Date of Award
Doctor of Philosophy
Soil Science ( Soil Fertility) and Sustainable Agriculture
Antonio P Mallarino
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.
John David Jones
Jones, John David, "Managing and quantifying phosphorus in Iowa cropping systems for optimum agronomic and water quality benefits" (2021). Graduate Theses and Dissertations. 18519.