Sometime this month, Dr. John Lamb, professor in the Department of Soil, Water, and Climate at the University of Minnesota will begin a new career — retirement.  Although there was a function for department faculty and staff to recognize John’s accomplishments, I’m not aware of any public recognition of what he has contributed to agriculture in Minnesota.  Perhaps, John wanted it this way.  Nevertheless, I believe that it’s important to take a few minutes to recognize John’s contributions to the agricultural industry in Minnesota, students who have had the pleasure of having John for a teacher, ad the profession of Soil Science.

John was born and raised in South-Central Nebraska — the son of a highly respected County Extension Agent.  There, working with irrigated agriculture he learned the value of and rewards from hard work.  He carried those lessons with him throughout his entire career.  John has always worked hard in whatever he has done.  After earning the PhD degree, John applied for, was offered, and accepted the position of Soil Scientist at the Northwest Research and Outreach Center at Crookston.

While at Crookston, John developed an extensive and excellent research and Extension program focusing on the production of sugarbeets and small grains.  Communication was not a problem.  It was easy for John to talk with crop producers and his reputation for credibility traveled far and wide.  His excellent Extension presentations added to his positive reputation as a researcher dedicated to solving production problems in northwest Minnesota.

Then, there was the opportunity to move to St. Paul to participate in the MSEA program as well as moving into a teaching/research/extension appointment when that program ended.  His research program was outstanding.  The current nitrogen fertilizer suggestions for the sugarbeet crop have increased the percentage of sugar in the beet while maintaining yield.  The end result has been more profit for the grower.  These suggestions are based on John’s solid research program.  Because of John’s leadership in developing the research base, we now have a consistent size for grid cells to be used when the grid strategy is used for collection of soil samples in precision agriculture.  Also, let’s not forget his leadership in describing management practices that can be used to overcome iron deficiency chlorosis (IDC).

As I watched John’s  career it was obvious to me that teaching was his first love.  It takes a special person and faculty member to get closely involved with students.  John was one of those.  He thoroughly enjoyed watching students, succeed at both the undergraduate and graduate level.  I don’t know the actual number; but, there are many who have benefited from their participation in the classes taught by John.  They  learned much more than what was in the book.  They learned the value of common sense in problem solving.  They learned how to apply facts and logic to real world problems.  They learned the value of communication in all aspects of agriculture.  They observed the principles of the Land Grant University in action.  These are concepts that are frequently forgotten/ignored in today’s teaching programs at some Land Grant Universities.  I know of very few faculty who can excel at both teaching and research aat the same time.  John did.

I don’t know what John has planned for retirement.  I do know that he has a Harley and loves to ride.  I suspect that there will be a considerable amount of time devoted to that activity.  I don’t believe that he will be putting leaches on a hook in an attempt to catch fish.  So, John, enjoy whatever you choose to do.  Have a very enjoyable retirement — you’ve certainly earned it.



I’m sure that at one time or another we’ve all benefited from the use of the internet.  However, there can be problems.  There is no filter for information posted on the internet.  Anyone can post anything and what is posted may or may not be factual or true.  The majority of the posted information, I’m sure, is accurate and backed by good science.  Some information, however, is bogus.

That was the situation earlier this spring when there were claims that the amount of N held by soils as NH4-N could be determined by the Cation Exchange Capacity (CEC) of soils.  Those claims prompted a response from Mr. Fred Vocasek.  That response follows.  Mr. Vocasek is Senior Lab Agronomist for Servi-Tech and is a Certified Crop Advisor.  Servi-Tech is an independent crop consulting firm that works primarily in Kansas, Nebraska, Oklahoma, and some parts of Iowa.  There are several consultants with this organization and Mr. Vocasek prepared the following for these employees.

In his article, Mr. Vocasek uses fundamental principles of soil chemistry, other soil properties and basic arithmetic to show that the claims were not true.  It seems that those who originated this claim did not completely understand either soil chemistry or mathematics.  Once good science coupled with common sense trumps perception.  The article by Mr. Vocasek follows:


“When we look at the historical rule of thumb, 10 times the CEC can be applied in one shot. If a grower has a CEC of 20, that soil can safely hold 200 pounds of N at one time,” says Darren Hefty.  Another “urban legend” for agriculture, courtesy the co-host of Ag PhD TV.  I warmed up my calculator to illustrate reasons why this so-called rule-of-thumb is just a myth.

Cation exchange capacity (CEC) is the calculated ability of a soil to hold positively-charged ions (or cations) on the negatively-charged clay and colloid surfaces.  CEC is expressed as “milliequivalents per 100 grams” or “meq/100g”.  The percentages you see at the lower right-corner of the soil report are the relative amount of each individual cation as a percentage of the total CEC/

First, if we run the math, each milliequivalent of the CEC could potentially hold a total of 140 ppm of NH4-N.  With a 10-inch sample depth, that’s 420 lb of nitrogen per acre.  Thus, a soil with a CEC of 20 meq/100g could theoretically hold a total of 8400 lb N/ac – if the ammonium displaced all of the other cations like calcium and potassium.

A second reason is found  in the original research from 1947.  When anhydrous ammonia became readily available after World War II, it was commonly applied by bubbling into the irrigation water flowing through an open canal.  Two Purdue University researchers* injected anhydrous ammonia into several different soils and measured the losses.  The equivalent rate was 600 lb N/ac injected at a 4-inch depth.  They found a only 16% loss from an air-dry Plainfield sand, but ZERO loss when the same Plainfield sand was field moist.  They only found a 3% loss when they injected ammonia into a field moist beach sand.  Moral of the story: depth, moisture, and texture play a huge role in ammonia retention.

Third, is to consider the large amount of water that is held even in a dry soil.  51 lb of ammonia will dissolve in 100 lb water at 68°F.  It would require at least 57.3 gallons of water to dissolve the 38.8 gallons of liquid ammonia containing 200 lb N.  The application zone described earlier (3-inch radius x 17, 424 feet) would have about 1,368 cubic feet of pore space at 40% porosity.

At field capacity (assumed 60% water-filled pore space), that zone would hold 6,141 gallons of water.  If the soil was 50% moisture depleted, that still leaves 3,070 gallons of water just in the injection zone – over fifty times as much water as needed to dissolve the ammonia.  Oh yeah … I forgot about the water that is held in the other 42,000 cubic-feet of soil in that acre-foot.  Plenty of potential water.

Fact is that ammonia losses occur when the soil is in poor condition – too wet or too dry.  When the field is wet and slabby or dry and cloddy, gaseous ammonia can leak upward through large voids between the slabs or clods.  If soils are in good working condition, they should have little problem retaining anhydrous ammonia.  The true rule-of-thumb is “If you can’t smell it, you aren’t losing it.”

Gaseous anhydrous ammonia losses can be minimized with better field conditions, narrower application spacings, and/or greater application depths.  The farmer can’t manage CEC, but he can manage these field factors to manage potential ammonia loss.

* (Jackson, M.L. and S.C. Chang. 1947. Anhydrous ammonia retention by soils as influenced by depth of application, soil texture, moisture content, pH value, and tilth.  Agronomy Journal 39:623-633.)




Corn production on irrigated sandy soils is an important enterprise throughout Minnesota.  The large majority of acres devoted to this enterprise is found in central Minnesota.  Yet, other small, localized areas of sandy soils are scattered throughout the state.   Management of nitrogen is an important factor for corn grown under irrigation.  Management of this input is the focus of this blog.

The determination of the RATE of nitrogen fertilizer to apply is one of the most important management decisions.  Beginning in 2006, the concept used for making suggestions for rate of fertilizer nitrogen changed.   Yield goals were discarded being replaced by: 1) price of a pound of fertilizer N ,2) value of a bushel of corn ($/bu.) and the grower’s attitude toward risk.

Some suggested rates of fertilizer nitrogen (N) for production of irrigated corn on sandy soils are listed in Table 1.  These suggestions are derived from research conducted in fields of cooperating farmers since 2007.  The first step is to calculate the N price/crop value ratio.  to do this, divide the price of a pound of fertilizer N by the value of a bushel of corn (usually obtained from the Chicago Board of Trade).  For N at $.50 per pound and corn valued at $5.00 per bushel, this ratio is 0.10.  Suggested N rates for several ratios are listed in the center column of Table 1.  An appropriate range for each ratio is listed in the right hand column.  Use the lower rate in the range if the corn producer is conservative  For more aggressive producers, use the higher rate in the range.



These N rate suggestions are appropriate for production situations where corn follows corn, small grains, potatoes, or other non-legume crops.  Some N CREDITS for common legume  crops are: soybean (30 lb. N /acre), harvested alfalfa (100 lb. N/acre), and edible beans (20 lb. N/acre).

Nitrogen in IRRIGATIO WATER is also a credit.  If the concentration of nitrate-nitrogen is higher than 10 ppm, this N should be accounted for and will vary with planned or intended amounts of irrigation water to be used.  Don’t make any adjustments if the concentration of nitrate-nitrogen is less than 10 ppm.  Don’t ignore or neglect the amount of N applied in a started fertilizer as well as the N supplied in the 18-46-0 or 11-52-0 when calculation the total amount of N applied.

The impact of TIMING of fertilizer N for irrigated corn production has been the focus of considerable research.  This research leads to the conclusion that split applications  are superior to single applications for corn production on sandy soils.  There can be a considerable amount of flexibility in these split applications.  My preference for ranking the split application is as follows.

1. N in a starter, 2/3 of total chosen as a siredress application; remainder with the irrigation water

2. N in a starter, weed and feed, split sidedress applications (no preplant

3. preplant N, N in a starter, sidedress N N added to the irrigation water

4. N in a starter, sidedress application

5. preplant N, N in a starter, two sidedress N applications

These N management programs are ranked in order of preference.  Both economic and environmental were consequences in formulating the priority listing.  Selection #1 probably has the lowest potential for negative environmental consequences.  The highest potential for leaching of nitrate-nitrogen is associated with choice #5.

There are, of course, various ADDITIVES that can be added to N fertilizers for the purpose of reducing the probability of N loss.  Some work; some don’t.  At this time, a brief review is probably in order.  The products, N-Serve, and Instinct are formulated for the purpose of delaying the conversion of ammonium-N  (NH4-N) to nitrate – nitrogen  (NO3-N.  They work, and when these products are used, the conversion is delayed 7 to 10 days.  The most obvious plan is to use when 82-0-0 is applied before planting.  Use of these products is not suggested if anhydrous ammonia is used for a sidedress application.

The product, Agrotain, is designed for production situations when urea is used in some part of the fertilizer program.  This product delays the conversion of urea-N to ammonium-N.  The delay lasts for 7 to 10 days and, then, conversions of N in soils proceeds s usual.  Use of this product is a good choice if 46-0-0 or 28-0-0 is applied without incorporation before planting.  This product is not suggested if these two N sources are to be incorporated.  Rainfall and/or irrigation water will incorporate any fertilizer containing urea.  The amount needed to produce incorporation is about 0.25 inches.

The product, ESN, does not affect conversion of N in soils.  Instead, it is a slow release N fertilizer that is probably best suited for preplant N applications.  It is more expensive than other N sources.  Therefore, the best fit is probably a mixture of this product with urea, broadcast and incorporated.

There are several other products that are marketed with claims that they affect conversion of N in soils.  Research has shown that these products do not work as advertised.  I’ve recently noticed that a new product, Take-Off, is being marketed as an additive for fertilizer N.  The advertising  suggests that it will accelerate nutrient acquisition and assimilation.  This appears to me to be a new concept and, of course, there was no supporting data.  Sounds like more foo-foo juice to me.

To some, planning a fertilizer program for irrigated sandy soils might be confusing and even overwhelming.  That’s not really the case.  The plan can be flexible and still provide for optimum profit without having an negative impact on the environment.




Use of  strip trials as a learning as a way to learn is becoming more popular across the Corn Belt.  This is to be expected.  Crop producers have a thirst for information.  With GPS technology and yield monitors, and the use of common sense, it’s not difficult to establish strip trials for the purpose of evaluating a concept or compare one or more products or rates of a product.  There are, however, some important considerations for the conduct of a strip trial.  These begin with planning before planting and continue with appropriate interpretation of the data following harvest.  These considerations are summarized in the paragraphs that follow.


IN THE PLANNING PROCESS, SIMPLICITY RULES — Speaking from years of experience, when planning, it’s very easy to bite off more than you can chew.  What looks easy or simple on paper can be a logistical problem when you go to the field.  So, make comparisons simple.  If comparing rates of nitrogen fertilizer for corn, for example use no more than three rates.  It’s nice to have a control  (the variable of interest is not used).  The treatments to be compared must be repeated in the field  at, least  three times.  If comparing rates of nitrogen fertilizer for corn, for example, use no more than three rates.  It’s nice to have a control (the variable of interest is not used).  The treatments to be compared must be repeated at least three times.  The replication must be in the same field.  It is almost a waste of time if fields are used as replications.  If a control is used, it should also be replicated three times.

SITE UNIFORMITY — The day of selection of the site for a strip trial is probably the most day for the entire project.  Soil uniformity is a must.  There is no easy and simple procedure that can be used to correct for lack of soil uniformity at the site.  There are several tools that can be used to select for soil uniformity.  The Soil Survey should not be ignored.  Soil test information based on either grid or zone sampling can also be very valuable.  Time spent in selecting a uniform site is time well spent.

PRODUCTION PRACTICES — Once a specific comparison has been selected it’s very important to keep other production practices constant.  For example, information from a strip trial designed to compare nitrogen rates has little value if varieties are changed in the trial area.  Except for the factor of interest, keep all other production practices constant across the strip trial area.  Two production practices that change across the strip trial cannot be changed at the same time.  Careful planning for this type of project takes time and thought.

DATA COLLECTION — Unless there are special reasons to do otherwise, samples collected from treatments at any strip trial site should be collected at the same time.  This practice reduces variability in the data.  Considering yields, use of  combine yield monitors or weigh wagons is certainly appropriate.  Although this may be obvious to most, it is essential to record yields from each strip separately.

STATISTICAL ANALYSIS — There’s a reason for repeating (replicating) each treatment at least three times.  The project is not complete until the data collected have been analyzed with a mathematical procedure called “statistical analysis”.  I think that we all realize that there is variability across any field.  With all factors being equal, we could combine four strips across any field and the yields would not be the same.  So, when we see differences in yield, the obvious question is: “Is the difference in the yield the result of a real difference caused by the factor being considered or variability across the field?”  Statistical analysis is the tool needed to answer this question.  There is no other way to answer this question.

Let’s look at an example illustrating the importance of statistical analysis.  Using strip trials in different counties, two rates of nitrogen were compared.  There were three strips of each rate.  For a field in Kandiyohi County with corn following a soybean crop, yields from the lower nitrogen rate (149 lb. soil + fertilizer N/acre) were 123, 157, and 170 bu./acre for the three strip receiving this rate.  These three yields average to 150 bu./acre.  For the higher nitrogen rate (199 lb. soil + fertilizer nitrogen), the three yields were 157, 176, and 166 bu./acre.  This averages 171 bu./acre.  Using these arithmetic averages, the initial conclusion is that the higher nitrogen rate was better than the lower nitrogen rate  It would certainly appear that 171 bu./acre is better than 150 bu./acre.  If statistical analysis is used, however, the difference in yield is not statistically significant.  Why?  This conclusion is the consequence of substantial variability among three replications.  In other words, the arithmetic difference is due to variability in yield across the field rather than the factor being compared.

For the same project, a strip trial was used on a field in Carver County.  The corn/soybean rotation was used.  The low nitrogen rate was 102 lb./acre and the higher nitrogen rate was 151 lb./acre.  Yields from the three strips with the low nitrogen were 181, 196, and 195 bu./acre with an average of 191 bu./acre.  For the high nitrogen rate, yields from the three strips were 208, 210, and 207 bu./acre with an average of 208 bu./acre.  Statistical analysis of this yield data showed that the difference between 191 bu./acre and 208 bu./acre was not due to variability in the field.  It was, in fact, the result of the rate of nitrogen applied.  Notice that variability among the three replications for each nitrogen rate was small.  Thus, we can say with confidence that there was a REAL difference in yield caused by the rate of applied nitrogen.

Nearly everyone involved with strip trials wants to present an economic analysis of the yield data.  This is logical.  HOWEVWE, an economic interpretation is only valid if differences between or among treatments is STATISTICALLY SIGNIFICANT.  Otherwise, we make a serious MISTAKE that could have serious economic consequences.  For the Kandiyohi County field, the difference in yield could have been caused by treatment applied or natural variation in the field.  We have no way of knowing the real cause.  For the trial in Carver County, we are sure that the difference in yield was due to the rate of nitrogen applied.  Use of statistical analysis allows us to reach this conclusion.  Now economic interpretation can be applied to the results.

SUMMING UP — Use of strip trials is a good  way to make comparisons between or among factors that affect crop production.  In addition, these comparisons can be conducted in growers’ fields.  However, it’s not an easy task to do an accurate job.  Good planning is needed at the beginning and STATISTICAL ANALYSIS is essential at the end.  There are too many comparisons where statistical analysis is ignored and only arithmetic averages are used.  Without statistical analysis, there can be any number of interpretations of the data.  Statistical analysis eliminates the potential for confusion.




Looking ahead to the 2015 growing season, there has not been a dramatic improvement in commodity prices.  And, at this time, I’m hearing grain market analysts that offer any hope of major improvement.  Likewise, the three major expenses in crop production (fertilizer, seed, land rent) have not changed much when compared to the last two or three years.  Crop producers are concerned and are asking if they can reduce rates of broadcast applications of phosphate and potash without having a negative effect on soil test values for phosphorus (P).  There has been some research conducted at the regional Experiment Stations that help in addressing this concern.  These data become more meaningful because the studies were conducted over a period of years starting in 1986 and terminating in 1993.

For this study, phosphate fertilizer, supplied as 0-46-0, was applied annually in a corn – soybean rotation at the Southern Research and Outreach Center (Waseca) as well as the West – Central Research and Outreach Center (Morris).  The 0-46-0 was to supply 50 and 100 lb. phosphate per acre.  There was also a control where phosphate was no applied.  Other nutrients were applied as needed to provide for optimum crop production.  Corn and soybean yields were measured and annual soil samples ( 0 to 6 inches) were analyzed for P.

This blog is written to describe changes in soil test P each year when phosphate application was terminated after the 1985 growing season.  Crop yield, of course, varied with location and weather during the growing season.  At the  Waseca location, corn yields were usually in the range of 180 bu./acre while soybean yield was in the range of 50 to 55 bu./acre.  At the Morris location, corn yield was about 160 bu./acre and soybean yield was about 50 bu./acre.

Soil test values for the Waseca and Morris locations are shown in Figures 1 and 2 respectively.  Some interpretation of the results is probably appropriate.  At Waseca, the soil test value for P (Bray test) was initially about 7 ppm.  With no phosphate applied, this value decreased by about 0.6 ppm per year.  This decline was about 2.25 ppm per year when the annual broadcast was 50 lb./acre prior to 1986.  When the phosphate rate at this site was increased to 100 lb./acre, the decline was 3.1 ppm per year.  These declines are shown in Figure 1.




Soil properties were at the Morris location.  There  was a higher  soil pH with elevated levels of calcium carbonate.   With no phosphate applied, the rate of decline in soil test P was .26 ppm per year.  Annual application of 50 lb./acre prior to 1986 had increased the soil test P value to 17 ppm.  Without additional phosphate, the decline was 1.5 ppm P per year.  Over the years, soil test P (Bray test) the use of 100 lb. phosphate annually had increased to 36 ppm.  The decline from this value was 2.7 ppm P per year when the phosphate application ceased.

Results from these two locations illustrate several points.  First and most importantly, if no phosphate fertilizer is applied, there is no steep drop-off in soil test P.  Decline is gradual and can be corrected with added phosphate when profit return to crop production.  If phosphate rates are reduced instead of eliminated, the reduction  in soil test values for P will be more gradual.  For those growers who have high or very high soil test values for P, the decline in soil test values will not be noticed in measured yields.  It is also doubtful if small declines in soil test P will affect yields unless soil test values are in the very low range.

Phosphate rates applied in the study are identified by the symbols on the respective lines.  For both locations, the solid diamonds are associated with the control treatment ( no phosphate applied ).  The white triangles ( both sites ) represent the treatment of 100 lb. phosphate applied per acre from 1974 through 1985.  The dark  squares represent the annual application of 50 lb. phosphate per acre during the same time period.

Again, the declines in soil test P shown in Figures 1 and 2 show what might be anticipated if application of phosphate fertilizer was stopped completely.  Dramatic declines in soil test P would not be a consequence of reduced rates.  A reduction in rate of phosphate would be a good practice in a plan to get profit from crop production in 2015.  A switch  to a banded application of phosphate is another management practice that is encouraged.  When switching to a band,   instead of a broadcast application, the phosphate rate can be cut in half without reducing yield.




Various products and/or concepts that pertain to crop production seem to cycle with time.  I’m never surprised.  There are foo-foo juice products that have disappeared only to appear sometime later under a different name.  Likewise, there are concepts that have been proven by research to be bogus.  Yet, they don’t die.  There appear again.  It seems that there are always some who attempt to make money from Minnesota farmers by selling revived foo-foo juice products or bogus concepts.  To paraphrase a line from a once-popular song: “everything old is new again”.

Recently, there has been a revived promotion of CATION EXCHANGE CAPACITY (CEC) and CATION RATIOS.  The CATION RATIO concept has sometimes been referred to as “BALANCED SOIL FERTILITY”.  So, some review of what we know about CEC and balanced cations is probably appropriate at this time.

The concept of CEC and it’s relationship to crop production was first researched in New Jersey in the mid-1940’s.  At that time, researchers measured the CEC of soils as well as the exchangeable cations (Ca++, Mg++, K+).    The CEC is a nearly constant property of soils that is directly related to soil texture.  Sandy soils have relatively low CEC values.  BY contrast, fine textured soils have high CEC values.  The exchangeable cation values (Ca++, Mg++, K+) vary with other soil properties — mainly soil pH.

In the New Jersey soils, the researchers measured the exchangeable cations in a “productive soil” and a “non-productive” soil.  They calculated the ratios of one cation to another.  For example, the ratio of Ca++ to Mg++ was 6.5 to 1.  Alfalfa was the test crop.  So, it was thought that a “productive” soil should have a Ca to Mg ratio of this value.  These researchers neglected one important piece of information.  This was that lime had been used on the “productive” soil but not on the “non-productive” soil and the sandy soil had an acid pH.  The lime supplied Ca++.  Do you suspect that productivity of the alfalfa crop was a consequence of the use of lime rather the magic ratios?  In the years that followed, numerous research projects were conducted through the Midwest for the purpose of investigating the effect of cation ratios on crop production.

There were the comparisons of fertilizer recommendations provided by various Soil Testing Laboratories.  Some followed the cation ratio concept.  Others Used the sufficiency approach based on the response of crops to measured levels of available nutrients by standardized, routine analytical procedures.  Although costs of fertilizer recommended by these approaches varied considerably each year for extended periods of time (14 years in Nebraska), crop yield was not affected.  Fertilizer recommendations based on the cation ratio concept were much higher than those that were based on the sufficiency approach.

The results of the Midwest research led to the conclusion that the ratio of one cation to another in soils had no effect on crop production.  Crop response to fertilizer was the result of the nutrient supply in the soil — not ratios.  Nutrient supply is measured by the standard analytical procedures.  The crop has no interest in ratios.  Given the uniformity of the conclusions of these research projects, it appeared that the “ideal ratio” or “balanced nutrient” concept was dead and had disappeared from our knowledge base that pertained to soil fertility and fertilizer use.

Land Grant universities in the northern and western Corn Belt have published reports that document the bogus nature of the ideal cation ratio concept.  Staff at Agvise Laboratories have worked hard and listed the links to these reports on the Laboratory web site.  The web address is: agvise.com if anyone is interested in the detailed reports.

The concept of IDEAL CATION RATIOS has been thoroughly research for several crops.  There is consistency in the results of this research.  This concept is not in any way related to effective and economical fertilizer recommendations.  In fact, use of this concept has a high probability of producing less than optimum recommendations for use of potash fertilizers on sandy soils.

The concept of IDEAL CATION RATIOS as a basis for fertilizer recommendations is truly bogus and has no place in Minnesota agriculture.  Please use this ratio concept if you want to waste money on fertilizer purchases in 2015.  Those who advocate the use of this concept are not up to date in their understanding of modern principles of soil fertility.  They’re still working in the 1940’s.  It was WRONG THEN and it’s WRONG NOW.



In Minnesota, soil water has a major impact on crop production.  We affect soil water by irrigating the sandy soils and using tile drainage to eliminate excess water for situations where internal drainage is poor to very poor.  Soil water is also linked to concerns with environmental quality.  In fact, there are some misguided individuals who believe that tile drainage is the cause of all sediment reaching Lake Pepin.  So, it’s appropriate to take a detailed look at soil water and the relationship to crop production in this state.

We begin by recognizing that there is a  substantial amount of pore space in any volume of soil that is occupied by both air and water.  In general, any volume of soil is about 50% mineral and organic matter and 50% pore space.  After a heavy  rain, most of the pore space is filled with water  At this point, soils are pictured as being SATURATED.  At this point, soil pores are filled with water.  Depending on soil texture, some of the water drains through the soil profile.  This water is defined as GRAVITATIONAL water.  This is the water removed via tile lines when soil drainage is such that tile lines are needed for optimum crop production.  When all gravitational water is removed, the soil is defined as being at FIELD CAPACITY.

At field capacity, plants continue to use soil water.  Without added rainfall or irrigation, water use by plants continues and plants begin to wilt when the water supply in the soil cannot keep up with evapotranspiration.  There is a soil moisture content at which plant begin to wilt.  There is also a soil moisture content where wilted plants do not recover when water is added.  This moisture content is defined as the PERMANENT WILTING POINT (PWP).  Soil moisture percentage is not zero at PWP.  A film of water attached to soil particles is not available to plants and is not used by plants. Even in the driest conditions, there is still a small amount of water in the soil.  The moisture between field capacity and PWP is known as AVAILABLE WATER reported as inches per foot of soil.  Amounts of available water are affected by soil texture and are listed in the following table.  This table also lists the water present at PWP for the various soil textures.  Note that the silt loam texture — not the clay texture — holds the highest amount of available water.

Soil Texture and Soil Water

Nearly everyone recognizes that tile drainage removes excess soil water thereby stimulating the movement of oxygen (air) into the soil pores.  When water flow through tile lines stops, the “available water” remains.  This water, of course, is used by crops until the permanent wilting point is reached.  TILE DRAINAGE DOES NOT REMOVE  AVAILABLE WATER.   If we understand this fact, we cannot accept the nonsense argument that tile drainage causes excess removal of “available water”.  Therefore, tile drainage cannot be blamed for accelerated erosion of the banks of the tributaries that reach the Minnesota River, and, then, into Lake Pepin.

As plants grow, water is absorbed through the root hairs.  Oxygen is required for this absorption process.  With saturated soils, oxygen is either present in small amounts or not present.  Although there is plenty of water in these situations, it’s not easily used by plants.

If plants use more water than amounts supplied by  rainfall and/ or irrigation , roots must explore larger volumes of soil.  When the entire rooting zone contains moisture, the majority of the water used comes from the soil close to the soil surface.  If this is not adequate, roots grow deeper and absorb water from lower depths.

This pattern of water use has a relationship to tile drainage.  If tile drainage stimulates early root growth, early plant growth is enhanced with subsequent increases  in the use of soil water.  If more soil water is used by crops, less is available for loss through tile lines.  Thus, more water is used across the landscape and does not move into rivers and streams.



In Minnesota and throughout the United States, the popularity of urea as a nitrogen fertilizer has been increasing in recent years.  Applied as either a dry material (46-0-0) or as a component of 28-0-0 (50% of the N comes from urea), this N source is easy to apply, calibration of application equipment is not complicated and, when compared to anhydrous ammonia (82-0-0), safety concerns are diminished.  Therefore, it’s appropriate to take a detailed look at how one factor (moisture) after urea application can affect the efficiency of use of this popular N source.

First, some basics.  In soils, urea is dissolves in soil water and with hydrogen (H+) and in the presence of the urease enzyme is converted to ammonium (NH4-N) and bicarbonate (HCO3-).  Ammonia (NH3) is formed in an intermediate step.  This conversion follows the following reaction:  (NH2)2 (urea) + urease + 2H2O +H+——>NH4+ + HCO3 (bicarbonate).  The urease enzyme is present in all soils and there is no need to supply as an additive.  This reaction in soils can be delayed by using a urease inhibitor.  the product, Agrotain has been proven to be effective as a urease inhibitor.

The  bicarbonate further reacts with H+ to form carbon dioxide (CO2) and water (H2O) according to the following reaction:  HCO3- + H+——> CO2 + H2O.  Both reactions consume H+ temporarily increasing soil pH around the reaction site.  The H+ is present in the soil.  In this chemical reaction.  In this chemical reaction, there is a temporary increase in the ratio of NH3 (ammonia) to NH4 (ammonium).  The formation of NH3 before NH3 is called the intermediate step.  The NH3 is subject to loss by volatilization   unless the urea is incorporated into the soil during application or immediately after application.  Detailed research has shown that loss of N by volatilization ranges from 15% to 40% of the N applied.  Therefore, it’s important to focus on some form of incorporation of urea as a best management practice.

There are, of course, several options for incorporation.  The fertilizers, 46-0-0 and 28-0-0, can be knifed in below the soil  surface.  With the use of the knife with or without a coulter, the NH3 formed after application is absorbed by water in the soil and there is no loss by volatilization.  To be most effective, the knife should be adjusted so that the fertilizer is placed at a depth of 4 to 6 inches.  This is especially important for sidedress applications.  If broadcast on the soil surface before corn planting, incorporation can be achieved by using a variety of tillage implements.  Again, incorporation to a depth of 4 to 6 inches is suggested.  Whether applied in a band or broadcast, urea on the soil surface without incorporation SHOULD NOT be a part of a nitrogen management plan unless there is the option of incorporation with irrigation water.

So, how much water is required for incorporation?  In order to begin to answer this question, researchers in Oregon accurately measured N loss as NH3  from a single application of 100 lb.N/acre to wheat.  Various amounts of  water were applied in a single  irrigation to the actively growing wheat crop.  Nitrogen loss as NH3 was measured for 24 days after application of the fertilizer N.  The soil was a fine sandy loam having a pH of 6.5.  There was no incorporation of the urea.  There was no rainfall during the 24 days that the loss of NH3-N was measured.

The majority of the ammonia loss occurred in the first 8 days.  With no water applied, 59% of the applied N was lost.  With only a small amount water applied (.05 inches), loss decreased to 53% of the amount of N applied.  With the application .3 inches of irrigation water, nitrogen lost as NH3-n decreased to 15%.  Approximately 5% of the applied N  was lost when the amount of irrigation water was increased to .5 inches.

The irrigation water was incorporating the urea into the sandy soil.  Incorporation improved as the amount of water that was applied was increased.

In Minnesota, however, we don’t have the luxury of irrigating every acre of corn.  If we’re fortunate enough to apply urea just before a rain , incorporation with a knife system or some method of tillage is not needed.  However, we cannot depend on rain after a broadcast application of urea.  In addition, the data collected show that small showers are not effective.  It would be best to have at least .25 inches in any rain event after urea application.  For production systems where irrigation is available, it’s relatively easy to incorporate broadcast urea.

Looking ahead as the use of urea or fertilizers containing urea increases, the management plan should include some method of incorporation.  Any ammonia-N lost by volatilization is gone and cannot be recaptured.  There’s no potential for use by the crop.  It’s simply money lost.




In October, I received a request from the Land Stewardship Project soliciting contributions.  Normally, I don’t pay much attention to letters of that nature.  However, there were some words and/or phrases that caught my eye.

To begin the letter writer stated: “I am writing  to you about the nearly silent, devastating destruction of our land that is happening every day.”  Sounds ominous doesn’t it?  The world as we know it may come to an end very soon.   The writer continues by describing ” bare, black fields  shedding huge amounts of life-sustaining topsoil to wind and rain” on a drive to western Minnesota.  “Huge amounts”—really?  Of course, the writer blames all of this degradation and destruction on the widespread use of modern practices.

These statements are obviously based on perception and emotion.  So, what are the facts?  To get some real world edge-of-field data , we turn to information gathered in the Discovery Farms-Minnesota initiative.  In this effort, fields of 11 cooperating farmers from across the state are being monitored.  The farms are representative of farm enterprises throughout Minnesota.  In this blog, I will discuss soil loss information collected from three of these farms.  Loss of nitrogen and phosphorus will be discussed in future blogs.

A farm in the rolling hills of southwestern Minnesota is the most recent Discovery Farm.  A flume was built at the edge of the field having about 25 acres.  Water flowing the flume was sampled and sediment concentration was measured.  From flow and concentration information it is possible to calculate soil loss in terms of pounds per acre.  In 2014, that loss was 73 lb./acre.  Of this total, approximately one-third was in the snow melt.  The remainder was measured in runoff following heavy rains falling between June, 14 and June 16 (about 8 inches).  This low amount of sediment soil loss is attributed to residue remaining on the soil surface as a consequence of the use of a no-till planting system.  Even though the silt loam texture in the field crusts easily and the crust reduces rain infiltration, the surface residue was effective was reducing soil lost due to erosion.  This can hardly be described as “devastating destruction”.

Now, let’s move from the rolling hills to the nearly level prairie of Blue Earth County.  There are 26 acres in this monitored field having a slope of 1.9%.  To date, information has been collected for three years.  This field is representative of many, many acres in southern Minnesota.  Sediment loss was 74 lb./acre, 76 lb./acre and 480 lb./acre for 2012, 2013, and 2014 respectively.  A substantial amount of this sediment loss was in the snow melt (40%) in 2014.  This cooperating farmer finishes hogs in confinement and all manure is injected followed by a chisel plow tillage operation.

In Goodhue County, we monitor a field from a livestock enterprise.  The soil has a silt loam texture and the field has a slope of 6.7%.  Hog manure is injected in an alfalfa/corn rotation.  The manure is used to supply nutrients needed for corn harvested for silage.  When in corn, the field is seeded to winter rye to minimize soil loss.  Sediment loss was 47 lb./acre, 21 lb./acre, 205 lb./acre and 307 lb./acre in 2011, 2012, 2013, and 2014 respectively.  The field was planted to corn in 2013 and 2014 .  This explains the jump in sediment loss for 2013 and 2014.  This loss was measured even though the field was planted to winter rye.  Again, a substantial amount of soil lost was measured in soil melt.

The Discovery Farm-Minnesota project measuring soil loss at the edge of the field has not found that bare fields are shedding huge amounts of life-sustaining topsoil.  On the contrary, the information collected has shown is minimal across this state.  This provides evidence that crop producers today, are using excellent management practices that keep soil on the landscape.

The information collected in the Discovery Farm-Minnesota initiative is real.  There is no perception and emotion to distort what is measured.



From time to time, critics of modern agriculture argue that modern production agriculture have severely reduced or destroyed soil organic matter thereby causing harm that cannot be repaired.  This important component of soils has been measured in numerous studies and observations.  The conclusions do not support this argument.  But, before changes in soil organic matter can be discussed, it would be good to go back and look at some of the basics.

Most of the organic matter in soils (on average, about 5% by weight)  exists as humus.  This is the dark material formed when microbes decompose plant residues added to the soil.  This material becomes attached to the mineral particles of the soil and, therefore, decays slowly over time.  In our soils derived from prairie vegetation, there was a fairly rapid decline when these soils were first put into production.  This decline , however, has slowed dramatically and, in many production systems, there has been a slow and gradual increase in the organic matter content of soils.

The benefits of soil organic matter (SOM) have been recognized for many years and can be briefly listed as:

1. SOM is a slow release form of nitrogen, phosphorus, and sulfur for both plant nutrition and microbial growth.

2. SOM increases the capacity of soil to hold water

3. SOM is a buffer against rapid changes in soil pH.

4. SOM acts as a cement holding silt and clay sized particles together thereby contributing to the granular structure of soils.  The granular structure increases pore space thereby increasing resistance to erosion, especially erosion by wind.

5.  SOM plays a major role in the soil’s ability to tie up or absorb potential pollutants.  It provides a safe storage place where microorganisms can degrade often toxic materials over time.

Usually, there are not too many opportunities to measure soil organic matter content in situations where data are collected over time.  We have that opportunity in the Discovery Farms-Minnesota project.  In the fields of cooperating farmers, soil samples are collected annually to determine if there are any changes in soil properties as affected by the crop management practices used by the cooperating farmers.

A Discovery Farm was started in Goodhue County in the fall of 2010 and, except for 2012, soil samples from a depth of 0 to 6 inches have been collected each year.  The crop rotation was alfalfa in 2010,2011 and 2012 with corn harvested for silage in 2013 and 2014.  Injected hog manure is used as the source of nutrients.  The organic matter was 3.1% in the spring of 2010.  This percentage was 3.9%, 2.9%, and 3.4% in 2011, 2013 and 2014 respectively.  This amount of variability  is frequently observed when soil properties are measured over time.  There was, however, no substantial drop in organic matter content over time.  This certainly does not match with the argument of some who believe that modern farming practices are destroying the organic matter content of our soils.

In fact, the amount of organic matter contained in the residue of today’s high yielding crops is largely returned to the soil with a potential to increase the soil organic matter content.  This is another plus for modern agriculture.




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