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Maize growers wanting to get the most from slurry and manure are being advised to manage applications very carefully this winter. Wet autumn conditions... Test soil and slurry to achieve better maize in 2024

Maize growers wanting to get the most from slurry and manure are being advised to manage applications very carefully this winter.

Wet autumn conditions followed by rain during December and the ongoing decline in phosphate and potash applications over recent years mean soil indices are suffering, says NRM agronomy manager Allison Arden.

“It’s a worrying situation and one that absolutely underlines the importance of regular testing of soil, slurry and FYM testing so you can base remedial action on facts rather than assumptions,” Ms Arden explains.

Traditionally maize growers have been able to rely on large volumes of phosphate- and potash-rich farmyard manure and other organic sources. But these need managing carefully to make sure they address nutrient needs without impacting on the environment.

“As phosphate and potash fertiliser applications continue to decline, it’s possible that the phosphate and potash levels supplied by manures might not be sufficient to optimise establishment and deliver healthy, high yielding crops,” says Ms Arden.

“An index of O for P means 115kg/ha needs to be applied each year to maintain target values and for K this is 235kg/ha each year.  Maize is a large, hungry crop that removes a lot of nutrients from the system every time it is harvested.

Ms Arden says: “Modern maize varieties are capable of consistently producing 40t/ha freshweight forage yields and in some of the better areas of the country this can be considerably more.”


Maize silage with a 30% dry matter content removes 1.4kg phosphate and 4.4kg potash for every tonne harvested, she points out. A 50t/ha crop, will therefore remove 70kg/ha of P and 220kg/ha of K from the soil.

“It’s very easy to see how soil indices quickly decrease particularly if you’re soil index is already low, which our testing suggests is more widespread than you would think,” says Ms Arden.

“Crop deficiencies are not just a problem for the maize plants growing during the season but can create a legacy of problems for following crops due to the high removal rate of nutrients. Phosphate is especially important in making sure plants get off to the best start possible.”

Potassium plays a key role in the flow of water, nutrients and carbohydrates around the plant. Low indices of either can result in stress on maize plants. As well as reducing yields, this can also increase the incidence of diseases such as fusarium and eyespot.

Taking a phosphate and potash holiday is usually always a false economy. Building P and K levels in the soil can take up to five years, so crops grown on low index soils may see a significant yield penalty because of these deficiencies for a considerable time.”

Regular sampling essential

The starting point for managing phosphate and potash in maize is to carry out regular sampling of soil and slurry, says Allison Arden.

“Soil sampling is an absolute must now from both cost-efficiency and environmental points of view. You need to know exactly what’s in the soil as there can be big variations not just in phosphate and potash but nitrogen too.”

Maize needs the correct volume of organic material applied based on crop need, the nutrient status of the material applied and the soil indices. You really should be testing 25% of productive land every year and rotate this around the farm so all soils are being test every four years.

“Only when you know what nutrients are already in your soil, can you start to make decisions about how much and when to apply materials. Testing manures and slurries for their nutrient content is equally important.

Results can help refine crop management plans to account for the nutritional value of these valuable resources. Slurry and manure testing also helps reduce reliance on expensive inorganic fertilisers and helps optimise crop nutrition.

How Nutrient Management Plan can improve performance

Livestock producers should consider a nutrient nutrient management plan to address any soil nutrient imbalances, say experts.

Farmers are increasingly looking to test their soil and manure as one way of reducing expensive artificial inputs. NRM Laboratories suggests there has been a 40% increase in the number of manure samples being tested yearly.

A nutrient plan is essential to plan a farm’s forage requirements and to help maximise their yields while reducing costs, with the quieter months a great time to devise one, says Lisa Hambly, head of grassland and forage agronomy
at Mole Valley Farmers.

Business performance

“A nutrient management plan isn’t a bit of paper to sit on the shelf,” she says. “This is an interactive tool where inputs and cropping can easily be amended according to the changing requirements of the livestock diet.

“What is put on the soil can also influence animal health. It’s vital to link the soil to the animal and realise what you put on the soil and treat the soil with can make a difference to animal health, productivity, and profitability.

“Likewise, what you feed your animals will also influence the quality of the farmyard manure or slurry, which is why it’s important to get it tested and input your farm numbers into the plan.”

Knowing what is happening in the soil and slurry will also pinpoint areas for improvement. Having excess can be as bad as not having enough of one mineral. Excess minerals can also cause an antagonistic effect.

“If you don’t measure, how can you manage? Potash in fields grazed by dairy herds can get very high, and as magnesium gets locked up when there are high potash levels, it’s important to know what is going on.”

Timing important

Ensuring you soil and manure samples are taken at the correct time is essential for accurate results, says Sajjad Awan, soil and crop nutrition agronomist at NRM Laboratories.

“Timing of sampling is critical. If you take a soil sample when it is too dry or wet, the results will be very different. The mineralisation of nutrients is low when the soil is dry, which can impact the available phosphorous in the soil.

“Secondly, stick to taking samples when soil conditions are the same by recording when you took the samples and the conditions to gain a like-for-like comparison. Looking at trends over the long term will give you a good idea of which direction you are heading.”

The type of soil test will also direct the sample that is needed.

For example, if a farmer wants a soil carbon test, guidelines suggest a sample should be taken from 30cm deep, compared to 7.5-15cm deep for a standard soil test. Soil samples also shouldn’t be collected following applications of slurry.

Informed decisions

Dr Awan encourages farmers to work with experts to use the results to make informed decisions. For instance, pH is the single most important factor for nutrient availability. A pH of 6-6.5 allows the maximum respiration rate of the soil microbes

“This means nutrient mineralisation will also be high when soil microbes are fully active. Our data has shown that the rate of respiration rests on the right pH. If this isn’t right, there will be implications down the line.”

Likewise, when it comes to testing slurry, experts on the podcast advised taking samples as close as possible to the application date as the nutrients could be lost from the manure/slurry when stored for an extended period of time.

He adds: “The mean value of total nitrogen from one tonne of cattle manure could range from £3-£75 per tonne. The value of the major nutrients applied could be worth £3,000 for every 20t/ha of manure applied – or as low as £100, which is why it’s important to get it tested.”

Testing manure just before application will consider any dietary changes that can impact results. “Animals that are fed protein retain about 20-25%, and three-quarters are excreted, so if your feeding has changed, most likely the value of nutrients will have changed.”

Slurry specialist unveils biggest separator yet

The Bauer Group’s Fan Separator subsidiary is introducing its biggest press screw slurry separator yet – which can do the work of two or three smaller machines.

The PSS8 has a capacity of 65m³ per hour. It is aimed at large dairy farms wanting to ease the management, storage and field application of cow slurry, as well as for large-scale biogas production.

Separating farm slurry into liquid and solid opens up options for further processing and reuse, especially as the solid material can be turned into compost or used as an attractive bedding material, particularly for dairy cows housed in cubicle sheds.

The liquid fraction can more easily be managed, stored and spread on fields as fertiliser, one option being a ‘dirty water’ irrigation system.

The new model retains the proven press screw concept while the components have been enlarged.

It boasts a 2200mm long and 350kg heavy auger supported by a head bearing, a 400mm screen and built-in auger is driven by a 30kW electric motor running at 400V/50Hz.