There has been a notable decline in soil fertility nationally and the impact is even more serious on farms with heavy soil types. On heavy soils, there is the potential to increase annual grass production by 30% where soil pH, phosphorus (P) and potassium (K) status is optimised.
Seven dairy farms farming on heavy soil types are participating in a monitoring and development programme and contributing key data on farm performance. The farms are deemed heavy (ie, predominately clay mineral soils) and are located in high rainfall areas of the southwest of Ireland. The Heavy Soils Programme (HSP) has been operating since 2010.
The programme is focusing on all aspects of profitable and sustainable dairy farming on heavy soil types. Soil fertility is a key focus for the programme in order to enhance the underlying production potential of these, often more challenging, soil types.
The importance of soil pH and appropriate liming strategies has emerged as a key target for boosting overall soil fertility and farm productivity.
Changes in soil fertility 2013-2016
It has been firmly established in research that soil pH must be corrected as a first step in overall improvement in soil fertility status. HSP farms embarked on a programme of soil fertility improvement in 2010.
The low initial soil pH on these farms was due in part to a trend of low usage of lime nationally, with higher nitrogen usage masking the impact of low pH on grass growth. Fertiliser plans prepared in 2013 indicated a lime requirement of, on average, 90t of ground limestone per annum. A comprehensive soil-testing programme takes place across all the heavy soils farms in December each year. The impact of these lime applications over time on the soil pH across the milking block area of the HSP farms is summarised in Table 1.
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Average soil pH has increased from 5.8 to 6.3. All of the seven farms showed a pH increase. The farms continued to focus on applying lime in 2016 to bring all paddocks to target pH of 6.3. No noticeable change in soil trafficability has been observed by the farmers largely due to quantities applied being limited to 2t/acre (5t/ha) in any one application.
Average fertiliser costs in 2015 were 3.3c/l on the heavy soils farms, with lime accounting for 0.42c/l of that cost. Phosphorus status increased on four farms and decreased on three farms (Kiskeam, Doonbeg and Listowel).
Higher offtake issues combined with high fixation capacity remain the key factors militating against improved P status on these farms. Potassium status remained static between 2015 and 2016, with only two farms recording an improvement in K status.
Lime and loss through drainage/rainfall losses
The HSP farms are in high rainfall areas. Therefore, lime losses are estimated to be high, at up to 625kg/ha/year. This equates to a loss through drainage alone of 1.2t/acre over a five-year period. In addition, lime required to counteract acidity from chemical N use and loss in milk/meat means a maintenance requirement of 2t/acre every five years is required on these farms. In effect, any lime applied in 2011-2014 was only keeping pace with the maintenance requirement and was not having an impact on lifting farm soil pH.
Timing of lime application
The experience of the HSP farms shows that lime can be applied at any time of year when ground conditions are suitable. Outside of the normal application peaks at reseeding and late autumn, monthly lime usage statistics suggest that very little lime is applied in the spring. April can be an ideal time to apply lime when ground is well grazed out. June/July is another suitable time after silage has been harvested or as surplus bales are taken out (stubble available) and when ground conditions are good for spreading.
Impact of lime application observed on HSP farms
Paddocks that were at soil pH 5.5 on HSP farms in 2013 and are now at soil pH 6.3 and grew an additional 2t/ha of grass DM in 2016.Farms that are now at target pH notice a much faster response to applied fertilisers. When soil temperatures are good, paddocks are easily achieving the 21-day pre-grazing target cover of 1,500kg/ha of grass DM. This had taken 26-28 days to achieve previously. This has led to more surplus silage of high quality being harvested during the main growing season, which gives a significant boost to the winter feed supply – an invaluable resource on farms with heavy soils and longer winters.In 2016, the Athea farm had an average soil pH of 6.5. As well as supporting a dairy herd stocking rate of 2.5 cows/ha, the farm also produced an additional 70t of silage DM in the form of 390 surplus bales of silage equivalent to 10 bales/ha (almost four bales per cow). The farm grew 11.4t/ha and utilised 9t/ha of grass DM.Paddocks are better grazed out by the herd and palatability of grass has improved.Grass has a better root structure, better tillering and less open swards.Good progress is being made in increasing soil pH to target. The challenge for these farms is to put a strategy in place to maintain lime status in the years ahead.Farmers aware of the risk of excessive lime use reducing soil trafficability have split the lime applications over time (max 2t per single application). This has worked well for building soil pH without negatively affecting soil structure.Financial benefits of lime
application on HSP farms
An evaluation of the cost of lime application compared with benefits of the additional grass production is shown in Table 2. This analysis assumes that increasing the soil pH from a starting point of 5.5 up to the target of 6.3 will improve grass production by 2t/ha of DM. This increase in pH will initially require 10t/ha (4 t/acre) of lime, half in year one and the balance in year three. After the initial high lime application, an average application per year of 1t/ha is assumed to maintain the soil pH thereafter.
![]()
Click for full-size table
The analysis shows that the increased grass production brings a return on investment in and after year two. However, it is worth noting that the benefits of lime will show grass production responses in the year of application, especially with lime applied in late autumn or winter in advance of the following year. In just three years, the return from applying lime is €2.58 for every €1 spent on lime. By the end of year nine, this return increases to €6.44 per €1 spent on lime.
Read more
Special focus: fertilisers
There has been a notable decline in soil fertility nationally and the impact is even more serious on farms with heavy soil types. On heavy soils, there is the potential to increase annual grass production by 30% where soil pH, phosphorus (P) and potassium (K) status is optimised.
Seven dairy farms farming on heavy soil types are participating in a monitoring and development programme and contributing key data on farm performance. The farms are deemed heavy (ie, predominately clay mineral soils) and are located in high rainfall areas of the southwest of Ireland. The Heavy Soils Programme (HSP) has been operating since 2010.
The programme is focusing on all aspects of profitable and sustainable dairy farming on heavy soil types. Soil fertility is a key focus for the programme in order to enhance the underlying production potential of these, often more challenging, soil types.
The importance of soil pH and appropriate liming strategies has emerged as a key target for boosting overall soil fertility and farm productivity.
Changes in soil fertility 2013-2016
It has been firmly established in research that soil pH must be corrected as a first step in overall improvement in soil fertility status. HSP farms embarked on a programme of soil fertility improvement in 2010.
The low initial soil pH on these farms was due in part to a trend of low usage of lime nationally, with higher nitrogen usage masking the impact of low pH on grass growth. Fertiliser plans prepared in 2013 indicated a lime requirement of, on average, 90t of ground limestone per annum. A comprehensive soil-testing programme takes place across all the heavy soils farms in December each year. The impact of these lime applications over time on the soil pH across the milking block area of the HSP farms is summarised in Table 1.
![]()
Average soil pH has increased from 5.8 to 6.3. All of the seven farms showed a pH increase. The farms continued to focus on applying lime in 2016 to bring all paddocks to target pH of 6.3. No noticeable change in soil trafficability has been observed by the farmers largely due to quantities applied being limited to 2t/acre (5t/ha) in any one application.
Average fertiliser costs in 2015 were 3.3c/l on the heavy soils farms, with lime accounting for 0.42c/l of that cost. Phosphorus status increased on four farms and decreased on three farms (Kiskeam, Doonbeg and Listowel).
Higher offtake issues combined with high fixation capacity remain the key factors militating against improved P status on these farms. Potassium status remained static between 2015 and 2016, with only two farms recording an improvement in K status.
Lime and loss through drainage/rainfall losses
The HSP farms are in high rainfall areas. Therefore, lime losses are estimated to be high, at up to 625kg/ha/year. This equates to a loss through drainage alone of 1.2t/acre over a five-year period. In addition, lime required to counteract acidity from chemical N use and loss in milk/meat means a maintenance requirement of 2t/acre every five years is required on these farms. In effect, any lime applied in 2011-2014 was only keeping pace with the maintenance requirement and was not having an impact on lifting farm soil pH.
Timing of lime application
The experience of the HSP farms shows that lime can be applied at any time of year when ground conditions are suitable. Outside of the normal application peaks at reseeding and late autumn, monthly lime usage statistics suggest that very little lime is applied in the spring. April can be an ideal time to apply lime when ground is well grazed out. June/July is another suitable time after silage has been harvested or as surplus bales are taken out (stubble available) and when ground conditions are good for spreading.
Impact of lime application observed on HSP farms
Paddocks that were at soil pH 5.5 on HSP farms in 2013 and are now at soil pH 6.3 and grew an additional 2t/ha of grass DM in 2016.Farms that are now at target pH notice a much faster response to applied fertilisers. When soil temperatures are good, paddocks are easily achieving the 21-day pre-grazing target cover of 1,500kg/ha of grass DM. This had taken 26-28 days to achieve previously. This has led to more surplus silage of high quality being harvested during the main growing season, which gives a significant boost to the winter feed supply – an invaluable resource on farms with heavy soils and longer winters.In 2016, the Athea farm had an average soil pH of 6.5. As well as supporting a dairy herd stocking rate of 2.5 cows/ha, the farm also produced an additional 70t of silage DM in the form of 390 surplus bales of silage equivalent to 10 bales/ha (almost four bales per cow). The farm grew 11.4t/ha and utilised 9t/ha of grass DM.Paddocks are better grazed out by the herd and palatability of grass has improved.Grass has a better root structure, better tillering and less open swards.Good progress is being made in increasing soil pH to target. The challenge for these farms is to put a strategy in place to maintain lime status in the years ahead.Farmers aware of the risk of excessive lime use reducing soil trafficability have split the lime applications over time (max 2t per single application). This has worked well for building soil pH without negatively affecting soil structure.Financial benefits of lime
application on HSP farms
An evaluation of the cost of lime application compared with benefits of the additional grass production is shown in Table 2. This analysis assumes that increasing the soil pH from a starting point of 5.5 up to the target of 6.3 will improve grass production by 2t/ha of DM. This increase in pH will initially require 10t/ha (4 t/acre) of lime, half in year one and the balance in year three. After the initial high lime application, an average application per year of 1t/ha is assumed to maintain the soil pH thereafter.
![]()
Click for full-size table
The analysis shows that the increased grass production brings a return on investment in and after year two. However, it is worth noting that the benefits of lime will show grass production responses in the year of application, especially with lime applied in late autumn or winter in advance of the following year. In just three years, the return from applying lime is €2.58 for every €1 spent on lime. By the end of year nine, this return increases to €6.44 per €1 spent on lime.
Read more
Special focus: fertilisers
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