Once it rains …. what happens to my grass?

Stock have generally done well in the dry conditions this year because feed quality in the desiccated pastures has been reasonable. When the rain finally comes, the quality will crash, and stock will go backwards.
Sunday, 29 March 2020

** This article is written by BakerAg and was originally published in AgLetter. Readers are invited to find out more about AgLetter at http://www.bakerag.co.nz/agletter

When it rains the cell walls of the plants collapse, feed quality disappears and the plants rot. It is estimated up to half the grass available is lost after rain because it is dead and decays quickly.

Another thing to watch is that the DM content of new grass is low (below 15%) because of its rapid growth, so supplement will still be needed even when there is plenty of fresh feed available. Therefore it is critical to have plan to carry on with your supplementary feeding regime for at least 2-3 weeks following the rain to allow pastures to recover (not overgraze) and stock to continue holding condition.

How does my grass recover? (Source: Massey University)

In a drought, tillering doesn't happen, more spring tillers die and those that survive are stressed. The period immediately following a drought is critical to allow autumn tillering to occur, otherwise pastures will thin out in winter, production will be poor, and weeds will invade. There are three ways grasses recover once rain falls:

  • Plants that are still alive but growing slowly due to lack of moisture can quickly recover, green up, and be back into production. While this greening up can occur within a day or two of rain, growth rates will take several weeks to recover, as roots are small and tillers are re-building.
  • Dormant plants where above-ground parts have died back, but buds at ground level are surviving, can begin tillering from these buds when rain falls.New green shoots can be seen in the base of dead pasture within 1–2 weeks after rainfall, but recovery in terms of pasture growth rates will still be several months away.
  • Pastures where most of the plants have died will have to recover from seed.

How far behind “normal” are my feed covers?

Keep a reality check on your position

It’s too easy to accept the dry as a “norm” and end up wearing big production loss because you weren’t proactive enough. Seek an outside opinion if you’re having trouble reading or accepting these numbers below and fathoming the response.

An outside opinion can be more objective about your position. Don’t blame yourself for things not going to plan. Focus on adapting to the “reality” of what’s around you and respond to it.

Stocktake

BakerAg monitors a number of properties in the Wairarapa and Tararua. Many farms are currently sitting at covers of 1000 to 1250 Kg DM/ha. This would look like 1.5 to 2cm of pasture height on your FARMAX sward stick (Summer).

Typically, the farms monitored would have covers of 1700-1800 kg DM/ha at this time of the year in a normal season. The gap in feed covers we are seeing is therefore circa 550kg DM/ha. Let’s quantify this in supplement terms:

  • 550kg DM equals 2.5 bales of baleage /ha (220kg DM per bale).
  • 550kg DM equals 640kg of feed barley /ha.
  • 550kg DM equals 46kg N/ha at a 12:1 response (100kg/ha urea).

Let’s say your farm is 700 ha effective. To get back to normal feed covers/reserves on every hectare of your farm you would need to fill to hole with supplements using either:

  • 2.5 bales of baleage on every hectare = 1750 Bales of baleage, or
  • A pile of 640kg of feed barley on every hectare = 448 tonnes of barley, or
  • When it is green, apply 100kg of urea to every hectare = 70 tonnes of urea.

What is my daily Feed Demand per Ha?

We strongly suggest you work out your daily feed demand and liveweight/ha (see end of AgLetter for worksheet). Below is a 700 ha summer dry Wairarapa farm that has been reducing feed demand steadily through the autumn. The current feed demand is 10.4 kg DM/ha and the liveweight/ha is 476 kg.

If I’m eating this ... and growing this … what is going to happen?

We have estimated what pasture growth rates would look like below with different recovery times. Like a Friesian bull, there will be compensatory growth in our pastures once it rains with May and June. Pasture growth rates can be higher post a drought because of stored N and S, depending on the pasture damage. Remember ryegrass will still grow well at a soil temp of 10 0C (soil temp on the 15th May 2019 was 130C on a Wairarapa farm). Bring on shorts at duck shooting and full dams!

This is a crude supply and demand exercise, but what is clear is that we need to be building feed covers for winter now, but with a daily deficit in April and little surplus in May/June this property would struggle to build enough feed going into winter without more intervention. Enter your demand and your estimated PGRs to see the outcome.

Note: Every farm is different, but bigger decisions would need to be made if we don’t get a recovery until the start of May.

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