Nutrient and Fertiliser Management
Essential nutrients nitrogen, phosphorus(P), potassium (K) and lime are required by plants in order to grow and achieve optimum production. Nutrient management plans provide farmers with information on how to grow crops to their potential from their farming system. This information includes when to apply nutrients, where to apply nutrients and how to apply to achieve optimum fertiliser usage and uptake by plants.
Soil is the most important asset on our farms to successfully grow crops. It is essential that best practice is adopted with good nutrient management to maintain and improve soil fertility as to achieve expected crop yields.
The first step is to establish where level of soil fertility is present. This is achieved by taking a soil sample. When taking a soil sample, take from same soil type, cropping history and management. A single sample should be taken every four years with a maximum area of 4Ha. Soil fertility for both P and K is based on an index system.
For further information on soil fertility including for high organic matter soils please click here.
|Table 1: The Soil Index System
|Response to Fertillisers
|Unlikely / Tenuous
|Sufficient / Excess
When soil fertility levels are established you can now begin to match crop requirements to crop demands.
While more intensive farms have a target of index 3 for P and K for other less intensive farms it may be more practical to target index 3 for certain fields, e.g. silage fields. Maintaining soil fertility at a lower index may be sufficient to grow the quantity of grass required for lower intensity farms.
See Teagasc publication ‘Major and Micro Nutrient Advice For Productive Agricultural’ to identify crop needs based on soil indexes from soil sample.
Rules and Regulations:
Fertiliser application rate for crops are determined by complying with the necessary legally binding requirements of the EU Nitrates Directive.
Nutrient Management Planning
Nutrient management planning is required to balance nutrient inputs (mainly N, P, K and lime) with crop requirements. Nutrient applications may result in losses to water by runoff or leaching.
The solution is to take soil samples and prepare an NMP every 4 years. Nutrient management planning allows farmers to maintain appropriate soil fertility by applying the right fertilisers in the right place on the farm, at the right rate and at the correct times of the year.
Critical Source Areas (CSA’s)
These are higher risk areas on farms that can potentially deliver increased levels of nutrients to water.
On poorly drained heavier soils, where overland flow is the pathway for nutrients during heavy rainfall, CSA examples include: a break in a hedgerow alongside a water body or a sloped field converging towards a boundary watercourse.
Fields with free draining soils are a potential CSA as these are more susceptible to nitrate leaching.
It is important to identify such areas on the farm and target the correct actions: to reduce the source by applying nutrients appropriately or break the pathway for example planting a hedgerow or fencing off a riparian margin.
Fertiliser and Organic Manure – Timing, Location, Rate and Product
Nutrient losses to water will occur when spreading chemical or organic fertiliser if applied inappropriately. It is very important to maximise the nutrient use efficiency (NUE) by applying the right fertilisers in the right place on the farm, at the right rate and at the correct times of the year.
Chemical and organic fertilisers, slurry, farm yard manure etc., can be applied to farm land during the open period for application of chemical and organic fertilisers as outlined in SI 605 of 2017 The periods during the year that farmers cannot apply chemical and organic fertilisers are outlined in the table below:
Use the soil sample results and nutrient management plan to guide on the most appropriate rate and product to use. Consult with your advisor where required. Checking the weather forecast in advance of spreading fertiliser is critical to minimse runoff and leaching of nutrients.
It is best to apply slurry in spring or early summer on a cool, overcast day with good ground conditions (soil moisture deficit > 0mm). To maximise nutrient uptake, chemical fertiliser and slurry should be applied when the crop is growing (soil temp > 6 deg C) and no heavy rainfall forecast for at least 48hrs. On poorer draining soils this period should be longer.
Confirm the nutrient advice on the NMP plan with the farm map to ensure the right product is used in the right locations. Carefully select the fields that receive nutrients at the risky periods of the year (spring and autumn) when applying fertilisers. Fields with high connectivity to waters have increased potential for losses of nutrients.
The type of fertiliser to use depends on the advice and overall allowances highlighted on the NMP. Unfortunately, environmental pressures vary with different products.
Calcium Ammonium Nitrate can lead to nitrate losses through leaching and considerably higher losses of GHG’s (Nitrous Oxide). Standard Urea delivers higher ammonia losses to the air. The better product is Protected Urea as it reduces GHG emissions (by 71% compared to CAN) and Ammonia emissions (by 79% compared to Urea). It can also indirectly reduce nitrate losses to water.
Chemical Fertiliser Spreading
Chemical fertilisers should be applied precisely and accurately. Over-application of fertiliser is costly to the farmer and can lead to higher risk of nutrient losses through overland flow or leaching. Important factors to consider are fertiliser spreader setting, forward speed and even spreading.
Ensure the fertiliser spreader is correctly set and calibrated, select the appropriate tractor speed and avoid overlapping of spread widths. GPS technology systems should be used on farms with higher volumes of fertiliser usage. This ensures precision application of nutrients.
High organic matter (>20%) peat soils have much lower capacity to retain phosphorus. Applying chemical or organic P in excess of crop requirements will be lost to surface or ground water.
It is very important to only apply maintenance levels of P that match the crop demand during the growing season.
Importing/Exporting Organic Manure
The correct recording of the import and export of organic manures is critical for accurate NMP on both farms.
Where organic manures are transported between farms this has an impact on the overall levels of nutrients that can be applied and must be reflected in both farms NMP’s. Subsequent chemical fertiliser allowances must be adjusted to reflect this.
Disclaimer: All farms are unique and require careful assessment to ensure the correct measures are implemented. Please contact your local ASSAP Advisor for your individual enquiries.