Mitigation of Phosphorus and Sediment: Is there a cost-effective solution? Alison Bailey(1), John Quinton(2), Martyn Silgram(3), Carly Stevens(2) and Bob Jackson(3) (1) Department of Agriculture, University of Reading, Reading RG6 6AR, UK, (2) Environmental Science Department, Lancaster University, Lancaster LA1 4YQ, UK , (3) ADAS Wolverhampton, Wolverhampton WV6 8TQ, UK
[email protected]
Introduction The EU Water Framework Directive introduced across Europe in 2003 requires governments to set water quality objectives based on good ecological status and includes specific requirements to control diffuse pollution. Given the pivotal role that phosphorus (P) and sediment play in influencing water quality, and that agriculture is thought to be responsible for 50% of the inputs to surface waters, controlling the movement of these diffuse inputs from land to water bodies will become increasingly important. There are already a wide range of options for reducing soil erosion and the subject has received considerable research effort, however, there is significant potential to evaluate, modify, combine and improve the mitigation effectiveness of existing practices, particularly focused on reducing P losses using within field mitigation measures. The Mitigation Options for Phosphorus and Sediment (MOPS) project (2005 to 2008) is investigating the cost effectiveness of specific control measures, representing different levels of farmer intervention, in terms of mitigating sediment and P loss from combinable crops. Project outline Three contrasting case study farms in England covering vulnerable soil types and slope forms are involved in the project to discover which preventative techniques are the most efficient. The three field sites are the Allerton Trust farm in Loddington, Leicestershire which is on clay soils, ADAS Rosemaund in Herefordshire which is on silt soils, and Severn Trent Water’s farm at Old Hattons near Wolverhampton which is on sandy soils. The mitigation options are focused on within field measures and include different cultivation techniques, vegetative barriers, tramline management and crop residue management. In the first year of the project six treatments were investigated at
Loddington: ploughing up and down the slope, across the slope, and across the slope with the establishment, within field, of a beetle bank along the contour; and minimum tillage up and down the slope, across the slope, and across the slope again with a contour beetle bank. At Rosemaund plots were established to examine losses within and between tramlines and specifically tramline wheeling disruption using a cultivator fitted with a ducksfoot tine to disrupt the compacted surface of the wheeling after its establishment in the late autumn. At Old Hattons plots were established to examine the management of post harvest cereal straw residues which had either been baled and removed or chopped and incorporated into the soil. Cost effectiveness analysis To determine the cost effectiveness of the different mitigation options data for each of the case study farms are being collected for each treatment in each year. This focuses on (i) field records on crop establishment, fertiliser and spray applications and harvesting and (ii) the additional costs associated with the mitigation options. The analysis involves the construction of a simple spreadsheet model to examine impacts on individual cereal crop margins and thence the overall arable rotation. In the first instance, three farm level versions of the model have been developed to represent each of the three case study farms. The model includes both gross margin calculations and an ‘operating’ margin based upon labour and machinery costs which can be directly allocated to each crop enterprise. The operating margin goes beyond an enterprise gross margin as it includes some fixed costs, however, it is not a true net margin as certain building, land and general overhead costs are excluded. The resultant gross and operating margins reflect the impacts of the different mitigation options on the costs of crop establishment and fertiliser and agro-chemical applications. Once impacts on individual crop margins have been calculated, the impact on the overall arable rotation can be determined. To do this, each crop margin is multiplied by the percentage area that is grown on the farm taken from the 2006 harvest year farm records. The resultant rotational farm operating margin for each of the mitigation options, and any additional capital costs associated with these, then need to be compared with data on the runoff, sediment and P loss to determine how effective and hence cost effective the options are. Data for this has been collected over the winter period, October through to March, when erosion risk and hence soil and diffuse P loss is at its highest. Results Table 1 shows the impact of the introduction of the various mitigation options on the operating margin. At Loddington, minimum tillage improves the operating margin, however, there are additional costs and implications from the introduction of the in-
field vegetative strip. At Rosemaund and Old Hattons the additional tramline disruption process and straw incorporation activities reduce the operating margin. Table 1. Mitigation options: additional costs and impact on margin Site
Mitigation option
Additional cost
Loddington
Plough (control) Contour plough Contour plough with in-field vegetative strip Minimum tillage Contour minimum tillage Contour minimum tillage with in-field vegetative strip Plough (control) Tramline disruption Plough (control) Straw bale and removal Straw chop and incorporate
n/a n/a Year 1: £163/ha Each yr: £21/ha n/a n/a Year 1: £163/ha Each yr: £21/ha n/a n/a n/a n/a n/a
Rosemaund Old Hattons
Resultant operating margin £215 per ha £215 per ha £213 per ha £263 per ha £263 per ha £261 per ha £197 per ha £186 per ha £243 per ha £242 per ha £224 per ha
Initial results from the winter of 2005/06, which was quite dry compared to long term averages, indicate that at all case study farms tramlines are responsible for the majority of run-off, sediment and P lost, and that measures focused on this area as opposed to other within field measures may help in mitigating P losses. The results from Rosemaund show that, significantly, tramline disruption consistently and dramatically reduced run off and P fluxes to levels comparable to no-tramline areas. At the Loddington, the results also indicated that the use of beetle banks combined with contour cultivation could reduce runoff, soil and nutrient losses although this effect is not as clear as the difference between tramline and no-tramline areas. At Old Hattons, the results indicated that the treatments receiving 2.5t/ha straw chopped and incorporated consistently and substantially reduced surface run-off and total P loss per unit area compared with those where straw had been baled and removed. The first year results present some potentially interesting solutions for the mitigation of P and sediment loss from arable cropping, however, and at this early stage, no concrete conclusions can yet be drawn. Further work is ongoing on tramline disruption, and contour and minimum tillage combined with in field vegetative. In terms of cost-effectiveness, the extrapolation of the case study data to generic farm typologies and from a farm level to regional basis is also being undertaken.
