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more than 90 percent of the dozens of trials we have conducted. Utilizing this technology allows for reduced application rates due to increased efficiency (higher percentage of the phosphorus is taken up by plants) without reducing yields. In fact, in many cases yields have been higher with Carbond P. Trial results Yield and/or crop quality increases have been shown in a variety of crops, especially when soil test phosphorus concentrations are relatively low. A trial performed on sugarbeet with a soil-test concentration of 13 ppm bicarbonate extractable phosphorus on a pH 8.0 soil with 5.2 percent lime resulted in a somewhat typical response of what we have observed with Carbond P in various crops. The ammonium polyphosphate (10-34-0) resulted in an expected increase in yield over the control with a somewhat linear response as the rate increased from 50 to 100 pounds P2O5 per acre (see Figure 1). However, the Carbond P (7-24-0) achieved maximum yield at a much lower rate. Tests with a wide variety of crops have shown that Carbond P works best at lower rates. We comfortably recommend a reduction of 30 percent and suspect that the efficiency may be as high as 50 percent, although further work is needed to confirm this hypothesis. Figure 1. Yield increases for a sugarbeet field trial near Blackfoot, Idaho, in 2011. Ammonium polyphosphate (10-34-0) or Carbond P (7-24-0) fertilizer was applied at 50, 75, or 100 lbs P2O5 per acre in flat fan spray over about 12 inches of row prior to planting. Recommendations I recommend determination of the normal rate of phosphorus that should be applied based on research-based fertilizer trials and then a reduction of 30 percent (up to 50 percent) of phosphorus applied when using Carbond P. We have also performed several trials using Carbond P as a foliar application, which is also effective. However, foliar application should not take the place of soil applied phosphorus, but should be viewed as supplement when needed. Uptake efficiency and yield response have been greater when the phosphorus is soil-applied. In addition, our trials show that the phosphorus needs of sugarbeet plants are most important early in the season when the taproot has strong downward growth and little lateral growth—thus it is not exploring the phosphorus rich topsoil and, instead, is exploring the phosphorus depleted subsoil. Phosphorus deficiency at this time of year results fewer and less thick cambial rings. Yield potential is reparably lost when this happens and can even occur on soils with high residual phosphorus levels. Study results shown here were applied in a wide band over the seed row, which is effective The sugarbeet research trial evaluating phosphorus nutrition is shown. when soil test phosphorus is low. In soils with higher soil test phosphorus (common following potato crops), I normally recommend an application of a low rate (3-5 gallons per acre) of banded phosphorus directly below (3-6 inches) or on the seed (with caution to avoid salt damage). Alternatively, a low rate foliar application directed over the top of the plants at early stage (4-6 leaf) can be equally effective. I do not recommend applying late-season applications of phosphorus as they often cause reductions in sugar percentages. Once the plant begins exploring the top soil extensively (after 8-12 weeks), it is very efficient at scavenging for nutrients and excesses can be detrimental. n Editor's note: Hopkins is a certified professional soil scientist at Brigham Young University in Provo, Utah.   www.SugarProducer.com  29

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