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Oklahoma State University Stillwater, OK |
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Oklahoma Alfalfa |
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Oklahoma State University Stillwater, OK |
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Oklahoma Alfalfa |
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COMPARISON OF PHOSPHATE
FERTILIZER MATERIALS |
| Yield and Profitability. Once the decision has
been made to apply phosphate fertilizer, the next step is to decide which fertilizer to
use. Total alfalfa yield and profitability for the three common phosphate fertilizers
(Triple super phosphate-TSP, Diammonium phosphate-DAP, and Ammonium polyphosphate-APP)
applied at rates to provide 200 lb. P2O5/acre, is shown in Figure 1.
There were very little differences in two-year total yields among the different
fertilizers. The "APP knifed" treatment was knifed in, six inches deep, on 20
inch centers.
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| The return from these fertilizers, shown in figure 2,
was calculated based on July, 1995 prices (cost/lb P2O5 = $0.25 for
TSP; $0.27 for DAP; $0.37 for APP, FOB Enid, OK), and do not include application costs.
Because of the higher cost, there is about a $50/acre lower return from fertilizing with
the liquid APP when all materials are broadcast and incorporated preplant. When APP is
knifed in, the apparent slight yield benefit from banding offsets the higher cost of the
material.
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| Early Weed Growth Since 0-46-0 is not
commonly available, many producers must use 18-46-0 as their source of P2O5.
There has always been some concern that the nitrogen in DAP would promote weeds if high
rates were used. In this study the percentage of weeds was measured in the first cutting.
Results are reported in Figure 3. At the 100 lb rate there is an unexplainable large
percentage of weeds when APP was used, but not when DAP was used. The APP added only 29 lb
of nitrogen compared to 39 for DAP when both are used to add 100 lb P2O5.
At the 200 lb P2O5 rate (double the nitrogen at the 100 lb rate),
use of the ammonium phosphates caused a large increase in percentage of weeds in both
cases. For fields that have a potential weed problem, use of 0-46-0 instead of 18-46-0 can
help reduce the weed problems when high rates of phosphate are needed preplant.
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| Gordon V. Johnson, Nutrient Management Specialist Department of Plant and Soil Sciences Oklahoma State University |
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