March 2017 Monthly Management

Spring Fertiliser Advice–N, P & K for Grazing

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. Table1.gives a guideline on grazing 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.

Phosphorous (P) and Potassium (K) - Wherestraight Urea or CAN was applied in the first application the year, it is worth considering using compound fertilisers such as 18-6-12, 10-10-20 or 27-2.5-5 to supply P&K in the second application (especially low index 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 is to reduce the risk of grass tetany in spring grass plus excessive levels of K in grass silage. 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.

Nitrogen – is key driver for silage yields. The level needed will depend on the age of the sward, number of cuts taken each year and the grazing history. Too little or too much N will have an impact on DM production and overall quality. Recently reseeded swards (0-3 years) will have 25% higher nitrogen demand versus older swards/ permanently grazed fields due to their productive perennial ryegrass content. Typically, 100 units of N are required per acre for first cut silage. If nitrogen was applied in early spring, we generally assume that 20% of this remains available for silage prod after grazing.

Phosphorus and Potassium are essential to maximise 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 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. Chemical fertilizer and organic manures should kept at least one week apart. Contact the Drinagh advisory team for further fertiliser plans and information.

Tip of the Month - The 1-2-3 of the CMT

Early identification of mastitis gives you the best chance of cure, and of preventing persistent problems. Clinical cases will have obvious signs, such as clots in the milk or a swollen quarter, but what about the subclinical cases? These have no signs at all, other than a high somatic cell count (SCC). The California Mastitis Test (CMT) is a quick and easy ‘cow-side’ test that is useful for detecting subclinical mastitis by estimating the SCC of the milk. The test works on the principle that mixing milk with a reagent causes the somatic cells in the milk to rupture. When the DNA is released from these cells, it coagulates and forms slime-the more cells there are in the milk, the more “jelly-like” the result!

It is good practice to check all cows and 1st lactation animals with the CMT before including their milk in the bulk tank for the first time-that way you can be confident that any problem cows are picked up early, before they cause more trouble.

Three Easy Steps

1. 1. After discarding the first 3-4 squirts of foremilk, collect 2-3 squirts of milk from each quarter in each separate well.
2. 2. Add an equal amount of reagent to each well. Swirl the paddle gently, mixing for 10 secs.
3. 3. Look at the consistency of the fluid in each well (not the colour), and record the amount of gel reaction that occurs within 20 seconds (from none to almost solidified).
4. CMT kits are available from all Drinagh Co-Op stores and are very inexpensive. Replacement bottles of reagent can be purchased separately. This is one of the best investments to make in your dairy-go get one and start practicing!

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