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Phosphorus losses to surface waters following organic manure applications to a drained clay soil
Agricultural Water Management 57 (2002) 155±173
Phosphorus losses to surface waters following organic manure applications to a drained clay soil R.A. Hodgkinsona,*, B.J. Chambersa, P.J.A. Withersb, R. Crossc a
ADAS Gleadthorpe, Meden Vale, Mans®eld NG20 9PF, Nottinghamshire, UK b ADAS Bridgets, Martyr Worthy, Winchester SO21 1AP, Hampshire, UK c ADAS Boxworth, Battlegate Road, Boxworth CB3 8NN, Cambridgeshire, UK Accepted 27 February 2002
Abstract The effects of annual applications of farm manures (pig slurry (PS), broiler litter (BL) and cattle farmyard manure (FYM)), liquid digested sewage sludge (LDS) and inorganic phosphorus (P) fertiliser on P concentrations and losses in tile drain ¯ow from a calcareous clay soil were studied over four winter drainage seasons. The site was under arable cropping in South Eastern UK and had been intensively underdrained in autumn 1994. The tile drainage system comprised of plastic pipes covered with gravel back®ll and supplemented by 2 m spaced mole channels. Application of PS in November 1994, 4±6 weeks before the onset of winter drainage, resulted in high concentrations of dissolved P (up to 10 mg l 1) and total P (TP) in drain ¯ow (up to 75 mg l 1). TP losses following application of PS over this ®rst drainage season (1155 g ha 1) were increased four-fold compared to a control receiving no P (277 g P ha 1). The majority of the increased loss occurred in the ®rst drainage event due to the rapid transport of the PS through the macropores created in the soil following the installation of tile and mole drains 1 month before the slurry was applied. Application of BL, FYM, LDS and inorganic P fertiliser at maximum recommended rates did not signi®cantly increase P losses in any drainage season, nor did the PS in subsequent years. This study supports current guidelines on good agricultural practice, which recommends that liquid farm manures should not be applied to recently drained clay soils to avoid direct contamination and P enrichment of the drainage water. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Phosphorus; Livestock; Sewage sludge; Eutrophication; Drainage water
* Corresponding author. Tel.: 44-1223-569-238; fax: 44-1223-569-238/276-538. E-mail address: [email protected] (R.A. Hodgkinson).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 2 ) 0 0 0 5 7 - 4
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1. Introduction Phosphorus (P) inputs to surface waters can be critical in determining whether eutrophication occurs, with as little as 30 mg l 1 causing algal blooms (Smith et al., 1999). Reductions in point source discharges of P from sewage treatment works have focused attention on the contribution of diffuse inputs from arable and grassland farming systems to eutrophication. (Foy et al., 1995). Agriculture is now considered an important source of soluble and particulate P to both ¯owing and standing waters in many areas (Environment Agency, 1998; English Nature, 1997) and it is important that the site conditions under which these losses occur are characterised. In particular, recent research has identi®ed the increased risk of P loss associated with build-up of soil P and land use practices which encourage erosion (Heckrath et al., 1995; Chambers et al., 2000). Substantial loss of P in subsurface drainage water are widely reported following fresh applications of fertilisers and/or manures (Sims et al., 1998). Manure applications to agricultural land in the UK are an important source of P inputs with an estimated 66,000 t of P recycled to tillage land and 53,000 t recycled to grassland each year (Smith et al., 1998). Application frequently takes place in the autumn period (August±October) with ca. 50% of pig and poultry manures and ca. 25% of cattle manure applications made at this time (Smith and Chambers, 1993; Chambers et al., 1999). Autumn and winter applications of manure may accelerate P losses in drainage water, since soils are often at or above ®eld capacity moisture content (McAllister, 1976; Hergert et al., 1981; Phillips et al., 1981; Sharpley and Withers, 1994). The potential for P applied in animal slurries to remain in solution in soil macropores for a long time after application has been suggested as a possible mechanism for contamination of drainage water (McAllister and Stevens, 1981). The conditions that most favour P losses through pipe drains are those where subsurface ¯ow pathways are rapid, i.e. preferential ¯ow takes place (Stamm et al., 1997). These conditions occur in soils that either have a strongly developed natural macropore structure or where man-made macropores have been created through installation of mole drains, pipe drains or subsoiling ®ssures. The poorly draining clay soils of central, southern and eastern UK are commonly drained using pipes laid in a trench that is back®lled with permeable material up to the subsoil/topsoil interface. Mole drains are often installed over the system to improve drainage ef®ciency and ensure rapid water movement to the pipe drains. It has been estimated that around 6:4 106 ha of agricultural land in UK and Wales have been underdrained (Withers et al., 2000). There is little information in the UK on the factors determining the potential for P loss in drain ¯ow following P applications. In addition to soil type and the presence of a drainage system, other factors, such as the time period between manure application and the ®rst drainage event may be equally important in determining the potential for P loss. Knowledge and understanding of the controlling factors are needed in order to develop management guidelines to minimise P loss. The objectives of the study reported here were to quantify P losses following the application of different P sources to a drained clay soil in eastern UK. Preliminary ®ndings from the 1994±1995 drainage season were reported in summary in Smith et al., 1998.
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2. Materials and methods 2.1. Site establishment The site was located at an ADAS experimental farm at Boxworth (Cambridgeshire, UK) on chalky boulder clay of the Hanslope Association (Hodge et al., 1984) that had been in long-term arable production. This soil contains ca. 42% clay to a depth of 1 m and cracks strongly in summer, but becomes relatively impermeable to water in winter once it has reached ®eld capacity moisture content. It is representative of a large areas of productive arable land in eastern UK and has a hydrology of soil types (HOST) classi®cation of 21 (Boorman et al., 1995). The topsoil (0±20 cm) contained 510 and 15 mg kg 1 of total P (TP) and Olsen extractable P, respectively, 20 g kg 1 of calcium carbonate, 19 g kg 1 of organic matter and had a pH of 8.0. Twelve plots (24 m 48 m) each hydrologically isolated by a 1.3 m deep vertical polythene curtain were established in September±October 1994. The ®eld in which the plots were established had a slope of <1% and therefore, the amount of surface runoff generated from the site can be considered to be negligible. The experimental area was isolated from the rest of the ®eld by a pipe drain laid in a 1.1 m deep trench around its perimeter back®lled with gravel to ground level provide a hydraulic connection between the entire soil pro®le above 1.1 m and the pipe drain. This ensured complete hydrological isolation down to 1.1 m. A discrete underdrainage system, comprising of two 100 mm perforated plastic pipe lateral drains 24 m apart laid parallel to the ditch, was installed in each plot (Fig. 1). The pipe drains were laid at a depth of 90 cm and the trench above the pipe back®lled with permeable back®ll (gravel) to within 30 cm of the soil surface. The use of permeable back®ll is normal practice in the UK on heavy soils and it has two key functions. The ®rst is to provide a direct hydraulic connection between the base of the cultivation layer and the pipe drain intercepting lateral movement of water along this horizon and the second to connect the mole drains to the pipe drains. The laterals were connected to a 100 mm perforated main drain that was itself connected to a sealed pipe at the downslope edge of the plots and which connected the plot drains to the measuring weir. Mole drains were drawn down the full length of each plot in October 1994 at 55 cm depth and 2 m intervals. Discharge from each plot was measured using a 1/4 908 V notch weir tank in which water levels were measured by a ¯oat linked to a rotary potentiometer (Talman, 1979). Raw data were recorded at 5 min intervals on a datalogger, which triggered EPICTM (Montec, Salford, UK) automatic water samplers on a ¯ow proportional basis. 2.2. Treatments Inorganic fertiliser P (triple super phosphate (TSP)), pig slurry (PS), cattle farmyard manure (FYM), broiler litter (BL) and liquid digested sewage sludge (LDS) were surface applied and ploughed down annually to supply a target TP rate of 60 kg P ha 1. Treatment application dates were 14±18 November 1994, 19±27 September 1995, 1±7 October 1996 and 15±19 September 1997. Actual manure P loading rates, (Table 1), deviated from the target rates due to variations in the P content of the materials applied. P amendments were
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Fig. 1. Schematic diagram of plot drainage.
Table 1 Treatment application rates (m3 ha year Treatment
Control Inorganic P (TSP)
Block
1&2a
1
liquid manures or t ha
1
solid manures) and P loadings (kg ha 1) in each
1994±1995
1995±1996
1996±1997
1997±1998
Rate
Rate
Rate
Rate
P
P
P
P
Total P applied
±
± 60
±
± 60
±
± 60
±
± 60
± 240
PS
1 2
63 55
36 37
107 115
54 58
60 70
18 21
65 65
75 75
183 191
FYM BL
1&2a 1&2a
47 5
103 51
47 7
74 62
38 7
45 57
42 6
58 59
280 229
LDS
1 2
154 151
72 71
146 129
45 22
222 220
57 56
139 139
104 104
278 253
a Inorganic P, BL and FYM were applied from weighed amounts spread over the plot and thus there was no variation in amounts applied to plots within each treatment per year.
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compared with an untreated control in two randomised blocks. Each plot received the same treatment in each of the 4 years studied and the straw was returned to each plot each year after harvest. 2.3. Manure analyses Organic manure samples were taken in triplicate at the time of application. In the case of solid manures, the total mass of sample taken was ca. 1500 g; this was built up from at least 15 separate smaller samples that were taken as the manure was being weighed out prior to spreading. Similarly 1.5 l samples of liquid manure were collected as the tanker that was used for spreading was being ®lled. At the laboratory, the fresh solid manure samples were spread out on the bench, homogenised and then a representative 5 g subsample was taken for analysis. In the case of liquid manures, the bottle was shaken to ensure homogenisation and a 5 ml subsample taken. These subsamples were used for the determination of the amount of P extracted by water and 0.5 M sodium bicarbonate which were determined by equilibration with 100 ml of each extractant and shaking for 16 h. The supernatant liquid was decanted and ®ltered through a 125 mm Whatman no. 2 ®lter paper and P concentrations determined following the procedure of Murphy and Riley (1962). Fresh manure subsamples, either 200 g for solid manures or 200 ml for liquids, were air dried at 30 8C for 48 h followed by drying at 100 8C in a forced oven for 16 h and the residue milled to pass a 1 mm mesh. The dried samples were analysed for inorganic and TP (MAFF, 1986). 2.4. Drainage water sampling and analyses Water samples (200±300 ml volume) were collected on a ¯ow proportional basis into plastic bottles. Twelve drainage events were sampled in 1994±1995, six in 1995±1996 and six in 1997±1998. There were no drainage events in 1996±1997 due to lack of rainfall. Typically four±six samples were selected from each plot to characterise each drainage event. A 100 ml subsample was taken from each sample for analysis of P fractions. Samples were stored at 4 8C in polypropylene bottles prior to analysis, which was usually within 5 days of the storm event. Dissolved (<0.45 mm) molybdate reactive P (MRP), total dissolved P (TDP) and TP were determined colorimetrically (Murphy and Riley, 1962) in the case of TDP and TP following persulphate digestion (Anon, 1981). Where the MRP concentration was >100 mg l 1, TDP and TP concentrations were determined by ICP following aqua regia digestion. 2.5. Statistical analysis All statistical analyses were undertaken using Genstat (Alvey et al., 1982). Analysis of variance was performed, either on the raw data values or, to ensure that the conditions for analysis of variance to be valid were met, on transformed data. As the ¯ow response and hence the timing and number of samples from each plot was different, no attempt has been made to determine the statistical signi®cance of differences in P concentrations arising from the treatments. The P loss from each plot was calculated from individual plot drainage volumes and P concentrations and then corrected to the mean measured drainage value
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based on all the plots. Analysis of variance was then applied to the loss data generated in this way. 3. Results 3.1. Hydrology The median period when the soil at ADAS Boxworth, would be expected to be at ®eld capacity, and hence draining in response to rainfall, runs from the middle of December to late March (Smith and Trafford, 1976). In 3 out of the 4 years some ¯ow was recorded in December, but even during the wettest year studied, ¯ow was not initiated from all plots until early January. There was considerable variation between measured drainage from the plots in any single year. In particular, the drainage volume from one plot receiving BL was so large in all years (ca. ®ve-fold greater than the other plots) that it could not be used to estimate P losses and hence this treatment was not replicated. In the ®rst year (1994±1995), the autumn was wet and drain ¯ow commenced from some plots in early December. Winter rainfall (January±March) was above average at 171 mm, compared with the long-term average of 116 mm (Smith and Trafford, 1976) and this generated an average drainage volume of 140 mm from the plots during winter. In the following year, 1995±1996, the summer and autumn were dry and drainage did not start until late December. Winter rainfall (115 mm) was close to the long-term average and the average drainage volume for the plots was 110 mm. The third year (1996±1997) was very dry with a winter rainfall of only 56 mm and no measurable drainage was recorded. In the ®nal year of the study (1997±1998), winter rainfall was below average at 102 mm and drain ¯ow commenced in late December. In particular February was very dry (only 4 mm of rain compared to the long-term average of 32 mm) and as a consequence the average drainage volume generated for the winter period was only 13 mm. In contrast, the April±June rainfall (240 mm) was well above long-term average (128 mm) and as a consequence a further 55 mm of drainage occurred during the April±June period to give a total drainage volume of 68 mm. 3.2. Phosphorus concentrations in drainage water In the 1994±1995 drainage season, the PS applied in November 1994 substantially increased P concentrations in the drainage water (Fig. 2a±c). For example during the early drainage events TP concentrations from the PS plots varied from 1 to 75 mg l 1, whereas those on the control ranged from <0.05 to 0.37 mg l 1. TDP concentrations for the PS treatment ranged from 1 to 10 mg l 1 compared to <0.05 to 0.08 mg l 1 from the untreated control plots. In 1994±1995, initial drainage water from the plots to which PS had been applied showed visible brown discoloration and soluble P concentrations were ca. 38% of TP compared to ca. 13% from the control. These observations along with the high TP concentrations measured suggest direct movement of the applied PS into the tile drains. In contrast, the LDS, BL, FYM and inorganic fertiliser P treatments only caused small increases in
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Fig. 2. TP concentrations in drainage water: (a) control and inorganic P treatments; (b) FYM and BL treatments; (c) PS and LDS treatments.
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Fig. 2. (Continued ).
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Fig. 2. (Continued ).
163
164 R.A. Hodgkinson et al. / Agricultural Water Management 57 (2002) 155±173
Fig. 3. TDP concentrations in drainage water: (a) control and inorganic P treatments; (b) FYM and BL treatments; (c) PS and LDS treatments.
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Fig. 3. (Continued ).
165
166
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Fig. 3. (Continued ).
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Table 2 Mean drainage water flow corrected P loss in 1994±1995 (based on average flow of 140 mm per year) Treatment
TP (g ha 1)
Transformed TP (log10)
TDP (g ha 1)
Transformed TDP (log10)
MRP (g ha 1)
Transformed MRP (log10)
Control Inorganic P (TSP) PS FYM BLc LDS
277 135 1155 345 249 203
2.42 2.10 2.95 2.54 ± 2.27
33 10 476 29 74 54
1.51 0.98 2.61a 1.30 ± 1.72
37 39 436 60 68 50
1.56 1.51 2.58b 1.76 ± 1.69
± 336
0.21 0.30 0.21
± 111
0.05 0.35 0.25
± 96
0.08 0.28 0.20
F probability S.E.D. S.E.M.
S.E.D.: standard error of difference between means; S.E.M.: standard error of means. a Significantly different from control (P 0:08). b Significantly different from control (P 0:05). c BL not included in statistical analysis.
drainage water P concentrations compared with the untreated control. In the other two seasons when drainage occurred, 1995±1996 and 1997±1998, there were only small increases in drainage water P concentrations due to the treatments (Figs. 2a±c and 3a±c). In both of these years, occasional elevated concentrations were recorded from individual plots but these were randomly distributed and average P concentrations over the drainage season were unaffected. 3.3. Phosphorus losses in drainage water P losses, corrected to the average site drainage volume, were calculated for the 3 years when drainage occurred (Tables 2±4). The data from BL treatment was not included in the Table 3 Mean drainage water flow corrected P loss in 1995±1996 (based on average flow of 110 mm per year) Treatment
TP (g ha 1)
TDP (g ha 1)
Transformed TP (negative reciprocal)
MRP (g ha 1)
Control Inorganic P (TSP) PS FYM BLa LDS
137 247 132 162 176 125
43 120 70 94 50 28
0.0260 0.0093 0.0280 0.0135 0.0272 0.0384
38 105 59 84 42 23
0.0334 0.0108 0.0306 0.0158 0.0335 0.0458
F probability S.E.D. S.E.M.
0.82 115 115
± ± 55
0.41 0.015 0.015
± ± 50
0.38 0.018 0.017
S.E.D.: standard error of difference between means; S.E.M.: standard error of means. a BL not included in statistical analysis.
Transformed MRP (negative reciprocal)
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Table 4 Mean drainage water flow corrected P losses in 1997±1998 (based on average flow of 68 mm per year) Treatment
TP (g ha
Control Inorganic P (TSP) PS FYM LDS
83 92 106 110 259
1.90 1.93 1.95 2.00 2.39
± 63
0.528 34.6 0.209
F probability S.E.D. S.E.M.
1
Transformed TP (log10)
P)
TDP (g ha
1
MRP (g ha
P)
24 48 58 36 84
33 39 31 21 42
0.56 34.6 24.5
0.95 27.6 19.6
1
P)
S.E.D.: standard error of difference between means; S.E.M.: standard error of means.
statistical analysis of the data as measurements were only available from one plot and no data are presented for 1997±1998 as the number of samples were obtained were insuf®cient to make a robust estimate of P loss. In the ®rst drainage season (1994±1995), MRP and TDP losses were signi®cantly increased (P < 0:1) following the PS addition by 397 and 443 g P ha 1, respectively, compared with the untreated control (Table 2). Similarly, substantially increased TP losses were measured (878 g P ha 1), although this increase was not statistically signi®cant (P > 0:1). P losses from the LDS, solid manure and inorganic fertiliser P treatments were Table 5 TP content (kg m applied
3
liquids and kg t
Manure type
Year
PS
1
(fresh weight) solids) and percentage P fractions in the organic manures
TP
Water-soluble P (%)
NaHCO3-extractable P (%)
Mean
S.D.
1994±1995 1995±1996 1996±1997 1997±1998
0.63 0.51 0.30 1.15
0.11 0.03 0.004 0.19
65 71 30 59
91 94 60 90
FYM
1994±1995 1995±1996 1996±1997 1997±1998
2.19 1.58 1.17 1.37
0.16 0.32 0.04 0.19
16 10 14 17
25 27 39 31
BL
1994±1995 1995±1996 1996±1997 1997±1998
10.50 9.03 8.36 9.47
0.34 0.45 0.21 0.41
23 10 50 16
17 17 45 17
LDS
1994±1995 1995±1996 1996±1997 1997±1998
0.47 0.23 0.26 0.75
0.05 0.08 0.009 0.17
11 13 15 11
23 35 35 40
12
33
Mean
0.43
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not signi®cantly elevated compared to the untreated control in 1994±1995 (P > 0:1). Neither any of the organic manure treatments nor the application of inorganic P fertiliser caused signi®cant increases in the amount of P lost in drainage water compared to that measured from the control in either of the other two seasons when drainage occurred (1995±1996 and 1997±1998). 3.4. Manure phosphorus In the majority of samples analysed more than 90% of the total manure P was in the inorganic form. The TP content and proportions of manure TP extracted by water and sodium bicarbonate are summarised in Table 5. Despite the variable results, which clearly demonstrate the heterogeneity of organic manures, clear differences between manures were apparent. The key difference between the manures being that in three out of 4 years the PS contained a much greater proportion of the more mobile water-soluble and bicarbonate-extractable P than the other manures. 4. Discussion Of all of the treatments applied, only the PS application in November 1994 signi®cantly increased losses compared with the untreated control. This was most probably due to direct contamination of the drainage water with slurry since the samples collected were discoloured compared to samples collected from other treatments. Since the slurry was applied 4±6 weeks before the onset of drainage this suggests that some of the slurry was retained in soil macropores and then ¯ushed out by the ®rst two drainage events. This effect may have been exacerbated by additional macropores created during the recent installation of the underdrainage system in autumn 1994. Current best practice in the UK outlined in the MAFF's `Code of Good Agricultural Practice for the Protection of Water' (MAFF, 1998) recommends that organic manures should not be applied to land under certain conditions. These include ®elds that have been ``pipe drained, mole drained or subsoiled over the drains within the last 12 months'' or ``where the soil is cracked down to the tile drains or back®ll''. The ®ndings of this study thus support this guidance. This is particularly important advice given that there are an estimated 6:4 106 ha of drained agricultural land in UK and Wales, and that ca. 70% of PS and cattle slurry applications to land cropped with cereals takes place in the autumn±winter period (Smith et al., 2000, 2001). Concentrations of MRP in the drainage water in 1994±1995 of up to 10.0 mg l 1 were similar to those reported by Stamm et al. (1997) in drainage water immediately following the application of manure (4.8 mg l 1). Maximum TP concentrations of 75 mg l 1 were greater than those reported by McAllister (1976) in drainage water where dilute slurry had been applied to an intensively drained clay soil (10 mg l 1) but typical concentrations were similar. Hooda et al. (1996) in the week following a November cattle slurry application to a grassland soil was able to account for 19±42% of annual MRP losses in drainage water, with MRP concentration peaks as high as 12 mg l 1. The data from this study, therefore, are consistent with other studies and support the argument that manures are a signi®cant source of incidental P loss from agricultural land to water (Withers et al., 2000).
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Increased losses would logically have been expected from the LDS application in 1994± 1995 as well as the PS, especially since the hydraulic loading from the application of the LDS was much greater (up to 3.4 times). The proportions of the different forms of P in each of the manures may provide an explanation of the fact that only application of PS caused an increase in P losses. The PS contained on average the greatest proportions of P in the `easily mobilised' water-soluble and bicarbonate-extractable forms, 59 and 86%, respectively, compared with 12 and 33% for the LDS, 14 and 30% for the FYM and for the BL ca. 25% for both forms. A lower solubility of P in LDS compared to cattle FYM was found by Withers et al. (2001) and this was re¯ected in reduced P loss in surface runoff following sludge application. An additional factor in the study reported which may have reduced losses from the solid manures was that they were ploughed in after application. This will have intimately mixed the solid manures with the soil providing some protection against mobilisation and also disrupted continuity of macropores and ®ssures created by drainage installation. The fact that P losses were not increased by PS application in 1995±1996 when the soil was extensively cracked, suggests that other factors in¯uence P losses in drainage water. In the ®rst (1994±1995) drainage season, the manures were applied wet soils in midNovember 1994, which will have tended to reduce immobilisation of P, and the ®rst drainage event occurred in late December 1994, around 6 weeks after application. In the second and fourth years of the study, the manures were applied to much drier soils in midSeptember, which will have led to greater immobilisation and the ®rst drainage event did not occur until late December, around 14±16 weeks later. These results suggest that the combined effect of the time lapse between the PS application and onset of drainage and the soil moisture content at time of application may have limited amount of P lost in the other 2 years. Other workers have shown a link between the time gap between application and concentrations of P in surface runoff (Sharpley, 1997). Although, the delay between application and ®rst drainage event, was considerable in all years it is likely that any manure present in macropores would have remained a potential source of P loss, especially for those manures with a high degree of water solubility and/or under wet soil conditions. Only liquid manures have the potential to penetrate into macropores below plough depth and hence remain easily mobilisable under these conditions. Other research (Williams and Nichosoon, 1995) has also shown that P losses following application of dirty water were much lower when the soil had a soil moisture de®cit at the time of application. In this study, there was no evidence that the application of 60 kg ha 1 of inorganic fertiliser P to a `wet' soil in November 1994 increased losses, or in the 2 years when inorganic fertiliser P was applied to `dry' soils in September. This is in contrast to results obtained on a clay soil at Brimstone farm (Cannell et al., 1984) where an application of 33 kg ha 1 of inorganic fertiliser P to a wet soil in December 1994 showed a consistent trend for increased MRP concentrations and loadings in drain ¯ows over the whole of the 1994±1995 winter drainage season (Catt et al., 1998). However, other workers such as, Zwerman et al. (1972) and Leinweber et al. (1999) have reported that application of mineral P fertiliser did not result in greater losses in drainage water or in lysimeter leachates, respectively. The calcium carbonate content in the Denchworth top soil at Brimstone is <0.1% (Cannell et al., 1984), whereas in the Hanslope Association soils at Boxworth it is typically ca. 2% and free calcium carbonate is in evidence which will tend to
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lead to reduced losses of P in soluble forms both from organic manures and from mineral P fertiliser. The P losses measured following PS application were not large in proportion to the amounts applied but could have a signi®cant impact on any receiving water, depending on dilution in the watercourse and nature of the receiving water body. The application of solid manures, LDS and inorganic fertiliser P did not increase P loss above the untreated control. Thus, on the evidence of this study, placing restrictions on the timing of solid manure, LDS and inorganic fertiliser P applications in order to minimise P losses in drainage water would not seem justi®ed. 5. Conclusions The application of PS to drained clay soils can increase P concentrations and losses in drainage water. In this study, the elevated P concentrations were a result of direct contamination of the early drainage water ¯ows with slurry caused by rapid transport through mole drain macropores created in the soil, which may additionally have been exacerbated by recent installation of the underdrainage system. Application of LDS, FYM, BL and inorganic P fertiliser were not found to increase P concentrations and losses in drainage water. The results con®rm current guidelines to avoid applying slurries to drained soils where there is a likelihood of drainage occurring soon after land application (i.e. once the soil has returned to ®eld capacity). Potential factors determining whether increased P loss occurs following application of liquid manures include manure P solubility in water, continuity of soil macropore structures and soil moisture status during the period between application and onset of drainage. Acknowledgements This work was funded by the UK Ministry of Agriculture, Fisheries and Food, and UK Water Industry Research. The efforts of ADAS colleagues who assisted in carrying out the ®eld trials are also acknowledged.
References Alvey, N., Galwey, N., Lane, P., 1982. An Introduction to Genstat, Academic Press, London. Anon, 1981. Phosphorus in waters, effluents and sewages: determination of total phosphorus (TP) and total dissolved phosphorus (TDP). In: Methods for the Examination of Waters and Associated Materials, HMSO, London, pp. 26±28 (Appendix IV). Boorman, D.B., Hollis, J.M., Lilly, A., 1995. Hydrology of soil types: a hydrologically based classification of the soils of the UK. Hydrology Institute Report no. 126, Wallingford, UK. Cannell, R.Q., Goss M, J., Harris, G.L., Jarvis, M.G., Douglas, J.T., Howse, K.R., Le Grice, S., 1984. Study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil. Part 1. Background,
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experiment and site details, drainage systems, measurement of drain flow and summary of results, measurement of drain flow and summary of results, 1979±80. J Agric. Sci. Camb. 102, 539±559. Catt, J.A., Howse, K.R., Farina, R., Brockie, D., Chambers, B.J., Hodgkinson, R., Harris, G.L., Quinton, J.N., 1998. Phosphorus losses from arable land in UK. Soil Use Manage. 14, 168±174. Chambers, B., Smith, K., Pain, B., 1999. Strategies to encourage better use of nitrogen in animal manures. In: Tackling Nitrate from AgricultureÐStrategy from Science. MAFF Publications, London, pp. 27±36 (PB4401). Chambers, B.J., Garwood, T.W.D., Unwin, R.J., 2000. Controlling soil water erosion and phosphorus losses from arable land in UK and Wales. J. Environ. Qual. 29, 145±150. English Nature, 1997. Wildlife and Freshwater: An Agenda for Sustainable Management. English Nature, Peterborough, UK. Environment Agency, 1998. The State of the Environment of UK and Wales: Fresh Waters. The Stationery Office, London. Foy, R.H., Smith, R.V., Jordand, C.J., Lennox, S.D., 1995. Upward trends in soluble phosphorus loadings at Lough Neagh despite phosphorus reduction at sewage works. Water Res. 29, 1051±1063. Heckrath, G., Brookes, P.C., Poulton, P.R., Goulding, K.W.T., 1995. Phosphorus leaching from soils containing different phosphorus concentrations in the Broadbalk experiment. J. Environ. Qual. 24, 904±910. Hergert, G.W., Klausner, S.D., Bouldin, D.R., Zwerman, P.J., 1981. Effects of dairy manure on phosphorus concentrations and losses in tile effluent. J. Environ. Qual. 10, 345±349. Hodge, C.A.H., Burton, R.F.D., Corbett, W.M., Evans, R., Seale, R.S., 1984. Soils and Their Use in Eastern UK. Soil Survey of UK and Wales, Bulletin 13, Rothamsted Experimental Station, Harpenden. Hooda, P.A.S., Moynagh, M., Svoboda, I.F., 1996. A comparison of phosphorus losses in drainage water from two different grassland systems. Soil Use Manage. 12, 224. Leinweber, P., Meissner, R., Eckhardt, K.U., Seeger, J., 1999. Management effects on forms of phosphorus in soil and leaching losses. Eur. J. Soil Sci. 50, 413±424. MAFF, 1986. The Analysis of Agricultural Materials. Ministry of Agriculture, Fisheries and Food, Reference Book 427, HMSO, London. MAFF, 1998. Code of Good Agricultural Practice for the Protection of Water. MAFF Publications, London (PB0585). McAllister, J.S.V., 1976. Studies in north Ireland on problems related to the disposal of slurry. In: Agriculture and Water Quality. MAFF Technical Bulletin 32, MAFF, London, pp. 418±431. McAllister, J.S.V., Stevens, R.J., 1981. Problems related to phosphorus in the disposal of slurry. In: Hucker, T.W.G., Catroux, G. (Eds.), Phosphorus in Sewage Sludge and Animal Slurries. Reidel, Dordrecht, pp. 383±396. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chem. Acta 27, 31±36. Phillips, P.A., Culley, J.L.B., Hore, F.R., Patni, N.K., 1981. Pollution potential and corn yields from selected rates and timing of liquids manure applications. Trans. Am. Soc. Agric. Eng. 24, 139±144. Sharpley, A.N., 1997. Rainfall frequency and nitrogen and phosphorus runoff from soil amended with poultry litter. J. Environ. Qual. 26, 1127±1132. Sharpley, A.N., Withers, P.J.A., 1994. The environmentally-sound management of agricultural phosphorus. Fertiliser Res. 39, 133±146. Sims, J.T., Sinard, R.R., Joern, B.C., 1998. Phosphorus loss in agricultural drainage: historical perspective and current research. J. Environ. Qual. 27, 277±293. Smith, K.A., Chambers, B.J., 1993. Utilising the nitrogen content of organic manuresÐsome practical solutions to farm problems. Soil Use Manage. 9, 105±112. Smith, L.P., Trafford, B.D., 1976. Climate and Drainage. HMSO, London. Smith, K.A., Chalmers, A.G., Chambers, B.J., Christie, P., 1998. Organic manure phosphorus accumulation, mobility and management. Soil Use Manage. 14, 154±159. Smith, V.H., Tilman, G.D., Nekola, J.C., 1999. Eutrophication: impacts of excess nutrient inputs on freshwater, marine and terrestrial ecosystems. Environ. Pollut. 100, 176±179. Smith, K.A., Brewer, A.J., Dauven, A., Wilson, D.W., 2000. A survey of the production and use of animal manures in UK and Wales. Part I. Pig manure. Soil Use Manage. 16, 124±132. Smith, K.A., Brewer, A.J., Crabb, J., Dauven, A., 2001. A critical appraisal of animal manure management practice in UK and Wales. Part III. Cattle manure from dairy and beef enterprises. Soil Use Manage. 17, 77±87.
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Stamm, C., Gachter, R., Fluhler, H., Leuenberger, J., Wunderli, H., 1997. Phosphorus input to a brook through tile drains under grassland. In: Tunney, H. (Ed.), Phosphorus Losses from Soil to Water. CAB International, Wallingford, UK, pp. 372±373. Talman, A.J., 1979. Simple flow meters and water tables for field experiments. Technical Report 79/1, ADAS Field Drainage Experimental Unit, Trumpington, Cambridge. Williams, J.R., Nichosoon, R.J., 1995. Low rate irrigation of dirty water and its effect on drainage water quality. Agric. Eng. 50, 24±28. Withers, P.J.A., Davidson, I.H., Foy, R.H., 2000. Prospects for controlling non-point phosphorus losses to water: a UK perspective. J. Environ. Qual. 29, 167±175. Withers, P.J.A., Clay, S.D., Breeze, V.C., 2001. Phosphorus transfer in runoff following applications of fertiliser, manure and sewage sludge. J. Environ. Qual. 30, 180±188. Zwerman, P.J., Greweling, T., Klausner, S.D., Lathwell, D.S., 1972. Nitrogen and phosphorus content of water from tile drains at two levels of management and fertilization. Soil Sci. Soc. Am. Proc. 36, 134±137.
Phosphorus losses to surface waters following organic manure applications to a drained clay soil R.A. Hodgkinsona,*, B.J. Chambersa, P.J.A. Withersb, R. Crossc a
ADAS Gleadthorpe, Meden Vale, Mans®eld NG20 9PF, Nottinghamshire, UK b ADAS Bridgets, Martyr Worthy, Winchester SO21 1AP, Hampshire, UK c ADAS Boxworth, Battlegate Road, Boxworth CB3 8NN, Cambridgeshire, UK Accepted 27 February 2002
Abstract The effects of annual applications of farm manures (pig slurry (PS), broiler litter (BL) and cattle farmyard manure (FYM)), liquid digested sewage sludge (LDS) and inorganic phosphorus (P) fertiliser on P concentrations and losses in tile drain ¯ow from a calcareous clay soil were studied over four winter drainage seasons. The site was under arable cropping in South Eastern UK and had been intensively underdrained in autumn 1994. The tile drainage system comprised of plastic pipes covered with gravel back®ll and supplemented by 2 m spaced mole channels. Application of PS in November 1994, 4±6 weeks before the onset of winter drainage, resulted in high concentrations of dissolved P (up to 10 mg l 1) and total P (TP) in drain ¯ow (up to 75 mg l 1). TP losses following application of PS over this ®rst drainage season (1155 g ha 1) were increased four-fold compared to a control receiving no P (277 g P ha 1). The majority of the increased loss occurred in the ®rst drainage event due to the rapid transport of the PS through the macropores created in the soil following the installation of tile and mole drains 1 month before the slurry was applied. Application of BL, FYM, LDS and inorganic P fertiliser at maximum recommended rates did not signi®cantly increase P losses in any drainage season, nor did the PS in subsequent years. This study supports current guidelines on good agricultural practice, which recommends that liquid farm manures should not be applied to recently drained clay soils to avoid direct contamination and P enrichment of the drainage water. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Phosphorus; Livestock; Sewage sludge; Eutrophication; Drainage water
* Corresponding author. Tel.: 44-1223-569-238; fax: 44-1223-569-238/276-538. E-mail address: [email protected] (R.A. Hodgkinson).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 2 ) 0 0 0 5 7 - 4
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1. Introduction Phosphorus (P) inputs to surface waters can be critical in determining whether eutrophication occurs, with as little as 30 mg l 1 causing algal blooms (Smith et al., 1999). Reductions in point source discharges of P from sewage treatment works have focused attention on the contribution of diffuse inputs from arable and grassland farming systems to eutrophication. (Foy et al., 1995). Agriculture is now considered an important source of soluble and particulate P to both ¯owing and standing waters in many areas (Environment Agency, 1998; English Nature, 1997) and it is important that the site conditions under which these losses occur are characterised. In particular, recent research has identi®ed the increased risk of P loss associated with build-up of soil P and land use practices which encourage erosion (Heckrath et al., 1995; Chambers et al., 2000). Substantial loss of P in subsurface drainage water are widely reported following fresh applications of fertilisers and/or manures (Sims et al., 1998). Manure applications to agricultural land in the UK are an important source of P inputs with an estimated 66,000 t of P recycled to tillage land and 53,000 t recycled to grassland each year (Smith et al., 1998). Application frequently takes place in the autumn period (August±October) with ca. 50% of pig and poultry manures and ca. 25% of cattle manure applications made at this time (Smith and Chambers, 1993; Chambers et al., 1999). Autumn and winter applications of manure may accelerate P losses in drainage water, since soils are often at or above ®eld capacity moisture content (McAllister, 1976; Hergert et al., 1981; Phillips et al., 1981; Sharpley and Withers, 1994). The potential for P applied in animal slurries to remain in solution in soil macropores for a long time after application has been suggested as a possible mechanism for contamination of drainage water (McAllister and Stevens, 1981). The conditions that most favour P losses through pipe drains are those where subsurface ¯ow pathways are rapid, i.e. preferential ¯ow takes place (Stamm et al., 1997). These conditions occur in soils that either have a strongly developed natural macropore structure or where man-made macropores have been created through installation of mole drains, pipe drains or subsoiling ®ssures. The poorly draining clay soils of central, southern and eastern UK are commonly drained using pipes laid in a trench that is back®lled with permeable material up to the subsoil/topsoil interface. Mole drains are often installed over the system to improve drainage ef®ciency and ensure rapid water movement to the pipe drains. It has been estimated that around 6:4 106 ha of agricultural land in UK and Wales have been underdrained (Withers et al., 2000). There is little information in the UK on the factors determining the potential for P loss in drain ¯ow following P applications. In addition to soil type and the presence of a drainage system, other factors, such as the time period between manure application and the ®rst drainage event may be equally important in determining the potential for P loss. Knowledge and understanding of the controlling factors are needed in order to develop management guidelines to minimise P loss. The objectives of the study reported here were to quantify P losses following the application of different P sources to a drained clay soil in eastern UK. Preliminary ®ndings from the 1994±1995 drainage season were reported in summary in Smith et al., 1998.
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2. Materials and methods 2.1. Site establishment The site was located at an ADAS experimental farm at Boxworth (Cambridgeshire, UK) on chalky boulder clay of the Hanslope Association (Hodge et al., 1984) that had been in long-term arable production. This soil contains ca. 42% clay to a depth of 1 m and cracks strongly in summer, but becomes relatively impermeable to water in winter once it has reached ®eld capacity moisture content. It is representative of a large areas of productive arable land in eastern UK and has a hydrology of soil types (HOST) classi®cation of 21 (Boorman et al., 1995). The topsoil (0±20 cm) contained 510 and 15 mg kg 1 of total P (TP) and Olsen extractable P, respectively, 20 g kg 1 of calcium carbonate, 19 g kg 1 of organic matter and had a pH of 8.0. Twelve plots (24 m 48 m) each hydrologically isolated by a 1.3 m deep vertical polythene curtain were established in September±October 1994. The ®eld in which the plots were established had a slope of <1% and therefore, the amount of surface runoff generated from the site can be considered to be negligible. The experimental area was isolated from the rest of the ®eld by a pipe drain laid in a 1.1 m deep trench around its perimeter back®lled with gravel to ground level provide a hydraulic connection between the entire soil pro®le above 1.1 m and the pipe drain. This ensured complete hydrological isolation down to 1.1 m. A discrete underdrainage system, comprising of two 100 mm perforated plastic pipe lateral drains 24 m apart laid parallel to the ditch, was installed in each plot (Fig. 1). The pipe drains were laid at a depth of 90 cm and the trench above the pipe back®lled with permeable back®ll (gravel) to within 30 cm of the soil surface. The use of permeable back®ll is normal practice in the UK on heavy soils and it has two key functions. The ®rst is to provide a direct hydraulic connection between the base of the cultivation layer and the pipe drain intercepting lateral movement of water along this horizon and the second to connect the mole drains to the pipe drains. The laterals were connected to a 100 mm perforated main drain that was itself connected to a sealed pipe at the downslope edge of the plots and which connected the plot drains to the measuring weir. Mole drains were drawn down the full length of each plot in October 1994 at 55 cm depth and 2 m intervals. Discharge from each plot was measured using a 1/4 908 V notch weir tank in which water levels were measured by a ¯oat linked to a rotary potentiometer (Talman, 1979). Raw data were recorded at 5 min intervals on a datalogger, which triggered EPICTM (Montec, Salford, UK) automatic water samplers on a ¯ow proportional basis. 2.2. Treatments Inorganic fertiliser P (triple super phosphate (TSP)), pig slurry (PS), cattle farmyard manure (FYM), broiler litter (BL) and liquid digested sewage sludge (LDS) were surface applied and ploughed down annually to supply a target TP rate of 60 kg P ha 1. Treatment application dates were 14±18 November 1994, 19±27 September 1995, 1±7 October 1996 and 15±19 September 1997. Actual manure P loading rates, (Table 1), deviated from the target rates due to variations in the P content of the materials applied. P amendments were
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Fig. 1. Schematic diagram of plot drainage.
Table 1 Treatment application rates (m3 ha year Treatment
Control Inorganic P (TSP)
Block
1&2a
1
liquid manures or t ha
1
solid manures) and P loadings (kg ha 1) in each
1994±1995
1995±1996
1996±1997
1997±1998
Rate
Rate
Rate
Rate
P
P
P
P
Total P applied
±
± 60
±
± 60
±
± 60
±
± 60
± 240
PS
1 2
63 55
36 37
107 115
54 58
60 70
18 21
65 65
75 75
183 191
FYM BL
1&2a 1&2a
47 5
103 51
47 7
74 62
38 7
45 57
42 6
58 59
280 229
LDS
1 2
154 151
72 71
146 129
45 22
222 220
57 56
139 139
104 104
278 253
a Inorganic P, BL and FYM were applied from weighed amounts spread over the plot and thus there was no variation in amounts applied to plots within each treatment per year.
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compared with an untreated control in two randomised blocks. Each plot received the same treatment in each of the 4 years studied and the straw was returned to each plot each year after harvest. 2.3. Manure analyses Organic manure samples were taken in triplicate at the time of application. In the case of solid manures, the total mass of sample taken was ca. 1500 g; this was built up from at least 15 separate smaller samples that were taken as the manure was being weighed out prior to spreading. Similarly 1.5 l samples of liquid manure were collected as the tanker that was used for spreading was being ®lled. At the laboratory, the fresh solid manure samples were spread out on the bench, homogenised and then a representative 5 g subsample was taken for analysis. In the case of liquid manures, the bottle was shaken to ensure homogenisation and a 5 ml subsample taken. These subsamples were used for the determination of the amount of P extracted by water and 0.5 M sodium bicarbonate which were determined by equilibration with 100 ml of each extractant and shaking for 16 h. The supernatant liquid was decanted and ®ltered through a 125 mm Whatman no. 2 ®lter paper and P concentrations determined following the procedure of Murphy and Riley (1962). Fresh manure subsamples, either 200 g for solid manures or 200 ml for liquids, were air dried at 30 8C for 48 h followed by drying at 100 8C in a forced oven for 16 h and the residue milled to pass a 1 mm mesh. The dried samples were analysed for inorganic and TP (MAFF, 1986). 2.4. Drainage water sampling and analyses Water samples (200±300 ml volume) were collected on a ¯ow proportional basis into plastic bottles. Twelve drainage events were sampled in 1994±1995, six in 1995±1996 and six in 1997±1998. There were no drainage events in 1996±1997 due to lack of rainfall. Typically four±six samples were selected from each plot to characterise each drainage event. A 100 ml subsample was taken from each sample for analysis of P fractions. Samples were stored at 4 8C in polypropylene bottles prior to analysis, which was usually within 5 days of the storm event. Dissolved (<0.45 mm) molybdate reactive P (MRP), total dissolved P (TDP) and TP were determined colorimetrically (Murphy and Riley, 1962) in the case of TDP and TP following persulphate digestion (Anon, 1981). Where the MRP concentration was >100 mg l 1, TDP and TP concentrations were determined by ICP following aqua regia digestion. 2.5. Statistical analysis All statistical analyses were undertaken using Genstat (Alvey et al., 1982). Analysis of variance was performed, either on the raw data values or, to ensure that the conditions for analysis of variance to be valid were met, on transformed data. As the ¯ow response and hence the timing and number of samples from each plot was different, no attempt has been made to determine the statistical signi®cance of differences in P concentrations arising from the treatments. The P loss from each plot was calculated from individual plot drainage volumes and P concentrations and then corrected to the mean measured drainage value
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based on all the plots. Analysis of variance was then applied to the loss data generated in this way. 3. Results 3.1. Hydrology The median period when the soil at ADAS Boxworth, would be expected to be at ®eld capacity, and hence draining in response to rainfall, runs from the middle of December to late March (Smith and Trafford, 1976). In 3 out of the 4 years some ¯ow was recorded in December, but even during the wettest year studied, ¯ow was not initiated from all plots until early January. There was considerable variation between measured drainage from the plots in any single year. In particular, the drainage volume from one plot receiving BL was so large in all years (ca. ®ve-fold greater than the other plots) that it could not be used to estimate P losses and hence this treatment was not replicated. In the ®rst year (1994±1995), the autumn was wet and drain ¯ow commenced from some plots in early December. Winter rainfall (January±March) was above average at 171 mm, compared with the long-term average of 116 mm (Smith and Trafford, 1976) and this generated an average drainage volume of 140 mm from the plots during winter. In the following year, 1995±1996, the summer and autumn were dry and drainage did not start until late December. Winter rainfall (115 mm) was close to the long-term average and the average drainage volume for the plots was 110 mm. The third year (1996±1997) was very dry with a winter rainfall of only 56 mm and no measurable drainage was recorded. In the ®nal year of the study (1997±1998), winter rainfall was below average at 102 mm and drain ¯ow commenced in late December. In particular February was very dry (only 4 mm of rain compared to the long-term average of 32 mm) and as a consequence the average drainage volume generated for the winter period was only 13 mm. In contrast, the April±June rainfall (240 mm) was well above long-term average (128 mm) and as a consequence a further 55 mm of drainage occurred during the April±June period to give a total drainage volume of 68 mm. 3.2. Phosphorus concentrations in drainage water In the 1994±1995 drainage season, the PS applied in November 1994 substantially increased P concentrations in the drainage water (Fig. 2a±c). For example during the early drainage events TP concentrations from the PS plots varied from 1 to 75 mg l 1, whereas those on the control ranged from <0.05 to 0.37 mg l 1. TDP concentrations for the PS treatment ranged from 1 to 10 mg l 1 compared to <0.05 to 0.08 mg l 1 from the untreated control plots. In 1994±1995, initial drainage water from the plots to which PS had been applied showed visible brown discoloration and soluble P concentrations were ca. 38% of TP compared to ca. 13% from the control. These observations along with the high TP concentrations measured suggest direct movement of the applied PS into the tile drains. In contrast, the LDS, BL, FYM and inorganic fertiliser P treatments only caused small increases in
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Fig. 2. TP concentrations in drainage water: (a) control and inorganic P treatments; (b) FYM and BL treatments; (c) PS and LDS treatments.
161
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Fig. 2. (Continued ).
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Fig. 2. (Continued ).
163
164 R.A. Hodgkinson et al. / Agricultural Water Management 57 (2002) 155±173
Fig. 3. TDP concentrations in drainage water: (a) control and inorganic P treatments; (b) FYM and BL treatments; (c) PS and LDS treatments.
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Fig. 3. (Continued ).
165
166
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Fig. 3. (Continued ).
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167
Table 2 Mean drainage water flow corrected P loss in 1994±1995 (based on average flow of 140 mm per year) Treatment
TP (g ha 1)
Transformed TP (log10)
TDP (g ha 1)
Transformed TDP (log10)
MRP (g ha 1)
Transformed MRP (log10)
Control Inorganic P (TSP) PS FYM BLc LDS
277 135 1155 345 249 203
2.42 2.10 2.95 2.54 ± 2.27
33 10 476 29 74 54
1.51 0.98 2.61a 1.30 ± 1.72
37 39 436 60 68 50
1.56 1.51 2.58b 1.76 ± 1.69
± 336
0.21 0.30 0.21
± 111
0.05 0.35 0.25
± 96
0.08 0.28 0.20
F probability S.E.D. S.E.M.
S.E.D.: standard error of difference between means; S.E.M.: standard error of means. a Significantly different from control (P 0:08). b Significantly different from control (P 0:05). c BL not included in statistical analysis.
drainage water P concentrations compared with the untreated control. In the other two seasons when drainage occurred, 1995±1996 and 1997±1998, there were only small increases in drainage water P concentrations due to the treatments (Figs. 2a±c and 3a±c). In both of these years, occasional elevated concentrations were recorded from individual plots but these were randomly distributed and average P concentrations over the drainage season were unaffected. 3.3. Phosphorus losses in drainage water P losses, corrected to the average site drainage volume, were calculated for the 3 years when drainage occurred (Tables 2±4). The data from BL treatment was not included in the Table 3 Mean drainage water flow corrected P loss in 1995±1996 (based on average flow of 110 mm per year) Treatment
TP (g ha 1)
TDP (g ha 1)
Transformed TP (negative reciprocal)
MRP (g ha 1)
Control Inorganic P (TSP) PS FYM BLa LDS
137 247 132 162 176 125
43 120 70 94 50 28
0.0260 0.0093 0.0280 0.0135 0.0272 0.0384
38 105 59 84 42 23
0.0334 0.0108 0.0306 0.0158 0.0335 0.0458
F probability S.E.D. S.E.M.
0.82 115 115
± ± 55
0.41 0.015 0.015
± ± 50
0.38 0.018 0.017
S.E.D.: standard error of difference between means; S.E.M.: standard error of means. a BL not included in statistical analysis.
Transformed MRP (negative reciprocal)
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Table 4 Mean drainage water flow corrected P losses in 1997±1998 (based on average flow of 68 mm per year) Treatment
TP (g ha
Control Inorganic P (TSP) PS FYM LDS
83 92 106 110 259
1.90 1.93 1.95 2.00 2.39
± 63
0.528 34.6 0.209
F probability S.E.D. S.E.M.
1
Transformed TP (log10)
P)
TDP (g ha
1
MRP (g ha
P)
24 48 58 36 84
33 39 31 21 42
0.56 34.6 24.5
0.95 27.6 19.6
1
P)
S.E.D.: standard error of difference between means; S.E.M.: standard error of means.
statistical analysis of the data as measurements were only available from one plot and no data are presented for 1997±1998 as the number of samples were obtained were insuf®cient to make a robust estimate of P loss. In the ®rst drainage season (1994±1995), MRP and TDP losses were signi®cantly increased (P < 0:1) following the PS addition by 397 and 443 g P ha 1, respectively, compared with the untreated control (Table 2). Similarly, substantially increased TP losses were measured (878 g P ha 1), although this increase was not statistically signi®cant (P > 0:1). P losses from the LDS, solid manure and inorganic fertiliser P treatments were Table 5 TP content (kg m applied
3
liquids and kg t
Manure type
Year
PS
1
(fresh weight) solids) and percentage P fractions in the organic manures
TP
Water-soluble P (%)
NaHCO3-extractable P (%)
Mean
S.D.
1994±1995 1995±1996 1996±1997 1997±1998
0.63 0.51 0.30 1.15
0.11 0.03 0.004 0.19
65 71 30 59
91 94 60 90
FYM
1994±1995 1995±1996 1996±1997 1997±1998
2.19 1.58 1.17 1.37
0.16 0.32 0.04 0.19
16 10 14 17
25 27 39 31
BL
1994±1995 1995±1996 1996±1997 1997±1998
10.50 9.03 8.36 9.47
0.34 0.45 0.21 0.41
23 10 50 16
17 17 45 17
LDS
1994±1995 1995±1996 1996±1997 1997±1998
0.47 0.23 0.26 0.75
0.05 0.08 0.009 0.17
11 13 15 11
23 35 35 40
12
33
Mean
0.43
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169
not signi®cantly elevated compared to the untreated control in 1994±1995 (P > 0:1). Neither any of the organic manure treatments nor the application of inorganic P fertiliser caused signi®cant increases in the amount of P lost in drainage water compared to that measured from the control in either of the other two seasons when drainage occurred (1995±1996 and 1997±1998). 3.4. Manure phosphorus In the majority of samples analysed more than 90% of the total manure P was in the inorganic form. The TP content and proportions of manure TP extracted by water and sodium bicarbonate are summarised in Table 5. Despite the variable results, which clearly demonstrate the heterogeneity of organic manures, clear differences between manures were apparent. The key difference between the manures being that in three out of 4 years the PS contained a much greater proportion of the more mobile water-soluble and bicarbonate-extractable P than the other manures. 4. Discussion Of all of the treatments applied, only the PS application in November 1994 signi®cantly increased losses compared with the untreated control. This was most probably due to direct contamination of the drainage water with slurry since the samples collected were discoloured compared to samples collected from other treatments. Since the slurry was applied 4±6 weeks before the onset of drainage this suggests that some of the slurry was retained in soil macropores and then ¯ushed out by the ®rst two drainage events. This effect may have been exacerbated by additional macropores created during the recent installation of the underdrainage system in autumn 1994. Current best practice in the UK outlined in the MAFF's `Code of Good Agricultural Practice for the Protection of Water' (MAFF, 1998) recommends that organic manures should not be applied to land under certain conditions. These include ®elds that have been ``pipe drained, mole drained or subsoiled over the drains within the last 12 months'' or ``where the soil is cracked down to the tile drains or back®ll''. The ®ndings of this study thus support this guidance. This is particularly important advice given that there are an estimated 6:4 106 ha of drained agricultural land in UK and Wales, and that ca. 70% of PS and cattle slurry applications to land cropped with cereals takes place in the autumn±winter period (Smith et al., 2000, 2001). Concentrations of MRP in the drainage water in 1994±1995 of up to 10.0 mg l 1 were similar to those reported by Stamm et al. (1997) in drainage water immediately following the application of manure (4.8 mg l 1). Maximum TP concentrations of 75 mg l 1 were greater than those reported by McAllister (1976) in drainage water where dilute slurry had been applied to an intensively drained clay soil (10 mg l 1) but typical concentrations were similar. Hooda et al. (1996) in the week following a November cattle slurry application to a grassland soil was able to account for 19±42% of annual MRP losses in drainage water, with MRP concentration peaks as high as 12 mg l 1. The data from this study, therefore, are consistent with other studies and support the argument that manures are a signi®cant source of incidental P loss from agricultural land to water (Withers et al., 2000).
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Increased losses would logically have been expected from the LDS application in 1994± 1995 as well as the PS, especially since the hydraulic loading from the application of the LDS was much greater (up to 3.4 times). The proportions of the different forms of P in each of the manures may provide an explanation of the fact that only application of PS caused an increase in P losses. The PS contained on average the greatest proportions of P in the `easily mobilised' water-soluble and bicarbonate-extractable forms, 59 and 86%, respectively, compared with 12 and 33% for the LDS, 14 and 30% for the FYM and for the BL ca. 25% for both forms. A lower solubility of P in LDS compared to cattle FYM was found by Withers et al. (2001) and this was re¯ected in reduced P loss in surface runoff following sludge application. An additional factor in the study reported which may have reduced losses from the solid manures was that they were ploughed in after application. This will have intimately mixed the solid manures with the soil providing some protection against mobilisation and also disrupted continuity of macropores and ®ssures created by drainage installation. The fact that P losses were not increased by PS application in 1995±1996 when the soil was extensively cracked, suggests that other factors in¯uence P losses in drainage water. In the ®rst (1994±1995) drainage season, the manures were applied wet soils in midNovember 1994, which will have tended to reduce immobilisation of P, and the ®rst drainage event occurred in late December 1994, around 6 weeks after application. In the second and fourth years of the study, the manures were applied to much drier soils in midSeptember, which will have led to greater immobilisation and the ®rst drainage event did not occur until late December, around 14±16 weeks later. These results suggest that the combined effect of the time lapse between the PS application and onset of drainage and the soil moisture content at time of application may have limited amount of P lost in the other 2 years. Other workers have shown a link between the time gap between application and concentrations of P in surface runoff (Sharpley, 1997). Although, the delay between application and ®rst drainage event, was considerable in all years it is likely that any manure present in macropores would have remained a potential source of P loss, especially for those manures with a high degree of water solubility and/or under wet soil conditions. Only liquid manures have the potential to penetrate into macropores below plough depth and hence remain easily mobilisable under these conditions. Other research (Williams and Nichosoon, 1995) has also shown that P losses following application of dirty water were much lower when the soil had a soil moisture de®cit at the time of application. In this study, there was no evidence that the application of 60 kg ha 1 of inorganic fertiliser P to a `wet' soil in November 1994 increased losses, or in the 2 years when inorganic fertiliser P was applied to `dry' soils in September. This is in contrast to results obtained on a clay soil at Brimstone farm (Cannell et al., 1984) where an application of 33 kg ha 1 of inorganic fertiliser P to a wet soil in December 1994 showed a consistent trend for increased MRP concentrations and loadings in drain ¯ows over the whole of the 1994±1995 winter drainage season (Catt et al., 1998). However, other workers such as, Zwerman et al. (1972) and Leinweber et al. (1999) have reported that application of mineral P fertiliser did not result in greater losses in drainage water or in lysimeter leachates, respectively. The calcium carbonate content in the Denchworth top soil at Brimstone is <0.1% (Cannell et al., 1984), whereas in the Hanslope Association soils at Boxworth it is typically ca. 2% and free calcium carbonate is in evidence which will tend to
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lead to reduced losses of P in soluble forms both from organic manures and from mineral P fertiliser. The P losses measured following PS application were not large in proportion to the amounts applied but could have a signi®cant impact on any receiving water, depending on dilution in the watercourse and nature of the receiving water body. The application of solid manures, LDS and inorganic fertiliser P did not increase P loss above the untreated control. Thus, on the evidence of this study, placing restrictions on the timing of solid manure, LDS and inorganic fertiliser P applications in order to minimise P losses in drainage water would not seem justi®ed. 5. Conclusions The application of PS to drained clay soils can increase P concentrations and losses in drainage water. In this study, the elevated P concentrations were a result of direct contamination of the early drainage water ¯ows with slurry caused by rapid transport through mole drain macropores created in the soil, which may additionally have been exacerbated by recent installation of the underdrainage system. Application of LDS, FYM, BL and inorganic P fertiliser were not found to increase P concentrations and losses in drainage water. The results con®rm current guidelines to avoid applying slurries to drained soils where there is a likelihood of drainage occurring soon after land application (i.e. once the soil has returned to ®eld capacity). Potential factors determining whether increased P loss occurs following application of liquid manures include manure P solubility in water, continuity of soil macropore structures and soil moisture status during the period between application and onset of drainage. Acknowledgements This work was funded by the UK Ministry of Agriculture, Fisheries and Food, and UK Water Industry Research. The efforts of ADAS colleagues who assisted in carrying out the ®eld trials are also acknowledged.
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