Degree Type

Dissertation

Date of Award

2021

Degree Name

Doctor of Philosophy

Department

Agronomy

Major

Soil Science ( Soil Fertility) and Sustainable Agriculture

First Advisor

Antonio P Mallarino

Abstract

Management decisions concerning phosphorus (P) fertilization affect the profitability of crop production and potential water quality impairment. Soil testing for P provides a useful diagnostic framework to assess P bioavailability that informs management decisions to optimize P use in nutrient management and mitigate environmental impairment. Management factors such as tillage and P fertilization strategy can influence crop yield and the potential for soil and P losses with surface runoff. Investigation into which forms of soil and P losses that do occur from corn-soybean rotations in Iowa systems can inform which methodologies best quantify forms of P that will pose greater effects on water quality and which management decisions minimize losses while maintaining agronomic productivity. This research field calibrated a recently widely-adopted soil P test that uses weak organic acids with corn and soybean yield to identify critical soil-test P concentrations. The weak organic acids test extracted less soil P and performed more poorly than currently routine tests at relating soil-test P to crop yield. A second study was conducted to quantify the effect of P fertilization strategy and tillage on soil and P losses with runoff in a corn-soybean rotation in Northwest Iowa. Corn yield and soil loss were the highest with tillage, the combination of tillage and broadcast P resulted in the highest runoff TP loss, and the dissolved-reactive fraction of the total P loss was much higher with no-till. The combination of chisel-plow/disking and annual subsurface band placement of P fertilizer led to the lowest losses of dissolved-reactive P and total P, while optimizing crop yields. A third study compared multiple methods for measuring soluble P in runoff, and how management factors in Iowa cropping systems affect their performance. The results suggest that assuming only soluble, orthophosphate-P determined by colorimetric method may underestimate soluble P concentration in runoff and losses from crop fields and will be influenced by tillage and P fertilization source in corn-soybean rotations similar to Iowa soils.

DOI

https://doi.org/10.31274/etd-20210609-80

Copyright Owner

John David Jones

Language

en

File Format

application/pdf

File Size

135 pages

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