Increase in Phosphorus Losses from Grassland in Response to Olsen‐P Accumulation

Abstract

The Olsen-P status of grazed grassland (Lolium perenne L.) swards in Northern Ireland was increased over a 5-yr period (March 2000 to February 2005) by applying different rates of P fertilizer (0, 10, 20, 40, or 80 kg P ha(-1) yr(-1)) to assess the relationship between soil P status and P losses in land drainage water and overland flow. Plots (0.2 ha) were hydrologically isolated and artificially drained to v-notch weirs, with flow proportional monitoring of drainage water and overland flow. Annually, the collectors for overland flow intercepted between 11 and 35% of the surplus rainfall. Single flow events accounted for up to 52% of the annual dissolved reactive phosphorus (DRP) load. The Olsen-P status of the soil influenced DRP and total phosphorus (TP) concentrations in land drainage water and overland flow. Annual TP loss was highly variable and ranged from 0.19 to 1.55 kg P ha(-1) yr(-1) for the plot receiving no P fertilizer and from 0.35 to 2.94 kg P ha(-1) yr(-1) for the plot receiving 80 kg P ha(-1) yr(-1). Despite the Olsen-P status in the soils ranging from 22 to 99 mg P kg(-1), after 5 yr of fertilizer P applications it was difficult to identify a clear Olsen-P concentration at which P losses increased. Any relationship was confounded by annual variability of hydrologic events and flows and by hydrologic differences between plots. Withholding P fertilizer for over 5 yr was not long enough to lower P losses or to have an adverse effect on herbage P concentrations.

Minimising nutrient transfers from poultry litter field heaps

“…Therefore, by inference, the existing method of field storage of broiler litter (T2) used in Northern Ireland does not increase P transfers from fields. The impact of higher soil P on increased P concentrations in runoff, which was clearly identified in the mixed ANOVA model, is in agreement with what is now a well recognized positive correlation between soil P and P loss in runoff from both arable and grassland soils, and reported in many studies (Vadas et al 2005;Watson et al 2007). …”

Organic and inorganic P reserves in rain-fed and irrigated calcareous soils under long-term organic and conventional agriculture

“…tested in calcareous soils (Leytem et al, 2005). In temperate soils, the labile-Pi (NaHCO 3 -Pi) status of the soil has been shown to directly influence both the total and the dissolved concentration of P in the land drainage waters and overland flow (Watson et al, 2007). In a recent study of calcareous soils receiving high amounts of manure, we observed that the amount of both organic and inorganic labile-P forms did not significantly differ from those found in soils receiving mineral fertilisers (Romanyà and Rovira, 2007).…”

Assessing the Long Term Impact of Phosphorus Fertilization on Phosphorus Loadings Using AnnAGNPS

“…This suggested that under sustained, long term high P fertilizer applications, there is a buildup in soil P level that results in significant higher P loadings at the watershed outlet. Field studies done by others also show that P application to agricultural soils exceeding P uptake by crops leads to P accumulation in soils in the long term, and this accumulation results in higher P loss to water [10,30,31]. Studies also show that it could take up to 10–50 years to see this build up depending on the soil properties, amount of P applied and cropping systems [30].…”