• Evaluation of Amendments to Control Phosphorus Losses in Runoff from Dairy-Soiled Water

      Fenton, Owen; Serrenho, Ana; Healy, Mark G.; Department of Agriculture, Food and the Marine, Ireland; RSF 07 525 (Springer, 2011-11)
      Amendments with the potential to reduce phosphorus (P) losses from agricultural grassland arising from the land application of dairy-soiled water (DSW) were investigated. Optimal application rates were studied, and associated costs and feasibility were estimated. First, batch tests were carried out to identify appropriate chemicals or phosphorus sorbing materials to control P in runoff from DSW. Then, the best four treatments were examined in an agitator test. In this test, soil—placed in a beaker—was loaded with DSW or amended DSW at a rate equivalent to 5 mm ha−1 (the maximum permissible application rate of DSW allowable in a 42-day period in Ireland). The soil was overlain with continuously stirred water to simulate runoff on land-applied DSW. Optimum application rates were selected based on percentage removal of dissolved reactive phosphorus in overlying water and the estimated cost of amendment. The costs of the amendments, per cubic metre of DSW, increased in the order: bottom ash (1.55 €), alum (1.67 to 1.92 €), FeCl2·4H2O (3.55 to 8.15 €), and lime (20.31 to 88.65 €). The feasibility of the amendments, taking into account their cost, potential adverse effects, public perception, and their performance, decreased in the order: alum > FeCl2·4H2O > bottom ash > lime. Amendments to DSW could be introduced in critical source areas—areas where high soil test P and direct migration pathways to a receptor overlap.
    • Evaluation of chemical amendments to control phosphorus losses from dairy slurry

      Brennan, Raymond B.; Fenton, Owen; Rodgers, M.; Healy, Mark G. (Wiley; British Society of Soil Science, 14/04/2011)
      Land application of dairy slurry can result in incidental losses of phosphorus (P) to runoff in addition to increased loss of P from soil as a result of a buildup in soil test P (STP). An agitator test was used to identify the most effective amendments to reduce dissolved reactive phosphorus (DRP) loss from the soil surface after land application of chemically amended dairy cattle slurry. This test involved adding slurry mixed with various amendments (mixed in a beaker using a jar test flocculator at 100 rpm), to intact soil samples at approximate field capacity. Slurry/amended slurry was applied with a spatula, submerged with overlying water and then mixed to simulate overland flow. In order of effectiveness, at optimum application rates, ferric chloride (FeCl2) reduced the DRP in overlying water by 88%, aluminium chloride (AlCl2) by 87%, alum (Al2(SO4)3·nH2O) by 83%, lime by 81%, aluminium water treatment residuals (Al-WTR; sieved to <2 mm) by 77%, flyash by 72%, flue gas desulphurization by-product by 72% and Al-WTR sludge by 71%. Ferric chloride (€4.82/m3 treated slurry) was the most cost-effective chemical amendment. However, Al compounds are preferred owing to stability of Al–P compared with Fe–P bonds. Alum is less expensive than AlCl2 (€6.67/m3), but the risk of effervescence needs further investigation at field-scale. Phosphorus sorbing materials (PSM) were not as efficient as chemicals in reducing DRP in overlying water. The amendments all reduced P loss from dairy slurry, but the feasibility of these amendments may be limited because of the cost of treatment.
    • Incidental phosphorus and nitrogen loss from grassland plots receiving chemically amended dairy cattle slurry

      Brennan, Raymond B.; Healy, Mark G.; Grant, Jim; Ibrahim, Tristan G.; Fenton, Owen; Teagasc Walsh Fellowship Programme (Elsevier, 2012-12)
      Chemical amendment of dairy cattle slurry has been shown to effectively reduce incidental phosphorus (P) losses in runoff; however, the effects of amendments on incidental nitrogen (N) losses are not as well documented. This study examined P and N losses in runoff during three simulated rainfall events 2, 10 and 28 days after a single application of unamended/chemically amended dairy cattle slurry. Twenty-five hydraulically isolated plots, each measuring 0.9 m by 0.4 m and instrumented with runoff collection channels, were randomly assigned the following treatments: (i) grass-only, (ii) slurry-only (the study-control), (iii) slurry amended with industrial grade liquid alum comprising 8% Al2O3, (iv) slurry amended with industrial grade liquid poly-aluminum chloride (PAC) comprising 10% Al2O3, and (v) slurry amended with lime. During the first rainfall event, lime was ineffective but alum and PAC effectively reduced dissolved reactive P (DRP) (by 95 and 98%, respectively) and total P (TP) flow-weighted-mean-concentrations (by 82 and 93%, respectively) in runoff compared to the study-control. However, flow-weighted-mean-concentrations of ammonium–N (NH4–N) in runoff were increased with alum- (81%) and lime-treated (11%) slurry compared to the study-control whereas PAC reduced the NH4–N by 82%. Amendments were not observed to have a significant effect on NO3–N losses during this study. Slurry amendments reduced P losses for the duration of the study, whereas the effect of amendments on N losses was not significant following the first event. Antecedent volumetric water content of the soil or slope of the plots did not appear to affect runoff volume. However, runoff volumes (and consequently loads of P and N) were observed to increase for the chemically amended plots compared to the control and soil-only plots. This work highlights the importance of considering both P and N losses when implementing a specific nutrient mitigation measure.