At this moment in time, fertiliser advice can be targeted at two categories of farmers – those with some nitrogen spread and those that have no nitrogen spread. For those with no nitrogen spread, the advice is to get some out when conditions are suitable. Suitable conditions are dependent on three things – whether or not the soil is travelable, whether heavy rain is forecast and whether soil temperatures are up around 5°C–6°C. With the current weather and soil conditions, it is not suitable for spreading nitrogen in most cases.
However, when the weather does improve, farmers that haven’t spread any nitrogen so far should start spreading. The response to chemical nitrogen is lowest in spring, at around 10kg of grass for every 1kg of N applied.
The thing is, that extra 10kg of grass is a very valuable feedstuff, both in terms of cost and quality. It is much better quality than silage and higher in energy and protein than most concentrates.
A response of 10kg of grass to 1kg of N means that if 30kg/ha of N is applied in early spring, 300kgDM/ha of grass will be grown. On a 40ha farm, this equates to 12t of extra feed grown, over and above what the grass would grow without any applied nitrogen. Therefore, it makes sense to spread nitrogen early in the season.
In terms of rates, avoid spreading any more than 25 to 30 units/ac of nitrogen at the moment. This would satisfy all the nitrogen requirements of the farm for the month of March. How much to spread in early April will depend on your demand. Most dairy farms will have a high requirement for grass in April and May, so an application of 40 to 50 units/ac in early April is advised. Both of these applications can be spread
Nitrogen spread
Farmers that spread nitrogen in late January or February have sufficient nitrogen out for now. Their next application should take place in mid-March. Again, how much to spread will be determined by the farm’s grass demand, but an application of 30 to 40 units/ac of nitrogen is advised in most cases. These farmers can then follow the cows with fertiliser on the second round of grazing in April.
Other nutrients
Nitrogen is the most important nutrient for plant growth, but other nutrients such as phosphorus, potassium and sulphur have a big part to play too. The advice over the last few years has been that the earlier deficiencies in any nutrient are corrected, the better. When it comes to phosphorus (P) and potash (K), you are feeding the soil so that it can feed the plant. If the soil is deficient, then the plant will be too.
A plant’s requirement for both nutrients will change depending on growth rates. They tend to have a low demand in spring because they are growing slowly, but a deficiency in any nutrient will reduce the growth rate even further.
The maintenance requirement for P and K for a high-yielding field (15tDM/ha) is 20 units/ac of P and 40 units/ac of K. This is to maintain the soil at the index it is currently at. To build up soil fertility, extra P and K will be required. Index 1 soils will need 36 units/ac of P and 90 units/ac of K, while index 2 soils will need 28 units/ac of P and 65 units/ac of K. This is on top of the maintenance dressing.
At low soil indexes, the total amount of fertiliser required is very high so it is costly to address, but it could also lead to losses if too much is spread at once. There is another complication with K, in that high levels of K in the grass can cause an increase in grass tetany and milk fever. Therefore, higher K applications should be targeted at the end of the grazing season, when the risk of it affecting animal health will have decreased.
Phosphorus should be drip-fed throughout the grazing season, but front-loaded to the spring. The ideal time to start spreading P and K is in March, to ensure the plant will not be deficient coming into April and May.
Many farmers will go with a compound-type fertiliser in March, with products like 18:6:12 plus sulphur getting very popular, as they tick a lot of boxes in terms of N, P, K and sulphur.
Sulphur deficiency is becoming more of a problem, as the amount of sulphur in the atmosphere is decreasing. The advice is to spread sulphur at a rate of 10% of the total amount of nitrogen spread. Therefore, if 200 units/ac of nitrogen is spread, then 20 units/ac of sulphur should be spread. This should be drip-fed throughout the early part of the growing season.
Slurry
Slurry has the ability to provide a lot of the nutrients required. Every 1,000gal of slurry is roughly equivalent to one bag/ac of 5:5:30. However, that’s presuming the slurry is high in dry matter and thick. Diluted slurry from open yards or lagoons will have lower nutrient levels. Due to its constituents, slurry is more suited to silage ground than grazing ground. It is an important source of nitrogen on grazing ground in early spring.
While the amount of land being grazed this February is less than normal due to the weather, any fields that have been grazed will be able to take slurry, which means the P and K application that would have been spread in March can be forfeited.
Nitrogen types
There is a big emphasis on using protected urea instead of CAN. The reason for this is that CAN fertiliser releases nitrous oxide, which is a greenhouse gas. Moving towards urea-based products is a good way to reduce nitrous oxide emissions.
However, one of the problems with urea is that it has high ammonia emissions. Urea that is treated with an inhibitor releases much lower levels of ammonia. It should be pointed out that ammonia emissions from urea are low in spring anyway.
Farmers that have no nitrogen spread to date should spread 25 to 30 units/ac when conditions are appropriate.There is a valuable response to nitrogen in early spring.Front load phosphorus and apply most of the potash towards the end of the season.Slurry is ideal for silage ground. Read more
Dairy management: getting cows out to grass
Watch: how fertiliser quality affects spreading accuracy
At this moment in time, fertiliser advice can be targeted at two categories of farmers – those with some nitrogen spread and those that have no nitrogen spread. For those with no nitrogen spread, the advice is to get some out when conditions are suitable. Suitable conditions are dependent on three things – whether or not the soil is travelable, whether heavy rain is forecast and whether soil temperatures are up around 5°C–6°C. With the current weather and soil conditions, it is not suitable for spreading nitrogen in most cases.
However, when the weather does improve, farmers that haven’t spread any nitrogen so far should start spreading. The response to chemical nitrogen is lowest in spring, at around 10kg of grass for every 1kg of N applied.
The thing is, that extra 10kg of grass is a very valuable feedstuff, both in terms of cost and quality. It is much better quality than silage and higher in energy and protein than most concentrates.
A response of 10kg of grass to 1kg of N means that if 30kg/ha of N is applied in early spring, 300kgDM/ha of grass will be grown. On a 40ha farm, this equates to 12t of extra feed grown, over and above what the grass would grow without any applied nitrogen. Therefore, it makes sense to spread nitrogen early in the season.
In terms of rates, avoid spreading any more than 25 to 30 units/ac of nitrogen at the moment. This would satisfy all the nitrogen requirements of the farm for the month of March. How much to spread in early April will depend on your demand. Most dairy farms will have a high requirement for grass in April and May, so an application of 40 to 50 units/ac in early April is advised. Both of these applications can be spread
Nitrogen spread
Farmers that spread nitrogen in late January or February have sufficient nitrogen out for now. Their next application should take place in mid-March. Again, how much to spread will be determined by the farm’s grass demand, but an application of 30 to 40 units/ac of nitrogen is advised in most cases. These farmers can then follow the cows with fertiliser on the second round of grazing in April.
Other nutrients
Nitrogen is the most important nutrient for plant growth, but other nutrients such as phosphorus, potassium and sulphur have a big part to play too. The advice over the last few years has been that the earlier deficiencies in any nutrient are corrected, the better. When it comes to phosphorus (P) and potash (K), you are feeding the soil so that it can feed the plant. If the soil is deficient, then the plant will be too.
A plant’s requirement for both nutrients will change depending on growth rates. They tend to have a low demand in spring because they are growing slowly, but a deficiency in any nutrient will reduce the growth rate even further.
The maintenance requirement for P and K for a high-yielding field (15tDM/ha) is 20 units/ac of P and 40 units/ac of K. This is to maintain the soil at the index it is currently at. To build up soil fertility, extra P and K will be required. Index 1 soils will need 36 units/ac of P and 90 units/ac of K, while index 2 soils will need 28 units/ac of P and 65 units/ac of K. This is on top of the maintenance dressing.
At low soil indexes, the total amount of fertiliser required is very high so it is costly to address, but it could also lead to losses if too much is spread at once. There is another complication with K, in that high levels of K in the grass can cause an increase in grass tetany and milk fever. Therefore, higher K applications should be targeted at the end of the grazing season, when the risk of it affecting animal health will have decreased.
Phosphorus should be drip-fed throughout the grazing season, but front-loaded to the spring. The ideal time to start spreading P and K is in March, to ensure the plant will not be deficient coming into April and May.
Many farmers will go with a compound-type fertiliser in March, with products like 18:6:12 plus sulphur getting very popular, as they tick a lot of boxes in terms of N, P, K and sulphur.
Sulphur deficiency is becoming more of a problem, as the amount of sulphur in the atmosphere is decreasing. The advice is to spread sulphur at a rate of 10% of the total amount of nitrogen spread. Therefore, if 200 units/ac of nitrogen is spread, then 20 units/ac of sulphur should be spread. This should be drip-fed throughout the early part of the growing season.
Slurry
Slurry has the ability to provide a lot of the nutrients required. Every 1,000gal of slurry is roughly equivalent to one bag/ac of 5:5:30. However, that’s presuming the slurry is high in dry matter and thick. Diluted slurry from open yards or lagoons will have lower nutrient levels. Due to its constituents, slurry is more suited to silage ground than grazing ground. It is an important source of nitrogen on grazing ground in early spring.
While the amount of land being grazed this February is less than normal due to the weather, any fields that have been grazed will be able to take slurry, which means the P and K application that would have been spread in March can be forfeited.
Nitrogen types
There is a big emphasis on using protected urea instead of CAN. The reason for this is that CAN fertiliser releases nitrous oxide, which is a greenhouse gas. Moving towards urea-based products is a good way to reduce nitrous oxide emissions.
However, one of the problems with urea is that it has high ammonia emissions. Urea that is treated with an inhibitor releases much lower levels of ammonia. It should be pointed out that ammonia emissions from urea are low in spring anyway.
Farmers that have no nitrogen spread to date should spread 25 to 30 units/ac when conditions are appropriate.There is a valuable response to nitrogen in early spring.Front load phosphorus and apply most of the potash towards the end of the season.Slurry is ideal for silage ground. Read more
Dairy management: getting cows out to grass
Watch: how fertiliser quality affects spreading accuracy
This is a subscriber-only article
SHARING OPTIONS: