply put, trees need cold temperatures to slow (or stop) their growth activities. When temperatures are too mild, trees do not receive adequate “chill hours” and break dormancy in an energy-deficit condition. In other words, trees don’t sleep well and awaken stressed.

 

 

Spring root-flush:

In California, normally happens with prunus species like almond, early peach, plum, nectarine, apricot and cherry varieties, in the 3rd to 4th week of January. This activity begins when soil temperature (in top 2-4”) reaches 45°F and precedes bloom by approximately three weeks. Buds visibly swell with water and nutrients. The new hair-root growth is needed to support the upcoming crop with water and nutrients. Once root-flush is underway, growers should take advantage by beginning fertigation or soil fertility applications. Nutrient focus should be on root health and crop support.

 

Temperature:

Soil temperature is a major driving factor in the onset of spring rootflush. Currently, soil temperatures, in California are 50-52°F (well above 45°F) due to the high volume of rain (4-5”) that has fallen in the past four to five weeks and continues to saturate much of the state. California has another 4-6” of rain forecast in the next week. Due to this increase in soil temperature, rootflush is now underway.

 

Chill hours:

http://fruitsandnuts.ucdavis.edu/Weather_Services/chilling_accumulation_models/Chill_Calculators/?type=chill  [Check your current chill hours]

Another concern is that “chill hours” are below normal for early January and trees are not getting the rest they need. Rootflush is underway and therefore so is root respiration. Respiration is the plant process of “burning up” or releasing stored nutrient energy for plant use. This is a problem because new roots are using up nutrient energy that is meant for the upcoming bloom.  Due to these circumstances, an energy deficit is beginning that cannot be restored from dormant rest. If you enter the bloom stage in an energy deficit (stressed) condition, it will affect the plant’s ability to pollinate, set and “stick” crop. One symptom of bloom stress is “June drop”. Plants self-regulate by aborting excess crop to ensure they do not run short on nutrients. They are programmed to know how much crop load they can support based on their health and availability of nutrition.

 

Feed the Soil:

When short on “chill hours”, the next-best alternative is to supply energy to the plant via “plant-ready” nutrition. Treatment emphasis should be on the soil, since the roots are already at work. Using an orthophosphate source provides much needed “plant-ready” phosphorus for root growth and health. A unique root benefit is a fungicide-like response within the rootzone. This is especially important in waterlogged conditions. Unlike polyphosphate fertilizers, orthophosphate is not temperature dependent. This means it is readily absorbed by new roots in cold soil temperatures (<63-68°F). In addition to feeding the soil, this is also an ideal time to re-inoculate the rhizosphere with soil microbiology. The more diverse your soil microbiology, the better your soil-nutrient and water efficiency you will experience. Dr. William Albrecht said, “We must not forget that microbes are what make a living soil ‘alive’…microbes, eat at the first sitting…Plants eat second. Plants and microbes must be in symbiotic activity and not in competition for fertility if our productive soils are to be maintained.” So, how productive are your soils? As the farmer, it is good stewardship to know and make necessary adjustments to nurture the soil and ensure it is still productive for the next generation.

Here’s to your success!

 

 

 

 

 

 

 

Citrus and Cold, Waterlogged Winter Soil management



Freezing Temperatures in young citrus block.

Winter can be a challenging time for growing citrus. While these conditions can vary from year to year, it pays to be prepared for the worst…just in case.

During extreme temperatures, plants are put under a high stress load and often maturing a crop at the same time. This creates an added level of severity to the plant stress. There are many options for dealing with freezing conditions. Today, let’s concentrate on managing “waterlogged”, cold soils.

As a soil and plant nutritionist, I focus on good, balanced soil and plant nutrition to best equip plants to tend to themselves even during stress events. It takes time to adjust soil nutrient levels when they are imbalanced and time is a limiting factor, when Mother Nature comes calling with freezing temperatures. Soil nutrient levels, especially the Base Saturation cations (K⁺, Ca⁺⁺, Mg⁺⁺, Na⁺ and H⁺), should be based upon the soil texture (sand, silt or clay) and adding “more” than what is needed, is not better. This is especially true with calcium and magnesium. Calcium creates pore space and affects the amount of air in the soil. Having surplus amounts of calcium can have a negative impact and actually compete against other needed cations, like potassium and magnesium, by displacing them. Magnesium is equally important, as it affects the soil’s moisture level and like calcium, too much magnesium can create tight-soil conditions that limit water percolation and/or competition with other needed cations. Together, these two need to make up 80% of the total Base Saturation of cations and directly affect your soil-water efficiency and percolation rate. A correct Ca:Mg ratio (i.e. 68% Ca:12% Mg) is important to nutrient efficacy all year round…but especially in times of water saturation and cold soil.

Irrigation water is used to manage cold temperatures and provide affordable protection of a few degrees; it can be the difference between protected and freeze damaged fruit. When this must be done for an extended period of time, the water is applied faster than the plant and/or soil can move it through the soil profile and field saturation occurs. Water saturation creates multiple issues, while cold/freezing air temperatures are present already (stressor); the rootzone is deoxygenated due to irrigation water (stressor), plants are often nutrient deficient due to cold soil temperatures (stressor) and if trees are sprayed with a canopy protectant, respiration is dramatically reduced (stressor). This is a bad mix of stressors, but it happens more often than you might expect.

 

Soil Microbiology - The Missing Link...

Microbiology is foundational to soil health, efficient water usage and nutrient availability/uptake. Applying specific strains of microbiology in the fall, helps prepare the plant and rootzone for wintertime stress events. There are many species and subspecies available, so getting the right type(s) is important.

 

During winter we know certain things to be true:

1.      Phosphate is energy and necessary for plant vitality and to manage stress.

2.      All nutrients, with the exception of nitrogen, move into the plant in phosphate form.

3.      All nutrients, with the exception of nitrogen, are unable to move from the soil/rootzone into the plant until the soil temperature reaches 65 °F.

4.      Nitrogen (nitrate) is a mass-flow mover and susceptible to leaching with heavy amounts of water.

5.      “Waterlogged” soil is depleted of oxygen. Roots cannot grow without oxygen and can actually start to die in 24-48 hours depending on the severity of the conditions.

6.      “Waterlogged” soils stimulate anaerobic microbial activity that feed on the organic matter/humus in the soil and produce methane gas (waste-product), which is highly toxic to roots. This condition will not improve until the rootzone gets air re-introduced into it (oxygenation).

Now, with that in mind, you can see why good, balanced nutrition and nutrient availability is so important. Microbiological activity makes this a reality. Let’s look at how certain groups of microbiology help during cold, wet, winter conditions.

To keep things simple, let’s focus on just two groups that are beneficial in keeping the rootzone active and aerated. Lactobacillus and Yellow soil yeast. Both are proficient at producing high levels of true organic acids (O.A.), right in the rootzone; some of these are citric, acetic, lactic, malic, gluconic, etc. These types of O.A.s are more efficient than humic or fulvic acids as they act much akin to plant enzymes. They are very proficient at “cleaving” fixed nutrients from soil particles and also in keeping them available for later plant use…even during winter. These Organic Acids are not temperature dependent and are exceptional “plant-ready” chelating agents for moving nutrients into plants that would otherwise not be usable until the soil warms. In fact, adding these types of microbes and the O.A.s they produce to your soil will also lessen nitrogen leaching, by conversion into “plant-ready”, non-leachable forms, like proteins and amino acids. In these forms, the nitrogen is stored within the root system for later use, when needed.

In addition to the nutrient chelating plant benefit, the microbiology also increases the oxygen (O₂) capacity of the soil through the production of carbon dioxide (CO₂). A byproduct of active microbes is CO₂ production. Therefore, a benefit of higher microbial population and activity is an increased CO₂ level. As CO₂ is released, it ascends rapidly to the soil surface and creates tiny pores in the soil. It is much the same, as when you pour a carbonated drink into a glass and the CO₂ gases (fizzes) off rapidly. Now imagine the gassing/fizzing action in your soda glass, but from within the rootzone rising up to the soil surface. “Gas exchange” occurs when CO₂ reaches the soil surface and releases to the atmosphere. This rapid rising creates a vacuum within the soil pores and, as a result, oxygen is pulled back down into the soil (oxygenation) via the pores to maintain equilibrium.

Another benefit from Lactobacillus is in the production of bacteriocins. Bacteriocins are specialized natural antibiotics and antibiotic-like compounds. They are vital to maintain soil, root and plant health within the rootzone. They are both gram^- and gram⁺ compounds that directly antagonize methanogenesis anaerobes and soil borne pathogens.

In essence, by adding these specific strains of microbiology you are altering the microbial population to your benefit.

Fall soil inoculation will build microbial population and diversity, in time, to combat the cold, wet soil issues of winter for a better soil and crop response.

Adding microbiology is not a substitute for balanced soil nutrition, but it is an important tool in making your existing soil nutrients more efficient and available for plant use.