March 2019 Monthly Management

Spring fertiliser advice, fertiliser recommendations for first cut silage, synchronising of heifers

3 April 2019

Spring Fertiliser Advice

Nitrogen (N) – The amount of nitrogen fertiliser applied to grassland will depend on the quantity of grass production required and the background release of nitrogen from the soil. The quantity of grass required will depend on the grass sward type, stocking rate and animal type while the background nitrogen will depend on the soil, clover content and whether the sward is old or newly sown. Table 1. gives a guideline on grazed swards for dairy production - this will depend on several factors including overall farm system, soil type, weather, livestock turnout and housing date. Nitrogen rates need to be adjusted where slurry has been applied and compliance with NAP regulations taken into account.

Table 1: Recommended rates of N fertiliser (kg/ha) for grassland during the year where approximately half of the farm is cut for first-cut silage and the amount of second-cut is kept to a minimum (0 - 30% of the grassland area)
March April May June July Aug Sept Total N
≤ 85 25 15 40 (32)
106 15 28 15 15 73 (58)
128 28 35 25 23 111 (89)
149 29 44 26 26 17 142 (114)
170 34 53 42 42 31 202 (162)
180 32 32 48 38 38 28 216 (173)
191 31 41 54 37 37 37 237 (190)
200 30 53 53 37 37 37 27 274 (219)
210 31 54 54 56 37 37 37 306 (245)
≥ 210 32 49 55 38 38 38 28 278 (222)

Phosphorous (P) and Potassium (K) - Where straight Urea or CAN was applied in the first application the year, it is worth considering using compound fertilisers such as 18-6-12 or 27-2.5-5 to supply P & K in the second application (especially low index soils).

Low index soils can also be targeted with slurry to maximize nitrogen content in the spring while also getting some necessary P&K onto these soils. Typical recommendations for phosphorous are to apply 50% in the spring and the remainder to be applied over the growing season across 2 to 3 applications. In the case of Potassium requirements, maintenance rates should be applied during the growing season and apply build up rates at the back end of the year – this reduces the risk of grass tetany in spring grass and excessive levels of K in grass silage.

Fertiliser Recommendations for First Cut Silage

Nitrogen - similar to grazing requirements, the amount nitrogen required to spread for first cut silage will depend on the age of the sward, number of cuts taken each year and the grazing history. Recently reseeded swards (0-3 years) will have 25% higher N demand versus older swards. Typically, 100 units of N are required per acre. If nitrogen was applied in early spring, assume that 20% of this remains available for first cut silage. Nitrogen rates may need to be increased by up to 20% in newly sown leys as silage yields would be greater than those of older leys.

Fertiliser Options
No Slurry Cattle Slurry
3,000 gal/ac
1 100 32 140 3.5 bags/ac 0-7-30
4 bags/ac CAN
3.5 bags/ac
2 100 24 120 3 bags/ac 0-7-30
4 bags/ac CAN
3 bags/ac
3 100 16 100 5 bags/ac 15-3-20
1 bag CAN
3 bags/ac
4 100 0 0 4 bags/ac CAN 4 bags/ac

Phosphorus and Potassium are essential to maximize grass yields therefore adequate supply of these nutrients in the soil is critical. Build up and maintenance requirements should be taken into account when deciding what levels of P and K are needed for a productive crop of silage. For target index 3 soils, 20 units of phosphorous and 100 units of potassium will be sufficient, however if soils are deficient in these nutrients, then a higher fertiliser input is needed.

Organic manures like cattle slurry and farm yard manure are an effective source of N, P & K and can provide a large proportion of crop P and K requirements at relatively low cost. 1,000 gallons of cattle slurry at 7% DM has a similar value of one bag of 5-5-30 fertiliser. Organic manure and chemical fertiliser application should be kept one week apart. Contact the Drinagh Advisory team for further fertiliser plans and information.

Synchronising of Heifers

Synchronisation is an excellent way of increasing the number of heifers served to artificial insemination (A.I.) with minimum heat detection.

The advantages of synchronisation include:

  1. All heifers will be served within a short period of time
  2. Repeats will occur in short proximity - facilitating prompt heat detection
  3. Higher numbers of heifers will calve in February. This will also give them the best chance of calving early for their second & third lactation thus ensuring longer survival in the herd.
  4. Heifers can be served to high EBI, daughter proven easy calving sires to reduce any potential problems next spring. This also ensures that the farm is producing early born, well-bred high EBI replacements next year.

For a synchronisation programme to be successful, ensure that all heifers are fulfilling the following criteria:

  1. Meeting the minimum target weights: Regardless of breed, heifers should be at target weight for breeding. If some heifers are behind target but within 20-30kg of intended kgs, breed them at the start, avoid delaying them 3 weeks and recover the extra body weight gain required during the breeding season.
  2. On a rising plane of nutrition: Heifers should be on a good quality diet from now on. Reducing nutrition during the breeding season will result in lower conception rates.
  3. Vaccines: Ensure that all vaccines specific to your own farm have been administered prior to the breeding season

Cost effective Synchronisation protocol for heifers

Monday 24th April Day 1 - 7 A.I heifers on heat. Will get 1/3 of heifer bred this week.
Monday 1st May Day 7 - 8 Inject PG to the remaining 2/3 of heifers not bred. (New syringe & needle, preferably dry skin)
Tues – Thurs 2nd - 5th May A.I heifers when on heat. Majority will be on heat 48-72 hours post injection. Be extra vigilant at this time
Friday 12th May Day 18 Re Inject all heifers not bred with PG – 11 days post the 1st injection. Should be very few heifers.
Monday 15th & Tuesday 16th May A.I heifers when on heat or 72 and 96 hours post 2nd PG
*PG: Prostaglandin – Estrumate, Lutalyse, Enzaprost (prescription only medicines)

Note: If lower than 30% of heifers bred after the 1st seven days, then investigation is required. Other issues may be present such as heifers not cycling or poor heat detection. If heifers are not cycling, then prostaglandin is unlikely to be successful