Fall Programs and Fertility  11/20/17 12:57:39 PM


Fall applied nitrogen?
While it may save time for spring field work, are there risks involved?
Growers need to consider several things: 1) soil temperature (currently in the mid to high 50’s at 4” depth but will warm with 70 degree weather) and 2) soil moisture. Why the concern over temperature and moisture?
When anhydrous ammonia is applied, it reacts with soil moisture to form the ammonium ion (NH4), which can readily attach to clay particles in the soil and is not subject to losses at that point. Over a period of several weeks, NH4 can be converted, through a series of steps known as nitrification, to nitrate (NO3) if soil temperatures are above 50 degrees F. In fact, nitrification begins to occur at soil temperatures of 30 degrees, and increases as soil temperature increases. Soil moisture also is a factor in the rate at which this occurs. A simplified illustration of the process is:
Ammonium à Nitrite à Nitrate
(NH4)           (NO2)     (NO3)
Two groups of bacteria are involved in the conversion process: nitrosommonas in the conversion of ammonia to nitrite, and nitrobacter are responsible for converting nitrite to nitrate. These steps occur in rapid succession to avoid a buildup of nitrite (NO2)  in the soil. The end result, nitrate (NO3),  is the form of nitrogen that is susceptible to leaching. Therefore, it is necessary to delay fall ammonia applications  after soil temperatures have fallen below at least 50 degrees, meaning a decrease in the activity of the bacteria. The more nitrogen that is maintained in an ammonical form, the less chances for losses between now and next planting season, since
Another reason to consider soil moisture conditions is the potential losses by applying anhydrous ammonia into hard and/or dry soil. This form of N has a high attraction to water, which is necessary to “hold” ammonia in the soil, and reduce losses immediately after injection. If there is a problem with loosing ammonia to the air, then growers may need to: 1) wait for better soil moisture conditions (wetter), 2) consider the use of covering disks on the ammonia applicator or 3) implement the use of an N-Serve, or urease inhibitor type additive in the anhydrous application. These additives can aid in minimizing anhydrous losses in warm and drier conditions..
Fall Soil Sampling and Fertility--REVIEW
This is a again a recurring discussion every fall.  Our point of view doesn’t change all that much—it adjusts with the year we just are completing to the year that is to come.  Fall is the time to sample soils and make fertilizer decisions as necessary to get fertility to the desired maintenance levels prior to next season.
A couple of redundant topics/developments from long-term no-tillers are:
Continued surface fertility applications can result in higher concentration of nutrients (stratification) in top 3 inches of soil, over time.  This higher concentration of nutrients may be a concern when receiving your soil analysis after sampling this fall.   Although it would be better for a more uniform distribution of fertility though out the profile, these concentrations near the soil surface has not caused any yield reduction.   
In no-till, the greatest concentration of root growth occurs near the soil surface, because the surface residue keeps the soil surface cooler and more moist near the surface.   This has not proven to be an issue in corn on corn or rotation practices and across many acres the yield and agronomic performance has improved.
Let’s review some of the basic utility and placement facts regarding fertility-(some of this may seem repetitive, but good for review.)
  • Nitrogen: There are many options for nitrogen application when no-tilling. Below is a list of some of their pros and cons.
  • Anhydrous ammonia (NH3) – Likely the most economical nitrogen source, apply mainly in the fall, but is also applied in a spring preplant or sidedress. Knife in at a depth of 6” using an applicator with coulters to cut through the residue an insure proper sealing after the soil temperature at 6” is below 50 degrees.. Avoid applying close to planting in the spring as it may cause seedling injury.
  • Liquid Nitrogen (UAN 28-32%) – Sometimes more expensive, can be
    broadcast alone, used as a herbicide carrier, or injected. Nitrogen from urea, a component of UAN solutions, can often be lost to ammonia volatilization if broadcast on a moist soil surface, especially under windy conditions.  Ammonia losses are generally greater on a soil surface with high residue cover.  Urease inhibitors can be used to prevent urea hydrolysis from occurring before the fertilizer moves into the soil matrix.
  • Ammonium Nitrate – More expensive and not always available. Ammonia loss potential following surface broadcast applications is reduced compared to urea or UAN solutions.
  • Phosphorous and Potassium: Phosphorous and potassium requirements are the same regardless of which tillage practice you employ.
  • P & K application rate should be based on soil test and realistic yield goals.
  • Generally it is best to broadcast apply P & K in the fall because the risk of compaction is less in the fall than in the spring.
  • Fall application allows rainfall and snow melt to move P & K into the soil
    surface rooting zone.
  • Micronutrients: Micronutrient availability does not appear to be significantly affected by the absence of tillage. Soil pH has the greatest impact on micronutrient availability so monitoring soil pH is important.
  • Starter Fertilizer: No-till corn will generally benefit from starter fertilizer
    more than conventionally tilled corn, especially if soil fertility levels are low to
    medium. Use starter fertilizer rates containing 30-40 lbs of N/acre.
  • In no-till, the soil stays cooler which reduces nutrient availability and root growth early in the season.
  • Early in the spring microbes will utilize available nitrogen from the soil to break down crop residue making it unavailable for seedling growth.
  • Starter fertilizer tends to offset the slow growth period corn seedlings often
    go through around the 3rd- and 4th-leaf stage.
  • The best results have been obtained with starter injected two inches
    away from the plant and 2 inches below the soil surface.  The thin knife/coulter assemblies are recommended.
See coming newsletters for our starter fertilizer trial results!
Soil pH—We spend a lot of time in row-crop production addressing this key component to our annual crop recipe.  You can have all the fertility in the world in your soil, BUT, if the soil pH is wrong, your fertility is un-available to the crop.
  • pH/Liming:  For corn and soybeans soil pH levels can range from 5.5 to 7.5.  Optimal levels are closer to 6.5 to 6.8 for corn and 6.0 to 6.5 for soybeans.1
  • Lime requirements should be based on buffering the top 2-3 inches of soil.
  • The amount of lime applied at one time should be reduced by 50-70% with no-till compared to conventional tillage.
  • Studies show that lime slowly works itself down into the soil in the absence of tillage at a rate of about 1 inch/year, thus more frequent  application of       smaller amounts of lime are recommended.
  • Apply the lime in the fall or on frozen ground to avoid compaction.  Since soybean response to lime is usually greater than that of corn it is advisable to lime ahead of soybeans if possible.
Other tips:
  1. Consider the 2-Ton Rule—If your soil test recommends 3.5 Ton of lime are needed on the soil, apply 2-Ton, wait 3 years, soil sample again and apply the remaining lime required.  REASON:  Certain soils are only able to so much lime at once---the remaining amount of lime is not lost, just less effective.
2) Apply only the recommended rate of nitrogen to corn the year after liming; soil requires about 4 lbs. of lime on acid soils to buffer each pound of nitrogen applied as NH3 or UAN
1Ferguson, R.B., De Groot, K.M. 2001 Nutrient Management for Agronomic Crops in Nebraska. University of Nebraska Cooperative Extension EC01-155-S University of Nebraska-Lincoln. Lincoln NE
WE like to pay attention to phosphorus in the fall!—Unlike Nitrogen, it is not mobile in the soil.--Like nitrogen, phosphorus is mobile inside the plant and as plants mature, much of the phosphorus moves into the seed or fruit.  Phosphorus is a key component of the molecules that provide ENERGY to plants and, thus, is important in photosynthesis and respiration.  Phosphorus is also a key component of the DNA and RNA nucleotides responsible for the genetic code and protein synthesis.  Phosphorus, as phospholipids, is also a key component of plant membranes and affects their permeability.  Large quantities of phosphorus are required in young cells and plants where the rate of metabolism is high and cell division is rapid.  Because of its importance in promoting seedling growth, phosphorus is a major component of many starter fertilizers.  Phosphorus has many effects on crops.  It encourages root development, early season growth and seedling vigor, tillering in small grains, improves resistance to drought and cold temperatures, hastens maturity and increases yield. Phosphorus deficient plants often have purplish areas on leaves, stems, and branches.  Phosphorus deficiency slows respiration more than photosynthesis resulting in a buildup of plant sugars.  High sugar levels encourage higher levels of anthocyanins which are purple pigments.  This symptomology can also be caused by cold temperatures, soil compaction, and crop varietal differences.  Phosphorus deficient plants can also appear darker green or "bluish" green and are generally stunted due to reduced cell division, but they later become pale and yellowish-green.  Fall is a great time to access needs and make phosphorus applications to start the process of making it plant available!
Replacing what you harvest is many times overlooked when setting up fertility plans for the next season.  A typical question of the recent weeks is: “If I harvest 200 bushel corn or 60 bushel soybeans and I fertilized for 150 bushel corn and 40 bushel soybeans—how much do I have left?”  Good question with a number of associated issues dealing with setting up fertility plans for next year.  Consider the following table.  We have used this reference for a number of year’s now—still a good STARTING point.
Nutrient Removal for Corn       Nutrient Removal for Soybeans  
Corn nutrient requirements       Soybean nutrient requirements    
(150 bushel acre grain yield-       (Soybean yield of 40 bushels/acre)  
9,000 pounds of stalk yield                
    Removed   Total       Removed   Total
    in Grain in Stalks Uptake     in Grain in Stalks Uptake
    Pounds Per Acre   Nutrient   Pounds Per Acre
  135 100 235   Nitrogen (N) 188 127 315
  64 36 100   Phosphorus (P2O5) 44 30 74
  42 144 186   Potassium (K2O) 66 576 142
    14 11 25   Sulfur (S)   5 15 20
    0.15 0.3 0.45   Zinc (Zn)   0.05 0.3 0.35
1.  Franzen, D. and J. Gerwing, 1997, Effectiveness of Using   *Most all of the nitrogen required is supplied
Low Rates of Plant Nutrients.  North Central Regional Publication through the soil and the atmosphere through
341. Univeristy of Nebraska, Lincoln, Lincoln NE.     symbiotic fixation.     
              **  Soybeans fixate approximately 1 lb of
2.  Voss R.D. 1993. Corn. In W.F. Bennett (ed). Nutrient   nitrogen into the soil for every  
Deficiencies and Toxicites inb Crop Plants. Am.     bushel of grain produced.  
Phytopathological Society, St. Paul MN.              
From this table we can get handle of how much is potentially left for a harvested grain standpoint.  You cannot actually tell how much is left without soil sampling for fertility levels of the respective nutrient.  The reason is this---Without soil sampling it is difficult to determine how much of the nutrients applied this spring to your crops were made plant available given this year’s conditions.  With excessive soil moisture levels, nutrients (nitrogen as example) may not have been made totally plant available during the growing season due to leaching. 
John W. McNamara
Wiles Bros. Inc.
606 Wiles Road
Plattsmouth NE. 68048
(402) 298-8550--Office
(402) 499-3870--Cell
(402) 298-7174--Fax
Copyright DTN. All rights reserved. Disclaimer.
Powered By DTN