Organic Phosphorus Composition and Potential Bioavailability in Semi-Arid Arable Soils of the Western United States

Abstract

The organic P composition of semi-arid arable soils is largely unknown, but such information is fundamental to understanding P dynamics in irrigated agriculture. We used solution "P nuclear magnetic resonance (NMR) spectroscopy and phosphatase hydrolysis to characterize organic P in semi-arid arable soils from the western USA (organic C 2.0-30.7 g C kg' soil, clay 2-48%, pH 5.2-8.2, CaCO 3 <1-480 g kg -' soil). Total P concentrations ranged from 220 to 1210 mg P kg-' soil, of which between 12 and 45% was extracted with NaOH-EDTA. Inorganic orthophosphate was the dominant P compound, but concentrations determined by solution "P NMR spectroscopy were consistently greater than those determined by molybdate colorimetry. Concentrations of organic P were relatively small, and were dominated by orthophosphate monoesters (11-130 mg P kg-' soil), with smaller concentrations of orthophosphate diesters (0-7 mg P kg-1 soil). Pyrophosphate was present in almost all soils at concentrations up to 14 mg P kg -' soil. Bicarbonate-extractable organic P ranged from 1.7 to 22.8 mg P kg -' soil, of which between 37 and 87% was hydrolyzed by phosphatase enzymes, suggesting its bioavailability. Soil organic P concentrations were positively correlated with mean annual precipitation, organic C, clay, and oxalate-extractable metals (Al, Fe, Mn), and negatively correlated with mean annual temperature and soil pH. However, CaCO3 concentrations were not significantly correlated with any soil property. These results indicate that equilibrium levels of organic P in semi-arid arable soils are controlled by a balance between the physical protection offered by the soil matrix and the suitability of the environment for biological productivity.

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…The hypothesis that non-biomass organic phosphorus dominates in bicarbonate extracts is supported by the speciation of phosphorus in such extracts, which is dominated by phosphate monoesters and is, therefore, similar to the whole-soil organic phosphorus extracted in strong alkaline solution [63,64].…”

The composition of organic phosphorus in soils of the Snowy Mountains region of south-eastern Australia

“…However, surprisingly few researchers have examined the role of climate on soil organic P. Turner et al (2003a) suggested that climate was a key driver of the low SOM concentrations reported for a series of semiarid arable cropping soils. The authors found that decreasing organic P concentrations correlated with increasing temperatures, whereas soil organic P increased with increasing precipitation.…”

Organic matter and pH affect the analysis efficiency of 31 P-NMR

“…The same results were also discovered in soil samples, but not in sediments at the regional scale (McDoell and Stewart, 2006;Dou et al, 2009). Turner et al (2003a) suggested that higher adsorptive surface area and lower microbial activity are beneficial for the existence of Po. On the contrary, alkaline soil, which is mainly characterized by CaCO 3 , has a lower ability for holding organic carbon and Po, so the NaOH-EDTA had a weak ER in extracting Po from calcicolous soil (Turner et al, 2003a).…”

“…Turner et al (2003a) suggested that higher adsorptive surface area and lower microbial activity are beneficial for the existence of Po. On the contrary, alkaline soil, which is mainly characterized by CaCO 3 , has a lower ability for holding organic carbon and Po, so the NaOH-EDTA had a weak ER in extracting Po from calcicolous soil (Turner et al, 2003a). In this study, the reason that ER and pH show a positive relationship is that acidic sediment, which has a higher ability to hold organic matter than alkaline sediment, was distributed in southern China.…”