Ensuring grassland is provided with exactly the right nutrients not only makes sense financially, but will also bring big benefits to the bottom line.
Drawing together a nutrient management plan based on up-to-date soil analysis results not only makes financial sense, but is also now a mandatory requirement for all farmers.
Under ‘The Farming Rules for Water’, which came into effect in April last year, all ‘cultivated land’ must be soil sampled a minimum of every five years (see soil analysis panel).
This includes any land – such as permanent pasture – which has had fertiliser or manure applied within the last three years. These soil tests must be used as the basis for a nutrient management plan.
Philip Cosgrave, grassland agronomist for Yara, says there are some strong reasons for adopting such a approach.
“We need to start growing grass with the same detail as we grow a crop of wheat. This means we need a plan in place to optimise each cut of silage,” he says.
Agri-Food and Biosciences Institute soil scientist Suzanne Higgins puts the cost of a standard soil test at about £5/hectare (£2/acre) when labour is costed in.
If this can be used to save purchased fertiliser costs, which can be more than £200/ha (>£80/ acre), depending on the formulation, then the potential return on investment are marked.
Only by soil testing will producers truly understand the individual nutrient requirements of each field, and that is where the ultimate savings will be made.
Monitoring soil indexes from year to year will highlight where soil fertility is declining, and this is due to crop off take over time being greater than what has been applied. Knowing this you can then redistribute nutrients within your farm to greater effect.
“We’re trying to achieve or maintain a P index of 2 and a K index of 2-. Whether it’s a threeor five-cut system, the aim is to maximise the yield and quality from each forage hectare.
“During peak grass growth [>100kg/DM per day] in April and May the grass crop has a daily phosphate and potassium requirement of 0.7 and 3.6kg/ha respectively.
If the soil can’t release these levels of P and K daily then nitrogen cannot be used efficiently to drive high levels of daily DM production. Yield reductions of up to 30% can result if the crops P and K requirements are not met,” he says.
Soil testing is the first part of a four-part process for formulating a farm nutrient management plan. The RB209 Fertiliser Manuals form the basis for all calculations and should be referred to for the subsequent steps:
Use RB209 Section 3 Grass and forage crops to establish the nutrient requirements of specific crops.
There are two tables in RB209 (page 10) which provide guidance on silage ground P and K requirements depending on whether you know your expected grass silage yields or not. If you are unsure, use the standard values for P and K recommendations after each silage cut. Grazing ground figures are available separately.
Use the Soil Nitrogen Supply (SNS) calculations in the RB209 Nutrient Management Guide to calculate nitrogen levels.
Sulphur is considered an essential nutrient in maximising dry matter yield and protein percentage in both grazed and conserved grass (see Use sulphur as standard panel).
Sulphur should be applied on all grass grown on:
The next step is understanding what nutrients you have on-farm in the form of slurry and farmyard manure (FYM).
The RB209 Fertiliser Manual Section 2 Organic Materials, provides guide values for the nitrogen levels of a typical dry matter slurry. However, Mr Cosgrave says it is well worth testing your farm’s supplies as in practice, NPK levels, can vary considerably.
He explains: “The standard book value for cattle slurry is 6% dry matter, but on two grass trials last year in Derbyshire and Devon, where we tested each farm’s slurry, one had a dry matter of 3.3%, while the other was 1.56%. That shows how you can be way off the mark by assuming a standard book value.” (see Table 1).
He advises testing slurry and FYM at least two to three times a year and using this to balance mineral fertilisers.
You can subtract the nutrients that were applied in the manure from the crop requirement to work out the shortfall needs to be filled with mineral fertiliser (see Table 2).
Mr Cosgrave urges producers to select a mineral fertiliser based on what their soils require, rather than reaching for the same product year-on-year because it is what they have always used.
“Split the farm up into areas with different P and K indexes and formulate mineral fertiliser recommendations based on that,” he advises.
Possible scenarios, where a traditional fertiliser grade would not be the right choice might be on a silage field with a P index of 0 or 1. In this case, a high P compound like a 20-8-11+S should be used instead of a traditional silage grade to build soil P reserves.
A field with a high P index (3 or more) might not need mineral P if slurry was applied, so a zero P silage grade would be best suited for this example.
Including sulphur in mineral fertilisers as standard will help boost nitrogen use efficiency, dry matter yields and grass protein levels, according to Yara’s Philip Cosgrave.
Since the reduction in atmospheric sulphur dioxide emissions, the level of sulphur in the air – and hence the soil – has declined substantially. This has resulted in more than 80% of UK grassland soils being deficient in sulphur.
The two essential plant amino acids, cysteine and methionine have a requirement for Sulphur, so if levels are lacking, plant proteins are not formed optimally.
Mr Cosgrave says: “When you apply sulphur on grassland, you typically get an increase in dry matter yields, but also an increase in protein percentage.
If grass has an adequate supply of sulphur, more of the nitrogen is found as protein. Whereas, sulphur deficiency results in less of the nitrogen being found as protein and more in the form of nitrate and free amino acids.”
Soil type will effect its responsiveness to sulphur, however in general, farmers could expect to see a 10-30% increase in dry matter yields from sulphur.
First cut silage has a particularly high demand for sulphur and regardless of soil type should receive a sulphur application.
Medium and light soils, and soils with lower organic matter content show the greatest response to sulphur in subsequent cuts.
Maintaining the optimum soil pH has many benefits, including:
Applying gibberellins to grassland in early spring could boost grass growth by 20kg DM/ha/ day or more and help those farmers wanting to quickly fill a forage gap this spring.
Gibberellins are naturally occurring growth enhancers that all plants produce. They help to increase cell size and numbers, enabling greater photosynthesis, plant metabolism and, in turn, increase growth in leaves and roots.
NuFarm’s Brent Gibbons adds: “If grass has been heavily grazed, the plant produces gibberellins to try and boost grass growth.”
UK research on 10 farms showed that a spring application resulted in an average extra 500kg DM/ha over a 21-day period. This led to a 8:1 return on investment thanks to grass growth and milk yield.
Mr Gibbons believes gibberellins have a role to play on most farms.
He says: “It’s relevant to all grassland farmers and especially ones short of forage that want to get off to an early start this spring.”
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