Precision N application test costs 'outweigh returns'
Precision application of nitrogen can improve yields, but the costs of testing currently outweigh improved returns, according to new research from Plant and Food Research, MPI and Ravensdown.
The project highlighted the value of catch crops as a tool to capture and use nitrogen left in the wake of winter forage crops, provided the correct management principles were followed.
The researchers carried out trials at both plot and farm scale to determine how to make the most effective use of catch crops to reduce nutrient losses while generating dry-matter.
Speaking a recent workshop, Brendon Malcolm says catch crops mop up N and reduce drainage by taking up water. However, timely sowing with the appropriate winter-active species was important to make the most effective use of these crops.
July-sown oats had the greatest impact on reducing nitrogen losses. At paddock scale, oat crops were capturing up to 100kg N/ha by the end of the leaching period, N that would be otherwise be lost to the environment.
Yields in catch crops grown for green-chop silage were typically between 8-10t/ha with a maximum of 12t DM/ha.
Malcolm says while the oats sown in July were very slow to come away, they were still capturing significant amounts of N through the root system, despite the lack of above-ground foliage.
Growing a crop at a time of year when the paddock would normally be bare, does add to bottom line and an onfarm trial looking at an ex-kale crop showed that it only took a crop of 2-3t/ha to break even.
Returns per hectare were greater in the direct drilled crop versus the crop established with tillage – $1,620 versus $1,520/ha. However, Malcolm acknowledged that tillage was sometimes necessary to provide good seed-to-soil contact if the field surface was too pugged from the previous forage crop – like fodder beet.
Peter Carey says early sowing is one of the most important factors with catch crops.
“The key point is sowing as early as you practically can.”
Modelling carried out in Canterbury on freedraining soils showed the earlier the sowing, the greater the amount of N captured.
A sowing date trial comparing crops sown on 11 July, 3 August and 31 August highlighted the importance of early sowing. By harvest in November, there remained a big difference in the crops despite the three-week difference in sowing dates.
“Some years you just cannot get on the paddock – maybe one in every five years – and you just can’t do anything about that,” Carey explains.
He adds that they focused on oats because they are robust, will germinate at lower temperatures and produce quality green-chop silage.
A trial comparing Italian ryegrass, with Triticale and oats showed oats (Intimidator) to be the stand-out performers in terms of both dry-matter yield and nitrogen captured.
For more information about catch crops go to B+LNZ’s Knowledge.
