Smart Fertility — Speaking About N&P

Happy June to all who visits and reads our blog!  Mike Petersen here for just a brief bit of Introduction of our new Agronomist Mick Goedeken.  Mick is jumping in where angels fear to tread these days; that is right alongside of me the  Soils Guy for Orthman.  He is learning real quick that soil jammed under the fingernails is a common occurrence around here and digging to look at plant root systems as deep as need be is the modus operandii.  I have asked Mick if being down on his hands and knees is a bad thing for his posture and back, he has not complained yet.  Mick hails originally from up near Columbus, Nebraska and has a rich background in the Ag World which both of us find extremely helpful and aids our speaking with growers all across the globe for Orthman Manufacturing.  Before Orthman (he started in April 2021) he worked as the research agronomist for Central Valley Ag out of the Waco, Nebraska site.  His contact information is under the Contact Us tab or right here:  Mick Goedeken, 402-860-2489, or email: mgoedeken@orthman.com.

So please welcome Mick and read his first sashay into the Precision Tillage blog realm of writing and offering up-to-date material that fits the scope of Orthman Manufacturing, how we address fertility and important concepts of fertility management in today’s Agriculture.  I am pleased that he is working with me as we communicate how Agronomics affect the Top company of Strip Tillage, very likely Worldwide.
Mick Goedeken, Precision Tillage Agronomist – Out Standing in His Field

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Many outside the Ag industry complain about nitrogen use efficiency(NUE) for corn being poor and not good enough.  They also point fingers and blame the American farmer for Phosphate pollution.  This blog article will examine smart soil fertility and how we can improve NUE and phosphorus use efficiency (PUE).  Is it possible to improve NUE and PUE on American farms?  Is it possible to improve efficiencies and maintain yield and profitability?

Let’s look at NUE first.  Throughout time the NUE of corn production has seen continual improvement.  Figure 1 from the USDA compares average N rates to average US corn yield.  From this graph we can calculate NUE by dividing the average N rate by the average yield.  If we look at 1970 and 1980 both years averaged 1.35 lbs N/bu of corn.  When we look at 1990 the US average was 1.15 lbs N/bu then improved to 1.0 in 2000 and by 2010 had improved to 0.89 lbs N/bu of corn.  Over the 40 year period we have seen an improvement of 0.46 lbs N per bu or about 0.11 improvements every ten years.  I would say that improvements in genetics, farming practices, a better understanding of soil microbiology, and N management have helped us improve NUE.  Corn grain removes 0.67 lbs N per bushel of corn therefore, it is the opinion of this agronomist that NUE cannot dip below 0.67 lbs N/bu without robbing N from soil organic matter.  Realistically I feel that an NUE between 0.70 and 0.75 is both attainable and sustainable.

Figure 1: USDA Data Comparing Nitrogen Use from 1965-2010

How can we improve NUE? Understandably every operation is different and each individual field within an operation can be managed differently.  When N is applied quite simply there are four things that can happen it can go up, down, in the plant or into organic matter.  N goes up through gaseous losses to the atmosphere and can be volatized ammonia, N2, NO or N2O from denitrification or plant loss as NH3 due to excessive uptake.  Figure 2 has a Nitrogen cycle from Oklahoma State University where yellow indicates N losses and green indicates N additions. When nitrogen goes down it is in the form of leaching or moving below the rooting profile in the form of NO3-N.   Nitrogen can move into the plant as ammonium NH4-N or nitrate NO3-N.  Most N moves into the plant in the nitrate form through mass flow.  Finally N can be immobilized into the organic matter pool.  Some agronomists and scientists consider the immobilization to organic matter as a loss but others such as myself consider it as a storage that can be used later.  Many have tried to manipulate the nitrogen cycle over the years but Mother Nature will only allow attempts to be short lived.  For example, nitrogen stabilizers can help prevent volatilization for a short time (usually 7- 10 days) by preventing the urease enzyme from interacting with urea containing fertilizers.  Likewise, nitrification inhibitors can slow or stop nitrification for a short term (usually 10 days to 2 weeks) by slowing or stopping the nitrification pathway typically by disturbing the bacteria nitrosomonas and nitrobactor that are responsible for converting ammonium to nitrate in the soil.  Utilization of urease inhibitors and nitrification inhibitors are one step to improving NUE.  The most dramatic changes to NUE can be gained by gaining an understanding of when the corn crop needs or uses N.

 

Figure 3 is adapted from How a Corn Plant Develops (see graphic to your left) and will help us better understand when N is needed for corn production.  If we look at the corn crop over 120 days then split that into 40 day increments it helps us understand when N is used.  During the first 40 days corn only uses 15% of its N needs while during the 2nd 40 days it uses 65% of its needs leaving the final 20% being used in the last 40 days.  This is why I find front loading N baffling and especially 100% fall anhydrous programs that can lead to yield loss, financial loss and cause pollution of ground and surface waters.  For example NH3 applied November 15th for corn planted April 15th must be available 5.5 months after application. This is a lot to ask of any product but even more by a product that is vulnerable to loss.  Loss of N is minimized in systems where N is spoon-fed through irrigation applications where 45 to 75% of the N is applied through fertigation.   Understandably, this is not always an option but split applications can still be utilized. For example 25% of N with Strip Till followed by 25% with the planter and 50% sidedress would spread the N loss risk out a lot and insure that N was available during the peak need during the plants second 40 days. Decreasing risk leads to less loss and more available N and can lead to more yield therefore increasing NUE.  Take a look at your NUE and think about spreading your risk is there any option to add another N application to your system that could help you improve NUE on your farm.  Is there room in your system for 1 more application with 20% of the uptake occurring in the last 40 days if we can find a way to apply N later our NUE will improve.

Figure 2: Nitrogen Cycle  Courtesy of Oklahoma State Univ.

 

 

 

Phosphorus use efficiency (PUE) is more difficult to calculate and evaluate than NUE.  The reason for the difficulty is because of the multitude of forms in the soil along with the number of reactions that can occur to each form.   There are differing opinions on how to measure and calculate PUE.  Crop recovery efficiency is calculated by knowing uptake from where P was added and where no P was added calculating the difference and dividing by the amount of P applied.  This always requires a check and can’t be calculated after the fact if a check was not left for comparison.  Another method known as the partial nutrient balance (PNB) is calculated as P uptake by the plant divided by P fertilizer applied.  PNB can be expressed as P removal-to-input ratio or as a percent.  If the PNB is greater than 100% then the plants are removing more P than is being applied resulting in mining of P from the soil.  Conversely if PNB values are extremely low then the P is being used inefficiently.  Typically values for PNB range from 50-70% but can also be higher.  I prefer PNB because I can calculate this post-harvest just by knowing the yield and the P application rate.

Because there is legitimate concern for rock phosphate reserves and how long they will last we must utilize our P as efficiently as possible.  Agronomists, growers and researchers need to explore other P sources that are available, look into new technologies; recycle waste products and most of all utilize P with good agronomics.  In order to improve P efficiency we need to make sure we are managing P in a good agronomic fashion by applying the P with the four R’s (Source, Time, Rate, Place), also make sure that we lime acid soils to help keep P available while managing P with some form of site specific technology at a density that can be managed on your farm. In either liquid or dry forms banding P is more efficient than broadcasting either no-till or incorporated because there is less soil and fertilizer interaction therefore limiting the amount of P tied up by the soil.  In short we can calculate a PUE and from that look at our own operations to find ways to improve PUE and make adjustments to our farms to improve our stewardship and demonstrate to the general public that we are doing a great job with what tools we have.

 

In a world where food production is so vital and yet so ridiculed we have to promote ourselves.  Share with a stranger today how you are improving NUE or PUE on your farm.  Let them know that you are trying hard to be a good steward every day.  Show everyone that by improving nutrient use efficiencies the American farmer is producing more with less in order to feed the growing population. At the Orthman research farm and trials with partners across the globe we are studying different forms of fertilizers and comparing placement of fertilizers to improve both NUE and PUE.  Our Orthman team is committed to demonstrating and recommending the most efficient practices for crop production.