Pecan General Cultivation and Nutrition
Larry Zibilske, Ph.D.
The Pecan is one of the most popular of the large backyard shade trees but is of great commercial value as well, being cultivated on large and small scales for nut production. Native to America, pecans are commonly found along river bottoms in Midwestern, eastern and southern states. Both native and varietal selections are used for nut production. However, most often, and most profitably, grafted varietal types generally referred to as “papershell” are used for nut production. On a commercial scale, management can include marketing the valuable saw wood when underperforming trees need to be replaced. There are very many grafted varieties from which to choose, some growing better in particular regions. Whether planted as an ornamental shade tree, or for nut production, the pecan must be managed with a good nutrition and irrigation plan to ensure it lives up to its double status as a beautiful tree that produces tasty, healthful nuts.
This widespread appeal results in pecans being planted in varied soil and environmental conditions, reflecting the resilience of the tree. Despite their widespread adaptability, they often don’t do very well in areas where insufficient rainfall or poor soil drainage exists, and do much better when they receive adequate care. Nutritional issues with pecans go well beyond the usual N-P-K issues of growing other crops. Anyone considering commercial production of pecans must be willing to monitor the trees and soil conditions to ensure the best possible production. Successful production practices are characterized by pro-active and continuous attention to the needs of the trees.
Starting Off Right
Good tree management starts with selecting the best location for the orchard. The best soils include deep sandy loams overlying clay (best for water storage). A site with good air drainage and surface water drainage is ideal, so look to hilltops and pastures for the best location. Proper planting techniques include a pre-plant soil test to determine which nutrients should be placed into the planting hole. These will normally include the major nutrients, Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S), and several “trace” elements, Zinc (Zn), Nickel (Ni), Iron (Fe), Boron (B), Copper (Cu), and Manganese (Mn). Don’t be fooled by the term, “trace”. Trees require these elements; they’re just needed in smaller amounts than other elements. Please refer to the nutrient deficiencies photos. Pecans do best in soils with a slightly acidic pH, around 6. The photo above attests to the durability of pecans. These are growing in tight, high pH (7.6), heavy clay blackland soil with little drainage. Many weeks can pass without rain. The nuts are typically diseased, poor or nil. These trees have a lot of problems, particularly in the micronutrients and traces. Mix the recommended nutrients with the soil removed from the hole. If planting multiple trees, make sure they are placed no closer than 50 feet from each other. In an orchard setting, spacing may be very much closer — see Orchard Notes at the end of this paper.
Also, see the paper mentioned on P.8, in No.8 for other recommendations. For more tree planting and root care guide information, please see the last pages of this paper.
Pecans do not produce well if they are crowded and are often thinned once good establishment has been attained. Refer to the Tree Planting Guide papers for more for details. Briefly, make sure you buy trees with healthy root systems. Gently remove them from the container, remove from the roots as much of the container medium as possible, and spread out the lateral roots in the planting hole. Back fill completely, filling air pockets around the roots. Make sure the root flare, the first division of trunk into root, is positioned such that it will be above the soil surface when done. Backfill with the native soil which has been mixed with the recommended fertilizers determined from soil test results. This is also the best, perhaps the only, time to inoculate the roots with ectomycorrhizal fungi to start the process of enhanced tree nutrition and health. Inoculating new planting stock will help to counter cotton root rot, a serious disease in many parts of the country.
As more backfill is added and distributed in the hole, the tree will begin to support itself–make sure the tree trunk in straight and use loosely-tied guys to support it. Water the tree so that the soil never dries out during the critical establishment phase. Planting stresses the tree and it must be kept in moist (but not wet) soil to allow new roots to begin growing.
Native pecans are found most commonly along rivers, creeks, and streams. This suggests they grow best where soils are deep and water availability is stable. Develop a plan for frequent watering and follow it. Mature pecans need about 60 inches of water annually to thrive, so an irrigation system is often necessary to provide the needed water. Although pecan trees grow to enormous size and have deep roots, most of the water they use comes from the top three feet of soil, mostly from around and well beyond the drip line of the canopy. Deeper soil water is used mainly for survival in dry periods. It can seem overwhelming, but pecans need continuous access to water. Less water is needed for young trees, about 5 gallons per day, but this must be increased as the orchard matures. Monitor leaf health to watch for signs of overwatering. Leaves will begin to turn a dark color and wilt. Some irrigation technologies can accommodate liquid forms of fertilizer, allowing simultaneous irrigation and fertilization (“fertigation”).
As mentioned, pecans need a lot of water. Few serious growers can rely on rainfall to supply the large amount of water needed to satisfy tree needs. Using ground water or surface water resources, pecans may be irrigated by flooding the entire orchard, running water into the orchard by means of irrigation furrows, or by using sprinkler heads placed strategically in the orchard that distribute water from pressurized lines. Of these, one of the more favored technologies is drip irrigation. There are advantages and disadvantages of all irrigation systems. The one that works best in any particular situation will be determined by local conditions. With drip irrigation, low pressure water lines are distributed through the orchard and are fitted with emitters near trees to allow water to escape the line and enter the soil. Emitters commonly supply water at 2 gallons per hour, allowing a slow infiltration into the soil around the tree. This method is considered to be the most effective in conserving water resources. Micro-irrigation are “ground hugging” sprinklers that wet a larger area than drip emitters, and are popular for orchards on sandy soil. Lateral movement of water is not as great on sandy soil as on finer-textured soils, so Micro-irrigation can distribute water more evenly in sandy conditions.
Success with irrigation depends on how well the system is designed, installed, operated, and maintained. In addition, water quality problems can be a “deal breaker”. Water quality is unfortunately often overlooked in planning an irrigation system. It is vital to determine the quality of the water available for irrigation before embarking on the installation of an expensive irrigation system. Water may be salty, contain “hardness” chemical compounds such as calcium, magnesium, or iron and can have other conditions that can affect long-term orchard productivity, such as carbonates. These conditions can severely limit or even prohibit use of a particular water source. Hence, it is best to determine water quality first by having it tested. It should be rechecked regularly, because quality can change over time and use.
How much fertilizer is needed in subsequent years is determined from soil and leaf testing. Soil testing may be necessary only every three years, but leaf testing, and petiole testing on fruiting tips should be done at least annually. July is often recommended as leaf testing month. Application of the N, P, K, Ca, Mg, and S is most often done via soil application of dry materials to the soil (if fertigation is not employed). The grower may choose to provide fertility by using conventional fertilizers, by adding only organic materials, or by a combination of the two. Compost may be applied in Spring to provide a slow, steady nutrient supply and to promote beneficial soil microbial activity. A combination of conventional fertilizers and compost can be used to satisfy the nutrient demands of the trees – with the compost providing a fertility foundation which can be supplemented with conventional fertilizers as needed.
Some of the major nutrients and trace elements can be applied foliarly. Good absorption of these nutrients (especially chelated trace elements) takes place when sprayed directly onto the leaves which bypasses potential problems with tie-up of trace elements in some low organic matter, high pH soils.
The soil’s capacity to provide nutrients to the trees will be improved over time if steps are taken to improve soil organic matter level and microbial activity in the orchard. This state is achieved by use of composts, cover crops and biological soil inoculants in the alleys of the orchard. The soil will reach a stage of improvement in which much of the tree nutrition will be taken care of biologically. This greatly simplifies the tasks of the grower and reduces fertilization costs.
Nutrients and Their Functions
When nutrient problems limit plant growth, it is often due to multiple nutrient deficiencies. Each nutrient is responsible for a main effect on plant physiology, but may also have a secondary rôle as well. The following discusses how nutrients are used, and of the sometimes overlapping activities of different nutrients in plant functions:
Nitrogen (N) is needed in large amounts and therefore most likely to be limiting plant growth. It is a main constituent of proteins, enzymes, and of the chlorophyll molecule, the light capturing molecule in leaves. Photosynthesis is greatly impaired where nitrogen is limited. Growth and reproduction can be substantially stunted when nitrogen available to the plant is limited.
Phosphorus (P) follows nitrogen in the amounts needed for good plant growth. It is used in photosynthesis. It is essential for seed and fruit development, synthesis of oils, sugars, starches, and is a structural part of nucleic acids, phospholipids, and ATP. Further, it is also involved in controlling basic enzyme reactions and in the regulation of metabolic pathways. Root development is dependent on an adequate supply of P and it contributes to stress resistance. It is needed for flowering as well.
Potassium (K) follows phosphorus in amounts needed for plant nutrition. It participates in protein production, photosynthesis, fruit quality and sugar transport, disease resistance.
Calcium (Ca) is part of plant cell wall structure, participates in nutrient transport into the cells, and is involved in stress adaptation. It also functions to counteract salt and organic acid accumulation in plants.
Magnesium (Mg) is used in the structure of the chlorophyll molecule and essential for photosynthesis. It also functions in many plant enzymes needed for growth.
Sulfur (S) is necessary for protein production. It also functions in photosynthesis, root growth, seed production, and helps alleviate some abiotic stresses on the plant.
Zinc (Zn) is used in carbohydrate production in plants and serves to regulate the movement of sugars within the plant. It is essential in plant growth regulation.
Nickel (Ni) is used in converting urea to ammonia via the urease pathway. Recent research has shown ‘mouse ear’ of pecan, which leads to leaf margin necrosis, is caused by a severe Ni deficiency.
See Notes about Nickel at the end of this paper.
Iron (Fe) Essential for formation of chlorophyll, hence is a central structural component in photosynthesis. It is also a structural part of other enzyme systems, synthesis of sugars and other carbohydrates, and is essential for flowering and fruit development.
Manganese (Mn) participates in plant metabolism as an activator of the enzymes involved in nitrogen uptake and incorporation.
Copper (Cu) is needed for chlorophyll and some enzyme reactions. It may be involved in enzyme synthesis, as well.
Chlorine (Cl) is needed for root and shoot elongation, and functions in photosynthesis.
When the soil or fertilizer nutrient source is insufficient for good plant growth, deficiency symptoms appear. It is important to remember that “adequate nutrient supply” is a two-part concept. It is defined as the total amount of the nutrient in the soil reservoir (i.e., is there enough of the nutrient in the soil to satisfy the plant’s total need?), and the rate at which it can be supplied to the plant (i.e., can the soil and environmental conditions work together to deliver an adequate amount of nutrient to the plant?) Often, one or both conditions are not met and results in nutrient deficiencies in the plant.
Symptoms of deficiencies are most often manifested as visual symptoms on leaves or fruit. The signs are sometimes clear, but at times, similar visual symptoms can be caused by more than one nutrient deficiency. Complicating the issue is the fact that environmental stresses and diseases can mimic symptoms of nutrient deficiencies.
In pecan, N, K, and P, can manifest similar symptoms. Only close examination can distinguish the causes of the symptoms. This is why it is very important to have leaves tested to evaluate the entire suite of nutrients. From those results, treatments can be formulated to remediate all of the deficiencies. Leaf tissue sampling must be done correctly to ensure good results.
Please see “Pecan Leaf and Petiole Sampling” available here for details. Deficiencies in the major nutrients can be treated with a combination of soil and foliarly applied fertilizers. It is advisable to work toward improving the soil, making it more biologically controlled at least for the major nutrients. This may take some time, however, so in the meantime, foliarly apply trace elements.
Alternate bearing is a significant production problem in pecans. There is not yet a complete picture of the reasons behind the phenomenon, but a large part of the problem is that the nuts contain a lot of oil, around 70% of them is lipid. It takes an enormous amount of energy to fill the nuts with lipids, much more than for other alternate bearing fruit trees that store mainly carbohydrates. Hence, alternate bearing appears to be much less a problem in citrus. Likely other contributors to alternate bearing include water, nutrient deficiencies, and weeds. Multiple stresses occur commonly, so several smaller “fixes” will help.
While it is likely that plant hormones play an important role in affecting flower initiation, they are likely responding to biochemical conditions in the plant at the time of flower initiation. As much of the tree’s energy reserves and carbohydrate production is being funneled to the developing nuts, to be turned into lipids, little is left to start next year’s nut crop by flower bud initiation. Nutritional intervention during fruit maturation and after harvest may reduce the stresses on the tree, allowing a better flower bud initiation for next year. Organic practices have been shown to reduce alternate bearing, probably by moderating nutrient and water stresses by improving the tree’s resistance to stresses.
Research points to a strong effect of the size of the carbohydrate pool in dormant trees on fruit development the next year. Other research supports this. Later maturing varieties, on which leaves are retained longer, appear to have better carbohydrate reserves due to late season photosynthesis. A soil and crop management plan that includes attention to the energy, nutrient, and water needs of trees following harvest appears to be a promising approach to reduce the tendency for alternate bearing.
Cover Cropping and Soil Building
Orchard management practices should include cultivating and maintaining a green orchard floor. The presence of a low-growing crop of grass or legume contributes to the health and productivity of the pecan trees above it. The most common configuration is a grass crop down the row middles that is maintained by mowing, while a plant-free zone is maintained under the trees with herbicides. The main purposes of the green strips are to keep down weeds, and to provide a traffic-accessible lane for spray applications and for harvest operations.
Planting a cover crop beneath the pecan canopy can improve the productivity and health of the pecan orchards and generally fulfills the requirements for effective cover crops. Clovers are a common choice.
The contribution to tree nutrition occurs by the nutrient gathering capacity of the legume. When grown together, pecans and legume roots become intermingled. Legumes “fix” nitrogen from the air and, as nitrogen compounds are pushed out of the roots, the nitrogen can be transformed by other microbes into a form that can be absorbed by pecan roots. “Cross-feeding” is common among plant types, and using legumes in this manner is an effective way to provide some of the needed nitrogen for trees. The cover crop also “mines” nutrients from the soil and traps them in organic form. Later, as clover roots decay, those nutrients are released and taken up by the pecan roots in the vicinity. The transfer of Phosphorus, Calcium, Magnesium, and many other essential elements to the trees is facilitated by the association of different plant types.
Legume flowers also attract insects, many of which are predators of pecan pest insects. Providing refuge for beneficial insects contributes a biocontrol aspect to pecan production. Complete control may not always be achieved, but support of beneficial insects in the pecan orchard can help reduce chemical sprays to avert crop loss to insect pests.
As with any other crop, a cover crop needs to be managed properly. Clover and grass mixes can be maintained by grazing animals, or can be mowed and baled as a hay crop, adding another crop being produced from the pecan orchard. Cover crops provide a tidy appearance to the orchard and improve access to the traffic ways after a rain. Check locally for information on the best grasses and legumes to use in pecan orchards, as these will differ between the wide climatic ranges in which pecans are grown.
Cover crops are an important part of soil building that enhances the long-term health and productivity of orchards. Pecans respond very well to improvements made in soil quality. Building soil quality in centered on improving soil organic matter. Where soil organic matter is adequate, trees benefit from the increase in the size of the nutrient storehouse. This helps ensure the trees will have access to the nutrients and water they need throughout the growing season and help prevent nutrient deficiencies and the stress of inadequate water supply. Where soil organic matter is adequate, soil microbes control much of the processes providing nutrients to the trees. This natural relationship between trees and soils just seems to work better, not only for tree nutrition, but also for root disease suppression. Beneficial microbes grow actively in soils with adequate organic matter. They help control populations of pathogenic microbes that can cause root diseases of pecan.
Soil building starts with increasing organic matter inputs in the orchard. Composts, manures, compost teas can all be used to supply nutrients and combat diseases. Amending the soil with these organics on a regular basis will help turn the orchard over to the soil microbes. Over time, the improvements achieved with organic matter amendments will pay many times over in healthier, more productive pecans.
PLANTING SUGGESTIONS – SOME THINGS TO KEEP IN MIND.
CERTAIN PESTICIDES MAY CARRY OVER INTO THE NUTS!
- Transplanted trees in general are almost always planted too deep as-delivered to you, whether in containers or balled and burlapped (B&B), but then even more deeply planted by the installer or you, most of whom have “delusions of adequacy”. Then, volcano soil and mulch are often heaped on… Remember that trees in Nature almost always grow from nuts, seeds or seeds in fruit that fall to the ground and generally end up only half-buried, at most. Accordingly, the tree sprouts on the surface, where the root flare is formed. For the tree to thrive, the root flare must be exposed!
- Container trees will most often be tightly root-bound – B&B trees typically are not. Both are most often too deep – frequently with adventitious roots growing out of the trunk above the root flare and lower roots extending above the root flare. These conditions may certainly severely retard the development and growth of the tree, and lead to disease and insect infestation – sometimes for years – and sometimes lead to eventual failure. Because they may not be able to establish an adequate lateral (and tap) root system, they can also be unstable – leading to sudden fall-over.
We have already seen that a tree can be dramatically too deep in the container, but we have never seen a tree fail because it was planted too shallow – they would die because the roots dried out or were overwatered. Roots explore the soil profile and will occupy only the soil depth where the environment is acceptable in terms of æration, drainage, moisture and nutrients. Accordingly, in a porous or sandy soil, the roots will grow deeper; in a tight, heavy clay or compacted soil, the roots will be shallow. The roots will also be shallow when deep watering is not practiced. Shallow roots result in instability.
Remember that the newly-planted tree will very likely settle – so plant it with the root flare at least two inches above the surrounding terrain. See the previous TREES papers for illustrations and more details. Don’t worry about any roots above the root flare being in the air – they’re not supposed to be there in the first place. If they are not large and not a significant part of the total replanted underground root mass, cut them off. Beware girdling roots!
- A major cause of tree failure for new plantings and two years thereafter, is watering problems. For mature trees, aside from construction-related root loss, failure is often due to over-watering. However, in predominately wet soils, the Number One Cause of tree decline and/or death seems to be BURIED ROOT FLARES. Trees in urban settings are frequently over-watered, due to sprinklers, rainwater accumulation, etc. resulting in an anærobic soil – drowning the roots – this may be exacerbated by limiting the root development area – by such as sidewalks, foundations, etc. – which may also concentrate and hold water.
Trees planted in the country (commercial orchards) or spacious lots without irrigation often fail or have limited nut yields, due to lack of water – especially during hot and dry times. Pecans love water! – but in well-drained soils. Pecans do not like wet feet! Remember that water applied in the immediate vicinity of a newly-planted tree will be wicked away by the surrounding less-moist (or dry) soil. The roots must not be allowed to dry out. Frequently monitor soil moisture after planting to establish a watering schedule. Monitoring can be easily accomplished using a Soil Probe. Deep and infrequent watering is very much better than little and often. After the tree has established itself, some roots will have grown down to water reserves in the subsoil (below 12 inches), allowing watering intervals to become less frequent.
- Proper and balanced nutrition is a must – especially for newly-planted trees to thrive. Stressed plants are particularly susceptible to disease and insect pressures. Most tree stress is first caused by improper planting, then by water and nutritional problems – particularly the micronutrients and Trace Elements. Note that pecans have some particular requirements for these. Organic fertilizers are the safest to avoid root burn – while even these can be overdone, they do provide a much greater safe latitude over most chemical fertilizers.
- Bare-Root Planting can be the most successful approach, but keep in mind that this can be an arduous task that has to be carefully performed – especially when pruning and teasing out the roots. The small feeder roots are easily damaged or broken. Water is the primary key to the success of this approach. Most container media is largely nutritionally inert.
- The planting hole should be several times larger in diameter than it is deep. If you insist upon planting the tree right out of the container, the extra space is backfilled with loose soil to provide easy root penetration and æration. If bare-rooting is employed, the hole needs to be large enough to accommodate the fully-extended roots – if you have good success in teasing them out, this can result in a really large-diameter hole.
- With small holes dug with a shovel, some say to avoid a perfectly circular hole with smooth sides – as this can encourage the development of encircling roots. It is said that it is preferable to make the hole with a series of irregular flat sides and angles to promote root growth straight into the surrounding soil. A good alternative to this is to inject water into the soil to the depth of the hole a few inches outside of the hole parameter. This will loosen and break down hard walls, making it easier for root penetration.
With large holes using a mechanical tree planter/spade – break and roughen glazed sides of the hole with a spade. Soil should be kept ærated and loose for easier root penetration, then covered with mulch. The survival rate using this approach is reported to be 99.9%. Aeration plays a big rôle in survival – roots and soil life require Oxygen. Heavy or compacted soils can encourage roots to circle without proper hole preparation.
- Another approach to Bare-Root Planting – per the University of Georgia – Briefly, when the tree is dormant, prune the off the limbs, most lateral roots and cut the tap root back to 18 – 24 inches. This essentially reduces the tree to a stick. This approach also requires a hole deeper but smaller in diameter than the previous method. Fill the hole about half-way with water and start backfilling with soil. Continue with the water and backfilling until the water reaches surface level, then turn it off. Continue backfilling until the soil is level with the surface. This technique eliminates any air pockets around the roots. Also, hard sides of the hole are broken down. During this process, maintain the proper tree depth per our instructions. Again, a lot too high is much better than a little too deep.
For a full and detailed description of this method, together with recommendations on establishing a pecan orchard, see a very excellent paper (Bulletin 1314) by Lenny Wells at
HOWEVER, our instructions concerning planting depth, container trees and fertilization supersede and replace those mentioned in the paper.
- The best time to plant is when the tree is dormant – late Fall, Winter and early Spring. Other times can be highly problematic.
- Inoculating with ectomycorrhizal fungi — Inoculation is most effectively and thoroughly done by soaking the roots for at least 30 minutes in the mycorrhizal suspension using a water soluble or suspendable form.
- Water quality can be extremely important and is often overlooked. Water that is high in NaCl (salt) can be difficult to remediate (results in salt build-up in the soil); however, biological soil inoculants can be quite effective in remediation). Water that is high in carbonates and bicarbonates (CaCO3 – “Lime”) can be easily corrected with acid. A treated water pH of 6.5 is the highest target number. Be aware that magnetic and electronic devices purported to prevent mineral buildup in plumbing do not claim to remove it – they claim to only keep the Calcium and other ions in solution or suspension to prevent deposits in pipes – to eventually still end up in your soil!
- If you are going to plant a B&B tree in the burlap – or one right out of the container, at least wash or blow off the surface soil until you can see the root flare! – You’ll likely see the root ball being much shorter than it started off being. If, as we have seen, surface and adventitious roots are so dense as to obscure the flare and you can’t prune them, use your best guess – a lot shallow is better than a little deep – and beware the girdling roots.Again, it is almost impossible for you to plant a tree too shallow – but it is very easy and natural to plant it too deep!
And again, correct watering practice to maintain proper soil moisture is essential – most especially when the root system is limited, bound and/or shallow! After that, Nutrition!
- Backfill the hole with native soil mixed with about one-third compost. One of the many qualities of compost is that it has a very high CEC and therefore readily holds nutrients for later release to the tree. Using a heavily amended non-native medium that roots really like may promote them to circle in the hole to stay in the “sweet” zone – especially in heavy or compacted soils (roots have no sense of long-term consequences).
- If you have an area that is bedrock with only a foot or so of topsoil, it is usually a waste of time and money to attempt planting most any tree for all of the reasons discussed. Plant something else that is very shallow-rooted, instead.
- Mulch – We often see too much of a good thing. The layer of mulch or compost should be 1-1/2 inches thick ABOVE THE GROUND (NOT ABOVE THE ROOT FLARE) – no thicker – and never touching the trunk or root flare! See our TREES: GENERAL PLANTING AND ROOT CARE GUIDE-1 Agronomy Note for more details.
Long-term applications of bicarbonates to a highly calcareous soil can lead to very serious soil problems. A reliable method of measuring pH is important if correction is needed. If you’re using city, utility district or co-op water, obtain a mineral analysis report from the department.
If you’re irrigating from a pond, well, lake, river or stream, get an irrigation (mineral) water analysis performed.
There can be more problems with water than just salt and bicarbonates. Poor or bad water can seriously damage the chemistry and physical properties of your soil. See our Soil Guide, Water Guide, Salty Water and Salty Soil papers for details. Note that a pesticide assay (very expensive!) is not included in any lab’s standard analysis of soil, water or compost. A germination test is typically used to detect the presence of pesticides.
Well-established pecan trees have feeder roots that can extend out to a radius well beyond twice the height of the tree.
The “conventional wisdom” concerning the canopy “drip-line” generally applies only to young trees.
When considering a location for a commercial operation, no less than correct soil pH range, soil physical qualities and water availability/quality are all essential!
We have many more free relevant and downloadable Agronomy Notes relevant to Pecans at AskThePlant.com.
Tree Spacing – Pecans may be planted very much closer in an orchard than in an ornamental setting – to as little as 20 feet. The actual spacing will depend upon your cultivation practice – management of limb growth to make hedgerows. Some growers prefer to aggressively keep limbs trimmed to limit wood growth to direct the trees’ energy to making nuts and to allow sunlight into closely-spaced rows. There can be a number of variations in tree and row spacing, even within the same orchard.
- The soil is deficient in water soluble (tree-available) Nickel compounds. The soil can also be deficient in any other [insoluble] Nickel compound. Generally speaking, Nickel becomes less available with increasing soil pH. It can also be made unavailable by excesses of other metals.
- Zinc is especially successful in blocking Nickel uptake by the tree. Petioles or leaves that assay high in Zinc will almost certainly assay low in Nickel. Bringing Zinc into balance, along with the other micronutrients and trace elements is essential.
IF A SOIL TEST REVEALS THAT THE SOIL IS DEFICIENT IN NICKEL OR HIGH IN ZINC, GROWING PECANS COULD BE PROBLEMATIC.
Micronutrients and trace elements are most efficiently applied to, and absorbed by the tree when they are foliarly applied.