When applied under the correct conditions to a growing crop, slurry can be a valuable source of nitrogen (N), phosphorous (P) and potassium, or potash (K), as outlined in Table 1.
However, the nutrient content in slurry is highly variable and, in many cases, the amount of P and K present can be overestimated.
For instance, the availability of N, P and K nutrients in slurry will be affected by factors such as:
The amount of meal fed to cattle during winter.The type of fertilizer applied to silage swards.The nutrient offtake in silage swards.The dilution rate.The time of application and weather conditionsApplying slurry in the correct conditions in spring will achieve the best response from available nutrients. As the season progresses, the nitrogen content of applied slurry can be reduced by as much as 50%.
The loss in nitrogen content is greatest if spreading slurry during bright, sunny periods with a splash plate (atmospheric loss). To get the most from slurry, the best practice is to apply during cloudy, cool or damp weather (similar to urea) or with a trailing shoe/injection system.
Slurry value analysis
This spring, slurry samples were taken for laboratory analysis from some of the programme farms. The amount (units) of N, P and K per 1,000 gallons of slurry is outlined in Figure 1.
The results are based on 10 samples and represent samples taken from dry cows and weanlings fed a silage-based diet with low levels of concentrate (1kg to 2kg supplementation for weanlings) and finishing cattle with a higher concentrate allowance.
While the units of nitrogen and phosphorus are similar to the standard value given to slurry, the amount of potassium in slurry is being greatly overestimated on the programme farms.
The point has to be stressed that this analysis is for the programme farm samples and does not apply to all farms.
However, it shows that many other farmers could be applying slurry with lower than expected nutrient values.
The information shows how following the standard figures and relying solely on slurry to supply the 96 units of K required for first-cut silage could be resulting in soil fertility being depleted.
For example, farmers with slurry values of 22 units and 24 units K are only applying 55 units or 60 units K compared with 95 units if using standard values.
In this scenario, the sward will require a top-up of K in the form of a compound or straight fertilizer to fill the shortfall in nutrients.
The programme advisers have been working closely with the programme farmers to develop nutrient plans to build soil fertility to ensure that crop requirements are being met.
This is the reason for the programme farms using greater quantities of 10:10:20, 18:6:12 and cut sward when closing off silage ground.
The higher usage of P and K fertilizer is increasing the fertilizer component of variable costs but will add long-term to improving fertility of the soil and increasing grass output/quality.
Compound fertilizer
Slurry will generally maintain P and K levels for soils at index 3. However, at lower indices, the programme farms are using a compound fertilizer to meet crop requirements and gradually lift soil fertility levels.
Compound fertilizers are more expensive than CAN on a per tonne basis. However, fertilizer prices should not be compared solely on a bag-by-bag or tonne basis.
In nutrient-deficient soils, applying a compound fertilizer rather than CAN will increase yield, which makes them competitively priced when compared with straight nitrogen.
For example, applying three bags of CAN per acre costing €320/t has a fertilizer cost of €48/ac (€16/bag).
Assuming that the sward yields 6t/ac of grass silage, the CAN fertilizer costs €8/t of silage produced. Compare this with using three bags of cut sward (24:2.5:10) costing €380/t (€19/bag). This is a cost of €57/ac for the three bags applied. Assuming that the sward yields 7t of silage per acre, then the fertilizer is basically costing the same as €8/t of silage produced.
Importance of nutrients
Soil fertility will determine what type of fertilizer needs to be applied to a crop to maximise growth rates and, inevitably, crop yield.
Soils are ranked from index 0, where they are extremely deficient in P and K. In such soils, growth rates will be inhibited and unlikely to produce the type of yields the plant is capable of.
In grassland, soils with index 0 will experience delayed growth in spring and a faster reduction in growth in autumn, unless compound fertilizers are being applied.
Index 3 is the ideal soil fertility level for grassland. Slurry is normally capable of supplying the required amount of P and K for grazing ground to support high growth rates.
Improving soil fertility is part of every participant’s grassland management plan and is a key component in increasing output through higher stocking rates.
While slurry has been applied on most farms, it is worth remembering the above analysis. Soil results are the starting point in identifying the soil fertility on farms and putting a nutrient management plan in place.
Given the variance in slurry analysis this year, further sampling will be carried out on slurry produced this winter.
Fertilizer plans are also being relooked at in some cases and decisions may be taken to apply P and K fertilizer in the coming weeks where shortfalls may have occurred.
The importance of each nutrient is summarised below:
Nitrogen is needed by the plant to drive growth. Soils lacking in nitrogen will often appear yellow-green rather than dark, lush green. At this time of year, the variation in soil nitrogen can be seen in grazing fields where grass is usually darker around dung pats and is in huge contrast to the rest of the field. Phosphorus is important as it regulates root development and nutrient uptake. Soils with an index 1 for P will see yields drop by 1.5t DM/ha compared to soils at index 3. This is the equivalent of four to five round bales of silage per acre. Where swards have been damaged from poaching, applying a P-based fertilizer is needed to help repair plants roots. Applying P in the spring through slurry or bagged fertilizer will stimulate nutrient uptake at low soil temperatures and kickstart grass growth.Potash (K) is important for growth because it regulates the movement of water through the grass plant and, therefore, plant nutrients. High-potash swards can be more drought-resistant than low-potash swards. They will also be less open. Potash will also influence the protein content in grass swards. Swards that have K regularly applied will produce silage with a higher feed value, which increases animal performance during winter.
When applied under the correct conditions to a growing crop, slurry can be a valuable source of nitrogen (N), phosphorous (P) and potassium, or potash (K), as outlined in Table 1.
However, the nutrient content in slurry is highly variable and, in many cases, the amount of P and K present can be overestimated.
For instance, the availability of N, P and K nutrients in slurry will be affected by factors such as:
The amount of meal fed to cattle during winter.The type of fertilizer applied to silage swards.The nutrient offtake in silage swards.The dilution rate.The time of application and weather conditionsApplying slurry in the correct conditions in spring will achieve the best response from available nutrients. As the season progresses, the nitrogen content of applied slurry can be reduced by as much as 50%.
The loss in nitrogen content is greatest if spreading slurry during bright, sunny periods with a splash plate (atmospheric loss). To get the most from slurry, the best practice is to apply during cloudy, cool or damp weather (similar to urea) or with a trailing shoe/injection system.
Slurry value analysis
This spring, slurry samples were taken for laboratory analysis from some of the programme farms. The amount (units) of N, P and K per 1,000 gallons of slurry is outlined in Figure 1.
The results are based on 10 samples and represent samples taken from dry cows and weanlings fed a silage-based diet with low levels of concentrate (1kg to 2kg supplementation for weanlings) and finishing cattle with a higher concentrate allowance.
While the units of nitrogen and phosphorus are similar to the standard value given to slurry, the amount of potassium in slurry is being greatly overestimated on the programme farms.
The point has to be stressed that this analysis is for the programme farm samples and does not apply to all farms.
However, it shows that many other farmers could be applying slurry with lower than expected nutrient values.
The information shows how following the standard figures and relying solely on slurry to supply the 96 units of K required for first-cut silage could be resulting in soil fertility being depleted.
For example, farmers with slurry values of 22 units and 24 units K are only applying 55 units or 60 units K compared with 95 units if using standard values.
In this scenario, the sward will require a top-up of K in the form of a compound or straight fertilizer to fill the shortfall in nutrients.
The programme advisers have been working closely with the programme farmers to develop nutrient plans to build soil fertility to ensure that crop requirements are being met.
This is the reason for the programme farms using greater quantities of 10:10:20, 18:6:12 and cut sward when closing off silage ground.
The higher usage of P and K fertilizer is increasing the fertilizer component of variable costs but will add long-term to improving fertility of the soil and increasing grass output/quality.
Compound fertilizer
Slurry will generally maintain P and K levels for soils at index 3. However, at lower indices, the programme farms are using a compound fertilizer to meet crop requirements and gradually lift soil fertility levels.
Compound fertilizers are more expensive than CAN on a per tonne basis. However, fertilizer prices should not be compared solely on a bag-by-bag or tonne basis.
In nutrient-deficient soils, applying a compound fertilizer rather than CAN will increase yield, which makes them competitively priced when compared with straight nitrogen.
For example, applying three bags of CAN per acre costing €320/t has a fertilizer cost of €48/ac (€16/bag).
Assuming that the sward yields 6t/ac of grass silage, the CAN fertilizer costs €8/t of silage produced. Compare this with using three bags of cut sward (24:2.5:10) costing €380/t (€19/bag). This is a cost of €57/ac for the three bags applied. Assuming that the sward yields 7t of silage per acre, then the fertilizer is basically costing the same as €8/t of silage produced.
Importance of nutrients
Soil fertility will determine what type of fertilizer needs to be applied to a crop to maximise growth rates and, inevitably, crop yield.
Soils are ranked from index 0, where they are extremely deficient in P and K. In such soils, growth rates will be inhibited and unlikely to produce the type of yields the plant is capable of.
In grassland, soils with index 0 will experience delayed growth in spring and a faster reduction in growth in autumn, unless compound fertilizers are being applied.
Index 3 is the ideal soil fertility level for grassland. Slurry is normally capable of supplying the required amount of P and K for grazing ground to support high growth rates.
Improving soil fertility is part of every participant’s grassland management plan and is a key component in increasing output through higher stocking rates.
While slurry has been applied on most farms, it is worth remembering the above analysis. Soil results are the starting point in identifying the soil fertility on farms and putting a nutrient management plan in place.
Given the variance in slurry analysis this year, further sampling will be carried out on slurry produced this winter.
Fertilizer plans are also being relooked at in some cases and decisions may be taken to apply P and K fertilizer in the coming weeks where shortfalls may have occurred.
The importance of each nutrient is summarised below:
Nitrogen is needed by the plant to drive growth. Soils lacking in nitrogen will often appear yellow-green rather than dark, lush green. At this time of year, the variation in soil nitrogen can be seen in grazing fields where grass is usually darker around dung pats and is in huge contrast to the rest of the field. Phosphorus is important as it regulates root development and nutrient uptake. Soils with an index 1 for P will see yields drop by 1.5t DM/ha compared to soils at index 3. This is the equivalent of four to five round bales of silage per acre. Where swards have been damaged from poaching, applying a P-based fertilizer is needed to help repair plants roots. Applying P in the spring through slurry or bagged fertilizer will stimulate nutrient uptake at low soil temperatures and kickstart grass growth.Potash (K) is important for growth because it regulates the movement of water through the grass plant and, therefore, plant nutrients. High-potash swards can be more drought-resistant than low-potash swards. They will also be less open. Potash will also influence the protein content in grass swards. Swards that have K regularly applied will produce silage with a higher feed value, which increases animal performance during winter. 
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