Long-term changes in grassland soil phosphorus with fertilizer application and withdrawal

Citation

Cade-Menun, B.J., Doody, D.G., Liu, C.W., Watson, C.J. (2017). Long-term changes in grassland soil phosphorus with fertilizer application and withdrawal. Journal of Environmental Quality, [online] 46(3), 537-545. http://dx.doi.org/10.2134/jeq2016.09.0373

Plain language summary

Phosphorus (P) is an essential nutrient for plant growth. Long-term phosphorus (P) applications can increase soil P concentrations to concentrations that are much higher than required by plants. This excess P from can be lost from soils in runoff, and can cause water quality problems. Stopping fertilizer applications can help to solve this problem. However, once fertilization stops, it may take time for soil P concentrations to decline. While P fertilization adds orthophosphate, little is known about changes in other soil P forms during P build-up and drawdown. This study examined changes in P pools and forms in grazed grassland plots from Northern Ireland. Between 1994 and 1999 all plots received 8.3 kg P ha-1 yr−1 with variable rates of N (100-500 kg N ha-1 yr−1). From 2000 to 2005, plots received 0, 20, 40, or 80 kg P ha-1 yr−1 and N at 250 kg N ha−1 yr−1; from 2005 to 2010, no P fertilizer was applied to any plots. In 2005, soil P pool concentrations at the highest P fertilization rates were significantly elevated compared to 2000, but had decreased to 2000 concentrations by 2010. In soils receiving no P, soil P pool concentrations were significantly lower than 1994 only in 2010. There were few changes in P forms, except in the orthophosphate added from fertilizer. For these soils, fertilizer application and subsequent withdrawal influenced inorganic P more than organic P.

Abstract

Long-term phosphorus (P) applications can increase soil P concentrations in excess of agronomic optima, posing a risk to water quality. Once fertilization stops, however, it may take time for soil P concentrations to decline. Whereas P fertilization adds orthophosphate, little is known about changes in other soil P forms during P buildup and drawdown. This study examined changes in P pools (total P, Olsen P, Mehlich P, and waterextractable P) and P forms determined by 31P-nuclear magnetic resonance spectroscopy (P-NMR) in grazed grassland plots from Northern Ireland. Between 1994 and 1999, all plots received 8.3 kg P ha-1 yr-1 with variable rates of nitrogen (100-500 kg N ha-1 yr-1). From 2000 to 2005, plots received 0, 20, 40, or 80 kg P ha-1 yr-1 and 250 kg N ha-1 yr-1; from 2005 to 2010, no P fertilizer was applied to any plots. In 2005, soil P pool concentrations at the highest P fertilization rates were significantly elevated compared with those in 2000 but had decreased to 2000 concentrations by 2010. In soils receiving no P, soil P pool concentrations were significantly lower than those in 1994 only in 2010. There were few changes in P forms determined by P-NMR. Orthophosphate followed the same trend observed for the soil P pools; total organic P, total inositol phosphates, and total orthophosphate monoesters and diesters were highest in 2010 in the soil receiving no P fertilizer for 10 yr. For these soils, fertilizer application and cessation influenced inorganic P more than organic P.

Publication date

2017-01-01

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