High chemical-fertiliser prices have placed a focus on obtaining the best nitrogen use efficiency on dairy farms.
Although fertiliser prices are at unprecedented highs, the spreading of chemical fertiliser remains an important task on dairy farms.
There are several methods that farmers use, i.e. blanket spreading and following the cows.
According to the Agriculture and Horticulture Development Board (AHDB), the best method of spreading fertiliser on dairy farms is following the cows.
This is according to grazing consultant Andre van Barneveld, who said that blanket spreading on the grazing platform risks cows eating high levels of nitrates.
By following the cows with fertiliser rather than blanket spreading, farmers can avoid luxury uptake of nitrogen (N) in the grass being grazed.
After fertiliser has been spread on grassland, plant nutrient uptake leads to a nitrogen spike in the leaf four to seven days post application.
This has an animal impact as it costs the cow energy to process and urinate this excess N, according to Andre.
This also has an environmental impact because the concentration of the discharged nitrate in the urine patches contributes to pollution.
“If that N is in the cow, you don’t get a response in the plant so it’s uneconomic,” the grazing consultant said.
Nitrogen use efficiency
To obtain the best N efficiency, fertiliser should be spread post-grazing, ideally as cows leave a paddock and walk to the parlour.
However, the basic rule of thumb is to stay 14-days ahead of the cows.
This means on a 21-day rotation, you spread one-third of the farm every week – if you have a large enough area.
This gives the grass a chance to use up the nitrogen and grow more leaf before cows graze the paddock again.
Andre added that: “The goal is to balance grass growth with demand and predict shortages, applying fertiliser to boost growth rates.
“When grass is in its vegetative stage, use 1kg N/ha/day, increasing this slightly to 1.5kg N/ha/day when in the reproductive phase.
“Don’t be tempted to skip a round of fertiliser in June if it starts to dry up, because a plant that is used-to chemical fertiliser gets stressed when in the aggressive reproductive phase and tries even harder to go to seed.
“If there is also moisture stress, the whole farm could go to seed,” he said.