Sunday, November 12, 2017

Gypsum: A valuable soil amendment and plant nutrient

Gypsum is a common mineral obtained from surface and underground deposits. It can be a valuable source of both calcium (Ca) and sulfur (S) for plants and may provide benefits for soil properties in specific conditions.

Gypsum is found in both crystal and rock forms. It generally results from the evaporation of saline water and is one of the more common minerals in sedimentary conditions. The white or gray-colored rocks are mined from open-pit or underground deposits, then crushed, screened, and used for a variety of purposes without further processing. Agricultural gypsum generally consists of CaSO4·2H2O (dihydrate). Under geological conditions of high temperature and pressure, gypsum is converted to anhydrite (CaSO4 with no water).

By-product gypsum comes from fossil-fuel power stations where S is scrubbed from exhaust gas. Gypsum is also a byproduct from processing phosphate rock into phosphoric acid. Gypsum from recycled wall board is finely ground and used for soil application.

Agricultural Use

Gypsum (sometimes called landplaster) is generally added to soils either as a source of nutrients or to modify and improve soil properties. Gypsum is somewhat soluble in water, but more than 100 times more soluble than limestone in neutral pH soils. When applied to soil, its solubility depends on several factors, including particle size, soil moisture, and soil properties.  Gypsum dissolves in water to release Ca and SO4, with no significant direct impact on soil pH. In contrast, limestone will neutralize acidity in low pH soils. In regions with acid subsoils, gypsum is sometimes used as a relatively soluble source of Ca for alleviation of aluminum toxicity. Some soils benefit from application of gypsum as a source of Ca. In soils with excess sodium (Na), the Ca released from gypsum will tend to bind with greater affinity than Na on soil exchange sites, thus releasing the Na to be leached from the rootzone. Where gypsum is used in the remediation of high Na soils, it generally results in the enhancement of soil physical properties – such as reducing bulk density, increasing permeability and water infiltration, and decreasing soil crusting. In most conditions, adding gypsum by itself will not loosen compacted or heavy clay soils.

 Management Practices
A well-known use of gypsum is to supply Ca for peanuts, which have a unique growth pattern. Gypsum is most commonly spread on the soil surface and mixed in the rootzone. Equipment exists that allows finely ground gypsum to be distributed through an irrigation system. Gypsum is sometimes prilled to make application more convenient for home and turf use.

Non Agricultural Uses
The primary use of gypsum is for building materials (such as plaster and wallboard). For construction purposes, gypsum is ground and heated (calcined) to remove most of the bound water, resulting in hemi-hydrate plaster (plaster of Paris). When water is later added, the powder reverts to gypsum and dries in a rock-hard state. Gypsum is  extensively used in many other applications, such as for water conditioning, in the food and pharmaceutical industries, and as a setting retardant in cement.

The original IPNI document is available HERE, as part of the Nutrient Source Specifics series.

Monday, October 23, 2017

A Check-Up Using Nutrient Deficiency Symptoms

Manganese-deficient soybeans
When the uptake of any of the essential nutrients is inadequate, the plant metabolism becomes disrupted and distinctive symptoms often begin to appear. Since nutrients are involved in specific growth processes, deficiency symptoms provide clues to what nutrient might be lacking. However, most nutrient deficiencies begin to interfere with plant productivity long before the symptoms become visible.

Plant tissue testing is needed to verify that a visual symptom is caused by a specific nutrient deficiency. This differs from soil analysis, which verifies a sufficient reserve of nutrients in the soil, but does not account for conditions that may be interfering with nutrient uptake by roots (such as cold, dry, or compacted soils).

Iron-deficient sorghum
When the cause of deficiency symptoms is known, it still must be determined if a prompt nutrient application will correct the problem. There may be economic constraints or difficulties getting equipment into the field to alleviate the deficiency. Foliar sprays of soluble nutrients are often useful to treat deficiencies as they appear during the growing season. Some nutrients may be added to irrigation water and applied via fertigation to correct plant shortages. However, nutrient deficiencies result in permanent loss of growth and plants may fail to recover from severe deficiencies even after corrective measures.
Foliar sprays can be used to correct deficiency

In general, leaf nutrient deficiency symptoms fall into general categories:
• Chlorosis (yellowing) may appear between the leaf veins or impact the entire leaf
• Necrosis (leaf death) usually begins at the leaf tip or edges, or appears between the leaf veins
• Lack of new plant growth as a result of the growing points dying and failure of new leaves to develop
• Accumulation of plant pigments (especially purple-colored anthocyanin)
• Overall plant stunting with normal or abnormal coloring

Boron-deficient citrus fruit
 A shortage of a nutrient does not immediately result in visible deficiency symptoms. Overall plant growth and metabolism is usually hindered for some time before visual symptoms are present. This so-called “hidden hunger” occurs with low levels of chronic nutrient deficiency, and is far more common than visible deficiency symptoms. By the time obvious visual symptoms first appear, the plant can no longer function properly.

Nutrient deficiency symptoms are most useful for diagnostic purposes (and correction) when they are identified as early as possible. Even when supplemental nutrients are applied to correct deficiencies, irreversible damage to yield or crop quality has likely already occurred.

Phosphorus-deficient guava
Environmental stresses also cause abnormal symptoms to appear on plant leaves that may not be directly related to nutrient deficiency. Additionally, plant disease, insect damage, herbicide impacts, or excessive salinity are examples of non-nutrient factors that cause leaf disorders and stunting.

Nutrient deficiency can cause secondary plant damage that is not readily visible. For example, potassium shortages have been shown to reduce plant resistance to various diseases and insects. Many turfgrass diseases are more common under nitrogen-deficient conditions. Maintaining an adequate supply of phosphorus reduces the severity of diseases such as root rot in wheat and barley, and minimizes various infections of corn and soybean.

E-book published by IPNI
 IPNI is developing guides to help growers identify nutrient deficiencies symptoms of important horticultural and agronomic crops. The first e-book was written by Drs. Pitchay and Mikkelsen (on broccoli) and is available for free for download from iTunes® or for small fee from Amazon®. A collection of outstanding images of deficiency symptoms of important world crops is available for purchase at the IPNI store. 

Friday, October 20, 2017

Need a Micronutrient Review?

We’ve all been taught that plants require essential nutrients, but are you keeping up as our understanding of plant nutrition continues to increase? There has been considerable discussion the past few years about the importance of managing nitrogen, phosphorus, and potassium according to the 4R principles of nutrient stewardship of “Right Source, Right Rate, Right Time, and Right Place”, however other nutrients need your attention too.

The essential role of micronutrients is too often overlooked since the quantity required by plants is quite small. For example, did you know that nickel was added to the list of essential micronutrients? While nickel deficiencies are rather rare, a trace amount is essential for specific enzyme reactions in plants. Did you know that cobalt is essential for nitrogen fixation within the nodules of legume roots? How about knowing that silicon is now recognized as a “beneficial” nutrient for many plants?

The Nutrifact series
has great summaries
of each essential nutrient
The International Plant Nutrition Institute recently completed a series of short fact sheets that describe the role of each of the essential plant nutrients. These brief publications will help you learn the latest information on the role each essential plant nutrient and can be viewed at:

All agronomy is local” is a phrase that summarizes the approach for getting the proper nutrient conditions for each field. Accomplishing the mandate to “keep it local” challenges the skill and knowledge of each farmer and crop adviser, especially as it relates to micronutrient fertilizer decisions. Farmers must continually review yield performance along with the results of soil and tissue analysis as everchanging guides to nutrient planning.

The appearance of plant micronutrient deficiency symptoms raises immediate concerns that something critical was overlooked in the planning stage and that crop yields will likely be reduced. Deficiency symptoms appear in the plant after the internal metabolism has been sufficiently disrupted to show visible problems. Even if no micronutrient deficiency symptoms are observed in the field, many farmers are now conducting their own simple trials to see if a certain micronutrient might be holding back their push for ever-increasing yields.

When a specific micronutrient is lacking, remember that not all fertilizer sources are equivalent in meeting crop needs. Selecting a form of micronutrient that will provide a soluble form of the nutrient requires careful attention. Very little micronutrient is actually needed by plants, but supplying it in an available form is a challenge.
Iron-deficient potato

Adding a small dose of the correct form of micronutrient at planting can be very effective at meeting crop requirements. Getting micronutrients delivered to plant roots can be a challenge if the fertilizer is not uniformly applied across the field. Foliar sprays containing micronutrients can also be useful, but often require repeated application.

Biofortification (increasing the nutrient content in crops) is an often-overlooked benefit from proper fertilization. The content of trace elements in crops reflect the soil properties the plants are grown on. Crop fertilization with appropriate micronutrients offers a simple and cost effective method of improving the nutritional value of food, especially in regions where pernicious malnutrition has had devastating impacts.

It is too easy to overlook the vital role that micronutrients play in successful crop production. Take another look at the principles of 4R Nutrient Stewardship and see if micronutrients are being overlooked as part of your plan.

Tuesday, November 22, 2016

Calcium Nitrate: excellent source of nitrogen and calcium

Calcium nitrate is a highly soluble source of two plant nutrients. Its high solubility makes it popular for supplying an immediately available source of nitrate and calcium directly to soil, through irrigation water, or with foliar applications.

Phosphate rock is acidified with nitric acid to form a mixture of phosphoric acid and calcium nitrate during the nitrophosphate fertilizer manufacturing process. Ammonia is then added to neutralize excess acidity. Calcium nitrate crystals precipitate via a temperature gradient and are separated as the mixture is cooled. With the ammonia addition and crystallization, a double salt is formed [5 Ca(NO3)2•NH4NO3•10 H2O, referred to as 5:1:10 double salt] and is considered the commercial grade of calcium nitrate. Hence, small amounts of ammonical N may also be present in this grade of calcium nitrate. 
Calcium nitrate is also manufactured by reacting nitric acid with crushed limestone forming either the 5:1:10 double salt or calcium nitrate tetrahydrate (Ca(NO3)2•4 H2O). The latter product is often produced as a wet crystal or a mesh and is subject to specific regulation with respect to handling and safety. Prilling and granulating are the most common methods of making particles ready for field use.
Calcium nitrate is very hygroscopic (absorbs water from the air), so when intended for soil application, proprietary coatings are applied to minimize moisture uptake. Calcium nitrate intended for hydroponics or fertigation does not contain a conditioner, or it may be sold as a clear fluid fertilizer ready for use.

Agricultural Uses:

Calcium nitrate is popular in agronomic situations where a readily soluble source of nitrate or calcium is needed. Nitrate moves freely with soil moisture and can be immediately taken up by plant roots. Unlike many other common N fertilizers, Ca(NO3)2 application does not acidify soils since there is no acidity producing nitrification of ammonium occurring. Broadcast applications of Ca(NO3)2 are desirable in some circumstances because the risk of ammonia volatilization is eliminated with its use. In addition, some crops prefer nitrate sources of N.

Applications of Ca(NO3)2 are also used to provide supplemental Ca for plant nutrition. Some soils may contain considerable amounts of Ca, but it may not be sufficiently soluble to meet plant demands. Since Ca is not mobile in the plant it is important to apply Ca just-in-time in critical growth stages. Solutions of Ca(NO3)2 are commonly added to irrigation water and to foliar and fruit sprays to overcome such shortcomings that can affect yield and/or quality (such as apple bitter pit), or to meet peak Ca demands during critical growth periods. Part of the popularity of Ca(NO3)2 also arises from its chloride-free nature and Ca(NO3)2 can have an ameliorating effect under saline growing conditions, combating the negative effects of Na and Cl-.

Research has shown that a healthy plant with adequate Ca alleviates biotic and abiotic stresses such as fungal disease, and stresses due to drought, heat, or cold. Hence Ca(NO3)2 is widely used in intensive cropping systems that have a high focus on crop quality.
Calcium-deficient broccoli

Management Practices

There are no special practices required for the use of Ca(NO3)2 beyond the need to keep nitrate from moving below the root zone.

To avoid precipitating insoluble fertilizer salts, Ca(NO3)2 should not be mixed with soluble phosphate or sulfate fertilizers in nutrient solutions or while fertigating. The extreme hygroscopic nature of solid Ca(NO3)2 makes it important to store it in a cool and dry environment.
Calcium nitrate (double salt) is not classified as an oxidizer by government agencies, so there are no special restrictions on transport and handling as there may be for ammonium nitrate. However calcium nitrate tetrahydrate is classified as a 5.1 oxidizing agent that can, in conjunction with oxygen, cause or increase the combustion of other materials and may require special attention depending on local regulations.

Non-Agricultural Uses:

Calcium nitrate is used for waste water treatment to minimize the production of hydrogen sulfide. It is also added to concrete to accelerate setting and reduce corrosion of concrete reinforcements.

This acticle is from a IPNI Nutrient Source Specific article on fertilizer materials available here:

Monday, May 30, 2016

Year of Soils: Soil Degradation Destroys Productivity

Who cares about dirt? Soil is the fragile skin on the earth that provides more than 95% of our food. Soil also provides an essential life-sustaining role in cleaning air and water.

When we lose our soil, many vital functions are also lost. It has been estimated that over 40%
of the soil used for agriculture around the world is already degraded or seriously degraded and that half of the topsoil on the earth has been lost during the last 150 years. Soil degradation is the slow decline in land quality caused by human activity. We have plenty of reasons to be concerned with this growing threat to food security.

Soils become degraded from both man-made activities and accelerated natural processes. Some impacts of soil mismanagement and degradation include compaction and poor drainage, depletion of essential plant nutrients, rapid loss of organic matter, accumulation of salts, and acidification. Soil degradation frequently accelerates soil erosion and may result in permanent loss of a soils productive capacity.

Soil degradation is a severe challenge that threatens the sustainability of crop and livestock
production worldwide. For example, in sub-Saharan Africa, about 65% of the land area is degraded, with devastating economic and human impacts.

Some major constraints to agricultural productivity in sub-Saharan Africa resulting from soil
degradation include soil acidity and aluminum toxicity, nutrient depletion, and soil erosion with resulting shallow soils. The slow process of restoring these soils begins by balanced addition of crop nutrients and lime, adjusting cropping rotations to include cover crops, and adopting practices to halt soil erosion.
Soil degradation in Sub-Saharan Africa (IPNI)

A major step in preventing soil degradation is proper use of plant nutrients. Fertilizers replace
essential plant nutrients removed in harvested crops, preventing nutrient exhaustion of the soil. Several recent studies show that proper fertilizer use maintains or improves soil microbial activity, boosts inputs of crop residue returned to the soil, and can maintain soil organic matter...all while enhancing crop yields.

The damaging effects of soil erosion are also felt off of the farm. Streams and lakes can
become clogged with sediment and nutrients lost from agricultural fields, damaging fish and aquatic life.

Erosion and soil degradation is usually a slow process, easily escaping our attention at first
glance. However, their cumulative effects are devastating on many levels. Farmers everywhere should consider how they can protect their precious soil resources. Their livelihood and their neighbors depend on careful stewardship of the soil beneath our feet.
Sediment-choked stream (Cornell Univ)

This article originally appeared in the IPNI quarterly publication: Plant Nutrition Today

International Year of Soils: Nutrients and Soil Biology

It is a tendency of some people to only think of plant nutrition in terms of how much fertilizer to add. This simplification may be understandable since a healthy crop reveals only the above ground plant; the roots that support the visible plant are seldom seen without further exploration. Plant roots grow in an incredibly complex soil environment, teeming with billions of organisms, particularly bacteria and fungi, which play a crucial role maintaining an adequate supply of plant nutrients for crop growth.
Complex interactions occur between plant roots and microorganisms (Haichar et al., 2014)
 There is still much to learn about the complex interaction between microorganisms and plant nutrition, but the importance of these relationships is clearly recognized. Living organisms have a crucial role in controlling the transformations of plant nutrients. In most soils, nitrogen (N), phosphorus (P) and sulfur (S) are mainly present in various organic compounds that are unavailable for plant uptake. Understanding the role of microorganisms in regulating the conversion of these organic pools into plant-available forms has received considerable attention from soil scientists and agronomists

The microbial conversions of nutrients into soluble forms take place through numerous mechanisms. Extracellular enzymes and organic compounds are excreted to solubilize nutrients from soil organic matter, crop residues, or manures. Organic acids released by microbes can dissolve precipitated nutrients on soil minerals and speed mineral weathering. Some nutrients become more soluble as microbes derive energy from oxidation and reduction reactions.

Mycorrhizal fungi are found in symbiotic association with the roots of most plants. These soil fungi can increase the supply of various nutrients to plants in exchange for plant carbon. The boost in P uptake provided by mycorrhizal fungi is especially important for crops with high P requirements or growing in soil with low concentrations of soluble P. Mycorrhizal fungi release various enzymes to solubilize organic P and they can extract soluble P from the soil at lower concentrations than plant roots are able to do alone.

Well-nodulated soybean root (Pioneer)
Biological N fixation is another essential contribution of microbes to plant nutrition. Specialized symbiotic bacteria living in root nodules can fix atmospheric N into ammonium-based compounds for plant nutrition. The most important of these organisms for agricultural plants are from the species Rhizobium and Bradyrhizobium. There are symbiotic N2-fixing bacteria that infect woody shrubs, and asymbiotic bacteria, such as Azospirillum, that provide N to the roots of grasses such as sugarcane.

An often-overlooked contribution of soil microorganisms to plant nutrition is their benefit to improving soil physical properties. Good soil structure enhances plant root growth, resulting in greater water and nutrient extraction. Individual soil particles are bound into aggregates by various organic compounds such as polysaccharides and glomalin. The small hyphal strands of mycorrhizal fungi also contribute to improved soil aggregation by binding small particles together.

A better understanding of the essential link between soil microbes and plant nutrition allows more informed management decisions to be made for proper stewardship of soil resources and for sustaining crop productivity.

This article originally appeared as part of the IPNI quarterly update: Plant Nutrition Today which can be accessed here

Wednesday, December 9, 2015

Year Of Soils: 4R Nutrient Stewardship and Soil Management

This year was designated as the International Year of Soil. This recognition gives us an extra opportunity to reflect on the importance of soil as the basis for plant growth, healthy animals, clean water, and maintaining life on earth. 

In recent years, much of the fertilizer industry has embraced the principles of 4R Nutrient Stewardship as a way that farmers can maximize their yields, improve nutrient efficiency, and reduce environmental impacts. This involves selecting the right source of nutrient, added at the right rate, applied at the right time, and put in the right place. Adopting the correct set of 4R principles requires planning, management, and flexibility to meet local challenges.

It is important to remember that 4R Nutrient Stewardship is not a single set of practices that stand alone in achieving these economic, environmental, and social goals. Careful nutrient management must be accompanied by a package of other production and conservation techniques to be successful.

A sophisticated jet airplane cannot launch into flight if it lacks an engine or is missing the jet fuel. Similarly, successful modern crop production requires all the components to work together to be successful. Modern nutrient management practices must be accompanied by other locally appropriate conservation approaches.

The concept of “Soil Fertility” integrates many factors such as soil physical properties (e.g., soil texture, structure, water, and air), biological properties (microorganisms and organic matter), and chemical properties (nutrient availability, pH). Clearly the 14 essential plant nutrients supplied from the soil are a vital part of growing a healthy plant that produces high yields. Despite their irreplaceable nature, the presence of an adequate nutrient supply does not alone make a fertile soil.

4R practices are not confined to only inorganic fertilizer, but they are applicable for both inorganic and organic nutrient sources. Organic and mineral fertilizers complement each other and best results for both crops and soil commonly occur when they are used together. For example, there is plenty of evidence that proper fertilization will commonly increase soil organic matter or at least slow its loss in cultivated soils compared with using no fertilizer.

As the end of the International Year of Soil draws near, remember the essential role that plant nutrients play in sustaining soil productivity. Proper 4R-based nutrient stewardship clearly has a positive contribution in this effort. But nutrient management is only one piece of the solution to maintaining our precious and irreplaceable soil resource.

Let’s make 4R Nutrient Stewardship more than a slogan. It needs to be implemented into a complex and continually changing conservation-based farming landscape that wisely preserves soil for generations to come. The conclusion of the International Year of Soil prompts a renewed reflection of the fundamental role of soil and the need for wise nutrient management.