Fueling the Growth of Alfalfa

Escher's staircase continues to ascend and descend

Perpetual motion?  Change straw into gold?  Who does not want to get something from nothing?  One of the first lessons taught in Chemistry class is that elements are always “conserved”.  Economists teach us that “there is no free lunch”.  When the gas tank in the car gets low, you’d better fill up again or get ready to walk.   No matter how you put it, the proper building blocks need to be in place for us to get the desired result.

For plants to produce sugar from air and water, they require sunshine and the proper mineral building blocks.  When any of these essential components are lacking, the plant simply lacks the fuel to reach its growth potential.

Healthy alfalfa

Alfalfa is the most important forage crop grown in the Western U.S., with over 35 million tons produced each year in the region.  Harvesting this huge amount of hay requires that all the essential building blocks are in place to keep up with the plant demand over a long growing season.  One ton of alfalfa contains an average of 60 lb K₂O and 15 lb P₂O₅.  This means that over 2 billion lbs of K₂O and half a billion lbs of P₂O₅ are removed by Western-grown alfalfa fields each year.

Alfalfa harvesting

Determining the nutrient need of alfalfa is important to sustain profitable hay yield and quality.  Even though huge quantities of nutrients are extracted from soil with each cutting, it is improper to over-generalize about fertilizer recommendations.  A number of factors, including soil type, historic fertilization practices, yield levels, and crop rotation can be quite variable and interact to influence the nutrient requirement of alfalfa.  Using tissue and soil testing is the best way to identify deficiencies and make accurate recommendations.

A well-managed nutrition program is essential for profitable alfalfa production.  In cases where production costs are high and profit margins are slim, special attention to proper fertilization is more important than ever.  For alfalfa, most commonly this means supplying adequate amounts of phosphate, potash, sulfur, magnesium, boron, and watching the soil pH to optimize yield, hay quality, and economic return.

Healthy alfalfa growth

Based on the soil test, the recommended amounts of phosphate and potash should be broadcast and incorporated before planting.  Soil samples collected each fall can then be used as a guide for amounts of fertilizer required for nutrient replacement.

In a recent report from Utah State University, Dr. Koenig documents the alfalfa yield boost that can result from proper fertilization with phosphate, potash, and sulfur.  In his experiments, fluid and granular forms of phosphate were equally effective at increasing hay yield.  Dr Koenig noted that potassium deficiencies are a relatively recent occurrence in many Western alfalfa fields.  A long history of harvesting high-yielding crops has depleted much of the naturally occurring K and has led to a growing number of deficiencies.

Rob Mikkelsen evaluating alfalfa

Fertilizing alfalfa is not a particularly glamorous thing to do.  But harvesting the profits from high-yielding crops depends on it.  Investing in the fuel for alfalfa growth means maintaining adequate nutrients in the rootzone to help the plants keep the “pedal to the metal”. 

Most alfalfa is converted to milk!

Scouting for Nutrient Deficiencies

When plants begin to look a bit ragged and not quite as vigorous as you would expect, they are likely experiencing some kind of stress that is limiting growth. Growth problems may be due to a number of factors, including pests, drought, or lack of adequate nutrition. To solve the problem, it is necessary to first diagnose it properly. It is relatively easy to check for disease and insect damage, or adequate soil moisture. Nutrient deficiencies can be more difficult to diagnose at first, but a quick review of terminology will help you know what to look for and how to describe it.

Chlorosis: 

Nitrogen deficiency (maize)

Indicates a yellowing of the leaf tissue. Since many nutrients are involved in chlorophyll formation and photosynthesis, many nutrient deficiencies can cause chlorosis symptoms. In general, chlorosis of the older leaves may be caused by a shortage of “mobile” nutrients such as nitrogen, potassium, and magnesium. Chlorosis of the younger leaves may indicate a deficiency of an “immobile” nutrient such as sulfur or iron. 

Zinc-deficient cotton

Iron-deficient maize

Interveinal chlorosis: When the leaf tissue turns yellow while the vein itself remains green. In grasses, this is commonly called “striping.” Many of the micronutrient deficiencies show this symptom. 

Firing: Leaf yellowing may be followed by the rapid death of the tissue as the symptoms move up the plant. The dead leaf tissue has been described as “scorched” or “fired”.

Necrosis: Severe nutrient deficiency will result in the death of plant parts or perhaps the entire plant. The dead tissue that remains on a still-living plant is called necrotic tissue.

Firing: Potassium-deficient cashew

Firing: Potassium-deficient maize

Abnormal color: Lack of adequate nutrition will cause some plant leaves to produce abnormal color compounds. This will vary between plant species…and some plants do not show any distinct symptoms. In addition to chlorosis, some plant nutrient deficiency symptoms include red and purple (phosphorus, magnesium), or sometimes a total bleaching of color (iron). 

Phosphorus deficient maize

Stunting: A lack of any of the essential nutrients will result in decreased growth and yield. This depressed growth may shorten the height of many crops and result in smaller harvests. Stunting is a general term that compares the decreased growth with plants that are not limited by a shortage of proper nutrition. Lack of adequate phosphorus frequently results in no visual symptoms other than overall stunting. 

Stunted canola (P deficiency)

While visible plant symptoms can be a useful guide for checking on crops, once they are noticable, the plant growth is already impaired and yield is being lost each day the deficiency continues. Additionally, some plants usually do not show distinct deficiency symptoms. For example, alfalfa rarely shows phosphorus deficiency symptoms, although it responds vigorously to adequate fertilization and nitrogen fixation is severely limited with phosphorus-limited alfalfa.

Do not wait until visible symptoms of deficiency show up before you plan your crop nutrition program. But when you are in the field, keep your eyes open for plants that do not look quite right and then figure out what is the problem. Use visual observations to back up your on-going program of soil testing and plant analysis.

Take Another Look at Chloride?

Chloride deficiency in wheat

Chloride (Cl) is an essential plant nutrient that is required for proper plant growth and yield.  Since it is needed in relatively small quantities, it is classified as a micronutrient.  Nevertheless, it is a critical and frequently overlooked component of a complete soil fertility program.  In the West, there has probably been more emphasis placed on avoiding excess levels of Cl and salinity than on regularly occurring deficiencies.  However, evidence continues to mount that there are many regions where crops could benefit from additional Cl.

Chloride plays several important roles in plants, but the crop response usually comes from a classical nutrient response and/or suppression of fungal diseases.  While many crops respond favorably to applied Cl, wheat and other small grains are the crops that receive the most Cl in the West.  Some wheat varieties exhibit Cl deficiency symptoms, also referred to as physiological leaf spot, under low soil Cl conditions.  The symptoms are similar in appearance to tanspot or septoria with no associated pathogen.  Chloride has been proven to suppress septoria, leaf spot, stripe rust, tanspot and common and take-all root rots in wheat.  Adequate Cl is demonstrated by increased yield, higher test weights, and greater kernel plumpness.

How Do I Get Chloride?

Chloride is an anion and moves freely in the soil with water.  Rainfall near the ocean tends to deposit sufficient Cl, but wheat-producing regions more than 200 miles from the coast may respond to Cl fertilization.  Irrigation water usually supplies adequate Cl to meet plant needs, however regions with rain-fed cropping may not have sufficient Cl for top plant performance and yield.

Research has shown that there is no difference in crop response to various Cl-containing fertilizers.  The most common Cl source is muriate of potash (0-0-67; 47% Cl). It comes in several colors, depending on the geologic source and how it is processed. Other excellent sources of Cl include magnesium chloride and calcium chloride.

White potassium chloride

Red potassium chloride

Mixed color potassium chloride

Will Chloride Fertilization Pay?

Substantial profit can result from Cl fertilization where it is needed.  Like all plant nutrients, Cl responses will only occur where there is an insufficient nutrient supply.  An adequate Cl supply will benefit small grain production by accelerating plant development, reducing lodging, and improving disease resistance. 

Given the demonstrated yield and quality boost that Cl provides for many crops, it is time to reconsider whether your crops will benefit from providing some of this overlooked micronutrient to your fertilization program.

Get the most from every drop of water!

Water-holding capacity

In areas where adequate moisture is a concern, agronomists talk about how to get the most yield from each inch of water in the soil, a term called water-use efficiency.  Imagine a field covered with a 24-inch sponge.  A sponge this size could hold between 10 and 12 inches of rain and store it.  The soil acts like this sponge, providing the nutrients and water to sustain crop growth.  We can manage this topsoil to get the most from the stored water.  Some common ways to make the most of this resource are to:

• Provide proper and balanced nutrition to grow a healthy plant with a vigorous root system that explores the deep soil profile for moisture



Crop residues conserve moisture

• Retain as much crop residue on the surface as possible to catch and retain water, reduce evaporation, and minimize erosion
• Select the appropriate crop varieties and utilize timely planting to avoid peak periods of moisture stress
• Control weeds that compete with crops for moisture
• Use the minimum amount of cultivation necessary to perform important field operations.  Each disturbance of the soil results in enhanced moisture loss.

Weeds waste valuable moisture

A look at wheat production in the Columbia Basin (Pendleton, OR) illustrates how water-use efficiency has increased over the last 35 years as a result of various practices.

Wheat production in Oregon

Between 1967 and 1996, spring wheat yields have increased an averaged of 1.2 bu/A each year in a wheat/fallow rotation.  Although there are swings above and below this average annual increase, the upward trend remains consistent.  Wheat yields in 1940 averaged 45 bu/A with a precipitation of 16.5 inches, resulting in 2.7 bu/ inch of precipitation.  Yields in the range of 85 bu/A in the 1990’s with the same amount of rainfall reflect a water-use efficiency of 5.1 bu/inch of rainfall- almost double the yield with the same amount of water!  

A great wheat crop

While several factors (such a improved genetics and pest control) have contributed to this remarkable improvement, USDA scientists report that proper plant nutrition is one of the most important contributors to this yield boost.  They report that this improvement reflects the “importance of having sufficient soil fertility to allow the wheat crop to take full advantage of additional soil moisture in favorable rainfall years.”

Careful attention to soil fertility and good soil management can go a long way towards converting every drop of available soil moisture into profitable yields!

(Payne, Rasmussen and Goller. 1997) Major factors influencing wheat yield improvement during the last thirty years. Available here: http://pwa.ars.usda.gov/pendleton/cpcrc/AnnualReport_Web/datafiles/1997/PDFsForWeb/042.pdf

What Potash Source Should I Use?

 Soils in the western U.S. are becoming depleted of potash.  Soils in this part of the country were commonly high in potassium when they were first cultivated long ago.  However, after many years of intensive cropping and repeated nutrient removal, many fields now require regular inputs of potash to maintain high levels of production.  High yielding crops remove large amounts of potassium in the harvested portion of the crop.

It’s little wonder that K deficiencies are becoming a common occurrence in so many fields.   For example, harvesting 9 ton alfalfa/A will remove over 450 lb K₂O.  Similarly, a potato yield of 450 cwt/A removes 500 lb K₂O and harvesting 40 ton/A of tomatoes will take off over 450 lb K₂O/A.  But this high rates of nutrient removal is not being matched with fertilization.  In Idaho, for example, an average of four pounds of potash are removed in crops for every pound that is added back.  In the Pacific coast states, over two pounds of potash are removed on average for every pound returned to the field as fertilizer.

There are many excellent sources of potash to replenish the soil’s nutrient reserve.  Some of the most popular include:

• Potassium chloride (Muriate of potash)     (KCl; 0-0-60)

• Potassium sulfate (Sulfate of potash)         (K₂SO₄; 0-0-50- 18S)
• Potassium-magnesium sulfate                    (K₂SO₄-2MgSO_4; 0-0-22-22S-11Mg)
• Potassium thiosulfate                                  (K₂S₂O_3; 0-0-25-17S)
• Potassium nitrate                                         (KNO₃; 13-0-44)

How are these sources different?

The potassium in all these fertilizers is identical and this nutrient will be rapidly available to the plant regardless of the source.  The primary difference is in the companion nutrients that come along with the potassium.

Potassium chloride can be red from traces of iron

Chloride  The importance of this essential nutrient is frequently overlooked.  Recent research has demonstrated that many crops respond favorably to chloride applications with greater yield and quality.  Like any soluble fertilizer, salt-induced damage can result if large amounts are placed in close proximity to seeds or seedlings.

White potassium chloride (MOP)

 

Potassium sulfate (SOP)

Sulfate All crops require an adequate supply of sulfur to develop proteins and enzymes.  Sulfur-deficient plants appear light green and have reduced yields. Sulfate that is present in potash fertilizers is immediately available for plant uptake, while thiosulfate rapidly converts to the sulfate form in the soil.

Langbeinite (K+Mg+SO4)

        Magnesium Because its vital role in chlorophyll, magnesium is first exhibited by yellow leaves in the lower part of the plant.  Magnesium requirements vary considerably, with legumes generally containing more of this element than grasses.

Potassium nitrate (NOP)

Nitrate An abundant supply of nitrogen is essential for all high-yielding crops.  For crops that prefer a nitrate source to an ammonium source of nitrogen, this potash source can be a good option.

There are many excellent potash sources available for meeting the nutrient requirements of crops.  When making a decision on which source to use, choose the one that meets your needs and provides the accompanying anion that will help keep your high-yielding crops in top shape.