Nutrient Management Planning
Nutrient management planning is simply balancing soil nutrient inputs with crop requirements to minimise the cost and environmental damage of over supply.
In practice this is achieved by:
- Carrying out a soil analysis.
- Managing farmyard effluents and manure responsibly.
- Basing fertiliser usage on the results of soil analysis, nutrients supplied by slurry and manure and the requirements of the following crops
The phosphate problem
The biggest single source of phosphorus (P) to Lough Neagh and Lough Erne is from agriculture, mainly due to the overuse of phosphorus in fertilisers and inadequate manure management.
In November 1997 a Responsible Phosphate Management campaign was organised jointly by the Department of Agriculture and Rural Development (DARD), the Fertiliser Manufacturers' Association (FMA), the Ulster Farmers' Union (UFU) and the Northern Ireland Agricultural Producers' Association (NIAPA).
The aim of the 3-year campaign was to improve farmers' awareness of the need to take action to reduce the problems caused by eutrophication resulting from excess phosphorus in water. The report Responsible Phospate Management on grassland farms (PDF 607 KB) (A joint initiative to improve farmers’ awareness of the phosphate problems and relevant corrective action …)is availble to view.
Why farmers need to manage phosphates
Phosphate is essential for both grass production and animal nutrition. However there is no advantage in supplying phosphate in excess of requirements. In certain situations, too much phosphate may adversely affect grass production. High levels of P near the soil surface may lead to shallow rooting, exacerbating grass ‘pull’ and drought-related stress.
The majority of soils on intensive farms are already at the optimum P level or higher. Around half the soils are above index 2 and it is unnecessary and indeed wasteful to apply fertiliser phosphate to these soils. Responsible maintenance of soil fertility means maintaining soil P index at the level appropriate to other inputs, particularly N, and no higher than index 2.
Slurry and farmyard manure and phosphate management
Cattle are not very efficient in utilising phosphate. Consequently, slurry contains most of the phosphate fed in a diet of silage and supplementary feedstuffs. Because more phosphate comes onto the farm in bought-in concentrates than leaves in milk or meat, most livestock farms have a positive P balance without any fertiliser P. On such farms, slurry can replace all the phosphate removed in grass cut for silage.
Fertilisers and phosphate management
Responsible use of fertilisers requires matching fertiliser use to crop requirements. In practice this means using either straight N or zero-phosphate (NK) fertilisers in preference to more traditional NPK fertilisers. Low phosphate NPK fertilisers are only recommended where soil P levels are known to be low and slurry can not be used.
Grass requires adequate nitrogen, phosphate and potash to produce high yields. Nitrogen and potash are readily leached from most soils and therefore these nutrients are required in small repeated doses throughout the growing season. But leaching of phosphate is only a problem at high soil P levels, so phosphate can be applied annually, or even at two or three year intervals, without losing yield.
Soil Sampling
Proper soil sampling is essential to obtain meaningful results from soil tests. A sample is made up of at least 25 small cores taken across the whole field.
- A soil auger is required when taking samples. Sampling augers and bags are available form your local DARD Agriculture Development Centres (ADCs). Use a 150 mm (6 in) auger for cropped land and a 75mm (3 in) auger for permanent grassland.
- Take one sample (25 cores) from each field. Very large fields should be subdivided into blocks of no more than 5 hectares for sampling. Take one sample from each block and identify as A, B, C etc (plus field number) on your map and on the sample. Small adjacent fields that are subject to the same management may be grouped together (maximum 5 hectares) Exceptionally, large areas (up to 12 hectares) that receive low levels of fertiliser and are subject to uniform management may be included in one sample.
- Enter your name, the correct field number and the farm survey number on the label on each sample bag.
- Use the auger to remove cores from 25 random spots across the field being sampled and place these in sample bag. The diagrams below show examples of suitable sampling techniques across differently shaped fields.
- Do not sample near water troughs, gates, headlands, trees, manure or urine patches or areas where stock shelter as these can influence the results.
- Samples should not be taken within 2 months of applying lime, fertilisers, manure or slurry.
Understanding your soil analysis
The main purpose of soil analysis is to measure:
- the phosphorus (P), potassium (K) and magnesium (Mg) in the soil that is available for plant growth;
- the soil acidity (pH)
Each nutrient is shown as a concentration (mg/l) and an index. For example a soil containing less than 9 mg/l of P has an index of "0", while soil with between 26 and 45 mg/l has an index of "3".
What the phosphorus (P) index means for grassland
| Soil P Index | What the P index means |
|---|---|
| 0 Deficient | Low phosphorus levels likely to be limiting production |
| 1 Medium | Adequate for most farms at nitrogen inputs up to 150kg per hectare (120 units per acre) and stocking rate under 1.75 LU per ha |
| 2 Optimum | Optimum for intensive grassland farms where nitrogen inputs are over 150kg per hectare (120 units per acre) and stocking rate is over 1.75 LU per ha |
| 3 High | High levels of phosphorus present. No yield response to added phosphate. |
| 4 and above Excessive | Excessive levels of soil phosphorus. No yield response to added phosphate. |
Fertilisers for grassland
The aim is to maintain a soil phosphorus index of 1 or 2 depending on level of production. Where the soil phosphorus index is 1 or 2 and current levels of production are satisfactory, continue with your usual fertiliser policy.
Where the soil phosphorus index is high (3 or above), the aim should be to reduce this to 2.
Lime
Insufficient use of lime on acid soils can cause yield reductions irrespective of how much fertiliser is applied. Follow the recommendations on your soil analysis report.
Potash fertilisers
Insufficient potash will reduce silage yields. Many farms have low potassium (K) indices on cutting ground. Where potash index is 2 or under on cutting ground, slurry alone may not meet silage requirements. Extra potash should be appliedas fertiliser. If P index is high and no slurry is applied it will be necessary to apply additional potash to make up the shortfall. Use NK or NKS fertiliser plus muriate of potash if necessary. However, to minimise risk of grass tetany (staggers) in grazing livestock, do not apply large dressings of potash in early or late season to grazed swards.
Arable land
The target index for phosphorus on cropping land is index 2. Only apply sufficient phosphate fertiliser to match crop requirements.
Fertiliser Recommendation Booklet
For further information on crop nutrient requirements and soil pH refer to the Fertiliser Recommendations Booklet (RB209)![[external site]](extlink.gif)
published by Department for Environment, Food and Rural Affairs (DEFRA).
published by Department for Environment, Food and Rural Affairs (DEFRA).To view PDFs 