NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Evaluation of amendments to control phosphorus losses in runoff from pig
slurry applications to land
C.J. O’ Flynn 1 , O. Fenton 2 , M.G. Healy 1*
1 Civil Engineering, National University of Ireland, Galway, Co. Galway, Rep. of Ireland.
2 Teagasc, Johnstown Castle, Environmental Research Centre, Co Wexford, Rep. of Ireland
E-mail: mark.healy@nuigalway.ie
Abstract
If spread in excess of crop requirements, phosphorus
(P) or nitrogen (N) losses from agriculture can lead to
eutrophication of receiving waters. One way to reduce
dissolved reactive phosphorous (DRP) loss from a soil
surface after land application of pig slurry is to
chemically amend the slurry. Batch experiments,
wherein a chemical and slurry are mixed, are a good
way to determine if chemical amendment is appropriate
to reduce water extractable phosphorus (WEP) of
slurry, but do not account for the interaction between
applied slurry and soil. An agitator test, wherein an
intact soil core, placed in a beaker, is overlain with
continuously-stirred water, enables achievement of
batch experiment results, but also simulates the
situation in which slurry is applied to soil, allowed to
dry, and then subjected to overland flow.
1. Introduction
The European Communities (Good Agricultural
Practice for Protection of Waters) Regulations 2010
(S.I. No. 610 of 2010), puts a limit on the amounts of
livestock manure that can be applied to land. If spread
in excess of crop requirements, phosphorus (P) or
nitrogen (N) losses from agriculture can lead to
eutrophication (Carpenter et al., 1998). According to
Gburek and Sharpley (1998), P export from soil can be
best managed by concentrating on P levels in
hydrologically active zones, known as Variable Source
Areas (VSAs), most likely to produce surface runoff.
The use of chemicals or P sorbing materials (PSMs)
may offer a potential solution to reduce P losses in
these areas. The aim of this experiment was to identify
and evaluate the most appropriate chemical
amendments and PSMs to reduce DRP from land
applied pig slurry.
2. Materials and Methods
2.1. Soil and slurry collection
Pig slurry from was taken from an integrated pig
unit in Teagasc Research Centre, Moorepark, Fermoy,
Co. Cork. Soil cores were taken from a high P-index
site in Co. Galway (typical of a pig farm).
2.2. Treatment selection
Eleven different chemical amendments were trialed
as part of the preliminary batch test. From this, six
different chemicals were selected to be added at three
105
different rates (low, medium and high) as part of the
agitator test. Two more treatments (unamended slurryonly
and grass-only) were also included. The slurry in
all cases was spread at 19 kg total P (TP) ha -1 .
2.3 Agitator test
Prior to the start of the agitator test, the intact soil
samples were cut to 45 mm and transferred into 1-L
glass beakers. The slurry and amended slurry was then
applied to the soil cores (t = 0 h), and left to interact for
24 h prior to the sample being saturated. At t = 24 h, the
samples were gently saturated by adding deionised
water to the soil over 24 h until water pooled on the
surface. Immediately after saturation (t = 48 h), 500 mL
of deionised water was added to the beaker. The
agitator paddle was lowered to mid-depth in the water
overlying the soil sample and the paddle was set to
rotate at 20 rpm for 30 h to simulate overland flow.
Water samples were taken throughout the 30 h of the
test and tested for DRP. pH readings were taken at start
and end of test.
3. Results
The most effective amendments at reducing DRP in
overlying water were (in decreasing order of
efficiency): alum (85%), flue gas desulphurization
(FGD) by-product (73%), poly-aluminium chloride
(PAC) (72%), ferric chloride (70%), flyash (56%) and
lime (52%). FGD was the most costly of all treatments
(€7.64/m 3 ), whilst alum was the cheapest (€3.33/m 3 ).
4. Conclusions
There is potential for use of chemical amendments to
reduce P loss resulting from land application of pig
slurry. As there are significant costs associated with the
use of these amendments, it is recommended that they
are used strategically in areas which are likely to have
potential nutrient loss problems. As land surrounding
pig farms tend to have high soil test phosphorus, the use
of amendments may be deemed necessary.
5. References
[1] Carpenter, S. R., Caraco, N. F., Correll, D. L., Howarth,
R. W., Sharpley, A. N., Smith, V. H. 1998. Nonpoint
pollution of surface waters with phosphorus and nitrogen.
Ecological Applications 8, 559-568.
[2] William J. Gburek and Andrew N. Sharpley. 1998.
Hydrologic Controls on phosphorus loss from upland
agricultural watersheds. JEQ 27, 267-277.