By Marcus McClure, AgroLiquid Regional Agronomy Manager
We know plants use micronutrients in very small amounts, but they are just as essential for plant growth as primary (N, P, and K) and secondary (S, Ca, and Mg) nutrients. Any one of them can limit growth and yield potential – and even cause plant death when deficient.
Why are micronutrient deficiencies increasingly being seen in the soil? There are several possible causes:
Increased yields due to various technology improvements have led to increased yields, meaning higher demand by the crop and more removal of micronutrients from the soil
Any type of land preparation which results in the removal of several inches of topsoil results in a deficiency of certain micronutrients on the cut areas
High phosphorus levels can cause micronutrient tie-up, leading to deficiencies
Let’s take a look at some of the micronutrients, and why they are important to the plant:
Boron is necessary for cell division and differentiation. It helps maintain a balance between sugar and starch and aids in the movement of calcium. Boron is also essential for the germination of the pollen grains and pollen tubes in plants and has a direct effect on yield. No pollination, no crop.
Cobalt plays a critical role in the overall growth of plants. Cobalt is necessary for the processes of stem growth, elongating the coleoptiles, and expanding leaf discs. A cobalt deficiency will reduce or stunt plant growth and reduce seed germination.
Copper aids in root metabolism and the utilization of proteins. Copper is essential for better stalks or stems and standability. It is also key to seed coat resiliency, disease control, test weight, and seed size.
Iron is required for the formation of chlorophyll in plant cells. It activates respiration, photosynthesis, and symbiotic nitrogen fixation. Low iron levels in the plant result in poor energy transfer from leaves to growing points or fruiting structures thus slowing growth and lowering yields.
Manganese plays a major role in the production of chlorophyll. It directly affects the health of the crop and whether a plant reaches maturity or not. Manganese deficiency is a widespread problem, but is most often found in sandy soils or in soils with a pH above 6.0.
Molybdenum acts as a catalyst in nitrate reduction, and in nitrogen transport and utilization within the plant. Molybdenum is also associated with disease resistance in plants.
Nickel is important in nitrogen metabolism because it is a component of the urease enzyme. Without the presence of nickel, urea conversion is impossible. It is required in very small amounts, with the critical level appearing to be about 0.1 ppm.
Zinc is necessary for chlorophyll and carbohydrate production. High yields are impossible without zinc due to its importance in growth, metabolism, and photosynthesis. High soil phosphorus, soil organic matter, biological activity, and irrigation play a role in zinc availability.
Most growers and agronomists focus on macronutrients to improve yields and crop quality. However, micronutrients obviously play a pivotal role in crop development. If micronutrient deficiencies persist year after year, they will continue to damage crops regardless of the nitrogen, phosphorus and potassium applied. Before adding micronutrients to the soil, it is important to know what the soil already has available. A soil test analysis that includes micronutrients will give a snapshot of what is available to the plant. The soil test is especially important because many micronutrient deficiencies cause similar symptoms in the plant and can be difficult to identify. Deficiencies can also be caused by many factors, such as soil pH, moisture, temperature, and the presence of other compounds or nutrient tie up. If a crop is not reaching its full potential, or the same problems keep appearing, contact you crop nutrition expert to help investigate potential micronutrient deficiencies.
The 2020 almond crop is upon us. Trees are beginning to break dormancy, soon full bloom will occur, and the honeybees will be busy pollinating what will be our highest yielding crop to date – we hope. There are many factors that will affect the yield potential of this year’s crop; some we can control and others we cannot. Mother Nature and the weather are out of our hands – all we can do is hope that it works in our favor. We can fight disease and insect pressure, but we cannot prevent it completely. One factor we do have complete control over, however, is our fertility program and ensuring we supply the trees with the nutrients they need to produce that high-yielding crop.
A great starting point for building your seasonal fertility program is by assessing what you have in the soil. Looking at a current soil sample will give you an idea of what needs to be done in season to ensure adequate fertility for maximum yields. There are multiple things to consider when reading a soil test. You may see that most or all of your nutrient levels read adequate or high; However, the ratios of some nutrients are more important than the levels. For instance, iron and manganese are antagonistic to each other. You may have adequate levels of both nutrients in your soil, but if the ratio is off, you may see symptoms of deficiency. You need more iron than manganese in the soil. The ideal ratio is 2:1 iron to manganese. The closer this ratio gets to 1:1, the more likely you will see an iron deficiency in season. The ratio of phosphorus to zinc is also an important factor. A ratio of 10:1 phosphorus to zinc is the ideal balance between these two nutrients. If phosphorus levels get too high, it may induce a zinc deficiency. These are just two examples of many ratios that should be addressed in your soil. A soil sample will ensure you have the information you need to get off on the right foot to maximizing this season’s yield.
Bud Break, Pink Bud, Bloom
During the period in which fruit buds are swelling, the trees are also working below the soil surface. A new flush of feeder roots are pushing out, and having an adequate supply of phosphorus and soil moisture is critical in the development of these new roots. Choosing a phosphorus fertilizer that is protected from tie-up in the soil ensures the most return on this investment. Following bud swell and new root development will be bud break, a period in which flower and pollen development are crucial. These fruiting buds that will become flowers are the fate of this season’s crop, so we do everything possible to protect and ensure their viability. Foliar applications of phosphorus, calcium, zinc, boron, and molybdenum can be beneficial, as they play important roles in all aspects regarding pollen.
The tree’s highest demand for nitrogen and potassium is from fruit set to harvest. Supplying these two nutrients in adequate amounts is crucial to achieve a high yielding crop. Nitrogen is a critical component of many plant parts and functions. It is needed to produce chlorophyll, DNA and RNA, and to synthesize amino acids. Studies have shown that for every 1,000 pounds of kernels removed, about 85 pounds of nitrogen are removed after accounting for fertilizer inefficiencies. Choosing a nitrogen fertilizer that is low in salts and less likely to leach or volatilize will ensure optimum uptake by the tree and give you the most return on your fertilizer investment. Potassium is also very important for many plant functions and is required in large amounts. Potassium plays a major role in the opening and closing of stomata, photosynthesis, translocation of sugars, and many other plant processes. Studies show that for every 1,000 pounds of kernels removed, around 90 pounds of K20 are removed. There are some important things to take into consideration when choosing a potassium source. Almonds are very sensitive to salts such as chlorides and hydroxides. Some fertilizers can even be toxic if applied at higher rates. Choose a potassium source that is free of chlorides and hydroxides to ensure maximum uptake and to minimize potential for crop injury.
Taking control of your fertility program this season will help achieve maximum yield potential. Again, there are multiple factors that are out of our control so taking advantage of the factors we can control is important. Choose your fertilizers this season with plant and soil health in mind to maximize your return on investment.
Since I have already lost the theme of this thread (being a tie with the beloved carol, The 12 Days of Christmas), I won’t try to draw a connection between four calling birds and potassium – although I’m sure I could if I tried hard enough.
Potassium in one of the primary plant nutrients. It is essential for the transport of sugars and the formation of starches and oils. Potassium helps to regulate the opening and closing of a leaf’s stoma which are important for the efficient use of water by the crop.
Potassium also promotes root growth, increases a plant’s resistance to disease and cold temperatures. It improves the size and quality of fruits, nuts and grains, and is essential in high-quality forage. Crops that produce large amounts of carbohydrates (sugars) require large amounts of potassium – sometimes even more th an nitrogen! Cotton, almonds, alfalfa, grapes, cherries, and peaches are all especially fond of potassium.
On to day three of crop our nutrients post. If you aren’t following along in our 12 Days of Crop Nutrients, be sure to check out day 1 – phosphorus, and day 2 – calcium. For our third day of crop nutrients, we’re going to discuss the micronutrient boron. It’s been said before, but it bears repeating: while crops needs less of a micronutrient, those nutrients are no less important to maximizing crop potential.
Boron is necessary for cell division and differentiation. It helps maintain a balance between sugar and starch and aids in the movement of calcium. Boron is also essential for the germination of the pollen grains and pollen tubes in plants and has a direct effect on yield. No pollination, no crop. In other words, it may be a micronutrient, but it’s no less important to crop potential than nitrogen, phosphorus or potassium.
Boron is a nutrient that becomes immobile once it is utilized within a crop. Therefore, it is essential to have an available boron “pool” within the soil throughout the growing season. Some symptoms of boron deficiency can include:
Shortened plant nodes
Thickened, brittle and curled leaves
Terminal growth dies and / or young growth tissue deteriorates
Reduced flowering and fruit set, poor seed set
Malformed or small fruits and physiological disorders associated with root and tuber crops.
Welcome to our second day of the crop nutrients post. Hopefully you caught our first day – where we focused on phosphorus. In the traditional Christmas carol, the second day is two turtle doves. Since I don’t have any clever alliteration ideas for this one, I am going to talk about a secondary nutrient: calcium.
Calcium is a secondary plant nutrient that stimulates root and leaf development, activates several plant enzymes, and is required by nitrogen-fixing bacteria. In the soil, calcium indirectly influences yield by reducing soil acidity. It also helps improve root growth conditions, molybdenum availability, and uptake of other nutrients. In the soil, calcium indirectly influences yield by reducing soil acidity, which in turn lowers the solubility and toxicity of manganese, copper, and aluminum.
Calcium is the third most important element in a plant. And, calcium is the fifth most abundant element on the planet. It makes sense that traditionally, growers don’t apply much calcium, because they assume the plant will get what they need from the soil. But, soil calcium is usually found in a form that is not easily taken up by plants.
As an example, in an apple tree, the leaves, new shoots, and fruit all take calcium. The nutrient will be found in the tissues and the root, but the fruit cannot compete with the other parts of the plant. Hence why the fruit often doesn’t get enough calcium. That is why calcium deficiencies are evidenced on the fruit, rather than the rest of the tree. In apples, a calcium deficiency causes a disorder known as bitter pit. Bitter pit is a physiological breakdown of the cell walls in the fruit that occur below the skin of the fruit. For that reason, when scouting for calcium deficiencies in fruit trees, it is important to test the fruit, rather than relying solely on leaf or soil tests. Signs of calcium deficiency common in all crops include abnormal dark green foliage, premature shedding of blossoms and buds, and weakened stems.
Further problems with the calcium levels in the plant, and therefore in the fruit, are often caused by changes in the weather. In high temperature, low humidity conditions, for example, transpiration will increase dramatically, causing the plant to use more water. In irrigated crops, if watering has not been well scheduled, even soils with good levels of calcium can have problems in the fruit caused by calcium deficiency, such as blossom-end rot in tomatoes. This is the time when we need a fast calcium fertilizer that can be applied by foliar.
Common symptoms of calcium deficiency:
Death of growing points
Abnormal dark green foliage
Premature shedding of blossoms and buds
Tip burn of young leaves (primarily in vegetable crops)
Is anyone else missing the Christmas carols? Because we’re in the midst of the 12 Days of Christmas, and because the lack of seasonal music has me feeling a little deflated, I’m going to borrow the theme of the beloved Christmas carol “The 12 Days of Christmas,” and turn it into the 12 days of crop nutrients.
Partridge in a Pear Tree – or Phosphorus (P)
The alliteration here demands that we feature phosphorus first.
Phosphorus is an essential plant nutrient and very important for numerous plant processes and crop production. It is a vital component of DNA and RNA, the building blocks of proteins and protein synthesis. The adenosine triphosphate molecule (ATP) molecule is responsible for storing and transferring all of the energy produced and needed by the plant. At the core of this ATP molecule are phosphates, responsible for all of the activity of ATP. Phosphorus also plays a major role in the stimulation of new root growth.
So, P is Important
Our crops clearly need phosphorus to thrive. So, what do we need to worry about when supplying P? “Tie up” within the soil is the primary concern with phosphorus fertilizers. In acidic soil conditions, P will tend to get tied up by iron, aluminum, and manganese. In basic soil conditions, calcium will be the major component of phosphorus tie up.
Phosphorus is most available to the plant in a soil pH range of 6.3-6.8. Common liquid fertilizers, such as ammonium polyphosphate (10-34-0) and orthophosphate (9-18-9), applied in the early spring will also have a likely chance of being tied up if a gypsum application was made in the fall.
Choosing a phosphorus fertilizer that is protected from tie up will ensure that you get the most out of your fertilizer investment and that your crop will receive the required amount of phosphorus needed.
Available P versus Usable P
Not to mention, applying phosphorus as a crop nutrient can be tricky. Just because phosphorus was applied to the soil does not mean that it is doing what you want it to do: feed the plant!AgroLiquid founder, Douglas Cook, was known to say that all applied fertilizer is available, but not all applied fertilizer is usable. Sounds funny, but it’s true. What’s the difference? All fertilizer is available to plants — it’s right there for the taking. But it may not be usable. In order for a nutrient to be usable, it must be close to the roots and it must be in a form that the plant can absorb.
Nutrients like nitrogen can be lost to leaching or volatility before absorption. Potassium can be strongly held by clay in the soil and not able to be taken up by roots since it is not in the soil solution. Phosphorus can also become unusable. Phosphate is negatively charged and can react with, or be fixed, by positively charged elements in the soil (cations). Plants cannot take up these compounds of calcium phosphate, aluminum phosphate or iron phosphate. Estimates are that the crop will utilize only around 20% of applied phosphate fertilizer during the season after application, and in following years, the amount becomes progressively less as it reverts to mineral forms. Again, the nutrients are there and available, but they are not always usable.
Out of Sight, Out of Mind
You cannot actually see the fate of phosphate molecules in the soil, so it’s not necessarily something growers are thinking about. If only a small percentage of your planted seed came up, you would probably be mad because you can see that loss. Similarly, only a small percentage of the applied phosphate is usable. However, you cannot see this, so it is not a concern. But it should be.
Placement is Key
Phosphate fertilizer works best if it is placed close to the seed at planting. In the picture at the left, it is apparent that phosphate fertilizer placement is affecting growth. Five rows of the plot had 5 gal/A of Pro-Germinator applied through the planter, and the sixth row had no planter fertilizer.
The rows with the In-furrow placement are tasseling, whereas the 2×2 placement has yet to tassel. Close inspection shows that the corn with the 2×2 placement is taller than the row with no fertilizer, but it is behind the rows with the in-furrow placement. This shows that phosphorus placement for earliest root access affects plant growth and yield. Additional testing at the North Central Research Station has shown that in furrow placement can out-yield 2×2 placement by almost 5 bu/A.
In order for phosphorus fertilizer to be most effective, it needs to be usable. Usability is increased by placement close to the seed row and protection from fixation losses. Pro-Germinator is the only fertilizer that does both.
Clearly, phosphorus is important for growing crops. It is involved in many functions within a plant like energy storage and transfer (ATP/ADP), protein synthesis, photosynthesis, nucleic acid (DNA/RNA) synthesis, nutrient movement through cell walls and many more processes. Therefore, it pays to make sure phosphorus does not become deficient in plants.
However, applying phosphorus as a crop nutrient can be tricky. Like all nutrients, phosphorus must be managed. In other words, just because phosphorus was applied to the soil does not mean that it is doing what you want it to do: feed the plant!AgroLiquid founder, Douglas Cook, was known to say that all applied fertilizer is available, but not all applied fertilizer is usable. Sounds funny, but it’s true. What’s the difference? All fertilizer is available to plants — it’s right there for the taking. But it may not be usable.
In order for a nutrient to be usable, it must be close to the roots and it must be in a form that the plant can absorb. Nutrients like nitrogen can be lost to leaching or volatility before absorption. Potassium can be strongly held by clay in the soil and not able to be taken up by roots since it is not in the soil solution. Phosphorus too can become unusable. Phosphate is negatively charged and can react with, or be fixed, by positively charged elements in the soil (cations). Plants cannot take up these compounds of calcium phosphate, aluminum phosphate or iron phosphate. Estimates are that the crop will utilize only around 20% of applied phosphate fertilizer during the season after application, and in following years, the amount becomes progressively less as it reverts to mineral forms. Again, the nutrients are there and available, but they are not always usable.
This may not be a concern to growers because you cannot actually see the fate of phosphate molecules in the soil. If only a small percentage of your planted seed came up, you would probably be mad because you can see that loss. Similarly, only a small percentage of the applied phosphate is usable. However, you cannot see this, so it is not a concern. But it should be.
Phosphate fertilizer works best if it is placed close to the seed at planting. In the picture at the left, it is apparent that phosphate fertilizer placement is affecting growth. Five rows of the plot had 5 gal/A of Pro-Germinator applied through the planter, and the sixth row had no planter fertilizer. The rows with the In-furrow placement are tasseling, whereas the 2×2 placement has yet to tassel. Close inspection shows that the corn with the 2×2 placement is taller than the row with no fertilizer, but it is behind the rows with the in-furrow placement. This shows that phosphorus placement for earliest root access affects plant growth and yield. Additional testing at the North Central Research Station has shown that in furrow placement can out-yield 2×2 placement by almost 5 bu/A.
Pro-Germinator has carbon encapsulation for protection against fixation losses that affect other forms of phosphate fertilizer. This is the Flavonol Polymer Technology that AgroLiquid developed to prevent fixation losses and enable extended nutrient release into the growing season. This also increases crop safety and can be effective at lower rates than those of conventional fertilizer like 10-34-0. In this experiment from the North Central Research Station, the lower rate of Pro-Germinator enabled a higher corn yield than that with the higher rate of 10-34-0. Closer inspection shows larger ear size and the darker yellow corn indicates advanced maturity.
In order for phosphorus fertilizer to be most effective, it needs to be usable. Usability is increased by placement close to the seed row and protection from fixation losses. Pro-Germinator is the only fertilizer that does both.
In a previous blog post, I wrote the first of a two-part series regarding the complexities of soil. The soil is an asset you may own, or you may lease, but much of the first article talked about what is needed to maximize the productive capacity of that asset. Owning versus leasing may dictate investments you are willing to make, but to produce a crop, an investment into crop nutrition will be necessary.
First, a quick review of part one. I discuss the nutrient holding capacity of the soil indicated on a soil test as Cation Exchange Capacity (CEC, highlighted in blue). Also, there are some key cations that comprise most of the holding capacity of the soil. The main cations are listed as percentages of base saturation. Calcium (Ca) should be around 70%. Once that numbers starts getting higher than 75%, it can have some negative impact on other nutrients (reference the green ovals below to see the impact of high Ca). Magnesium (Mg) should be around 15%. Potassium (K) is optimum at about 5%, sodium (Na) should be less than 2% and hydrogen (H) about 10-15%. They should total 100%. Hydrogen is the ion that causes acidity, so the more of it you have, the more acidic your soil will be (the orange ovals show the relationship between hydrogen and acidic pH, which is a pH<7). You correct this by adding desirable cations to replace the hydrogen. In high pH soils, you may need to add elemental sulfur to remove some of the cations. Good crop production can be obtained on less than an optimum balance of these cations, but numbers in the ranges given will help crops endure stresses of the growing season.
Looking at Relationships Between the Nutrients
With that overview, you can see that when looking at a soil test, there are many relationships that exist among nutrients and you shouldn’t just evaluate each nutrient on its own, or address it according to the number listed. In the example shown, you’d be tempted to look at the weak bray phosphorus (P1) test and apply a very high amount of phosphorus. But if that phosphorus is broadcast, the excess Ca represented by the 84.2% is just going to tie it up, rendering it unusable by the crop you are intending to feed. So when you are thinking about fertilizing your crop, you need to stay focused on what the crop will be able to use and not what you are applying to the soil. Much of the phosphorus that is in the soil on the test with the high Ca will never be used by the crop. The calcium-phosphorus bond is too strong for the plant to be able to extract the phosphorus from the calcium. This just illustrates one of many possible reactions that can limit the ability of a crop to utilize nutrients in the soil. Over time, some of the phosphorus will separate when Mother Nature provides rain and a fractional amount will be released.
Now for another critical area of a soil test, which often growers don’t focus on or even have tested for . . . micronutrients. At the bottom of the test shown, these levels are listed. It is common to think that soils either have them or they don’t. Certainly, there is some truth to that. Soils in some areas of the country are naturally high in specific nutrients. Minnesota soils typically have very high iron levels, which is interesting because at one time much of the Nation’s iron ore originated there. But also impacting micronutrient levels significantly is the balance of the soil. High levels of Ca, Mg, K and Na can crowd out micros. Often, zinc, manganese, and iron are the most common to have limited availability with excesses of cations. This can easily be seen when crops that have a high demand for these micronutrients are grown on these soils. Soybeans grown on the soil test with 84.2% calcium would be highly likely to exhibit a chlorotic look because iron and manganese are limited in availability as shown on the example soil test. Soybeans have a higher need for these nutrients than a crop like corn. Citrus is another crop that demands a lot of iron and manganese and would suffer in this soil.
Building Your Crop Nutrition Management Plan
The valuable part of a soil test, the reason you should routinely have your soil analyzed, is that this overview will help you prioritize investments into your asset of land. If you own the land, you can embark on measures that are longer-term fixes, such as implementing some practices to correct imbalances. Over time, the elevated calcium in the example could be lowered. But if your asset is rented, a long-term investment to correct imbalances can be a difficult decision; you are fixing someone else’s asset. If it can result in a fast payback, then maybe it is worth it. If your investment increases the productivity, then the owner may decide to try to grab more value as a result of improved productivity by increasing rent. So your improvement may actually cost you twice on a rented assets; once for the improvement and a second time if rent is raised. The overall soil test can help tremendously with making these decisions, or even having a conversation with the owner of your land to ensure you can recover your investment into their asset.
Decisions regarding crop nutrition can be complex as yield expectations rise and economics remain challenging. AgroLiquid takes measures to mitigate the impact of imbalances that exist by protecting our nutrition from many of the reactions that can occur. The purpose for using fertilizer is to feed the crop. Thinking about fertilizer in terms of how much is used by the plant rather than how much is applied to the soil is a critical step. A complete soil test is a good indicator of how much efficiency can be expected with applied crop nutrition. AgroLiquid’s unique protection improves efficiency dramatically. Couple that with a staff that has a thorough understanding of the nutrient relationships in the soil and you will receive a value that goes beyond the return on your investment.
The fall is the most popular time to soil test. Crops are harvested and attention can turn to the future. Future investments into fertilizer should begin with a soil test; they should end with a decision to get the most value out of your fertilizer dollar by adding skilled interpretation of the test with protected nutrition. AgroLiquid is where you will find both.
Fertilizing a crop, any crop, is getting more and more complex; why? To answer this question, we’ll do a quick review of the economic side, and then move into why it is important to look at things that haven’t traditionally been scrutinized.
Why does it seem like there is more focus on various aspects of crop production? A major reason crop nutrition seems to be getting more complex is due to the swings in commodity prices, which quickly change revenue, input costs and profit margins. A thinning profit margin requires higher levels of management or we fall victim to the cruelty of a capitalistic market. There was a time when fertilizer management only focused on N-P-K. As yields climb, we know that we are having to increase the productivity of N, P and K through the supporting roles of secondary and micronutrients, such as sulfur and zinc all the way through molybdenum.
To make matters worse, some of those supporting nutrients get pricey, so human tendency is to focus on the cheaper ones. Spending on extra nitrogen and potassium feels better than copper for sure. But what if copper holds the yield of your wheat crop back and the result is the 50 pounds of nitrogen you applied isn’t productive because it wasn’t supported by $5 worth of copper? Economics and our biases sometimes interfere with our decisions. Be aware of your tendencies and remember: balance is better than abundance in most instances.
Fertile Soil = Higher Yield, Right?
Everyone wants a fertile soil, but that alone does nothing. The expectation of a fertile soil is that it will share those nutrients with the crop. The production of a crop is what provides a return and that’s why we want nutrition to be associated with crop production. Fertile soils are generally productive, so there is a correlation – but not always. Excesses of some nutrients can interfere with the utilization of good levels of other nutrients. Higher rainfall amounts will cause some nutrients, such as potassium, to move down in the soil. With dry climates, high evaporation rates will keep cations at the surface. In addition, arid areas are often receiving irrigation water. Since the irrigation water generally carries other nutrients, the top of the soil starts acting like a coffee filter and the soil can take on the properties of the water. The result can be a potassium level that may have you gloating over how fertile you soil is, but could actually limit production. These factors matter as we manage crop nutrition. We can manipulate levels some, but then we’re back to economics to see if productivity will justify the expense.
Cation exchange capacity (or C.E.C., and pronounced like a short phrase: cat-I-on)
The C.E.C. shows us the nutrient and water holding capacity of the soil. This is the first indicator of the productive capability of a soil. The higher the number, the more water and nutrients it can store. I have seen all types of C.E.C. soils be productive. Low numbers can be challenging because they need rain or irrigation more often since these sandy soils don’t store much water. But crops root down well in a sandy soil and with sufficient water, they will reward you with outstanding yields. Higher C.E.C. soils hold more nutrients and water, providing a buffer between rain events. A low C.E.C number would be 1, requiring superb management, and a high number might go as high as 50 if a lot of organic matter exists. Typical soils range between 10 and 30. Some tests factor the organic matter into the nutrient holding capacity and with other tests, you need to account for it separately.
Calcium levels heavily influence soil productivity. I like a Ca base saturation range of 60-75%. Higher numbers will tie up, or crowd out, other nutrients. With a number higher than 75, I immediately look to see if it is tying up phosphorus and crowding out the micronutrient cations like zinc, iron and manganese. If it is, I need to make sure to allocate budget for these. This is a case of a low nutrient base saturation, such as phosphorus or one of the micros, and those low levels being related to an excess of something. In this example, it would be because of calcium. Phosphorus is very reactive with calcium and since zinc, iron, manganese and copper are cations, they can be displaced by high levels of calcium. Most commonly, you’d see associated low levels of zinc, iron and manganese . The importance of sulfur is elevated in this situation to counter high calcium levels. You aren’t only considering crop needs for sulfur, but also the ‘antidote’ effect it has on the elevated cation level of calcium. And banding near the root zone is important to limit exposure of the nutrients to reactivity of the high calcium levels. On the other end of the spectrum, at lower than desired calcium levels, below 60%, rhizobia bacteria don’t do their job as efficiently, so lime is needed, especially if a legume will be grown.
I look for Mg to be between 10 and 20%. Over 20, and compaction is more of an issue. An anaerobic condition can develop under heavy rain or even with severe drought. Under 10% and deficiencies begin to occur and applications should be made. Magnesium is central to chlorophyll development, so it is important to have enough of this nutrient available to your crop.
It should be between 3 and 8%. A low C.E.C soil should be in the high side of this range to supply ample amounts. If not, then it needs addressed. Rare instances of levels over 8% can exist and can restrict water infiltration. These high levels would most likely be found in low rainfall areas with high applications of manure or with potassium being brought to the soil through irrigation.
Any amount of hydrogen present means we are on the acidic side of the pH scale, meaning under 7. The higher the hydrogen number, the more acidic the soil. You’d like to keep your soil near the neutral level of 7. As soils become acidic, some nutrients are more readily released, such as iron and manganese. Often, you see crops that like high levels of iron and manganese grown in acidic soils, such as blueberries. But many beneficial microbes can’t survive in an acidic environment, so generally lime is needed to raise the pH. This is done by adding lime with calcium and/or magnesium, which displaces the hydrogen and brings the pH up. Rain and snow (H2O) bring H to the environment, so acidity slowly creeps back in. Also, various forms of nitrogen can contribute more than others. NH3 and the conversion of urea to NH4, then to NO3 through the nitrogen cycle, contribute to acidity. Don’t panic; these forms of nitrogen don’t cause a radical shift in pH, but over-applications do contribute additional hydrogen and creates some acidity.
Sodium mostly comes into play in arid areas where irrigation water is being applied, but can be a factor in low areas of fields where water stands and in areas with a shallow water table. A base saturation of sodium over 2% can limit production when temperatures rise and water is demanded by the plant to cool itself. Sodium holds on to water and can limit its movement into a plant. Generally, elemental sulfur would be used to counter this situation. Also, winter annuals typically do better if sodium issues are persistent. They are grown when transpiration rates aren’t as high, so the competition of sodium for water isn’t as critical. The source of sodium should be identified and treated if possible so that production options remain flexible.
Cation management greatly influences the productive capacity of your soil. Proper balance is important for other nutrient inputs to provide maximum return. Again, calcium in a range of 60-75%, magnesium between 10-20%, potassium between 3 and 8%, hydrogen less than 10% and sodium less than 2% will provide the most consistent yields through a variety of environmental conditions. Exceptions for specific crop reasons and economic limitations of amending soils can create a to manage around problems in this area. A perfect soil doesn’t always make sense. Where possible, it lowers risk of other stresses limiting production, but good production can come from less than ideal soils if they are properly managed.
In part 2 of this blog series, we’ll tackle the other nutrients and then look at how all cations and nutrients work together and interact with each other.
With almond and grape harvest underway here in California, it is easy to fall into the mindset that the finish line for yet another growing season is near. Unfortunately, that is not the case. In fact, the most important part of the growing season is still upon us. Postharvest irrigation and fertility can be the most crucial aspect of growing trees and vines. Growers, PCAs, and CCAs are always striving to increase yields and quality. Having a solid postharvest game plan plays a critical role in ensuring better yields and quality for next season’s crop.
After the stress of harvest, nitrogen, phosphorous, and potassium will begin to transition from leaves to spurs in almonds, and from leaves to roots and woody tissues in vines. In almonds, bud initiation and differentiation has already begun, so the fate of the 2020 crop is already underway. Water stress at this point in time will significantly reduce next year’s crop. Postharvest irrigation is also very important to ensure that the leaves stay active for as long as possible so they can continue photosynthesizing and storing much needed carbohydrates for next year’s crop. When dormancy breaks in early spring, trees and vines will be functioning solely on stored nutrients. Nutrient uptake from the soil is very minimal at this point due to cool soil temperatures as well as the lack of leaves. Adequate postharvest fertility to replenish nutrient reserves will ensure that your crop has the energy it needs to maximize production when dormancy breaks come spring.
Up to 20% of the total seasonal demand for nitrogen in almonds can be applied postharvest. This is also very similar for grapes. Postharvest nitrogen will help maintain leaf area and extend the time for photosynthesis to keep producing carbohydrates in the trees and vines. Postharvest N will also ensure that reserves are replenished and early shoot growth and leaf out will be strong in the spring. It is important to take in-season tissue samples into consideration when determining how much nitrogen to apply. Any soil-applied nitrogen in the nitrate form that is not taken up by the roots will be subject to leaching from rainfall and irrigations. Foliar-applied nitrogen is also a good choice for postharvest applications. It is common to use a fast acting nitrogen source in this situation, such as urea-based products.
The amount of phosphorous used by trees and vines is much less compared to the demand for nitrogen and potassium. However, this does not mean it is less important for optimal growth and yields. A postharvest application of phosphorous will promote healthy fall and spring root flushes, as well as ensure the trees and vines have a good energy source when dormancy breaks in the spring. Choosing a phosphorous fertilizer that is protected from tie up from cations in the soil is important and will ensure that it is free and available for the plant to uptake as needed.
Potassium demand in almonds and grapes is even higher than that of nitrogen. A postharvest application of potassium is essential in order to restore reserves, even more so if your yields were above average this season. Potassium is an important aspect in plant water relations and cell reproduction. If potassium reserves are deficient when dormancy breaks in the spring, new fruiting spurs will develop at a slower pace or even die prematurely as compared to a tree that has optimal potassium reserves. Root uptake is minimal at this point, so a soil application of potassium will serve to replenish K reserves in the soil. A postharvest foliar application of potassium is a great way to ensure you get the potassium into the trees and vines to replenish those reserves. Choosing a K product that is free of chlorides and hydroxides, as well as effective at penetrating the leaf cuticle and easily translocated once in the leaf will provide the greatest return on your fertilizer investment.
Zinc is a very important micronutrient that plays a major role in synthesizing auxins. These auxins ensure a uniform bud break and a good fruit set in the spring. Almonds are commonly zinc deficient. This is due to a number of reasons, including certain rootstocks that are not adequate at taking up zinc from the soil. Zinc deficiencies are also common in areas with alkaline soils. Zinc is fairly immobile in the soil so postharvest foliar applications are most effective at correcting deficiencies and restoring reserves.
Collecting hull samples to send off for boron analysis should be a staple in your postharvest game plan. Hull samples are the most effective indicator of boron levels in almonds. Boron is very critical for development of flowers, specifically pollen development and viability. If the hull analysis shows less than 80 parts per million boron, the trees are deficient and are most likely losing yield potential. Postharvest foliar applications of boron are an effective way to correct deficiencies and restore boron levels in the tree.
As you complete this year’s harvest, let your mind shift gears and begin thinking about next year’s crop. Its fate is already underway and having a solid postharvest irrigation and fertility game plan will ensure your trees and vines go into dormancy with adequate nutrient reserves. With a good postharvest fertility program, your crop will be off to a great start come spring and you’ll be well on your way to improving yields and quality year after year.