Abstract Using geographic information system techniques, hydrology of soil types (HOST) classes were combined with slope, rockiness, flood hazard and soil moisture deficit classes within a risk matrix to produce a slurry acceptance map for Northern Ireland (NI) on a 50 m grid. Moreover, due to the whole territory of NI being designated as a nitrate vulnerable zone, a nitrates action programme is to be implemented across the region in the near future and this is likely to restrict slurry applications to the growing season. To assess the risk classes associated with slurry applications during the growing season, an additional slurry acceptance map for NI was created in which the HOST factor was excluded from the analysis. The maps created showed that, for the period January–December, the majority (80%) of agricultural soils in NI were in the severe risk category following application of 50 m 3 ha −1 of slurry. However, this proportion was reduced to only 29% when the same volume of slurry was applied during the growing season, when the soils were not saturated and significant rainfall was not received in the period immediately after slurry application.
Abstract. Leaching of phosphorus (P) from agricultural land is the major cause of eutrophication of surface waters in Northern Ireland. However, soil testing using the Olsen method has shown that while soil P in some catchment areas of the Province is low, surface waters within these catchments are, nonetheless, every bit as eutrophic as other local catchments where soil P is high. Soil P measurements on over 6000 samples from Northern Ireland soils (A horizon only) have indicated that Olsen‐P values of improved grassland on most parent materials are linearly related to animal intensification. Exceptions are soils derived from peat, marl and basalt. For each of the latter soils, the measured Olsen‐P was shown to be around 10 mg L –1 lower than expected for farms with similar intensification on other parent materials. In particular, the mean Olsen‐P values of samples from basaltic soils under grass with total Fe above 62 g kg –1 and total Mg above 16 g kg –1 were significantly lower than those from basaltic soils with low total Fe (<37 g kg –1 ) and total Mg (<8 g kg –1 ). As a result of the depressed Olsen‐P value, excessive quantities of P may be applied to these soils to maintain a recommended soil P index thereby enhancing the potential for nutrient enrichment of adjacent surface waters. In such cases, coworkers have shown that acid ammonium oxalate may be a better extractant than bicarbonate as an indicator of plant‐available P.
Abstract The critical load approach has been proposed for evaluation of the need to reduce atmospheric emissions of metals that lead to transboundary transport and deposition across Europe. The present study demonstrates and evaluates the application of a critical load approach for national‐scale risk assessment of metal deposition in the United Kingdom. Critical load maps, calculated using critical limits based on pH‐dependent free metal ion activities, are presented. Current concentrations of lead and cadmium in soils are compared with two sets of critical limit values: First, limits based on the reactive soil concentration, and second, a pH‐dependent free ion critical limit function, which takes into account variable soil characteristics across the country. The use of these two models leads to different conclusions about which areas of the United Kingdom are at greatest risk, partly because of differences in the range of values of pH and organic matter in soils used in ecotoxicological experiments and in the national database. Critical loads were calculated based on free ion critical limits; the critical loads were lowest in the south and east of the country and were associated with higher soil pH, lower runoff, and lower soil organic matter.
Abstract Nitrogen balances and total N and C accumulation in soil were studied in reseeded grazed grassland swards receiving different fertilizer N inputs (100–500 kg N ha −1 year −1 ) from March 1989 to February 1999, at an experimental site in Northern Ireland. Soil N and C accumulated linearly at rates of 102–152 kg N ha −1 year −1 and 1125–1454 kg C ha −1 year −1 , respectively, in the top 15 cm soil during the 10 year period. Fertilizer N had a highly significant effect on the rate of N and C accumulation. In the sward receiving 500 kg fertilizer N ha −1 year −1 the input (wet deposition + fertilizer N applied) minus output (drainflow + animal product) averaged 417 kg N ha −1 year −1 . Total N accumulation in the top 15 cm of soil was 152 kg N ha −1 year −1 . The predicted range in NH 3 emission from this sward was 36–95 kg N ha −1 year −1 . Evidence suggested that the remaining large imbalance was either caused by denitrification and/or other unknown loss processes. In the sward receiving 100 kg fertilizer N ha −1 year −1 , it was apparent that N accumulation in the top 15 cm soil was greater than the input minus output balance, even before allowing for gaseous emissions. This suggested that there was an additional input source, possibly resulting from a redistribution of N from lower down the soil profile. This is an important factor to take into account in constructing N balances, as not all the N accumulating in the top 15 cm soil may be directly caused by N input. N redistribution within the soil profile would exacerbate the N deficit in budget studies.
Abstract. Because of the observed variability in soil available P (Olsen) contents, phosphorus budgets were used to predict changes in the soil P status of an intensively managed 6 ha grassland catchment in Northern Ireland. The P accumulation rate of approximately 24 kg/ha/y suggested an increase of soil available P (Olsen) of 1.0 mg P/kg/y. Soluble reactive phosphorus concentrations in drainflow measured on a daily basis for a two year period (January 1981 — December 1982) were compared with the two year period January 1990 — December 1991. The median concentration had increased by 10.0 μg P/1 in 1990/91 compared with 1981/82. This difference was only apparent in mean concentrations for the two time periods, after data associated with high flow events, which were more frequent in 1981/82, were excluded from the comparison. This rate of increase of 1.1 μg P/1/y, which was interpreted as reflecting an increase in soluble reactive phosphorus concentration in soil solution, is comparable to the increase in background soluble reactive phosphorus of 1.5 ± 0.54 μg P/1/y which was reported recently over a 17 year period from diffuse sources in the much larger (4400 km 2 ) Northern Ireland catchment of Lough Neagh.
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