Agronomy Advice

Make up for poor first cut yields by fertilising your second cuts

By: Philip Cosgrove

Achieving good second cut yields will be more important than ever this year, because of poor first cut yields and low silage stocks. Second cuts are capable of very high yields, with 15 – 17 t/ha (6 – 7 t/acre) of grass achievable on swards which have good yield potential.

Make up for poor first cut yields by getting your second cuts fertilised
Make up for poor first cut yields by getting your second cuts fertilised

It’s fair to say, that first cut silage yields have been disappointing. It’s no wonder considering the growth we’ve had during April and early May. Some have ended up grazing fields that were intended for the first cut, so with this in mind and low silage stocks, a good second cut will be more important than ever to put tonnes in the pit for the winter ahead.

Optimise fertilisation for second cut to maximise silage yields

If adequately fertilised, and with favourable growing conditions these second cuts crops are capable of 6 – 7 tonnes of fresh weight per acre, which isn’t far behind a good first cut. Slurry and fertiliser application rates are important considerations to make the most of second cut yield potential.

It’s best practice to apply fertiliser a week after the slurry has been applied. If no slurry is being applied, then spread the fertiliser within a couple of days of the first cut harvest or on closing up from grazing. It happens regularly that nutrients applications are delayed too long, which then results in lighter crops or crops needing a longer growing period, which in turn lowers silage quality.

If there is no slurry applied or low volumes on account of the risk of slurry contaminating second cut grass at harvest, then make sure to use an NPKS fertiliser like YaraMila SILAGE BOOSTER.

New swards have excellent yield potential and respond to higher nitrogen (N) rates of up to 100 kg/ha (80 units/acre). Older swards with a high proportion of perennial ryegrass (PRG) can be fertilised to 90 kg/ha (72 units/acre) N and old meadow swards which don’t contain much PRG should receive 70 kg/ha (56 units/acre) N.

Nitrogen drives yield but don't forget phosphate, potash and sulphur too

Phosphorus should not be overlooked for second cut silage. With 48 % of grassland soil samples showing that they require phosphate applications, make sure to check recent soil analysis and then calculate what phosphate your second cut requires. Each tonne of fresh grass requires 1.0 kg of P, so if this is scaled up to a 15 – 17 tonne crop the P requirement is 15-17 kg/ha.

Phosphate allows the plant to process light energy into biomass, so any soil availability shortfall is going to hamper grass growth rates. Also, grass phosphorus levels tend to drop in June, and it’s not clearly understood why this happens. By applying fresh phosphate, this dip can be avoided. If there is no slurry applied or low volumes on account of the risk of slurry contaminating second cut grass at harvest, then a phosphate fertiliser should be applied up to 17 kg/ha. If the soil P index is 1 or 2, then these fields will require a top-up of 20 and 10 kg/ha respectively if it hasn’t been applied earlier in the year.

Potassium should not be forgotten either, potassium offtake at 25%DM is 6kg/tonne fresh grass, so a 20t/ha (8t/acre) crop will remove 120kg/ha (96 units/acre) and this must be replaced. Teagasc soil analysis data from 2019 shows that 41% of grassland soil samples from dairy farms are now below the optimum soil potassium index 3. Potassium applications should take into account that silage crops have a high requirement for potassium, running at 6 kg per tonne of fresh grass silage. Potassium response trials have shown that for every 1 kg of potassium applied results in 5 – 7 kg of grass DM (25 – 30 kg of fresh grass). If you want to maximise yield potential on these 2nd cut’s, then 100– 116 kg/ha of K is required. This would require 28-33 cubic metres of cattle slurry per ha. If this volume of slurry isn’t being applied, then use a fertiliser with potassium.

Sulphur is an important nutrient, and it certainly merits using a fertiliser that contains sulphur on these second cuts. The response does vary according to soil type, regularity of manure applications and overwinter rainfall, but the majority of silage crops do respond to applications. On second cuts. 10 – 12 kg/ha (8 – 10 units/acre) of S is enough.

Don't delay application to avoid losses

Finally, don’t delay applying slurry and fertiliser. The slurry should be applied immediately after the first cut is harvested and then apply the fertiliser 5 – 7 days later. If slurry isn’t being applied, then get the fertiliser out as soon as possible but it’s important to order what fertiliser is required and have it ready for spreading.

A good second cut requires a proactive approach to ensure these crops are optimally fertilised, so just slurry and straight N might not be the most cost-effective option in the long run, if we compare the cost of homegrown silage versus purchased feed on a dry matter basis.

Find more information on grassland nutrition

Recommended grassland fertilisers

The following compound fertilisers are recommended for grassland and supply combinations of nitrogen plus sulphur (NS) or nitrogen, phosphate, potash and sulphur (NPK+S) in appropriate ratios for grassland and with the added benefit of selenium for improved animal health.

Latest advice background
Latest advice background
Grow the future | Grassland Sulphur Grow the future | Grassland Sulphur

Spreading nitrogen and sulphur at the same time means more grass

Applying fertilisers containing nitrogen and sulphur means the grass uses nitrogen more effectively, you get more kgs of dry matter per kg of nitrogen that you apply

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