Gypsum... What is it?

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.

Production

Gypsum mining, Utah

psum 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 wallboard is finely ground and used for soil application.

Chemical Properties:  Calcium sulfate

Name                          Formula & Composition                                Water Solubility

Dihydrate (Gypsum)      CaSO4·2H2O                                                2.05 g/L

           [23% Ca, 18% S, 21% water]                       [5,570 lb/acre foot]

Anhydrite                     CaSO4 [29% Ca, 23% S]                                2.05 g/L

Hemi-hydrate               CaSO4·¹/₂H2O                                             [Reverts to gypsum

(plaster of Paris)                                                                             when water is added]

Agricultural Use

Gypsum spreading

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 Ca2+ and SO42^-, 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.

Gypsum piles before spreading

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.

A pdf version of this post can be found here

What is Going on Underground? Don't forget the Roots!

Roots: The overlooked plant part?

We spend a lot of time and money to get crops the nutrition they need for maximizing growth and yield.  When planning for the next season, don’t forget about the part of the plant hidden beneath the soil surface.  

There are two obvious functions for roots that come to mind; anchoring the plant to keep it upright and getting the water and nutrients needed to support growth, but there many other things too. 

Roots release a large number of organic compounds that aid the plant in its growth.   As much as one-third of the carbon fixed through photosynthesis can be pumped out of the roots into the soil, assisting the plant in numerous ways. 

Root cap

Root systems 

The organic compounds released from roots are grouped into high molecular weight compounds such as carbohydrates and enzymes, and low-molecular weight compounds such as sugars and organic acids.  This zone surrounding the root is called the rhizosphere, typically extending a few millimeters in to the soil (about the thickness of a nickel).

A jelly-like substance is excreted at the root tip that reduces friction and physically protects the delicate cells at the root tip, aggregates soil particles, maintains a pathway for water and nutrient uptake, and influences the growth and development of surrounding plants and microorganisms.

These root exudates play a vital role in providing a constant nutrient supply for plants.  Some of them regulate microbial growth surrounding the roots.  Specific bacteria can be triggered to form nodules in legumes when signaled by the proper root exudates.  Other compounds induce spores of mycorrhizal fungi to germinate and assist the plant with phosphorus and micronutrient uptake.

Root meristem

Many exudates can directly improve nutrient availability.  For example, organic acids released from roots can solubilize phosphorus compounds in the soil.  Enzymes originating in the root can speed the release of phosphorus from soil organic compounds to a form that can be used for nutrition.  Specialized root compounds, called phytosiderophores, will chelate iron in the soil and enhance plant nutrition and growth.

Roots have the ability to modify the soil pH in the rhizosphere. Plants that receive nitrate as the primary source of nitrogen nutrition generally have an elevated pH in the rhizosphere.  However, plants that have an abundance of ammonium often cause their rhizosphere to become more acidic. 

The physical properties of roots are also important.  For example, the root length and the degree of branching is important for exploring soil resources.  A root system with a large surface area has greater opportunity for nutrient uptake.  The presence of abundant root hairs is beneficial for water and nutrient uptake.  It is estimated that up to three fourths of the total root surface area of many cultivated crops is provided by root hairs.

Tree roots in compacted soil

Healthy root systems are often unappreciated, but essential for vigorous plant growth and high yields.  Even after the crop is harvested, the decaying root system continues to provide benefits to the soil and to the following crop.  Providing an environment where nutritional, chemical, physical, and biological barriers are eliminated allows the crop to reach its full potential.  Don’t overlook what you can’t see.  

To view a pdf version of this post, go to here

The 4R's... Is it all about the Application Rate?

Fertilizer spreader

It seems that discussions by government regulators to minimize nutrient impacts immediately turn to reducing the rate of fertilizer application. While this approach has the advantage of simplicity and being easy to measure, a narrow focus on fertilizer application rate alone will consistently fall short of achieving the desired environmental and economic goals.

Selecting the Right Rate of fertilizer application is only one of the 4R’s that must be considered when making nutrient decisions. In addition to selecting the Right Rate, it is also essential to choose the Right Source, the Right Time, and the Right Place to get the maximum value. When one of these 4R’s is changed, it is necessary to evaluate how it impacts the remaining 4R factors.

Here are a few examples of how only modifying the fertilizer application rate may not achieve the desired results:

• It is important that growing crops have the right combination of all nutrients present in the rootzone, especially during periods of peak demand. If the nutrient supply during these critical times is not adequate to support growth then crop yields and quality will suffer.

• Nutrient applications should be made as close to the time of plant uptake as feasible. Some nutrients can be placed in the soil in advance of plant uptake because of their limited mobility; however other nutrients are at risk of loss if they remain in the soil for an extended period of time.

• When organic materials are used as a plant nutrient source, a period of mineralization is required before the nutrients are converted to a form that can be taken up by roots. Sufficient time is required for mineralization to synchronize nutrient release with plant uptake.

Elephant manure spreader?

• Adequate soil moisture is needed for dissolved nutrients to be taken up by roots. Uncertainties in rainfall patterns make the prediction of fertilizer rate an ever-changing target each year. When crops are irrigated, nutrient loss is closely associated with water distribution and irrigation uniformity across the field.

• There are numerous examples to show that when plants are not supplied with a balanced and appropriate supply of all the essential nutrients, none of them will be fully used to their potential. For example if a soil is low in K, then nitrate will not be properly taken up and may be more prone to leaching loss. 

 • Some fertilizer sources are more suitable for placement close to the seed than other sources, which may cause damage to germinating seedlings. Placing fertilizer close to the seed can provide some early-season growth stimulation in some circumstances.

Examples of controlled-release fertilizer

• Technology can be used to help keep nutrients in the proper place. For example the use of a nitrification inhibitor may reduce both nitrate leaching and denitrification losses from some N fertilizers. Similarly, a urease inhibitor can minimize ammonia loss and improve nutrient recovery from urea applied to the soil surface.

• Controlled-release technology can reduce the risk of nutrient loss and eliminate the need for multiple trips through the field to apply fertilizer. Enhanced nutrient recovery by plants is often reported when these nutrient sources are used.

• Custom blends of fluid fertilizers allow a precise combination of nutrients to be delivered to the soil in each drop. Each droplet provides uniform and consistent nutrition to the plant. Some compound fertilizers and additives are formulated to control the soil environment around the granule to enhance plant nutrient recovery.

Fertilizer is essential to sustaining food production

These few examples illustrate how an overly narrow focus on fertilizer application rate alone can cause growers to miss their overall objective—that is growing a high yielding and high quality crop that is both economically profitable and environmentally sound. When the 4R Nutrient Stewardship approach is implemented on each field, it is clear that no one of them can dominate nor be excluded. It is NOT all about the fertilizer application rate, because the source, time, and place decisions must all be considered to get the rate right.

A pdf version of this IPNI newsletter can be found at: HERE

What About the Water?

Water... handle with care

Of course farmers use a lot of water... they are shipping water (in the form of food) to you

 Agriculture is the largest user of fresh water in the world and as demand grows for more food production, conflicts regarding water use are inevitable. In some areas, additional investment in irrigation and water supplies may provide room for further expansion of irrigated cropland. However in most areas of western North America, water is no longer in abundant supply and ferocious arguments erupt over water allocation. Since new supplies of irrigation water appear unlikely, there is significant incentive to improve water use efficiency. The pressure on the agricultural industry to carefully conserve water resources will certainly intensify. 

Soil water during the drying process

Water uptake and plant nutrient absorption are closely related. When plant roots take up water, dissolved nutrients are carried to the root surface. When water uptake is restricted, the delivery of nutrients to the root also slows down. As the soil dries and the films of water between the particles shrink, the processes of mass flow and diffusion that bathe the roots with nutrients eventually come to a halt.

An impaired root system hinders water and nutrient uptake

Healthy roots and water use

An important step towards improving water use efficiency is to encourage healthy plant roots. Maintaining proper soil conditions will enhance the volume of soil that roots explore. For example, a soil that has a compacted zone or a hard pan will present a barrier to plant roots and restrict their use of moisture deeper in the soil profile. Similarly, when subsoil acidity is not addressed, plant growth is stunted and roots cannot grow deep into the soil to utilize water and nutrients.

Plants grown with adequate nutrition typically have larg­er tops and root systems compared with crops grown with an inadequate nutrient supply. These well-fertilized plants are generally larger and may have greater water loss (tran­spiration), but a lower transpiration ratio. In other words, the healthy plant may use more water, but will generally produce larger yields. This translates into more yield per gallon of water extracted from the soil. Another way to say this is that greater water use efficiency results from proper plant nutrition. 

How much water is in our food?

It seems like there is rarely enough water in western North America to meet everybody’s needs. Especially after several years of prolonged drought in many areas, farmers are stressed to learn that there may be insufficient water to grow their crops.

The amount of water required to grow a crop

A common cry from the urban areas is that agriculture uses more than its “fair share” of water. Some estimates have been made that more than 80% of developed water is go­ing to agriculture in many areas. Attention is drawn to the fact that agriculture loses too much water through cracks, seepage, and evaporation from the miles of canals and pipelines. These losses should be addressed when financing is available. 

Most consumers do not appreciate the large amount of water required to grow plants. A poorly understood concept is that a huge amount of water is indirectly delivered to cities in the form of food. A report by the Water Education Foundation documented the amount of water required to produce various foods in the western U.S. Their basic ap­proach was to divide average water use (evapotranspiration) by average yields to determine the gallons of water per pound of food produced. Since some of the water delivered to a farm is unavoidably lost as deep percolation, runoff, or soil moisture storage, the irrigation efficiency was assumed to be 70%. 

Using a typical 2,300-calorie menu proposed by the U.S. Department of Agriculture, the following meal was con­structed and the gallons of water required to produce that particular food item are shown.

The amount of water required to grow our daily food

Do farmers use a lot of water?
Yes… and we all benefit tremendously from their produc­tivity. The water may not only come from our faucets, but it also comes to us in every bite we take.

Proper plant nutrition is a vital key to achieving efficient use of water. Nitrogen deficiencies have an impact on the ability of a crop to convert available water into yield. Phos­phorus is important in stimulating seedling root develop­ment. This helps the plant explore more soil, increasing the recovery of nutrients and water. Potassium is often referred to as the regulator nutrient, influencing the water dynamics in plants. Nutrients play an essential role in allowing plants to convert water and sunshine into food.

For a pdf version of this post, go to: 

http://www.ipni.net/ipniweb/insights.nsf/$webcontents/DA8415D5BCDB35B985257A75006FE02A/$file/MIkkelsen_Drought_Insights_2012_final.pdf