Key to soil fertility is deeper than just grass reseeding

Grass dry matter on second rotation covers is surprisingly high at around 18%. Higher dry matters than this are typical on farms that are very exposed to the elements or are near the sea.

Dry matter has a huge influence on how much feed you have on farm, you should send a sample away to be analysed if in doubt.

The start date of the second rotation is dictated by cover/cow and pre-grazing covers on first grazed paddocks. Target of 140kg/cow that is, an average farm cover (AFC) of 420kg if stocked at 3LU/ha. Target pre-grazing covers of paddocks at the start of the second round is 1,000 to 1,100kg, dependent on stocking rate.

The ‘magic day’ is when growth rates meet demand. Following this, we will need to increase demand; close off silage ground and/or increase stocking rate on milking platform with heifers.

I always get asked about reseeding ground at this time of year as the low fertility paddocks show their poor productivity, low growth rates until temperatures increase in April. In my view reseeding a poor performing paddock is based on two things:

  • Is it fertility that is causing poor production, or;
  • Is it a high percentage of weed grasses

Fertility includes any compaction issues. There is little point in reseeding a paddock that has low P/K indices and a pH below 6.3 if the ryegrass per cent is above 70%, as it is the poor fertility that is suppressing production.

Investing in soil fertility across the farm will have more of a long term impact on tonnage grown than reseeding 10% of it. In terms of ‘investing’ – prioritise paddocks close to the parlour. Calcium is the main soil nutrient for improving soil structure; start with pH, then phosphorus and potassium. Depending on soil type, you will require 25 to 35 units sulphur per year. Half of this should be applied now.

Stretching out first round

As mentioned above, the target cover/LU by magic day is circa 140kg/LU. If the grass budget is showing that the AFC is or will be below that, we must increase supplement to reduce grass demand.

This will maximise the growth capacity of the farm. If you continue as is and hope for a miraculous growth rate to appear in 7 to 10 days, then you run the risk of dropping the AFC drastically.

This would result in very low grass availability at a time when we need to be gearing up spring calving herds for breeding and maximising milk solids output, not silage and concentrates input. Milk protein per cent is our best indicator of how well we are doing at maximising grass quality, energy intake by the cow and subsequently, kgMS produced.

How much is your herd eating per day? What is the grass demand per cow? This is dictated by cow type (and mature weight), length of time calved and percentage of heifers in the herd. The cows will tell you how much they need, allocate what you think they are eating and over 48 hours you will see if your assumptions are accurate, based on grazing residual and production output.

There have been a few cases of grass tetany this week. If paddocks are high in potassium and low in magnesium, these are high risk paddocks for grass tetany – particularly if grass is very leafy and cover is below 1,000kg/ha.

Ensure cows are getting adequate magnesium in the concentrates and also put extra magnesium in water troughs of potential problem paddocks. What is adequate magnesium in concentrates? It is usually 40g/cow/day, but up to 60g/cow/day if soil magnesium is either low or excessive. Either will result in low mag uptake by the plant.

Enjoy the end of the quota era, remember that sales people are potentially gearing up for it more than you.

Cathal McAleer is a grassland consultant working with individual farmers and facilitating discussion groups throughout Ireland.

You can contact Cathal on 087 160 2491 / 0044 7749 531679 or by email: [email protected]

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