414-15 Runoff Dissolved and Particulate Phosphorus As Affected By Tillage and Fertilizer Placement Methods in Corn-Soybean Rotations.

Poster Number 425

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Nutrients and Environmental Quality

Wednesday, November 18, 2015
Minneapolis Convention Center, Exhibit Hall BC

Mazhar U. Haq, Agronomy, Iowa State University, Ames, IA, Antonio P. Mallarino, 716 Farm House Lane, Iowa State University, Ames, IA and Matthew J Helmers, Ag & Biosystems Engineering, Iowa State University, Ames, IA
Abstract:
Application of excessively high P rates, inappropriate methods of application, and tillage can increase P with surface runoff. A 2-year study was conducted under natural rainfall to evaluate runoff P loss in corn-soybean rotations. Previous management for the site had resulted in 24 plots (30 by 6 m) with approximately optimum soil P (24 mg Bray-1 P kg-1), 12 with chisel-plow-disk (CH) and 12 with no-till (NT) histories, and three plots with above-optimum P (38 mg kg-1) and CH histories. Management systems implemented for plots testing optimum were the combinations of CH, NT, and P fertilization broadcast (BrP) or subsurface banded with the planter (BP) with each crop planted each year. The P rates were designed to maintain soil P, and were 50 kg P ha-1 BrP applied only before corn or 25 kg P ha-1 BP applied to each crop each year. The other three plots assessed remediation of the high-testing soil by NT, a rye cover crop for both crops, and no P application. All systems were replicated three times. Runoff measurements were volume, dissolved reactive P (DRP), bioavailable P (Fe-oxide coated filter paper method), total P (TP), and total solids. Corn yield was lowest with NT but tillage did not affect soybean yield. The P placement method did not affect yield of any crop. On average for the rotation, soil loss was highest for CH and lowest for NT (5.7 and 0.89 Mg ha-1). In plots receiving P, the annual mean total P loss was highest for BrP-CH (5.3 kg P ha-1) and lowest for BP-CH, BrP-NT, and BP-NT (2.2 to 2.5 kg P ha-1); whereas the annual DRP loss was highest for BrP-CH, BrP-NT, and BP-NT (0.84 to 1.1 kg P ha-1) and lowest for BP-CH (0.25 kg P ha-1). The high-testing soil managed with a cover crop, NT, and without P had the lowest DRP and TP loss (0.18 and 1.1 kg P ha-1). We conclude that when P is applied, various management options greatly reduced TP loss compared to CH with BrP but only CH with BP clearly reduced DRP loss compared with the other management systems. Discontinuing P application to the high-testing soil and implementing NT with a cover crop resulted in the smallest observed DRP and TP losses.

See more from this Division: ASA Section: Environmental Quality
See more from this Session: Nutrients and Environmental Quality

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