Agriculture, Ecosystems and Environment 105 (2005) 565–579 www.elsevier.com/locate/agee
Influence of cultivation methods on suspended solids and phosphorus concentrations in surface runoff on clayey sloped fields in boreal climate Markku Puustinen*, Jari Koskiaho, Kimmo Peltonen Finnish Environment Institute, P.O. Box 140, FIN-00251 Helsinki, Finland Received 11 September 2003; received in revised form 8 July 2004; accepted 26 August 2004
Abstract Methods for decreasing agricultural phosphorus (P) loadings to surface waters are needed to achieve good water quality. To reliably find out the efficiency of different methods in changing hydrological conditions, long-term experiments are of invaluable importance. Here the effects of various cultivation methods on total suspended solids (TSS) and P concentrations in – and the volume of – plough layer runoff (PLR) were studied in a sloping experimental field in southwest Finland during a 9-year period. Yearly means of PLR and flow-weighted mean concentrations from the treatment plots were compared with a control, winter wheat (Triticum aestivum) treatment (WW), of which the values assigned were equal to 1. No major differences were found in PLR for cultivation methods up and down slope, except for the cross-ploughing treatment (0.49). Normal ploughing and cultivation treatments produced the highest TSS concentrations (1.38 and 1.18, respectively), whereas values between 0.44 and 0.53 were measured for three treatments with reduced (or no) tillage. Particle-bound P (PP) concentrations closely followed those of TSS. Dissolved reactive P (DRP) showed contrasting behaviour, with the greatest treatment effects from the three reduced tillage treatments (1.58–2.29). This study showed that by changing over from intensive autumn tillage to permanent vegetation cover, erosion and PP loss were markedly decreased. Methods employing no autumn tillage and leaving an undisturbed soil surface during winter showed particularly high reductions in loading. The simultaneous increase in DRP loss is an undeniable drawback that should be resolved separately. This study, as a part of a wider complex of integrated studies, will be utilized in a decision-making tool for the assessments of loading effects and load reduction possibilities in terms of cultivation methods. # 2004 Elsevier B.V. All rights reserved. Keywords: Agriculture; Erosion; Nutrients; Water pollution; Runoff
1. Introduction * Corresponding author. Tel.: +358 9 40300354; fax: +358 9 40300390. E-mail address:
[email protected] (M. Puustinen).
Nutrient loading originating from agriculture has been monitored by the environmental authorities in small basins since the 1960s in Finland and reported at 5–
0167-8809/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2004.08.005
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10-year intervals. Kauppi (1984) showed that the mean phosphorus (P) loading was 0.57 kg ha1 year1 and nitrogen (N) loading 12 kg ha1 year1 during 1965– 1976. Later estimates were 0.9–1.8 kg P ha1 year1 and 7.6–20 kg N ha1 year1 for the period 1981–1985 (Rekolainen, 1989), 0.65–0.91 kg P ha1 year1 and 8.1–21.0 kg N ha1 year1 for 1986–1990, and 0.63– 1.4 kg P ha1 year1 and 7.9–15 kg N ha1 year1 for 1991–1995 (Vuorenmaa et al., 2002). Mansikkaniemi (1982) reported annual amounts of erosion of at most 5– 6 t ha1 in cases with exceptionally high annual precipitation and in highly sloping fields. With respect to the status of surface waters in Finland, the prevailing agricultural loading is problematic because it comprises 63% of the total anthropogenic P loading and 43% of the total anthropogenic N loading (Valpasvuo-Jaatinen et al., 1997). Thus, various environmental programmes aiming at significant decreases in loading regard agriculture as a central issue. In-field load reduction methods used to decrease SS, P and N concentrations are preferred because agricultural production in boreal conditions is based on rapid, efficient drainage of arable land. The objective here was to compare different cultivation practices, and to determine effective choices, for decreasing runoff, total suspended solids (TSS) and P concentrations in plough layer runoff (PLR) under boreal agricultural conditions and the annual and seasonal stability of the treatments in terms of TSS and P loading. The experiments were undertaken during 1989–2002 on a sloping field with different cultivation practices and types of plant cover.
2. Material and methods 2.1. Experimental field The experimental field (608480 N, 228370 E) was established in 1987–1988 on the land of a farm situated
in the close vicinity of the River Aurajoki. The experimental area is sloping (8–9%), which is a typical feature of the local fields. The soil in the plough layer of the experimental field is clay loam, of which the clay content is 44%. Below the ploughed surface layer (30, 50 and 90 cm), the clay content rises to over 60% (Table 1). According to the US Soil Taxonomy (Soil Survey Staff, 1998), the soil of the experimental area is a fine Typic Cryaquept (Uusitalo et al., 2000). According to the FAO system (FAO, 1988), the soil is Vertic Cambisol. The total area of the experimental field is 1.02 ha, divided into 12 plots (Fig. 1). Length of nine plots was 51 m and that of the three shorter ones, due to the bend of the river Aurajoki, only 36.5 m. Breadth of every plot was 18 m, half of which contributing to the measurements (‘‘net-breadth’’) because the plots were hydrologically isolated from each other by 4.5 m strips on both sides. During the second phase, wooden boards were installed between the plots for 15 m length at their lower ends to improve the hydrological isolation. The available P content of the soil (Table 2) was measured on five occasions and determined as an extraction of P from solutions of soil in water (1:60) and soil in acidified ammonium acetate (1:10). The P content of soil in the experimental plots was considerably higher than the mean P content of agricultural land in Finland (12.5 mg P l1 soil). The determined values of calcium, magnesium and potassium contents were typical for soils with satisfactory fertility values. The pH of the plough layer was favourable, but varied somewhat between the experimental plots. The rate of infiltration in the plough layer was 1.5 mm min1 (0.4–2.0 mm min1). The total porosity of the soil at 25 cm depth was 53% (45–58%), the dry density 1.56 g cm3 (1.48–1.69 g cm3), field capacity 47% (43–53%). In the experimental plots, runoff water was collected from the entire cultivated surface layer (25 cm). The collectors (9 m) were placed in a trench dug at the lower edge of the experimental (net) plots (Puustinen, 1994). The wall of the trench facing the
Table 1 Organic matter proportions and particle size fractions of silt and clay in different depths of the Aurajoki experimental field Depth (cm)
Organic (%)
0.02 mm (%)
0–20 30 50 90
6.1 4.7
43.6 60.0 60.9 60.9
13.3 14.0 18.9 19.7
17.3 14.2 14.7 14.2
25.9 11.8 5.4 5.3
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Fig. 1. Layout of the Aurajoki experimental field.
experimental plot was dug vertically upright at an angle of 908. A 6-cm thick layer of loose shingle was used to fill the space between the upright wall of the trench and the steel mesh that formed the front wall of the collector. 2.2. Field measurements and analyses Whenever continuous runoff lasted more than 1 week, the cumulated PLR was recorded twice per week. For shorter timed runoff events, the amount of PLR was recorded at the end of each event. Water samples were collected in the sampling receptacles for each PLR volume measured. This method of data
collection meant that within-runoff event variations in both PLR and concentrations remained unknown and that each data point represents the average over a runoff event. Water samples were analysed at the laboratory of the Southwest Finland Regional Environment Centre (SWREC). TSS were, at the very beginning of the experiment, determined gravimetrically according to the European Standard EN 872 (SFS, 1996) with a Whatman Nuclepore polycarbonate filter (Ø 0.4 mm). From 25 November 1991, TSS were determined as evaporation residue. Phosphorus was analysed with the molybdenum blue method (Murphy and Riley, 1962), based on the reactions between P and MoO4, Sb
Table 2 Mean P, Ca, Mg and K contents (mg l1) and pH in the plough layer of the Aurajoki field over the experimental period Period
Pwaterextr (mg l1)
Pacetate (mg l1)
1989 1992 1997 2000 2002
27.8 24.6 23.8 23.0 22.3
23.8 25.7 21.0 18.4 18.6
a
Analysed by the method described in Bowman (1988).
Ptota (mg l1)
Ca (mg l1)
K (mg l1)
2243
1802
2167 2062 2091
254 264 292
Mg (mg l1)
pH
490
6.50
384 377 378
6.07 6.04 6.16
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and ascorbic acid. In the TP determination, the sample was digested with K2S2O8 prior to the P analysis. Dissolved reactive P (DRP) was analysed from a filtered (Ø 0.4 mm) sample. Particulate P (PP) was obtained by subtracting DRP from TP. Precipitation data were measured at Turku Airport, which is situated 6 km northwest from the experimental field, and obtained from the Finnish Meteorological Institute. 2.3. Treatments The field experiments were carried out in two phases included nine experimental periods (ExpP). The first phase (ExpP I–IV) was carried out during 1990–1994 and the second phase (ExpP V–IX) during 1997–2002. A calibration period (CalP) was carried out at the beginning of both phases (1989–1990 and 1996–1997), during which the entire experimental field was planted with winter wheat (Triticum aestivum) (WW, see detailed description of the treatments below in this chapter). Each ExpP and CalP included three seasons (from September to May). In summer, there were no notable PLR events in the experimental field. For the necessity of the changed cultivation methods for the second phase, a 2-year intermission occurred between the phases. During the ExpP, two plots were planted with WW to serve as controls, against which the changes caused by differences in the examined cultivation methods were compared. The alternative treatments studied were classified by the intensity and season of tillage. The classification of the treatments and the most essential related information are presented in Table 3. The treatment plots were randomised. During phase I, fertilization followed as far as possible the normal practices of the area. Accordingly, relatively large amounts of fertilizers were used. During phase II, fertilization rates were reduced as required by the EU agroenvironmental regulations. The treatment operations performed along the slope mostly directed the flow towards the desired direction. However, even a small inexactness in working procedures induced the flow to go off-course via the side of a treatment plot. Crop yields were not measured. Normal ploughing (NP) was performed in autumn up and down the slope and cross-ploughing (CP) across (i.e. along the contour lines) the slope. Cultivation (CU) and
shallow stubble tillage (SST) were performed twice in autumn with a spring-loaded tooth harrow. Except for the deeper tillage, the CU procedure was similar to SST. NP and CP were classified as autumnal intensive tillage(1) and CU and SST as autumnal reduced tillage (2). In spring, the plots were harrowed and sown similarly with spring wheat. WW (calibration and control method) plots were ploughed in the latter half of August and harrowed and sowed during the first week of September (in exceptionally rainy autumns sowing was done later). WW was also applied without P-fertilizer (WWWP). The ground surface was crop covered (3) by tillers during winter in both treatments. The WWBZ treatment consisted of a 14-m buffer zone, i.e. an area sown with timothy grass, established at the lower end of a plot with WW. This treatment was classified as crop covered with buffer zone (4). In the stubble (STU) treatment, no work was performed after harvesting in autumn and the threshing waste was left chopped on the ground. In spring the tilling was made with a spring-loaded tooth harrow just before the sowing of spring wheat. The STU treatment was classified as reduced spring tillage (5). In the direct sowing (DS) treatment, winter wheat was sowed directly on stubble without tilling in autumn. In the grass ley (GL) treatment, the ground surface was covered with timothy grass during winter, harvesting of grass was done once every summer. The DS and GL treatments were classified as permanently crop covered (6). 2.4. Comparison of the treatment effects The principles of benchmark – or control – basins (Seuna, 1983) were applied to the data processing because this approach helps bringing out the differences solely due to the treatments by eliminating the inherent, spatial differences between the plots. During the calibration periods (1989–1990 and 1996– 1997), the control method (WW) was applied in all 12 plots, i.e. in 2 control plots and 10 (forthcoming) experimental plots, and the volume of PLR as well as SS and P concentrations in PLR were measured. Linear regression equations between the data from control plots and the (forthcoming) experimental plots were calculated for each variable, e.g. SS in control plot (x) was regressed against SS in experimental plot
Table 3 Tillage and sowing seasons, tillage depth, crop covering, and the mean fertilizer application rate per year and the length of tillers during the experimental phases in the Aurajoki experimental field
Autumnal tillages 1. Intensive tillage practices Normal ploughing (NP) Cross-ploughing (CP) 2. Reduced tillage practices Cultivation (CU) Shallow stubble tillage (SST) 3. Crop covered Winter wheat (WW) WW without P-fert. (WWWP) 4. Crop covered with buffer zone WW with buffer zone (WWBZ)
Number Tillage of ExpP season
Sowing season
Tillage Crop depth covering (cm)
Phase I
Phase II
N-fert. P-fert. Tiller Plot rate rate length (cm) no. (kg ha1) (kg ha1)
N-fert. P-fert. Tiller Plot rate rate length no. (kg ha1) (kg ha1) (cm)
9 4
Autumn Spring Autumn Spring
20–22 20–22
Uncovered Uncovered
145 145
25 25
6 1, 5
115 115
13 13
– –
1 –
9 5
Autumn Spring Autumn Spring
10–15 5–10
Straw Straw
– 145
– 25
– 2, 7
115 –
13 –
– –
5, 6 –
9 5
Autumn Autumn 20–22 Autumn Autumn 20–22
Tiller Tiller
168 –
34 –
8 to
