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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Winter 1994 be effective during plant growth. In no-till there is not enough tillage. Reduced tillage will give an intermediate amount of mixing. The benefit of banding may depend on the soil and vary from the same benefit to little benefit. It all depends on root growth stimulation in the band and the amount of roots contacting the phosphorus in the band or strip, as I often have called it. FJ: What practical difference is there between surface and subsurface banding of P and K? How can growers take advantage of each method? Well, I'd assume it's a matter of what type of tillage they're using and type of crop. I would expect we're talking about corn or soybeans here. There is a difference between P and K, because P stimulates root growth in the fertilized zone while K does not. With surface banding you are usually relying on tillage to mix P and K with some of the soil. With subsurface banding into an untilled soil layer there may be little mixing and not the chance for fertilizing as many roots. In subsurface applications down to 18 inches I've not had much success in increasing yield. However, there are soils where this does work and you should contact your local specialist. So the practical differences are determined by the individual situation. The grower has to account for his own particular operation and make the right choice. FJ: Would you expand a bit on the amount of soil needing fertilization to promote best nutrient uptake. You mentioned earlier about the band occupying five percent of soil volume. Let's put that between five and twenty percent of soil volume. You want to maximize the proportion of roots growing in the fertilized volume because plant roots have a maximum absorption rate. Increasing uptake comes by getting more roots in the fertilized volume. This has a greater effect than increasing the P or K level in a small soil volume and smaller number of roots. They're already absorbing nutrients at a maximum rate. So, fertilizing a greater volume of soil is a definite advantage to growers. They will be fertilizing a greater volume of roots. A good rule of thumb is there must be phosphorus uptake by half of the root system in order to maximize yields. FJ: When one goes to no-till, it's difficult to say I want to fertilize five percent of the soil---or twenty percent which would be the objective. That's where the problem lies, doesn't it? That's where the problem lies. What I'm saying is that when you're surface broadcasting in no-till you're fertilizing a pretty small volume of soil, because you're not mixing it with depth. However, you may be fertilizing five percent of the topsoil. Having all the topsoil well fertilized is the optimum situation and there will be little advantage in banding. Fertilizing a smaller soil volume is done to use fertilizer more efficiently. FJ: Then it's a question of patience if you want to build to levels in the five to twenty percent range. It might take the grower switching to no-till a while to get there. We 're talking a number of years. Yes. You have to build gradually. That can span some years. Of course, don't forget, a lot of these fields that formerly had been tilled and plowed already may have been well fertilized. They could have fairly good fertility levels down into the plow layer. FJ: But after a few years they're going to exhaust a lot of these nutrients. That's right. It will vary by nutrient, since N and K will be depleted most rapidly. FJ: So we're talking about a long-term program. Yes. By banding it down in the soil in a long-term program you'll see a gradual buildup. The important thing is to fertilize a sufficient layer of soil so that it can supply the plant by stimulating enough plant root growth in the fertilized volume. FJ: How would you manage N under no-till? I personally haven't conducted research in this area, but there are plenty of studies showing that efficiency improves in no-till when the N is placed under the residue, not on the surface where it can volatilize. FJ: Let's say a grower is considering a switch to no-till or reduced tillage. He has been injecting ammonia and surface broadcasting P and K. What advice would you give him? He may have built up a good level of P and K in the soil where he has been broadcasting and tilling the soil. Using no-till, broadcast P and K will remain near the surface but residue accumulation frequently maintains soil moisture there and a favorable place for root growth and nutrient uptake. If you band fertilizer on the surface, the higher concentration will cause nutrients to move a little deeper into the soil. Where reduced tillage is used after broadcasting fertilizer, it will be mixed deeper into the soil than with no-till, and banding could be an advantage. I would say it's a question of how much of an advantage you're going to have by placing some of the P and K four or five inches into the soil. In many cases, it
Fluid Journal 1996-1998