Phosphorus in pasture plants: potential implications for phosphorus loss in surface runoff

Abstract

Phosphorus (P) loss from land can impair surface water quality. Losses can occur from soil and plant components. While it is known that P losses increase with soil P concentration, it is not known how losses from pasture plants vary with soil P concentration or between different forages. We examined total P and filterable reactive P (FRP) in water extracts of plant shoots, used as a measure of potential P loss to surface runoff, in different forage species relative to soil P concentration in field trials and a glasshouse experiment. The mean total P concentration of 16 forage species in grazed field plots was greater (P<0.01; LSD 05 =117 mg kg −1 ) in legumes (3,480 mg kg −1 ) than for grasses (3,210 mg kg −1 ). Total plant P concentrations of grasses and legumes increased with soil Mehlich-3 P concentrations in both glasshouse and field trials with concentrations close to 6,000 mg kg −1 in arrowleaf clover at 680 mg kg −1 Mehlich-3 soil P. FRP in water extracts of plant shoots increased relative to plant total P as soil Mehlich-3 P increased, with the greatest concentrations shown by crimson clover and arrowleaf clover. Analysis of water extracts of ryegrass and clover herbage from a field trial showed that while FRP was increasing, phytase-available-P decreased significantly from about 70% of filterable unreactive P at the lowest Mehlich-3 P concentrations, to close to zero at 200 mg kg −1 Mehlich-3 P. The wide variation, and enrichment of FRP in water extracts and total P with increasing Mehlich-3 P among species, indicates that cultivar and site selection and sward management provide a potential option to mitigate P loss to surface waters.

Genomic Predictive Ability for Foliar Nutritive Traits in Perennial Ryegrass

“…This indicates that selective breeding for levels of micro-and macro-minerals is feasible and that genomic selection represents a strong option for pursuing improvement in these traits. In general, ryegrass cultivars that grow well under low soil P will compete less for P in the sward, increasing P availability for uptake to support legume growth (Easton et al 1997;McDowell et al 2011). For instance, Crush et al (2006), reported that in a mixed sward of ryegrass and clover (18% clover content), net annual flux of P into ryegrass was 4.7 times higher compared to clover.…”

Linking Soil Erosion to Instream Dissolved Phosphorus Cycling and Periphyton Growth

“…Following this the loam soil with native M3P concentration 20 mg/kg (labeled M3P20 hereafter) was spiked with different concentrations of superphosphate (9 g/kg total phosphorus (TP)) fertilizer. Fertilizer was added to increase M3P concentrations to 23, 30, 44, 62, 97, 187, 428, and 679 mg/kg (after McDowell et al ., ). It was then incubated for 168 days with periodic soil wetting to maintain an approximate soil moisture content of 30% by weight approximately equivalent to saturated field moisture.…”

Pronounced surface stratification of soil phosphorus, potassium and sulfur under pastures upstream of a eutrophic wetland and estuarine system

“…Selection of more P-efficient pasture cultivars is one possible change. Species and cultivars may differ greatly in shoot P concentrations at a given level of extractable soil P, and in external critical P requirements, with grasses generally presenting lower shoot P concentrations and a lower external critical P requirement than legumes (Ozanne et al 1969;McDowell et al 2011;Sandral et al 2015;Haling et al 2016). Thus, decreasing the rate of P-fertiliser addition to pastures to match the P requirements of grasses only, or of annual legumes with lower P requirements than the current widely-used species T. subterraneum, would reduce the size of the pool of readily-soluble P circulating through plants and top soil layers and thus reduce the risk of losses.…”