Making the most of manures

Published 5 June 15

Manure testing, application timing and technique are all key to helping farmers make the most of manure. That was the main message from Dr Lizzie Sagoo, Soil Scientist at ADAS speaking at the AHDB Dairy Research Day in Carmarthen.

With incurrent high fertiliser prices, Lizzie highlighted that making the most of nutrients in manures was key to keeping costs down on farm. ‘A 40m3/ha application of cattle slurry would typically supply 40kg of available nitrogen, 50kg of phosphate, 130kg of potash and 10kg of available sulphate per hectare. That has a nutrient value of £125 per hectare and can help reduce fertiliser costs significantly’ states Lizzie ‘however, manure nutrient content can vary between farms, and it is important that farmers get samples of their own manure analysed so they know what they are applying to their land. Applying slurry when the crop is growing and using bandspreading techniques can also help increase slurry nitrogen use efficiency by reducing ammonia emissions and allowing even slurry application’ .

Slurry hydrometer

Image 1 Slurry hydrometer demonstration with Dr Lizzie Sagoo

For slurries there is a good relationship between dry matter content and nutrient content. ‘Slurry hydrometers can be used on farm to obtain a quick measurement of dry matter content. From this we can then better estimate slurry nitrogen, phosphate and potash content and more accurately plan both manure applications and supplementary fertiliser applications to meet crop requirements’ she continues.

To make best use of manures, farmers should estimate the crop available nutrient supply. Lizzie showed how MANNER-NPK, a free software programme, can be used to estimate the crop available nitrogen, phosphate and potash supply and financial value of manure applications. The programme can also be used to test the effect of different application timings or techniques on nitrogen efficiency ‘MANNER-NPK shows that spring time applications are more beneficial than autumn, increasing nitrogen use efficiency of slurries on grass by as much as 10%’ states Lizzie. ‘This is due to a higher crop nitrogen uptake and a lower risk of nutrient losses to water’ she explains.

Lizzie also outlined how low emission application techniques (eg bandspreading and trailing shoe) can help improve nitrogen efficiency from manure. ‘These application techniques are beneficial as they offer a wider spreading window, reduce sward contamination, reduce odour and ammonia emissions, and allow more even application of slurry’ comments Lizzie. Research has also show significant yield benefits from these techniques, due to reduced N losses as ammonia. In trials from N.l., nitrogen use efficiencies were on average 11% higher from low emission techniques when compared with splashplate spreading. This gave a 22% increase in annual silage dry matter yields.