Use silage dry matter percentage to calculate aftermath fertiliser applications

Incorrect nutrient removal calculations using industry averages, rather than those based on actual dry matter percentages, yields and soil reserves, could leave many producers with lower than expected second cut silage yields. Every field is potentially different and will have its own nutrient requirements.

“A typical 20% DM silage will remove 1.7kg P2O5/tonne of fresh silage and 6kg K2O /tonne,” explains KW Alternative Feeds fertiliser manager Ian Moseley. “However, a 30% DM silage crop will remove almost 25% more phosphate and 20% more potash, leaving a deficit that could lead to lower second cut yields.

Mr Moseley recommends calculating aftermath fertiliser requirements using both soil and silage analysis. “Aiming for a soil index of 2 for both P and K will determine how much fertiliser is required to maintain soil reserves. Added to this should be the amount removed by your own crop.”

Removal of P & K for a 20t/ha crop (fresh weight) at different dry matter levels

20% DM 30% DM Difference per hectare (units)

P2O5 68 82 14

K2O 236 282 46

“Using industry averages for the amount of nutrients removed by a crop can result in under-applications and subsequent yield and quality penalties,” warns Mr Moseley.

“Calculating silage yields as accurately as possible will help get aftermath fertiliser applications right. Obtaining the weight of one full trailer and multiplying this by the number of loads per field should give a reasonably accurate figure to work with, and is much better than trying to guess a field’s yield,” Mr Moseley concludes.