Wednesday, October 17, 2012

Triple Superphosphate (TSP)... a great phosphorus fertilizer

Triple superphosphate (TSP) was one of the first high analysis P fertilizers that became widely used in the 20th century. Technically, it is known as calcium dihydrogen phosphate and as monocalcium phosphate, [Ca(H2PO4)2 .H2O]. It is an excellent P source, but its use has declined as other P fertilizers have become more popular.

The concept of TSP production is relatively simple. Non-granular TSP is commonly produced by reacting finely ground phosphate rock with liquid phosphoric acid in a cone-type mixer. Granular TSP is made similarly, but the resulting slurry is sprayed as a coating onto small particles to build granules of the desired size. The product from both production methods is allowed to cure for several weeks as the chemical reactions are slowly completed.
Mining rock phosphate in Morocco

The chemistry and process of the reaction will vary somewhat depending on the properties of the phosphate rock.

Agricultural Use
TSP has several agronomic advantages that made it such a popular P source for many years. It has the highest P content of dry fertilizers that do not contain N. Over 90% of the total P in TSP is water soluble, so it becomes rapidly available for plant uptake. As soil moisture dissolves the granule, the concentrated soil solution becomes acidic. TSP also contains 15% calcium (Ca), providing an additional plant nutrient.
Phosphorus-deficient lettuce
A major use of TSP is in situations where several solid fertilizers are blended together for broadcasting on the soil surface or for application in a concentrated band beneath the surface. It is also desirable for fertilization of leguminous crops, such as alfalfa or beans, where no additional N fertilization is needed to supplement biological N fixation.
Management Practices
The popularity of TSP has declined because the total nutrient content (N + P2O5) is lower than ammonium phosphate fertilizers such as monoammonium phosphate, which by comparison contains 11% N and 52% P2O5. Costs of producing TSP can be higher than ammonium phosphates, making the economics for TSP less favorable in some situations.

All P fertilizers should be managed to avoid losses in surface water runoff from fields. Phosphorus loss from agricultural land to adjacent surface water can contribute to undesired stimulation of algae growth. Appropriate nutrient management practices can minimize this risk.

                            Chemical Properties
Chemical formula:     Ca(H2PO4)2H2O 
Fertilizer analysis:     45% P2O5  (0-45-0)    15% Ca
                                    Water-soluble P:         Generally >90%
                               Solution pH               1 to 3

Non Agricultural Uses
Monocalcium phosphate is an important ingredient in baking powder. The acidic monocalcium phosphate reacts with an alkaline component to produce carbon dioxide, the leavening for many baked products. Monocalcium phosphate is commonly added to animal diets as an important mineral supplement of both phosphate and Ca.

A pdf version of this post is available here

Wednesday, October 10, 2012

Fertilizer is not a dirty word!

High crop yields often come under scrutiny because of the need for fertilizers and the perception of their potential environmental impacts. Newspaper articles, letters, and advertisements from well-intended, but poorly informed, citizens seem to perpetuate old myths and clichés about modern fertilization practices.

Fertilizer nutrients support human nutrition

The fact is, maintaining food production for the growing world population requires the use of new technology and the intensification of management to grow more food on the existing crop land...and fertilizer is essential for accomplishing this.

Sometimes I get tired of hearing about the negative fertilizer issues that are associated with our abundant, affordable, and nutritious food supply...a truly amazing supply of healthy food that is clearly unprecedented in the history of the world! Misapplication and misuse of agricultural fertilizers have undoubtedly occurred and their impact on the environment needs to be minimized. But to fairly judge the use of fertilizers, the risks of their use should be compared with their benefits for food production.

I have had people tell me that raising yields with commercial fertilizer is somehow immoral and dangerous for our soils... that strictly organic or specialty products will meet the demand of global food production. You probably know about the “stink test”... that is, when something smells fishy there is usually a reason why! Many of these ideas and claims just don’t pass stink the test.

The time has come for all of us dispel myths about fertilizers and nutrients, and to convey a correct message to a world which is becoming increasingly urbanized and removed from what agricultural production is all about... providing healthy food.

How Does Fertilizer Contribute to the Food Supply?
A survey of U.S. crop production estimated that average corn yields would decline by 40% without N fertilizer. Even greater declines would occur if regular additions of P and K were also halted. Numerous long-term studies have also demonstrated the contributions of fertilizer to sustaining crop yields. For example, long-term studies in Oklahoma show a 40% wheat yield decline would occur without regular N and P additions. A long-term study in Missouri found that 57% of the grain yield was attributable to fertilizer and lime additions. Similarly, long-term trials from Kansas show that 60% of the corn yield was attributable to fertilizer N and P.
Poor plant nutrition... maize
Few people appreciate that corn yields have continued to increase in the Corn Belt of the U.S. without a similar increase in N fertilization. In fact, N use efficiency has increased at least 35% in the past 25 years (where less N fertilizer is now required to produce a bushel of grain). Remarkably, more corn is being harvested without increasing N fertilizer application rates. Some of this improvement has also come from modern genetics and improved agronomic management.

Is Manure the Answer?
Use all nutrients wisely
Animal manure can provide a useful nutrient supply for growing crops...and it should certainly be used in the most beneficial manner possible. However, many people have the mistaken idea that manure has some special property for building soils. Manures contain no more nutrients than were present in the animal feed. Similarly, manures do not produce any organic matter that was not initially in the animal feed. No nutrients or organic matter are produced during the digestion process!

This means that whatever organic matter or nutrients that are present in manure are simply the result of harvesting crops from somewhere else. The hay, grain, or silage that is harvested to feed animals is simply taken from one field and then applied to another fi eld after passing through an animal... with the inevitable loss of nutrients and C to allow the animal to grow.

Animal manures rarely contain the essential plant nutrients in the proper ratio required for growing crops. Manure application frequently results in imbalances and accumulation of nutrients in the soil that can pose an environmental risk. Composts and manures can be good nutrient sources, but their mineralization depends on complex interactions of both soil and environmental factors that are difficult to predict, which commonly results in a lower efficiency than fertilizer.

In an on-going study in England (begun in 1840), applications of farmyard manure increased soil C and N to a greater extent than did fertilizer N. However, soil physical properties such as aggregate stability and water infiltration improved the most in the treatments receiving fertilizer N. Nitrogen leaching following the recommended manure application (75 tons/A/yr) was almost twice that from the fertilizer N treatment (250 lb

There will likely be more livestock and animal manure in the future, and these animals will consume more grass and crops that must be fertilized. But the animals will not provide new nutrients. Expanding urbanization means more organic waste and biosolids to manage. But resistance to application of these materials back on the land seems to be growing and their land application is banned in many countries.
Can Low Analysis Fertilizers Help?
I recently received a testimonial for a special fertilizer where a few pounds of a product with N-P2O5-K2O analysis of 8-2-2 was claimed to meet all the nutritional needs for 10 acres of crops! It bothers me that some educated people continue to believe these claims and provide a market for these products.

Advertisement for Cricket Manure
Consider for a moment that 2 lb of such a low-analysis fertilizer will provide about 3 oz. of N, and 1 oz. of P2O5 and K2O spread over the entire 10 acres. Then compare this with the removal of over 1,000 lb N, 500 lb P2O5, and 400 lb K2O in corn grain...or a high-yield potato crop on this 10 acres will remove 2,000 lb N, 300 lb P2O5, and over 2,000 lb K2O. Think about the cost of some of these products and the amount of nutrients in a small container and it just does not add up!

It might be great if manure composted in cow horns, homebrewed compost tea, or bat guano could meet the nutritional needs of large-scale food production, but this can never be the case.  Perhaps we are always on the lookout for short cuts or simpler routes to achieve consistently high yields.
Unfortunately, there are no ways to violate the laws of nature and science. You can’t grow a successful crop without providing the basic building blocks for the plant. This includes maintaining soil conditions, adequate water, and proper nutrition. When you hear that someone has a totally new concept for providing for the health of your crop, approach it with some initial skepticism and ask for documentation.

I marvel that people will eagerly buy the latest miracle product, but fail to sample the soil and to monitor their fields for fertility levels, pH, or nematodes. But remember the stink test; when something smells bad, there is usually a mess nearby. Proper crop nutrition plays a vital role in maintaining the world’s food supply. Use fertilizer appropriately to get the best results and don’t be afraid to speak out for farming practices that are such a benefit to humanity.

A pdf version of this post is available here

Monday, October 8, 2012

Water: Getting the most from every drop

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
  • 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.
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.

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!
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  pg 43-46) Major factors influencing wheat yield improvement during the last thirty years. Available here.

Thursday, October 4, 2012

Ammonium Nitrate as a Fertilizer

Young corn field
Ammonium nitrate was the first solid nitrogen (N) fertilizer produced on a large scale, but its popularity has declined in recent years. It has been a common N source because it contains both nitrate and ammonium and it has a relatively high nutrient content.

Large-scale production of ammonium nitrate began in the 1940s when it was used for munitions during wartime. After the end of World War II, ammonium nitrate became available as a commercial fertilizer. The production of ammonium nitrate is relatively simple, where ammonia gas is reacted with nitric acid to form a concentrated solution and considerable heat.

Prilled fertilizer is formed as a drop of the concentrated ammonium nitrate solution (95 to 99%) falls from a tower and solidifies. Low density prills are more porous than high density prills and are preferred for industrial use, while high density prills are used as fertilizer. Granular ammonium nitrate is made by repeatedly spraying the concentrated solution onto small granules in a rotating drum.

Since ammonium nitrate is hygroscopic and readily attracts moisture from air, it is commonly stored in air-conditioned ware­houses or in sealed bags. The solid fertilizer is usually coated with an anti-caking compound to prevent sticking and clumping. 
Fertilizer going into storage
Small quantities of carbonate minerals are sometimes added prior to solidifying, which eliminates the explosive properties of ammonium nitrate. These additives lower the N concentration and are sparingly soluble, making the modified product less suitable for application through an irrigation system (fertigation).

 Chemical Properties
              Chemical formula:                 NH4NO3
              Composition:                          33 to 34% N
              Water solubility (20 ºC):        1,900 g/L

 Agricultural Use
 Ammonium nitrate is a popular fertilizer since it provides half of the N in the nitrate form and half in the ammonium form. The nitrate form moves readily with soil water to the roots where it is immediately available for plant uptake. The ammonium fraction is taken up by roots or gradually converted to nitrate by soil microorganisms. Many vegetable growers prefer an im­mediately available nitrate source of plant nutrition and use ammonium nitrate. It is popular for pasture and hay fertilization since it is less susceptible to volatilization losses than urea-based fertilizers when left on the soil surface. 
Foliar fertilizer
Ammonium nitrate is commonly mixed with other fertilizers, but these mixtures cannot be stored for long periods because of a tendency to absorb moisture from the air. The very high solubility of ammonium nitrate makes it well suited for making solutions for fertigation or foliar sprays. 

Management Practices
Ammonium nitrate is a popular N fertilizer due to its ease of handling and high nutrient content. It is very soluble in the soil and the nitrate portion can move beyond the root zone under wet conditions. Nitrate can also be converted to nitrous oxide gas in very wet conditions through the process of denitrification. The ammonium portion is not subject to considerable loss until it is oxidized to nitrate.

Concerns over illegal use of the fertilizer for explosives have caused strict government regulation in many parts of the world. Restrictions on sales and transportation have caused some fertilizer dealers to discontinue handling this material. 

Transporting fertilizer
Non Agricultural Uses
A low-density form of prilled ammonium nitrate is widely used as an explosive in the mining industry, for quarries, and in con­struction sites. It is intentionally porous to allow rapid adsorption of fuel oil (termed ANFO).

Instant cold packs are made with two bags—one containing dry ammonium nitrate and the second containing water. When the barrier separating the bags is ruptured, the ammonium nitrate rapidly dissolves in an endothermic reaction, lowering the pack’s temperature to 2 to 3 ºC within a very short time.

A pdf version of this blog page is available here

Tuesday, October 2, 2012

Soil Quality Checkup

Well managed vineyard
WHEN we think about the important role that soil plays in the production of food and fiber for the world’s population, we realize that it is an irreplaceable resource that must be protected. Soil is the medium that supports plant growth and the source of most plant nutrients. Soil water and the soil atmosphere bathe the roots and keep the above-ground plant healthy and growing. A healthy soil environment is in everyone’s interest.

Definition of Soil Quality

Many people have attempted to define soil quality by measuring various soil characteristics and relating these to different management practices, productivity, environmental quality, or plant disease. But soil quality means different things to different people, depending on its intended use. For example, farmers generally want a soil that supports ideal crop growth year after year with a minimum of inputs. A highway builder is looking for very different soil proper- ties for a high-quality soil.
It has long been known that a major benefit of balanced crop fertilization aside from increasing crop yields and farm profitability is its effect on enhancing crop productivity and increasing the amount of organic matter that can be returned to the soil. Organic matter can positively influence soil properties such as structure, tilth, bulk density, and increased infiltration rates.

New Research—Mostly Good News for Soil Quality in California

A published article from the University of California reported on changes in soil quality that have occurred in the last 45 to 55 years (DeClerck, Singer, and Lindert. 2003.... click here). Soil samples collected primarily in 1945 were compared with samples collected at the same locations in 2001. These 125 sampling locations represented four major land uses throughout the state: tree crops (25 sites), row crops (44 sites), rangeland (48 sites), and vineyards (eight sites). Although these sites represent only a proportion of California agriculture, analysis of these historic samples provides an insight into changes in soil quality that have occurred throughout the state.

 Soil pH:  The average soil pH in 1945 was 6.9 compared with a value of 7.1 in 2001. This slight increase in pH is well within the acceptable range for plant growth and indicates no extreme changes towards acidification or alkalinization as a result of production practices.

Soil Salinity: The average soil salinity at the 125 sites significantly decreased during the 56-year period from 0.85 deciSiemens/meter (dS/m) in 1945 to 0.44 dS/m in 2001. The largest decrease in salinity occurred in soil used for row crops. This 48% average decrease in soil salinity likely reflects an improvement in management practices and in soil quality.
Soil Phosphorus (P): Concentrations of plant-available P (sodium-bicarbonate extractable) increased approximately 20% during this period, with significant increases occurring in land used for tree crops, row crops, and vineyards. The average P concentration in 1945 was 72 parts per million (ppm) and is now 85 ppm. The improved fertility status that has occurred will enhance the inherent productivity of the soil and increase the amount of crop residue that can subsequently be returned to improve the soil.

Soil Nitrogen (N) and Carbon (C):  The amount of total N and C significantly increased between 1945 and 2001— reflecting an accumulation of soil organic matter. Average soil N concentrations increased from 0.09% to 0.29% and soil C increased from 1.06 to 1.34% between 1945 and 2001. These changes in soil organic matter are typically reflected in better aggregate stability and water infiltration.

Check the soil all through the profile
Soil Texture:  The clay content of the samples consistently increased from an average of 10% to 13% for the period between 1945 and 2001. This increase in clay content may be a sign of accelerated soil erosion…which would have a negative impact on soil quality. While this increase in clay content is not great, erosion of topsoil can have very negative effects on crop production and water quality. Efforts to minimize soil loss should always be part of a farm management plan.

So What?
These results indicate that soil quality has generally been maintained or improved over the last 50 to 60 years of intensive management and cropping.  Does that mean that the status quo is fine? No, continued efforts must be made — especially to minimize soil erosion. The documented improvements in soil chemical properties and fertility reflect hard work over many years and we can’t afford to lose the advances that have been made.

However, for some soil properties, we are still losing ground. For example, a survey of soil test results for California in the 1980s revealed that between 20% and 40% of the samples were rated as medium or lower in potassium (K). This number has increased to 44 to 48% in the most recent surveys. We know that soils cannot be continually cropped and nutrients removed without depleting their native fertility and quality.

A soil scientist can evaluate suitability
Efforts to maintain high yields and soil quality are essential for long-term sustainability.  Careful management and utilization of modern technology accomplish this. The technology available in 2003 is beyond the wildest dreams of the farmers in 1945. For instance, the use of satellite-aided precision agricultural tools, computer-controlled water management, improved soil-testing techniques, rapid assessment of plant tissue samples… can all aid in protecting the quality of the precious soil resource and the environment. Let’s continue the progress that has been made and sustain our efforts to protect the soil.