Manure and Mineral Fertilizer Effects on Seasonal Dynamics of Bioactive Soil Phosphorus Fractions

Abstract

Seasonal fl uctuations in bioavailable soil P can infl uence soil test results and associated assessment of off -site transport risk. Our objective was to evaluate changes in soil P speciation and availability with time following applications of grain fed cattle (Bos taurus) manure or monoammonium phosphate (MAP). Beef cattle manure or MAP was applied at a targeted rate of 200 kg P ha -1 on a Pullman clay loam (fi ne, mixed, superactive, thermic Torrertic Paleustolls) in 2005 and 2006 and planted to grain sorghum [Sorghum bicolor (L.) Moench]. Soil samples (0-0.15 m) were collected before and throughout the growing season and analyzed for Mehlich-3 phosphorus (Me3P), 1:10 water-extractable phosphorus (WEP10), water extractable cations, pH, and fractions of bioactive soil phosphorus (TBIOP), which comprised 1:100 water extractable P, ethylenediamine-N,N,N`,N`-tetraacetate (EDTA)-exchangeable inorganic phosphorus (EEPi) and the EDTA-exchangeable phosphohydrolase-labile phosphorus (EPHP). Levels of soil Me3P, WEP10, and all fractions of TBIOP in MAP-amended plots fl uctuated signifi cantly (p < 0.05) during both seasons. Except for Me3P, manure amended plots also exhibited signifi cant (p < 0.05) seasonal variations in soil extractable P and a delayed release of P that extended well into the growing season. In contrast, fl uctuations in extractable soil P in unamended plots were not signifi cant except EPHP. In water extracts, a signifi cant (p < 0.05) dependence of solution P on pH and Ca suggested that precipitation-dissolution reactions contributed to observed seasonal fl uctuations in P. Fluctuations in total bioactive soil P were two to four times greater than aboveground biomass P highlighting the importance of accounting for seasonal dynamics in assessing off site P transport risks.

Spring Nitrogen Fertilization of Ryegrass–Bermudagrass for Phytoremediation of Phosphorus‐Enriched Soils

“…In those studies approximately 80 mg P kg soil −1 was removed in six repeated harvests of Marshall annual ryegrass and the STP level was reduced by 73 mg kg −1 ; whereas, five repeated harvests of common bermudagrass removed 64 mg P kg soil −1 and STP was reduced by 37 mg kg −1 . Most soil test P extractions do not extract significant organic P, but chiefly reflect the inorganic forms of P that may be bioavailable to growing plants (Schwartz et al, 2011). Thus, the organic P is converted over time to inorganic P forms measured cheifly by the soil test extractant.…”

“…Thus, the organic P is converted over time to inorganic P forms measured cheifly by the soil test extractant. Soil samples in the present study were obtained in September to minimize seasonal effects on soil test parameters (Schwartz et al, 2011). The overall percentage decrease in STP was somewhat greater at 9 Mg litter ha −1 (44%) than 18 Mg litter ha −1 (38%) (Table 6).…”

Seasonal Phosphorus Dynamics in a Volcanic Soil of Northern California

“…To isolate the behavior of fertilizer P, P extracted in control plots was subtracted from P extracted in treated plots to control for antecedent soil P cycling (Schwartz et al, 2011). This revealed a significant buildup of Fe/ Al-Pi from spring to fall in fertilized plots (Fig.…”

“…Fewer studies have investigated growing season changes in P fractions under field conditions. For example, He et al (1997) attributed seasonal variability in labile and Fe/Al-Pi fractions to variations in soil moisture independent of biological processes, while Schwartz et al (2011) attributed seasonal fluctuations in Pi to fluxes from microbial biomass. Nziguheba et al (1998) applied organic and inorganic sources of P and fractionated soils after 2 and 16 wk and found diverse P sources behaved differently with respect to P fractions.…”