Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/7/2005
Publication Date: 11/7/2005
Citation: Erich, M.S., Griffin, T.S., Porter, G.A., Mallory, E.B. 2005. The effect of phosphorus loading on degree of phosphorus saturation and phosphorus fractions in soils from a long term cropping systems study. American Society of Agronomy Abstracts. ON CD Interpretive Summary:
Technical Abstract: The Maine Potato Ecosystem study was initiated in 1991 in Presque Isle, Maine to examine the effects of different pest and soil management systems on the productivity, pest dynamics, soil characteristics, and economic viability of potato production. Although the specific rotations in the study changed in 1999, the study has maintained a comparison between two contrasting soil treatments: Amended, which receives manure, compost, and supplemental fertilizer versus Unamended, which receives only fertilizer. By 2004 Amended plots had received approximately 900-1100 kg total P per ha (different rotations received somewhat different levels of inputs), while Unamended plots had received approximately 350-440 kg total P per ha. Amended plots had also received greater than 44,000 kg total C per ha from the compost and animal manure. We determined degree of phosphorus saturation (DPS, the molar ratio of extractable P to extractable Al and Fe), soluble P, and soil test P (both Mehlich and modified Morgan) for a set of archived soil samples from this study. Fourteen years of amendments have significantly increased %C and total P levels in the soils. In addition, soluble P and DPS are significantly higher in Amended soils. Currently, DPS of about 0.32, and soluble P of about 1.5 mg per L, represent the breakpoint, with Amended soils usually above these values and Unamended soils usually below. Basing manure application on N supply, as in this study, typically results in additions of P significantly exceeding crop needs. The excess P builds up in soils increasing their potential to contribute soluble and particulate P to surface waters.