Reduced fertiliser costs and more milk solids means including clover in the sward could bring a benefit worth £215 per hectare, according to Irish research.
Grazing perennial ryegrass and white clover swards creates the potential to not only improve milk solids production per cow, but also reduce fertiliser costs.
A four-year trial carried out at Teagasc Moorpark in Ireland compared performance on perennial ryegrass-only leys receiving 250kg N/ha, with perennial ryegrass leys including clover.
The clover leys received either 250kg N/ha or 150kg N/ha.
Nitrogen was applied at the same rate and timings up until May on all treatments.
It was after May that the fertiliser was reduced for the remainder of the year on the clover 150kg N/ha treatment.
Results showed that herbage production remained the same (14.5t DM/ha) on clover leys receiving less N, while there was an increase in milk solids, leading to improved profit/ha (see panel).
Improving nitrogen efficiency is central to Yara’s agronomic advice, which stems around producing more from less.
Teagasc grassland research officer Michael Egan says these benefits will only be seen in swards where clover contents average 20-25% through the year.
“If you have sufficient clover in the sward, there is scope to reduce nitrogen application by up to 100kg N/ha in the later part of the season, June onwards,” he explains.
To maintain clover at this level, good grassland management, particularly at the start of the season, is of critical importance (see panel).
This is due to the fact grass will always grow faster compared to clover at the beginning of the year as clover has a higher minimum soil temperature requirement for growth compared to grass (8C vs 5C).
Unless grass is grazed sufficiently at this time, it will outcompete the clover, leading to clover reduction.
“The key is to manage clover well early on [before May], otherwise you will not have the clover later,” says Dr Egan.
“Chemical fertiliser is also an advantage for white clover at the start of the season when it is not fixing nitrogen itself, as it uses the chemical fertiliser for growth.” This means the usual rates of nitrogen should be applied up until May and then dropped back once clover is growing and fixing atmospheric nitrogen.
Maintained herbage production: The clover leys receiving 150kgN/ha produced the same amount of herbage versus perennial ryegrass leys getting 250kg N/ha (14.5t DM/ha/year)
+4% increase in clover: On the leys getting the lower rate of fertiliser versus those getting the higher rate (27% vs 23%)
+33kg milk solids/cow/year: Cows grazed on clover swards produced more milk solids compared to those grazed on perennial ryegrass-only leys
+€252/ha/year (£215): The benefit of having clover swards with 150kg N/ha applied versus perennial ryegrass-only with 250kg N/ha applied - as a result of increased milk solids and reduced fertiliser
+19% improvement in nitrogen efficiency: The nitrogen efficiency on clover leys receiving 150kg N/ha was 59% versus 40% on perennial ryegrass-only leys receiving 250kg N/ha
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