Growers Are Using Drones To Help Save The Colorado River

A drone soared over a blazing hot cornfield in northeastern Colorado on a recent morning, snapping images with an infrared camera to help researchers decide how much water they would give the crops the next day.

After a brief, snaking flight above the field, the drone landed and the researchers removed a handful of memory cards. Back at their computers, they analyzed the images for signs the corn was stressed from a lack of water.

This Department of Agriculture station outside Greeley and other sites across the Southwest are experimenting with drones, specialized cameras and other technology to squeeze the most out of every drop of water in the Colorado River – a vital but beleaguered waterway that serves an estimated 40 million people.

In this Thursday, July 11, 2019, photograph, United States Department of Agriculture engineering technician Kevin Yemoto guides a drone into the air at a research farm northeast of Greeley, Colo.

Remote sensors measure soil moisture and relay the readings by Wi-Fi. Cellphone apps collect data from agricultural weather stations and calculate how much water different crops are consuming. Researchers deliberately cut back on water for some crops, trying to get the best harvest with the least amount of moisture – a practice called deficit irrigation.

“It’s like almost every month somebody’s coming up with something here and there,” said Don Ackley, water management supervisor for the Coachella Valley Water District in Southern California. “You almost can’t keep up with it.”

Researchers and farmers are running similar experiments in arid regions around the world. The need is especially pressing in seven U.S. states that rely on the Colorado River: Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming.

In this Thursday, July 11, 2019, photograph, United States Department of Agriculture intern Alex Olsen, left, and engineering technician Kevin Yemoto work to set up a drone for flight over a research farm northeast of Greeley, Colo.

The river has plenty of water this summer after an unusually snowy winter in the mountains of the U.S. West. But climatologists warn the river’s long-term outlook is uncertain at best and dire at worst, and competition for water will only intensify as the population grows and the climate changes.

The World Resources Institute says the seven Colorado River states have some of the highest levels of water stress in the nation, based on the percentage of available supplies they use in a year. New Mexico was the only state in the nation under extremely high water stress.

The river supplies more than 7,000 square miles of farmland and supports a $5 billion-a-year agricultural industry, including a significant share of the nation’s winter vegetables, according to the U.S. Bureau of Reclamation, which manages most of the big dams and reservoirs in the Western states.

The Pacific Institute, an environmental group, says the river also irrigates about 700 square miles in Mexico.

Agriculture uses 57% to 70% of the system’s water in the U.S., researchers say. The problem facing policymakers is how to divert some of that to meet the needs of growing cities without drying up farms, ranches and the environment.

The researchers’ goal is understanding crops, soil and weather so completely that farmers know exactly when and how much to irrigate.

“We call it precision agriculture, precision irrigation,” said Huihui Zhang, a Department of Agriculture engineer who conducts experiments at the Greeley research farm. “Right amount at the right time at the right location.”

The Palo Verde Irrigation District in Southern California is trying deficit irrigation on alfalfa, the most widely grown crop in the Colorado River Basin.

Alfalfa, which is harvested as hay to feed horses and cattle, can be cut and baled several times a year in some climates. The Palo Verde district is experimenting with reduced water for the midsummer crop, which requires more irrigation but produces lower yields.

Sensors placed over the test plots indirectly measure how much water the plants are using, and the harvested crop is weighed to determine the yield.

“The question then becomes, what’s the economic value of the lost crop versus the economic value of the saved water?” said Bart Fisher, a third-generation farmer and a member of the irrigation district board.

Blaine Carian, who grows grapes, lemons and dates in Coachella, California, already uses deficit irrigation. He said withholding water at key times improves the flavor of his grapes by speeding up the production of sugar.

He also uses on-farm weather stations and soil moisture monitors, keeping track of the data on his cellphone. His drip and micro-spray irrigation systems deliver water directly to the base of a plant or its roots instead of saturating an entire field.

For Carian and many other farmers, the appeal of technology is as much about economics as saving water.

“The conservation’s just a byproduct. We’re getting better crops, and we are, in general, saving money,” he said.

But researchers say water-saving technology could determine whether some farms can stay in business at all, especially in Arizona, which faces cuts in its portion of Colorado River water under a drought contingency plan the seven states hammered out this year.

Drone-mounted cameras and yield monitors – which measure the density of crops like corn and wheat as they pass through harvesting equipment – can show a farmer which land is productive and which is not, said Ed Martin, a professor and extension specialist at the University of Arizona.

“If we’re going to take stuff out of production because we don’t have enough water, I think these technologies could help identify which ones you should be taking out,” Martin said.

Each technology has benefits and limits, said Kendall DeJonge, another Agriculture Department engineer who does research at the Greeley farm.

Soil moisture monitors measure a single point, but a farm has a range of conditions and soil types. Infrared images can spot thirsty crops, but only after they need water. Agricultural weather stations provide a wealth of data on the recent past, but they can’t predict the future.

“All of these things are tools in the toolbox,” DeJonge said. “None of them are a silver bullet.”

SOURCE: Soil and Water Conservation Society. 2 January 2020

World Ag Productivity Growth Is Slow

Agricultural productivity growth, a measure of the increased output of crops and livestock with existing or fewer inputs, is not keeping pace with global demands, according to the newly released 2019 Global Agricultural Productivity (GAP) Report.

Agricultural productivity growth is growing globally at an average annual rate of 1.63%. However, the report’s GAP Index shows that global agricultural productivity needs to increase at an average annual rate of 1.73% to sustainably produce food, feed, fiber and bioenergy for 10 billion people in 2050.

The report, which examines the pivotal role of agricultural productivity in achieving global goals for environmental sustainability, economic development, and improved nutrition, was released at the World Food Prize in Des Moines, Iowa on Oct. 15 by Virginia Tech’s College of Agriculture and Life Sciences.

While productivity growth is strong in China and South Asia, it is slowing in the agricultural powerhouses of North America, Europe and Latin America, the report’s authors said in a press release.

In addition, the findings show very low levels of productivity growth in low-income countries, where there are also high rates of food insecurity, malnutrition and rural poverty. Agricultural productivity growth in low-income countries is rising at an average annual rate of just 1%, the report warned. The United Nations’ sustainable development goals call for doubling the productivity of the lowest-income farmers by 2030.

“These productivity gaps, if they persist, will have serious ramifications for environmental sustainability, the economic vitality of the agriculture sector, and the prospects for reducing poverty, malnutrition and obesity,” said Ann Steensland, author of the 2019 GAP Report and coordinator of the GAP Report Initiative at Virginia Tech.

Historically, productivity growth has been strongest in high-income countries such as the United States, with significant environmental benefits. Due to widespread adoption of improved agricultural technologies and best farm management practices, global agricultural output has increased by 60%, while global cropland has increased by just 5% during the past 40 years, according to the report.

Between 1980 and 2015, productivity gains led to a 41% decrease in the amount of land used in U.S. corn production, irrigation water use declined 46%, greenhouse gas emissions declined 31%, and soil erosion declined by 58%.

The report also shows that animal agriculture in the U.S. has experienced similar productivity gains, dramatically reducing the environmental footprint of livestock production. According to Robin White, assistant professor of animal and poultry science at Virginia Tech, if livestock production in the U.S. was eliminated, total U.S. greenhouse gas emissions would decline by only 2.9%.

SOURCE: www.eco-gem.com/world

Are California Farmers Water Hogs?

In his commentary in the Wall Street Journal, California Farmers Aren’t the Water Hogs, Ted Sheely discusses the blame farmers are asked to take for the water shortage in California.

Sheely, a farmer himself in California’s San Joaquin Valley, argues that the media is not reporting the full picture.

“The second-worst thing about the drought is how farmers are bearing most of the blame. We hear one figure over and over: Agriculture consumes 80% of California’s water.

That statistic makes farmers like me look like gluttons—and it suggests that if we were to reduce our reliance on water just a little, then our state’s predicament would vanish like a puddle on a hot day.

Except that it’s not true. Farmers don’t use 80% of California’s water. While this figure has saturated the media’s coverage of the drought—it’s a fabrication of environmentalists who want to disguise that they “use” even more water than farmers.”

FarmlandFarmland

Farmland in Los Banos, Calif., in the San Joaquin Valley. PHOTO: LUCY NICHOLSON/REUTERS

Read the entire story in the Wall Street Journal: California Farmers Aren’t the Water Hogs

SOIL AND WATER CHEMISTRY PROBLEMS, SOLUTIONS AND FACTS (PART 3)

WATER

Water quality is highly dependent on the source of the water, which in most irrigated agriculture is either from snowmelt runoff or from underground aquifers accessed by wells.  Snowmelt runoff is lacking the salts necessary to maintain soil and crop health in California, the West, and many other parts of the world.  Inversely, well water sources often contain excessive amounts of salts, which are detrimental to crop and soil health. Both situations require calcium sulfate applications to sustain crop and soil health.

Snowmelt Runoff: Not Enough Salts:

A critical property of irrigation water is ECw, electrical conductivity of the irrigation water, (the amount of total dissolved salts in the irrigation water).  The problem with using water from snowmelt runoff is the low amount of total dissolved salts it contains (ECw).  Since pure water does not conduct electricity and salty water does, the more salts in the water the greater the conductance of electricity.  The rule of thumb for ECw is: if less than approximately 0.60 decisiemens per meter (dS/m), then calcium must be added.  The reason is because the pure water is contributing to leaching beneficial calcium below the root zone over time, and is not being replenished.

The application of EcoGEM’s calcium sulfate will quickly and effectively remedy low-salt irrigation water problems.

High Salts (Both Soil and Irrigation Water):

The opposite of when irrigation water is too pure is when the water contains too much salt. When soil and/or water have too much salt, the sodium, chloride and other harmful salts have detrimental effects on plants not only from the aspect of high levels of sodium in the soil in relation to levels of calcium, but also from high salts themselves.  Besides destroying soil structure, high salts in waters and soils can be harmful or fatal to the crops/plants when it accumulates in the root zone.  Sodium and chloride are particularly toxic to ornamentals and woody plants.

About 1/3 of all soils in the arid and semiarid regions of the United States have some degree of salt accumulation, primarily the anions Cl, SO42-, and HCO3 of the cations Ca, K, Mg, and Na.  The primary sources of these salts are weathering of rocks and minerals, ground and irrigation water, and fertilizers.

Once deposited or released in the soil, the salts move to or remain near the surface of the soil by upward-moving water, which then evaporates, leaving the salts behind.  Most crop plants cannot tolerate high levels of salts; therefore, placing limitations on some salt affected soils.  Salt buildup in an existing or potential danger on all irrigated land in the United States.  Continual application of water, all of which contains salts (especially reclaimed water), will continually increase the soluble salts in soils unless the soils have good soil structure and periodic leaching.

By cationic exchange reactions, calcium is used to replace sodium in saline and sodic (high sodium) soils (reaction 7 above).  The calcium will replace any sodium on the cation exchange complex (CEC).  What happens chemically is: calcium solubilized from gypsum replaces sodium leaving soluble sodium sulfate (Na2SO4) in the water, which is then leached out.

This is another reason for the application of EcoGEM’s calcium sulfate. Of all calcium compounds gypsum is considered the most convenient and inexpensive for this purpose.

High Bicarbonate in Irrigation Water:  Add an acid source to neutralize the bicarbonate in irrigation water so additional free lime (CaCO3) in the soil or irrigation system cannot form (reaction 4 above).  Also, the addition of gypsum to irrigation water will replace any calcium precipitated as free lime and will remove any bicarbonates from the soil solution (reaction 6 above).

Bicarbonates and carbonates will form free lime when the water evaporates (reaction 1 above), and this results in several negative consequences:

  1. When the water evaporates, the free lime has the ability to raise the pH of the soil and reduce available calcium. Also when free lime forms, available beneficial calcium will be precipitated out, further compounding the problem of not having enough calcium in the soil.
  2. The reduction of available calcium leads to loss of soil structure and reduced water infiltration that also reduces the normal leaching process by which salt buildup in the root zone is prevented.

Note:  Bicarbonate is also the most toxic anion that exists in relation to plant health.  Any amount in excess of 5.0 milliequivalents per liter (meq/L) is considered very high.

Benefits of Acid Injected Into Irrigation Water:

There are many forms of injectable acids that include (but are not limited to) N-pHERIC, pHAIRWAY, phos acid, sulfuric acid and sulfur burners.  Farms/parks/grounds are able to utilize acid for neutralizing bicarbonate and in some cases to increase water infiltration.

With the injection of acid into the irrigation water, hydrogen (H+) neutralizes the bicarbonate into water and carbon dioxide (reaction 2 above).  Acid can be introduced to the irrigation water either by a liquid acid (one of the above sources) or by a sulfur burner, which ultimately injects sulfuric acid into the irrigation water.

The pH of the irrigation water is usually lowered to a level of 6.0-6.2.  When the pH of the water is at this level, the amount of bicarbonate that remains in the water is approximately 1.0 me/L. While the addition of acid to the irrigation water will neutralize bicarbonate, there is a limited increase in water infiltration.  Since the pH of the water is not very acidic, the water is applying only a small amount of acidity or free hydrogen to the soil.  The acid will, therefore, neutralize only a small amount of free lime in the soil.  The neutralized lime will ionize to calcium ions (reaction 5 above)] therefore improving water infiltration.  As the free lime is neutralized in the top three-six inches of the soil, the acid will have less free lime to react with thus reducing the water infiltration.  Since the acid is primarily neutralizing the bicarbonate in the water, there will be less free lime being deposited on the soil for the acid to react with.

The first year of water injected acid applications, the water infiltration does tend to improve.  However, in the second and subsequent years the infiltration will return to its original disorder.  That is why the addition of EcoGEM’s calcium sulfate (gypsum) along with the acid is recommended to help amend and maintain soil structure.

SALINE/SODIC CLASSIFICATION OF SOILS

Class                           E.C. (ds/m)        pH           SAR (or ESP)       Soil Physical Condition

Normal                      <4                   <8.5                            <15                 Normal

Saline                         >4                   <8.5                            <15                 Normal

Sodic                          <4                   >8.5                            >15                 Poor

Saline/ Sodic            >4                   > or <8.5                    >15                 Poor

SOIL AND WATER CHEMISTRY PROBLEMS, SOLUTIONS AND FACTS (PART 2)

SOIL

Low pH Soil:

Add CaCO3 (lime) to neutralize the acidity, which will increase the soil pH (reaction 5 above).  Even though CaCO3 is a salt, it acts as a base in an acid soil.  Consequently CaCO3 causes the following events to occur in an acid soil, most of which take place simultaneously:

  1. Acidity is neutralized
  2. Base saturation (Ca and Mg) of the soil increases
  3. Ratios of basic cations adsorbed and in solution change
  4. Soil pH increases (as soon as the CO2 dissipates away), which in turn affects the solubility of most of the plant nutrients in a soil
  5. Toxic concentration of Al3+, Mn2+, and possible other ions, are neutralized (or otherwise inactivated)
  6. Acid weathering of primary and secondary minerals is curtailed by the decreased concentration of H+
  7. pH-dependent cation exchange complex (CEC) (i.e., negative charge) increases, adsorbing Ca2+ and Mg2+ from which it is hydrolyzed (mobilized) for ready uptake by plants or movement to lower depths in the profile
  8. pH-dependent anion exchange capacity (AEC, i.e., positive charges) decreases, forcing previously adsorbed anions such as SO42- into solution
  9. Dinitrogen fixation increases
  10. Nitrogen mineralization from plant residues and soil organic matter increases
  11. Electrolyte concentration increases with dissolution of lime, and where CEC dominates over AEC, the electrolyte disappears from solution as CO2 volatilize
  12. Hydroxyl ion (OH) concentration increases with dissolution of lime, and where AEC dominates over CEC, the increased OH ion concentration neutralizes + charges, forcing SO42- into solution

High pH Soil:

Add acid (H2SO4 or another acid source) to dissolve the free lime (CaCO3) that will lower the pH in the soil and ultimately produce Ca2+ and SO42- ions (gypsum) (reaction 4 and possibly 3 above).  Ionized calcium is now able to attract or flocculate the soil colloids thus increasing water infiltration.

SOIL AND WATER CHEMISTRY PROBLEMS, SOLUTIONS AND FACTS (PART 1)

Brent Rouppet, Ph.D., Soil  Scientist / Agronomist

Legend of Chemical Symbols

 

CaSO4·2H2O              gypsum (as it exists in nature)

Ca2+                            calcium ion (the form of calcium that plants use)

CaCO3                         free (or pure) lime (or limestone)

HCO3                         bicarbonate (the most toxic anion for plants)

Cl                               chloride ion

H+ (acid)                    the generic chemical symbol for any acid

OH–                                            hydroxyl ion

CO2                             carbon dioxide (an atmospheric gas)

S                                                   elemental sulfur (as it exists in nature)

SO42-                           sulfate ion (the form of sulfur that plants use)

K+                                                potassium ion

Na+                             sodium ion (very toxic to plants and harmful to soil structure)

Mg2+                                         magnesium ion (harmful to soil structure when insufficient calcium is present)

soil                             a soil particle that has a net negative electrical charge (attracts positively charged ions; e.g., sodium, magnesium, calcium, etc.)

Na2SO4                       sodium sulfate.  A non-electrically charged salt that can be leached through the soil with irrigation water

Common Soil and Water Chemical Reactions

2HCO3(bicarbonate) + Ca2+ (calcium ion)     →     CaCO3 (free lime)     + H2O    +     CO2

HCO3 (bicarbonate) + H+ (acid)     →     H2O   +     CO2

2S (elemental sulfur) +      3H2O     +     3O2    →       H2SO4 (sulfuric acid)

H2SO4 (sulfuric acid) +     CaCO3 (free lime)     →     Ca2+ (calcium ion)    + SO42- (sulfate ion)     +     CO2      +     H2O

2 H+ (acid) + CaCO3 (free lime)     →     Ca2+ (calcium ion)    +     CO2      + H2O

CaSO42H2O (gypsum) +     H2O     →    Ca2+ (calcium ion)     +     SO42- (sulfate ion)

Na+/Mg2+(sodium/magnesium ions)- [on soil] +     CaSO42H2O (gypsum)     →      Ca2+/Mg2+ (calcium/magnesium ions) – [on soil]     +       Na2SO4            (sodium sulfate)  [now leachable]

Building an Effective Fertilization Program Around Science-Based Nutrition (Part 2)

As an example, Dart points out that a crop developing leaves needs the right nutrient in the right form as the leaves are expanding. That’s the time to be applying zinc (Zn), phosphate, and nitrogen (N), because they drive leaf size. At the same time, you should be applying the micronutrients (magnesium (Mg), manganese (Mn), iron (Fe), copper (Cu). These are building blocks for the chlorophyll that is developing as the leaves grow and expand. If you apply these nutrients after the leaves have fully formed, or if you apply them in a form that doesn’t go into the leaf until after it fully forms, you don’t get the full value of the application.

Timing and formulation matter, which is why they are on the Five R list. Dart encourages growers to ask tough, science-based questions of anyone making nutrition recommendations to ensure they get a program that addresses all of the Five Rs. Questions he recommends include:

  • You’re recommending that I use this product — why? “Does this product have specifically and completely what I need at this stage of my crop?” asks Dart. “For example, growers need to pay particular attention to the micronutrients in their program because they drive the chlorophyll development, which is critical for photosynthesis, which in turn is critical for higher marketable yields and producing the sugars and flavor in melons and other fruit that leads to the customer coming back for more.”
  • When does my crop really need this particular nutrient and why? “The plant’s need for a particular nutrient is not a flat line through the plant’s life,” notes Dart. “Some nutrients have early peak demand, some mid or late season based on how the nutrient is used in the plant and the specific quality parameters required for that crop. Growers want to make the applications in the front end of the demand curve, not the top or
    the back end of the curve. That is when the nutrient is being used by the plant for maximum effectiveness and value.”
  • Am I over-applying anything? “This question often doesn’t get asked, so many growers end up applying too much of a specific nutrient, most commonly nitrogen. The quality of the end product can be heavily impacted by applying too much of some nutrients,” says Dart, noting that this issue doesn’t get enough attention, especially with high-value crops like melons, cucumbers, tomatoes, peppers, potatoes, or leafy vegetables.“For example, too high of a nitrogen-to-calcium ratio can hurt a crop’s texture, color, sugar, flavor, shelf life, and shipping quality, so you don’t want to push too much nitrogen and underuse calcium.” This is especially true on mid/late season nitrogen applications.
  • What is the best timing and formulation for making this application to ensure the plant will benefit from the nutrient? “This is a critical issue that can get easily overlooked, which results in wasted time and money,” says Dart. “Calcium (Ca) is a good example, because the fruiting parts of these vegetable crops can only take in Ca via foliar application during the cell division window of the fruit. At any other time, the Ca won’t go into the cell wall and be there for better texture, shipping quality, and shelf life. If you miss that window, it becomes a mis-timed application that won’t deliver the desired results and will waste money and packable yield.”“If you want to be a hero to the produce buyer and produce manager, do a better job on calcium and the Five Rs and you will reduce shrinkage — the second biggest expense in the produce department after labor costs.”
  • Why is the formulation that you’re recommending the right formulation to get this nutrient into the plant? “Delivering a nutrient the plant can use is all about the product’s formulation, and it is often overlooked in a nutrition program,” says Dart. “But the formulation matters because a foliar nutrient is only effective and has value if it gets into the plant completely and at the right time.”
  • Manufacturers are continually improving the fertilizers and nutrient products they bring to the market. Growers who understand the Five Rs and Science-Based Nutrition will be positioned to make the best choices for the best results, less waste, and increased economic returns.

Source: Growing Produce. August 2019

Building an Effective Fertilization Program Around Science-Based Nutrition (part 1)

Source: Growing Produce. August 2019

THE MULTIPLE BENEFITS OF GYPSUM

When purchasing gypsum or anhydrite, it is important to understand the many varied benefits and when they take effect in agriculture. As both a soil amendment and a crop nutrient source, both gypsum and anhyrite will remediate high magnesium and sodic soils, help manage saline irrigation waters, provide calcium and sulfur as crop nutrients, and improve soil structure. All of these benefits occur at different rates.

I invited a friend to a gypsum symposium this summer because I knew he had tried it, and he has an open mind when it comes to trying new ideas. However he declined and reminded me, “I haven’t had the best results from using gypsum in the past.” I recall a conversation we had about gypsum, and his expectation was that a gypsum application should create a response just like applications of nitrogen, phosphorus, or potassium. His was an unrealistic expectation, and my telling him so didn’t undo his perception.

Gypsum works to improve drainage in soils dominated with dispersive clays in four ways. One is immediate, one nearly immediate, the third occurs with a flush of root growth and soil biological activity, and the last is a change in structure.

First – When gypsum dissolves into soil water, it helps water move more freely. That’s an immediate effect, and it can be substantial as it improves drainage. Since gypsum doesn’t dissolve immediately, the effect is persistent. If surface ponding is an issue, gypsum should be concentrated within the first few inches of soil.

Second – Calcium displaces sodium and magnesium on the clay’s exchange sites and reverses the clay’s tendency to disperse. As flocculation and structure improve, drainage improves. This can’t happen until the gypsum has gone into solution and ion exchange occurs. The effect isn’t immediate but will happen during the season it applied. This benefit is even more persistent than the salt effect above.

Third – Once drainage improves, root growth renews, and the biology of the soil kicks in. The root flush occurs before the top growth flush can occur. This will occur in-season.

Fourth – Lastly, the process by which gypsum amends the soil is somewhat slow. It can take anywhere between 3 months and 3 years depending on the clay and organic content and the initial starting point of the soil. You might have to amend the soil for a few years to get the desired results.

If you apply gypsum to improve soil structure, set the right expectation. By 3 to 5 years after aN application of 1 to 2 tons or multiple applications of 1,000 to 2,000 pounds you should begin to see improvements in soil structure and tilth.

Dr. Dan Davidson, Agronomist. EcoGEM, Denver, CO

Plant Availability of Potassium in Soil Minerals: What’s Happening Near the Roots? (PART 2)

(continued): Plant roots can also exude their own acids and carbon compounds into the rhizosphere. These substances are released as the plant regulates the types and amounts of nutrients and other molecules in its roots. Finally, as roots take up K from the soil, they deplete K in the rhizosphere to concentrations much lower than the bulk soil. Very low concentrations of K near the root can trigger the release of K from mineral structures. All of these mechanisms arise from chemical and physical forces considered part of weathering. Rather than taking years, however, these processes working in the rhizosphere release K in a matter of days or weeks. Even with all these mechanisms, a plant may still not be able to access enough K from the soil to meet its nutritional requirements. Scientists have come up with a variety of measurements that differentiate conditions when plants are accessing enough K and when they are not. Soil tests and plant tissue tests that are calibrated to crop growth and development have been extremely helpful in this regard. Future improvements in the accuracy and precision of these tests will need to consider how plant varieties differ in their abilities to acquire K. How different varieties alter their rhizosphere environment will be an important consideration. [International Plant Nutrition Institute. Issue #1 2018]