Effingham, IL | Ron..NE ILL..10/48 - 7/28/2006 05:37
GTD Thanks for thorough explanation. Seems to be based on a lot of theory. Can you link me to plot work by U of MN or Mr Rehm? I'm not sure where facts/figures came from on 20-40% of b-cast spread was available to crop on 1st yr. But-I'll ask....why? Why only 20 (very little) to 40% (double the minimum)?
I believe it was Nyle Brady in his book, The Nature and Property of Soils, who established the 20-40% availability numbers. I do not have my copy of the book in front of me but I'm relatively sure that's where they come from.
The range (20-40%) is dependent upon the nutrient being applied and the chemical makeup of the soil. Environmental conditions as well as the root mass of the crop being grown can also have an impact on availability.
Plants take up nutrients 3 ways, by root interception, diffusion, and mass flow. Root interception is the method in which the plant takes up the least amount of nutrient. So it bears to keep in mind that crops such as corn which have a large fibrous root system only contact <5% of the total soil rooting volume with their extensive root systems. So when you brodcast apply fertilizer in that rooting volume, those roots come into contact with very little of the fertilizer of which you applied. Also, we know that P2O5 and K2O are held or "bound" very tightly to the soil, so diffusion (the movement of nutrients from an area of high concentration to an area of low concentration) extends the area of uptake only slightly beyond the root itself. Diffusion is the means by which the plant receives the majority of it's (immobile) nutrients, but this also means that the majority of a broadcast nutrient simply isn't available to the plant because the roots are not in close enough proximity to the fertilizer which is held within the soil. It's also worthy to note that a very small amount of the immobile nutrients such as P2O5 and K2O move with the soil solution (mass flow), so the contribution via this means of transport is minimal.
Does moisture availability & incorporation have anything to do with availability? Or-is it just a chemical change that must be undertaken to make it available?
It does to a certain extent. We do know that moisture, mechanical tillage, freezing and thawing, and shrinking and swelling of the soil particle can loosen the "bond" between the nutrient and the soil particle (bear in mind that this is an extremely simplified explanation of the method in which a cation (K2O) and an anion (P2O5) are bound by the soil), thus resulting in more nutrient available to the plant.
Why is banded fertilizer 50-60% available (your statement)? Where/how did they establish these percentages?
By banding fertilizer you are basically overloading the soils ability to "tie up" these nutrients. By concentrating a large amount of nutrients within a very small volume of soil, the soil does not have the ability to adsorb these nutrients, which leaves more of what you applied available to the plant. We know some of it is going to be adsorbed, but not nearly as much as what would be when broadcast.
I do not know who established the 50-60% range. From talking to various soil scientists I do know that these figures are generally accepted throughout the ag community though.
I believe you're saying any crop removes a specific amount of nutrients regardless of tillage/fertilizer method. I believe other strip till/banding advocates that posted here seem to disagree with that fact, saying band-supplied crops have a lower removal rate.
Yes, a plant removes approximately the same amount of nutrient regardless of the method of application. I've had many a conversation with several soil scientists in regards to this very same subject. Most are in agreement on this principle.
As I indicated in my previous post, I do think Dr. Rehm's research has caused a tremendous amount of misunderstanding as to the practice of reducing rates. As I have shown, his research does state that you can do so, but it's only recommended within a very short range of conditions. Most people do not realize these limitations and in some cases, a few people have downright misrepresented his findings.
Statements in posts below & links provided seem to say that banding w/1/2 rate works on lo-testing soils. So-on medium to hi-test soils could one assume for strip banding not using any fertilizer? I'd assume not. If you didn't use any replacement fertilizer, would you expect test values to hold or diminish...assuming average to above average crop removal (all rotation crops).
I would not eliminate the fertilizer in a medium or high testing situation for two reasons. First of all, over time you will pull your test values down which will result in a yield decrease. Second, environmental factors play an important part in nutrient availability. Even in a high testing soil, the soil goes through cycles in which it at times releases more nutrients than it does at other times. This is especially so during dry soil conditions. Even though the soil tests high, it does not mean that those nutrients are available throughout the growing season. If these periods of minimal soil release coincide with ear formation, pollination, or seed fill, you could potentially see a slight yield decrease. Again, by banding your fertilizer, it can help to overcome these conditions.
Soil test levels will diminish over time when not using any fertilizer at all. How quickly it will diminish is not easily predicted. I'm sure you've heard of or seen a person who was on a low rate Nachurs program and this persons yields were decent over an amazingly long period of time and then all of a sudden the bottom dropped out of his yields. This is a very common event. I've seen people who have been on these programs get by doing this 10-12 years and then boom, yields drop dramatically. What they have done is simply mined their reserves. What's interesting is the fact that the grower could not see any appreciable yield drop from one year to the next over that time period. They only noticed it when the bottom dropped out.
Are your tests showing no reduction in test values? I still wonder if rates aren't being reduced in banding to accomodate bin capacities in dry applicators (or liquid) during strip tilling.
You could be correct. I think many have fooled themselves into believing they can get by with less. One thing I always remind myself to heed Newton's Third Law of Motion which states; " For every action there is an equal and opposite reaction". This most certainly applies to almost everything we do.
[Edited for Spelling]
Edited by GTD 7/28/2006 17:51
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Reduced Rates of Fertilizer - In reference to Ron's posts
