The Nutrient Management Guide (RB209) helps you make the most of organic materials and balance the benefits of fertiliser use against the costs - both economic and environmental. It explains the value of nutrients, soil and why good nutrient management is about more than just the fertilisers you buy; it can save you money as well as help protect the environment.
Introduction
This section provides nutrient recommendations for both grass and forage crops. As with any crop, it is important to match nutrient inputs to the demands of the grass sward or forage crop. Doing this will increase nutrient use efficiency, optimise grassland productivity, prevent loss of excess nutrients to the environment and cut input costs by reducing the need for purchased fertilisers. For grass and forage crops, there are several factors that affect how efficiently nutrients are used by the plant. Nutrients applied through fertilisers or manures (especially nitrogen) will be used most effectively when there is:
• Good soil structure – compacted or poorly draining soils will hinder plant nutrient uptake and can increase gaseous release of N
• Balanced soil fertility – nutrient efficiency (particularly N) is higher when soils have optimal levels of phosphate, potash, magnesium and sulphur
• A moderate soil temperature – at low temperatures, nutrient uptake by the plant will diminish, leading to a higher risk of leaching
• Sufficient soil moisture – too much moisture will increase the risk of leaching losses, too little will curb plant growth and reduce nutrient uptake
• Optimum soil pH – very low or high soil pH will reduce the amount of nutrients available to the plant. Optimum soil pH for grassland is 6.0 for mineral soils, 5.7 for intermediate organic soils and 5.3 for peaty soils. Aim to raise pH to 0.2 units above the optimum
• Good sward composition – more productive sward species, e.g., perennial rye-grass and timothy, will be more responsive to fertiliser inputs
It is important to plan the amount of grass and forage crop production that needs to be achieved in each field, remembering that nutrient applications may need to be adjusted for seasonal and weather conditions.
Checklist for decision-making
Before applying fertilisers to grassland or forage crops it is important to:
1. Carry out a soil test (page 8).
2. Understand if the field is within a nitrate vulnerable zone (NVZ) and check the rules for application rates and timing for organic materials and fertilisers.
3. Assess soil structure.
4. Ensure drainage systems are maintained and functioning correctly.
5. Calibrate the fertiliser spreader.
6. Calculate any nutrient available for additions of organic materials (Section 2: Organic materials).
7. Consider the environmental risks of fertiliser or organic manure use, e.g. connectivity of water to field to water or proximity of sensitive habitat.
8. Keep good records of organic materials and fertiliser applications across the farm.
Grass and forage requirements
Well-managed grass remains the cheapest feed available to livestock farms. However, to make the most of this resource, it is important to know:
• How much grass the farm is capable of producing
• How much grass must be produced to meet livestock requirements
The recommendations presented in this guide use target dry matter yield to help determine the amount of nutrient required.
Points to consider
• Nitrogen response occurs in two stages: firstly, nitrogen is taken up rapidly and secondly, dry matter yield increases
• Nitrogen uptake is more rapid than yield increase and is less affected by some adverse conditions, such as short day length. It is necessary, therefore, to distinguish greening of grass (associated with nitrogen uptake) from actual growth
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