Wednesday, November 15, 2006
287-6

Effect of Choosing a Target Soil Phosphorus Level for Corn.

Charles Shapiro, Haskell Agricultural Laboratory, 57905 866 Rd., Concord, NE 68728-2828, United States of America and Richard Ferguson, University of Nebraska, Dept. of Agronomy & Horticulture, 377 Keim Hall (0724), Lincoln, NE 68583-0724.

An experiment was initiated in 2000 to establish Bray #1 P soil test levels of 15, 30 and 45 mg kg-1.  The site averaged 15 mg kg-1 before treatments were applied. Triple super phosphate (0-20 (actual P) -0) was applied at the rate of 22 kg ha-1 to increase the soil P levels one mg kg-1.  Initial applications increased soil P levels above the target levels and P was not applied for several years after the initial application on several experimental units. In addition to the three target levels there was a no N no P control, a no P control and P based on grain removal. The six year average of crop harvest, the no P with N treatment yielded 88 percent of the maximum yielding treatment. The target 15 Bray treatment yielded 94% of the maximum treatments. There was no difference in the 30 and 45 mg kg-1 treatments, which averaged 7.2 Mg ha-1 under rainfed conditions at Concord, NE.  The P removal treatment also yielded the same as the maximum treatments.  Soil test levels for the P applied at removal increased to 23.2 mg kg-1 at the end of the 2004 season and the no P applied treatments decreased to 13.3 mg kg-1.

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