The grass and clover study at Ballyhaise Agricultural College in Cavan shows how farmers can maintain pasture productivity and reduce dependence on chemical nitrogen fertiliser.
Helena Walsh and Donal Patton from the Teagasc Animal and Grassland Research and Innovation Centre in Moorepark discussed the study that is being carried out to investigate the transition from old perennial ryegrass swards receiving high rates of chemical N fertiliser application to new swards at similar high rates of chemical N fertiliser application.
The study compares the results to new grass and white clover swards receiving reduced rates of chemical N on a heavier soil type.
The trial
The current experiment is a five-year systems trial running from 2021 to 2025 with the initial three years (2021 to 2023) focused on the transition from old grass-only swards to new grass and grass with white clover swards through the combined process of full reseeding and oversowing.
The experiment consists of two sward types: grass-only swards which receive 250kg chemical N per hectare per annum and newly established white clover or oversown white clover swards which receive 125kg N per hectare per annum.
In May, June and July of each year, paddocks were reseeded with three high pasture profit index (PPI) grass varieties which consisted of Astonconqueror, Astonenergy and Glenfield with or without white clover using min-till cultivation. Twenty per cent of the white clover system area was oversown in May 2021 and July 2022 using an airseeder after a grazing event.
Chieftain and Crusader were the two medium-leaf clover varieties used for both sward renewal methods.
All reseeded swards were grazed at a pre-grazing yield of 1,200kg DM/ha, or below, while the white clover oversown swards were grazed at 800kg DM//ha for the remainder of the first-year post-establishment.
The chemical fertiliser remained the same for each year of the study.
Chemical N fertiliser was applied to grass swards at each rotation post grazing from 15 February to 14 September each year.
Results
The transition from old grass to newly established and oversown pasture had no significant impact on grazing characteristics.
Total pasture production was significantly reduced during the year of new sward establishment from 14,182kg DM/ha in old pastures to 8,925kg DM/ha, 8,561kg DM/ha, and 11,830kg DM/ha in newly established grass, white clover and white clover oversown swards respectively.
The significant reduction in pasture yield in newly established swards is attributed to extended closed periods between spray-off of the old swards and the first grazing of the new sward, which is mainly due to bad weather during cultivation and establishment.
The establishment of new grass and clover swards and to a lesser extent white clover oversown swards resulted in a significant reduction in chemical fertiliser application. This reduced from 229kg N/ha and 230kg N/ha for perennial ryegrass old and new, to 119kg N/ha for white clover oversown and 90kg N/ha for newly established white clover.
The researchers said that achieving a high level of white clover content (20% to 25%) is critical to replace chemical N fertiliser with the nitrogen fixed by clover without implications for total grass yield.
Sward renewal
The high level of reseeding from grass to white clover swards had a major impact on the overall feed budget on the farm. This is due to the annual grass growth within the year of establishment being significantly reduced.
Sward type had no effect on the winter feed shortage with perennial ryegrass 55% self-sufficient and white clover systems 56% sufficient. Both of these deficits in winter feed were made up by the importing silage from other parts of the farm at Ballyhaise but the researchers said the high level of reseeding is not recommended on commercial farms.
The study found that transitioning to the white clover system resulted in a modest increase in both milk yield (5,197kg and 5,092kg) and milk solids (473kg and 461kg/cow) for white clover swards when compared to grass-only swards, while there were no significant differences observed for milk composition (fat, protein and lactose) between the two sward types during the transition.
Similarly, body weight and body condition score were comparable for both sward types.
The establishment of new swards represents a considerable cost at farm level as it costs roughly €1,150/ha to do a full reseed with clover included as energy costs and contractor costs have gone up.
The study has shown that the establishment of grass with white clover swards increased farm profitability by €300/ha per year compared with the grass system alone, therefore this represents a significant short-term return on investment.
Winter feed
The study highlighted that due to the extent of reseeding that took place, Ballyhaise had a significant reduction in winter feed production and this impacted the ability to have winter reserves.
Helena Walsh highlighted it is important to plan in advance for additional feed reserves that will be required before starting to reseed, as this will ensure farmers have adequate winter forage reserves on their farms.
Comparison: reseeding v oversowing
Áine Murray and Alastair Pollock, researchers at Teagasc discussed the differences between reseeding and oversowing, which will both be required to convert the whole farm to a grass-white clover system.
Incorporating white clover in a full reseed is the most reliable method of establishing clover and provides the best opportunity for weed control.
Oversowing is a simple and lower-cost method of introducing white clover into swards.
Success depends on soil fertility, weather conditions at sowing, soil moisture, post-sowing grazing management and competition from the existing sward.
Paddocks for a full reseed should be identified and prioritised based on criteria such as poor pasture growth, age of sward, high weed content, etc.
The researchers highlighted the importance of the combination of reseeding and oversowing and advise farmers to reseed 10% and over-sow 15% of the farm each year.
When selecting suitable paddocks for oversowing, to ensure optimal opportunity of establishment a farmer must:
Choose ground with optimal soil fertility that has an index of three or less for both P and K and, ideally, has a pH of 6.5.Ensure the paddock has high perennial ryegrass content.Be aware of open-/low-density swards as dense swards prevent light getting to the new clover plant which will hinder the establishment.Ideally pick paddocks with a low weed content.
The Ballyhaise full reseed in 2021 at the start of the trial.
Reseeding
Studies show that spring reseeds provide the best results so farmers should aim for the months of April, May and June. Soil samples should be taken to identify the P and K requirement along with the soil pH.
Prepare a fine, firm seedbed and choose a cultivar as recommended by the “Irish Recommended List for cultivar selection”.
The sowing depth should be 10mm and the sowing rates for grass/clover in swards grazed by cattle is 28-30kg/ha along with 4-5kg/ha of white clover and for sheep the recommendation is grass at 25-28kg/ha and clover at 5-6kg/ha.
On N, 40kg N/ha should be spread at reseeding and also apply lime, P and K fertiliser, as required.
Oversowing
Weeds should be controlled in the previous year prior to oversowing clover.
Studies show that April is the best month for oversowing following a tight grazing.
Common methods of oversowing include direct drill, stitching in (must be used in sheep swards) or broadcast, which are equally successful as long as the right conditions, settings and post-establishment management are correct and sown at a rate of 5-6kg/ha.
The research experiment at Ballyhaise is comparing grass and white clover with grass only swards on drumlin type soils. The results of the first phase of the study showed that increased grass growth with less chemical nitrogen is possible in grass and clover swards. There was no difference in animal performance between the cows grazing grass only and grass and clover swards.
The grass and clover study at Ballyhaise Agricultural College in Cavan shows how farmers can maintain pasture productivity and reduce dependence on chemical nitrogen fertiliser.
Helena Walsh and Donal Patton from the Teagasc Animal and Grassland Research and Innovation Centre in Moorepark discussed the study that is being carried out to investigate the transition from old perennial ryegrass swards receiving high rates of chemical N fertiliser application to new swards at similar high rates of chemical N fertiliser application.
The study compares the results to new grass and white clover swards receiving reduced rates of chemical N on a heavier soil type.
The trial
The current experiment is a five-year systems trial running from 2021 to 2025 with the initial three years (2021 to 2023) focused on the transition from old grass-only swards to new grass and grass with white clover swards through the combined process of full reseeding and oversowing.
The experiment consists of two sward types: grass-only swards which receive 250kg chemical N per hectare per annum and newly established white clover or oversown white clover swards which receive 125kg N per hectare per annum.
In May, June and July of each year, paddocks were reseeded with three high pasture profit index (PPI) grass varieties which consisted of Astonconqueror, Astonenergy and Glenfield with or without white clover using min-till cultivation. Twenty per cent of the white clover system area was oversown in May 2021 and July 2022 using an airseeder after a grazing event.
Chieftain and Crusader were the two medium-leaf clover varieties used for both sward renewal methods.
All reseeded swards were grazed at a pre-grazing yield of 1,200kg DM/ha, or below, while the white clover oversown swards were grazed at 800kg DM//ha for the remainder of the first-year post-establishment.
The chemical fertiliser remained the same for each year of the study.
Chemical N fertiliser was applied to grass swards at each rotation post grazing from 15 February to 14 September each year.
Results
The transition from old grass to newly established and oversown pasture had no significant impact on grazing characteristics.
Total pasture production was significantly reduced during the year of new sward establishment from 14,182kg DM/ha in old pastures to 8,925kg DM/ha, 8,561kg DM/ha, and 11,830kg DM/ha in newly established grass, white clover and white clover oversown swards respectively.
The significant reduction in pasture yield in newly established swards is attributed to extended closed periods between spray-off of the old swards and the first grazing of the new sward, which is mainly due to bad weather during cultivation and establishment.
The establishment of new grass and clover swards and to a lesser extent white clover oversown swards resulted in a significant reduction in chemical fertiliser application. This reduced from 229kg N/ha and 230kg N/ha for perennial ryegrass old and new, to 119kg N/ha for white clover oversown and 90kg N/ha for newly established white clover.
The researchers said that achieving a high level of white clover content (20% to 25%) is critical to replace chemical N fertiliser with the nitrogen fixed by clover without implications for total grass yield.
Sward renewal
The high level of reseeding from grass to white clover swards had a major impact on the overall feed budget on the farm. This is due to the annual grass growth within the year of establishment being significantly reduced.
Sward type had no effect on the winter feed shortage with perennial ryegrass 55% self-sufficient and white clover systems 56% sufficient. Both of these deficits in winter feed were made up by the importing silage from other parts of the farm at Ballyhaise but the researchers said the high level of reseeding is not recommended on commercial farms.
The study found that transitioning to the white clover system resulted in a modest increase in both milk yield (5,197kg and 5,092kg) and milk solids (473kg and 461kg/cow) for white clover swards when compared to grass-only swards, while there were no significant differences observed for milk composition (fat, protein and lactose) between the two sward types during the transition.
Similarly, body weight and body condition score were comparable for both sward types.
The establishment of new swards represents a considerable cost at farm level as it costs roughly €1,150/ha to do a full reseed with clover included as energy costs and contractor costs have gone up.
The study has shown that the establishment of grass with white clover swards increased farm profitability by €300/ha per year compared with the grass system alone, therefore this represents a significant short-term return on investment.
Winter feed
The study highlighted that due to the extent of reseeding that took place, Ballyhaise had a significant reduction in winter feed production and this impacted the ability to have winter reserves.
Helena Walsh highlighted it is important to plan in advance for additional feed reserves that will be required before starting to reseed, as this will ensure farmers have adequate winter forage reserves on their farms.
Comparison: reseeding v oversowing
Áine Murray and Alastair Pollock, researchers at Teagasc discussed the differences between reseeding and oversowing, which will both be required to convert the whole farm to a grass-white clover system.
Incorporating white clover in a full reseed is the most reliable method of establishing clover and provides the best opportunity for weed control.
Oversowing is a simple and lower-cost method of introducing white clover into swards.
Success depends on soil fertility, weather conditions at sowing, soil moisture, post-sowing grazing management and competition from the existing sward.
Paddocks for a full reseed should be identified and prioritised based on criteria such as poor pasture growth, age of sward, high weed content, etc.
The researchers highlighted the importance of the combination of reseeding and oversowing and advise farmers to reseed 10% and over-sow 15% of the farm each year.
When selecting suitable paddocks for oversowing, to ensure optimal opportunity of establishment a farmer must:
Choose ground with optimal soil fertility that has an index of three or less for both P and K and, ideally, has a pH of 6.5.Ensure the paddock has high perennial ryegrass content.Be aware of open-/low-density swards as dense swards prevent light getting to the new clover plant which will hinder the establishment.Ideally pick paddocks with a low weed content.
The Ballyhaise full reseed in 2021 at the start of the trial.
Reseeding
Studies show that spring reseeds provide the best results so farmers should aim for the months of April, May and June. Soil samples should be taken to identify the P and K requirement along with the soil pH.
Prepare a fine, firm seedbed and choose a cultivar as recommended by the “Irish Recommended List for cultivar selection”.
The sowing depth should be 10mm and the sowing rates for grass/clover in swards grazed by cattle is 28-30kg/ha along with 4-5kg/ha of white clover and for sheep the recommendation is grass at 25-28kg/ha and clover at 5-6kg/ha.
On N, 40kg N/ha should be spread at reseeding and also apply lime, P and K fertiliser, as required.
Oversowing
Weeds should be controlled in the previous year prior to oversowing clover.
Studies show that April is the best month for oversowing following a tight grazing.
Common methods of oversowing include direct drill, stitching in (must be used in sheep swards) or broadcast, which are equally successful as long as the right conditions, settings and post-establishment management are correct and sown at a rate of 5-6kg/ha.
The research experiment at Ballyhaise is comparing grass and white clover with grass only swards on drumlin type soils. The results of the first phase of the study showed that increased grass growth with less chemical nitrogen is possible in grass and clover swards. There was no difference in animal performance between the cows grazing grass only and grass and clover swards.
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