After another wet winter, careful consideration is needed for fertiliser and manure application.
Following the second wettest winter on record and a cold, wet spring, careful planning of grassland fertiliser and manure applications is even more essential.
Jez Wardman, agronomist at Yara UK, says: “Even though many have applied their first application given we had such a wet winter, nutrient levels in swards may well be lower than usual at this time of year.
“With soils having been so wet, nitrogen will have been lost as a result of leaching and waterlogging.
“Leaching occurs in soils which are able to drain freely, while in waterlogged soils, there can be a gaseous loss of nitrogen, due to denitrification which increases under anaerobic conditions.”
Sulphur levels will be reduced as a result of increased leaching, says Mr Wardman, and while other nutrients, including phosphate, potash and magnesium, may be affected to a lesser degree, levels of immediately available nutrients will still need to be reassessed.
He says: “Yara trials have shown the benefits of a balanced nutrition programme rather than applying nitrogen alone and this applies to grass just as any other crop.
“Grass has a specific demand for nutrients, both macronutrients – N, P, K and S – and micronutrients, such as manganese and copper. If the crop nutrition program is well balanced, every 1kg of nitrogen will produce 22kg of dry matter [DM], however, if it is not, this return could drop to 16kg of DM.
“In financial terms, this return is about £3 for every £1 investment. Swards which are deficient in phosphate, potash and sulphur will not be able to make the most of any applied nitrogen. This is particularly relevant.
“Most mineral soils are poor at retaining sulphur and the wet weather will have exacerbated this problem.
“Almost half of the grass tissue samples analysed by Lancrop Laboratories last year were deficient in sulphur. The best indicator here is the N:S, ratio which should be 13:1 or less.
“Last year, however, 48 per cent of grass samples had N:S ratios higher than this, meaning nitrogen is not being used effectively and grass growth rate and quality will be reduced. This, in turn, will lead to lower silage yields and poorer quality. Those using grass for grazing would need to reduce stocking rates.
“The best plan of action is to always start with a nutrient management plan.
“The grade of fertiliser you select at this point does not have to be an exact match to the deficit between the crop’s requirement and nutrients supplied by organic manures.
“A balance can be carried forward in the rotation. However, balancing slurry and fertilisers in the way suggested avoids over-applying non-organic fertilisers, which is never ideal.”
The ability to variably apply nitrogen in arable crops has been around on-farm since the late 1990s when Yara first introduced the N-Sensor into the market.
This has grown in popularity in subsequent years and, while the number of crop specific uses has grown, the obvious omission has been grass.
Currently, grass yields in the UK and Ireland deliver six-10 tonnes/hectare (2.4-4t/acre) of dry matter (DM), which is, on average, less than half of its biological potential. One of the main reasons is poor or incorrect use of nitrogen fertiliser in terms of rate and times of application.
Yara company agronomist Ian Matts says: “Nitrogen response trials, conducted on six sites in the UK over the last two seasons, have shown optimum nitrogen rates of more than 300kg N/ha for a two-cut silage system.
“This is substantially more than the 170kg N/ha currently used on average for all silage.
“This suboptimal application is likely to be reducing yields by more than 1.3t/ha DM, equivalent to a net loss of £160/ha. With this in mind, and with funding from Innovate UK, we are in the process of developing the Yara N-Sensor, so far with very promising results.”
A first season of trial work, using the N-Sensor on grass, has given a good correlation between sensor reading and DM yield and nitrogen uptake in the crop, at all times through the season. This work was repeated for a second season in the UK and Yara Finland has also carried out the same trials to add to the dataset.
Mr Matts says: “We are still working with this data.
But, essentially, it is looking promising that the sensor readings are closely correlated with nitrogen uptake in the crop, so we are hopeful it will lead to a grass specific calibration for the N-Sensor to help better match nitrogen inputs to crop demand within fields.”