Slurry and digestate can perform a useful role in replacing or supplementing artificial fertiliser. FGinsight got some top tips on how best to use it from Tramspread director Laurence Baker.
The type of slurry will make a difference to crop performance. The key measurement is the amount of plant available nitrogen (N) in the slurry which can be determined by testing it before spreading.
Digestate and pig slurry are likely to be higher in N than cow slurry so if there is a choice to make and the crop needs the maximum amount of N available then opting for digestate, for example, will provide this. Crucially, the water content will determine the value of the slurry. Slurry or digestate stored away from rainwater will have a higher nutrient value because it will not have been diluted. Therefore, a source of slurry that has been kept in a covered store is preferable to maximise plant available N.
Slurry should be spread as soon in the season as possible. In some areas of the country this can be as early as February. Once the land starts to dry out it is ready for slurry. Spring crops will always benefit from having slurry applied early and then ideally another two applications during the season.
The applications should be approximately four weeks apart to allow the crop to absorb the nutrients. Applying slurry to stubble is cheap and good for the soil. However, the more effective use of slurry is when it is applied to the crop early. It is more expensive to have slurry applied to a crop, but the benefits can be seen almost instantly because unlike fertiliser the liquid slurry can be absorbed by the plant immediately.
For arable crops using dribble bars is an accurate method. Dribble bars come in lengths from 6m to 36m to cater for all widths of tramlines. Umbilical spreading reduces soil compaction and if the source of slurry is close enough to the crop the slurry can be pumped direct. Nurse bags and bag tanks are becoming ever more popular to enable direct umbilical spreading of bought in slurry.
Measuring the amount of slurry is crucial to understanding the amount of plant available N being applied to the crop. The Tramspread Isobus flow meter package connects a flow meter to the tractor’s GPS and can be used to adjust the application rate from the cab. An Agros Nova liquid manure testing kit is said to offer farmers laboratory test quality results. The nutrient value of the slurry in conjunction with the speed of flow can then be used to ascertain the amount of N applied per hectare.
The data in AHDB’s RB209 nutrient management guide helps to illustrate the savings available through testing slurry and applying it accurately. Calculating the available N, P and K of slurry can save significant sums of money. ADAS soil scientist John Williams has used the RB209 guide to equate this to between £215 and £265/ha, based on a season’s application of 95cu.m/ha of cattle slurry.
“Slurry is one of the most undervalued resources farmers have. If stored, tested and applied carefully with attention to nutrient value, slurry offers significant savings and environmental benefits,” concludes Mr Baker.