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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Timing of Broadcast Phosphorus Fertilization for No-Till Corn and Soybean

^a Department of Agronomy, Iowa State University, Ames, IA 50011
^b Former graduate student, Department of Agronomy, Iowa State University, Ames, IA 50011
^c currently at MVC Management Services, 508 Market Street, Audubon, IA 50025

^* Corresponding author (apmallar{at}iastate.edu).

Iowa research has shown a small and inconsistent grain yield response to P fertilizer placement methods for no-till corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. One reason for this result might be that P was broadcast in the fall (before snow and 4–5 mo before planting crops) with sufficient time to reach soil and active roots. We evaluated fall and spring broadcast P application for no-till corn and soybean by conducting 20 single-year trials during 3 yr in Iowa soils with 6 to 29 mg P 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 (November or December) or in spring before planting crops. We measured early plant growth (dry weight, DW), early plant P concentration and uptake (V5–V6 growth stage), and grain yield. Crop responses to P (P < 0.1) were observed at five corn sites and seven soybean sites for yield, three corn sites and three soybean sites for early DW, and six corn sites and five soybean sites for early P uptake. Yield responses occurred in soils with 21 mg P kg^–1. The timing of P application did not affect yield or early DW, and there were inconsistent differences for early P uptake at two sites. We concluded that the time of application did not affect the efficacy of P broadcast for no-till crops in this study, but results should not be directly extrapolated to regions with different soils and climate.

Abbreviations: DW, dry weight • STP, soil-test phosphorus