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Fluid Journal : Fluid Journal 2002-2004
ents at specific points in the soil, and e) subsequently greater N use efficiency. Benefits of surface banding N for re- duced-till row crops (Table 2) have been verified by university research and grower experiences. The same fac- tors affect N use from surface banding in these high-residue systems and re- sult in better crop responses to N. Surface banding can result in reduced leaf burn, especially in spring wheat and summer crops. Depending on date of application, leaf burn can be a prob- lem but is usually more cosmetic than yield damaging. NPKS Surface banding of NP, NPK, NS, and NPKS combinations brings some real advantages to nutrient-use efficiency for grasses, wheat, alfalfa, cotton, corn, grain sorghum, and other crops. In ad- dition to the benefits to N use effi- ciency described earlier, P is the nutri- ent that probably benefits the most from the special conditions produced by surface banding. Phosphorus availability declines as soon as it is applied, particularly on high pH or very acidic soils where P fixation is a greater problem. Surface banding or banding of any type pro- duces higher concentrations of P in or on the soil, which tends to slow or off- set P fixation. But higher concentrations alone are not enough to maintain the highest lev- els of P availability. If surface bands of P remain on the soil without incorpora- tion, the possibility of positional un- availability may work against ad- equate plant uptake of applied P. Posi- tional unavailability is particularly af- fected by dry soils that limit root ab- sorption of applied nutrients. Fluid Fertilizer Foundation (FFF) sup- ported research has shown how pre- plant band applications of N and P im- prove P uptake and subsequently crop yields as long as ammonium-N concen- trations in those bands are high. High concentrations of ammonium-N in soil P retention zones slow P fixation reac- tions keeping the P in a form that plants can readily absorb. Purdue University research in the 1950s showed how am- monium-N affects the physiology of P movement into plant roots. Many positive things go on at once to affect P availability. High concentra- tions of banded P slow P fixation. High concentrations of banded ammonium-N slow fixation even more and extend P availability. Banded ammonium-N ex- erts a physiological influence on P up- take. High concentrations of urea from UAN tend to slow hydrolysis of polyphosphates in 10-34-0 and high urea and ammonium concentrations slow nitrification. Addition of ammonium thiosulfate to the mixture has been shown to slow urea hydrolysis, slow nitrification, de- crease ammonia losses, and extend the presence of ammonium-N, which subse- quently extends P availability in the P retention zone. University and provincial agency re- search has shown that surface banding starters containing at least a 1:1 N:P2O5 ratio has performed just about as well for corn and wheat as conventional banding to the side and below the seed. We have always assumed that P does not move vertically. Starter response was not due to just N, was not very good when only 10-34-0 was used, and occurred on soils when soil test P levels were high. Why? USDA researchers at the National Soils Tilth Lab in Ames, Iowa, have shown us why these surface bands are effective sources of starter nutrients. Plotting the distribution of P beneath these bands, they have shown that P movement to depths of around 4 inches is possible in silt loam soils in the pres- ence of high ammonium concentrations (Figure 1). Water is likely a necessary component of such movement. This helps us understand better why surface banding P does work and pro- vides corn and sorghum producers with more flexibility in starter placement and gives growers the opportunity to use large planters that are not equipped for usual starter placement. Figure 1. Profile distribution of bio-available P 68 days after dribbling 15-30-10 (left) and 60-30-10 (right) two inches to side of corn row. 2 Fluid Journal Fall 2003
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