Reducing the risk of soil compaction when growing potatoes and the associated risk of water run-off, erosion and loss of plant protection products will be key for potato growers in 2013
In light of the challenging 2012 season, reducing the risk of soil compaction when growing potatoes and the associated risk of water run-off, erosion and loss of plant protection products will be key for potato growers in 2013 both for economic and environmental reasons. Dominic Kilburn speaks to a soil scientist whose work in the past three years could highlight some novel methods to help them do just that. Potato growers are at risk of losing about five per cent of rain and irrigated water from field run-off each season, with economic and environmental implications that they simply cannot afford to ignore. Research work over the past three years on shallow and moderate slopes has concluded that potato growers are at risk of losing about five per cent of rain and irrigated water from field run-off each season, with economic and environmental implications that they simply cannot afford to ignore.
However, work carried out by ADAS as part of Defra- and Potato Council-funded projects, has shown that novel post-planting management which is available now, and some novel approaches still in development, can mitigate water and soil run-off loss and are currently being considered as options in a future revision of Environmental Stewardship.Potatoes are inherently a high-risk crop, points out ADAS senior researcher and soil and water scientist, Dr Martyn Silgram, due to the cultivation operations prior to planting, the spraying operations post-planting and the late harvest. “Fields in potatoes are therefore inherently more susceptible to soil compaction and erosion than cereal fields,” he comments.
According to Martyn, compaction in potatoes comes from two areas; deeper compaction caused by bed-forming implements, and shallower compaction from de-stoning and post-planting traffic such as spraying operations. “Potatoes are very sensitive to compaction which can limit rooting depth, reduce water and nutrient availability, reduce surface infiltration rates and increase the risk of waterlogging, while tuber rot diseases and surface run-off are also a factor.”Tuber quantity and quality can be severely affected, and the more compaction there is the greater the potential loss of yield,” comments Martyn.
He says that, as well as loss of income through reduced yields, compacted stone rows between potato beds also offer irrigation and rain water a direct route off the field and, with 45 per cent of the country’s potato crops irrigated, a significant amount of water can be lost. “A huge amount of energy use and financial cost is put into spraying and irrigation systems and it’s key that water is managed efficiently and prevented from running off fields,” he points out.Research work on a loamy sand site near Telford began in 2010 and focused on establishing practical methods to minimise shallow compaction, erosion and run-off from potato rows.
Three locations were monitored: no stone rows; stone rows without traffic and stone rows which received traffic by sprayers etc. A fourth treatment monitored stone rows without traffic which had a winged tine used carefully to lift compaction just below the stones shortly after planting. “The first priority was to establish where the greatest risk of run-off was from potato fields,” explains Martyn (see Figure 1). Figure 1: Water lost as run-off from potatoes – Telford 2010 (Loamy sand, 5 slope, 130mm rain, 115mm irrigation) While the greatest loss of water in the trial was seen in the stone rows receiving traffic, as might be expected, Martyn points out that the traffic in this case was from post-planting sprayer wheelings which only occurred every 24m. “Of more concern perhaps is the loss from the stone rows every couple of metres which don’t receive traffic as there are so many more of these in a typical potato field, although ideally we need management tools to reduce losses from both areas.” The pass with a vertical winged tine underneath the layer of stones in a ‘no traffic stone row’ clearly demonstrated the greatest reduction in run-off, although Martyn notes that farmers may be wary of this method due to concerns over dislodging the carefully placed stones.Upscaling Figure 1 results to reflect field-scale practice (with greater numbers of no stone rows), then 4.2 per cent was lost via run-off out of a total of 354,000 litres of rainfall and irrigation water on the trial area over the whole season.In an identical trial run last year, but on a silty clay loam soil (to show the effects on heavier soils), the equivalent field-scale result showed a 5 per cent loss out of a total of 434,000 litres of rainfall on the trial area.”Irrespective of a difference in the seasons, and we know 2012 was a wet one, the percentage of water run-off was very consistent and it shows that we just can’t ignore it,” stresses Martyn, who claims that these run-off losses will introduce errors into farmers’ estimates of soil moisture deficit as well as posing environmental risks.Novel methods to reduce run-off
Having established the relative importance of no stone, stone and traffic stone rows in potatoes as pathways for run-off, work in 2011 on loamy sands studied the mitigating effects of some novel post-planting systems compared with a ‘control’ of stone rows without sprayer traffic. In addition to the vertical winged (duckfoot) tine, implements included a conventional tied ridger (an established system of creating mini water-holding reservoirs between rows), and a novel ‘Creyke’ profiler/roller in combination with angled tines. The latter is a new toolbar-mounted polymer roller which leaves the soil convex-shaped in the stone rows, while two angled tines ahead of the roller create grooves at the base of the shoulder of the facing ridges.The idea behind the Creyke roller and tines is that the indentations created by the tines allows water that runs down the ridges to be diverted back into the potato bed and towards the crop, as does the convex soil shape left by the roller in the stone row. This conserves water, nutrients and surface-applied products, keeps them near the crop and avoids them washing off fields down stone rows, explains Martyn.Options such as (l-r) vertical tines, Creyke roller/tines, a tied ridger and rotary tines (not pictured) are a big improvement on reducing water losses from potato fields.Compared with the stone control rows, which caused a 6.8 per cent loss of water in the trial, the implements fared considerably better with a 0.1, 2.4 and 1.1 per cent run-off loss of rainfall and irrigation water for the vertical tine, the tied ridger and Creyke roller/tine unit respectively.
Benefits were also seen in terms of sediment loss, continues Martyn.”Where the control lost 570kg/ha of fertile topsoil as sediment in run-off, all the implements showed a dramatic reduction in loss,” he adds.In 2012 trials (on silty clay loam), the tied ridger performed very well with only 2.3 per cent rainfall lost as water run-off (an 89 per cent reduction compared with the control). “This is a better performance than on lighter land the previous 2011 season, probably because the heavier soil was able to retain the ties for longer into the season. In 2012 on silty clay loam soils, the Creyke roller and angled tines reduced losses to 10 per cent of rainfall (a 50 per cent reduction).In addition, this trial included a novel Simba Great Plains three-bladed rotary harrow device. Previously trialed on cereal tramlines, this implement creates an offset pattern of shallow diagonal holes at the base of the stone row which improves infiltration, reduces ponding of water on the surface, and reduces run-off – in this case by as much as 98 per cent. ‘Trafficability’ was not affected.
“When you consider that mains water costs are often around 1.50/m3 and that run-off will take fertiliser and spray material with it, then what is clear is that these options are a big improvement on doing nothing.”Martyn says that some of these systems, such as the tied ridger and vertical winged tine can be used by growers this season if they want to make an immediate impact on their soil, water and nutrient management, while items such as the Creyke roller/angled tines and innovative Simba rotary harrow are still in development.”Anything that can work as effectively as these methods did in the challenging wet conditions of 2012 is certainly worth considering to help limit compaction and build resilience into potato farming systems,” concludes Martyn.*Any Farmers Guide readers requiring more information on this subject can contact ADAS’ Dr Martyn Silgram or email: [email protected].Reducing deeper compaction
On-going trials work this season by ADAS and SRUC (Scotland’s Rural College) will compare conventional deep potato cultivation methods, when bed-forming and de-stoning, with reduced pass and single pass systems, says Dr Martyn Silgram.
With a view to reducing deep compaction in potato beds, plough-based systems will be compared with Simba Great Plains’ DTX tine/disc/roller implement (ahead of bed-forming), as well as the George Moate Tillerstar that combines the work of a bed tiller, stone/clod separator and bedformer in one machine.
“There’s no doubt that deeper compaction in potato systems can be caused by bed-forming prior to planting and we want to evaluate whether compaction could be reduced by having fewer passes in the field, or by using a greater number of separate passes but with lighter machinery,”
says Martyn. Simba Great Plains’ DTX tine/disc/roller implement will be compared in ADAS and SRUC trials this season with plough-based systems with a view to reducing deep compaction in potato beds.