Frank Mickan DEPI, Ellinbank
A proven cost effective way to increase spring growth is to apply nitrogen (N) fertiliser. Given the relative warmth of this winter, N should have been getting applied regularly to boost winter growth this year. However, applying nitrogen this spring will also help increase fodder yields to replenish empty silage and hay storages. This article will cover some considerations when applying nitrogenous type fertilisers this season.
Applying N will increase dry matter (DM) production and allow shorter shut up times, which allows paddocks to return to the rotation earlier than if no N was applied. If other nutrients are holding back production, they should also be applied for best results. N fertilisers can also increase the proportion of tillering compared to seed head development which is great for feed quality and milk production. If applied well before the dry period, N application will encourage more plant and root growth which will allow plants to grow longer when conditions start to dry off. However, it can work in the reverse if the dry period occurs soon after (approximately two weeks) N application. The period between N application and harvesting should be at least four weeks and the protein levels will be two to four per cent higher. This will increase the buffering capacity of the grass at ensiling (grass will resist becoming silage), but not a problem if the forage is wilted before ensiling.
Urea is still the best value for money (cents per kilogram of DM per kilogram of N). Some farmers are applying Easy N + Gibberellic acid as a spray but a recent trial in south west Victoria, funded by WestVic Dairy, showed its cost to be about twice that of urea. The replicated trial compared these and several products and compared urea applied at 40 kilograms N/hectare in July, August, early September and early November and no fertiliser as the control. The ideal period in which to apply N is between two to three days before grazing and up to three days after grazing in conditions where grass growth is not constrained by moisture. The applied N from urea usually takes four to five days to be dissolved into the root zone and to be picked up by the plant. Nitrate levels peak in the plant about seven to ten days after application and conversion to protein peaks at about 16 to 18 days and nitrate levels usually drop off to acceptable levels by days 18 to 21 days. Annual and short type rotation ryegrasses accumulate nitrate whereas perennial ryegrasses do not. Many ryegrass cultivars now incorporate germplasm from both so be conscious of this.
Apply about 40 – 60 kilograms N/hectare in early spring. Applying too much more will be less efficient, especially if pasture is cut for the highest nutritive value at or near canopy closure, or about three to five weeks after grazing. There will be some carry-over (approximately 20 per cent) of N in the soil. Applying 45 kilograms N/hectare over twice the area will produce more extra feed at a cheaper cost per tonne DM than 90 kilograms N/hectare over half the area.
During this harvest make some observations for the future. Look carefully at the sward during mowing. How many dead, shrivelled up leaves are in the base and what percentage of reproductive tillers have seed heads? When the paddock has been harvested, take note of how yellow the paddock now looks. A paddock with early cut silage should look only slightly lighter green than a paddock grazed at the right time. Compare the regrowth of an early cut (or correctly grazed paddock) vs. a late cut paddock, ideally shut up at the same time. Yes, it may mean more paddocks to be harvested (at lower yields) but grazing/ harvesting management will maintain the pastures in better quality further into the season and silage quality will be almost spring grass quality.
Research conducted many years ago at DEPI Ellinbank compared the total spring/early summer growth (grazed grass + silage harvest + regrowth) with different times of shut up (early vs. late) and lengths of closure (4 vs. 6 weeks). An early, short lock up was better than an early long one, and both were better than the later lock up periods. This was reinforced by corresponding higher milk productions due to the higher quality of the pasture, silage and amount of regrowth.
Certainly higher N fertiliser rates and longer shut up periods (six to eight weeks) will reap higher silage yields from an individual paddock and may be considered to restock silage storages, but regrowth will be much slower and quality will be lower. This will be more so for N applied late September with long closures as many pastures will be into seed head production. With careful planning, you can cut more area but lock up for 4-6 weeks to get the higher silage reserves, and then reap the benefits of more pasture regrowth to take into summer.