Studies of intensive grassland farms have shown average nitrogen surpluses as high as 175 kg N/ha that’s 140 units/acre in old money. This means the bad news is NUE values can be as low as 23%. A staggering three quarters of the nitrogen entering the system isn’t captured in grass or silage or put another way, you are only farming with a quarter of what is in the system. Across the UK, the national surplus averages 83 kg N/ha, but this hides significant differences between farm types. Some can be as high as 220 kg N/ha, with the best arable practices as low as 30 kg N/ha. Arable systems are typically more efficient due to their lack of livestock. Grassland based dairy farms particularly those importing nitrogen via feed tend to leave a far bigger footprint.
Livestock systems are inherently more complex. This is because, in addition to bagged fertiliser and on farm manures, bought in feed brings considerable additional nitrogen. Without integrating all these sources into a joined up nutrient plan, it’s easy to end up over applying which is where the huge gap in nitrogen utilisation can appear.
This inefficiency shows up in multiple ways: nitrogen that’s applied ‘just in case’, every 30 days because Dad always did it; poor accounting for clover fixation due to lack of sward assessments; and uneven slurry applications all widen the gap (this is where slurry testing can be a useful tool). Every kilogram of unused nitrogen represents not only wasted spend, but increased costs on purchased proteins. The yield and quality loss also shouldn’t be ignored. Then there are the environmental issues whether this is through ammonia loss, nitrate leaching, or denitrification in wet, compacted soils.
Practical steps can help close this gap. Starting with realistic estimates of manure nutrient content based on livestock numbers, volumes, storage, and field histories enables more accurate fertiliser decisions. Fields closer to the farm historically have higher indices by default and require next to no additional livestock manures. This can also be expanded to crop specific fields. Maize, as a continuous crop, will build indices faster than most others due to returning a large amount back to the soil during harvest. Adjusting nitrogen applications based on previous inputs and targeted to field use silage aftermaths, grazed paddocks, or reseeds will all need different approaches.
Timing and method matter too. Moving away from splash plates and applying slurry with low emission equipment reduces losses dramatically. Fields with clover should be treated differently, and those receiving multiple cuts should be reviewed between harvests.
When ammonium nitrate is applied, the clover plant can readily absorb this nitrogen from the soil. This makes it less necessary for the clover to invest energy in fixing its own nitrogen, and thus leads to more wastage from the system.
At CMC, we support farms in making better use of applied nitrogen through targeted nutrient management planning with NavigatePro. This cloud based tool builds whole farm plans based on real nutrient flows, crop demands and field use, with flexibility to adjust as the season progresses.
To push efficiency further, we offer a range of proven and forward thinking products that help retain more nitrogen in the soil, reduce losses, and improve uptake. From amendments that stabilise nutrients in manured soils to bio based products that support root microbe function, we help close the loop between input and output.
Nitrogen planning isn’t just about applying less it’s about using what’s already on farm to better effect. There’s still a lot to gain.