Wednesday, November 7, 2007
320-7

Efficiency of Fall and Spring Broadcast Fertilizer Phosphorus Application for Corn and Soybean in No-till.

Sebastian R. Barcos, Antonio P. Mallarino, and Jacob R. Prater. Agronomy, Iowa State University, Ames, IA 50011

Previous Iowa research during many years has shown no large or consistent grain yield differences among broadcast, shallow band, and deep band P placement methods for no-till corn and soybean, although banding often was better for early growth. Lower efficiency for broadcast P sometimes has been shown in other regions. One reason for lack of differences in Iowa might be that broadcast P always was applied in the fall (4-5 months before planting) with sufficient time to reach soil and shallow roots by the time it was needed. This study evaluated the efficiency of fall and spring broadcast fertilizer P application for these crops and tillage system by conducting 15 trials during 2005 and 2006 on fields testing 6 to 28 mg kg-1 Bray-P1 (15-cm depth). Triple superphosphate was broadcast at 0, 10, 20, 30, 40, and 50 kg P ha-1 in the fall (usually in November) and in spring (7 to 10 days prior to planting). We measured soil P stratification (0-7.5 and 7.5-15 cm) with three soil-test methods (Bray-P1, Olsen and Mehlich-3), residue cover, early growth and P uptake (V5-V6 stage), and grain yield. There were no consistent or large differences between fall and spring broadcast P fertilization in fields where corn or soybean responded to P. Perhaps Iowa soil properties and usually humid climate explain the lack of difference among P placement methods for these crops.

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