Fertiliser and grazing management for autumn sown perennial pastures

 

Optimising the potential of autumn sown pastures in the tablelands pasture systems can be critical in overcoming the winter feed gap, leading to better livestock performance and profitability.

 

Grazing systems need to identify several key factors in order to maximise the grazing benefits from autumn sown pastures.

 

  1. Know the fertility status of the paddocks
  2. Have a pasture that is going to suit the class of livestock that is in the operation
  3. Understand and be able to apply optimal grazing management in order to maximise grazing benefit from those pastures
  4. Fertilise at the right time with the right product in order to maximise production

 

 

Nitrogen (N) - Nitrogen is the most common fertiliser used to increase pasture production and this is mainly applied by the product called Urea. When applying nitrogen to pastures, it is important to consider the following factors such as; that the pastures need to be actively growing, that the soils should not be waterlogged and that the fertiliser is best applied within three days of grazing or slashing. (NSWDPI, 2006).

 

Phosphorus (P) - Phosphorus is frequently a limiting nutrient to the growth of pastures. Phosphorus fertilisers can be applied to dry soil and split applications are preferable when using heavy rates. Highly productive temperate pastures require a soil test Colwell P of at least 75 mg/kg, for medium production the result should be 50 mg/kg (NSWDPI, 2006). Having low Colwell P levels may create favorable conditions for weeds and less productive pasture plants therefore limiting pasture production.

 

Potassium (K) - A large store of potassium is available in most soils. Potassium deficiency usually arises when plant removal is high. Hay and silage production removes large amounts of potassium from the soil. Potassium is relocated around the farm in dung and urine and should be replaced in areas of depletion. (NSWDPI, 2006).

 

Sulphur (S) – Sulphur can be the forgotten nutrient as many fertilisers have small amounts available. Single superphosphate is the most common fertiliser to supply sulphur to pastures and Gypsum supplies sulphur and calcium (Ca) to the soil.

 

 

 

Phosphorus (P) is vital for seedling and root development. It is recommended to sow with a minimum of 20-25 kg/ha of P. Nitrogen (N) at sowing is also important at assisting plants to a quick germination but too much (eg straight urea) can burn the seed. Products like MAP and DAP fertiliser blends are suggested for optimal establishment.

 

Refer to Tables 1-2 for suggested fertiliser and nutritional requirements. 

Table 1. Rates of common fertilisers to achieve 20 kg/ha of phosphorus
Table 2. The affect of drilling seed and fertiliser together compared with broadcasting on pasture production (DM kg/ha produced)

Depending on how nutrients are removed determines how much and what type of fertiliser needs to be applied to maintain production. Nutrients removed from paddocks through milk by dairy cows are different to those removed by wool production or live weight gain in sheep and beef, or haymaking.

 

Table 3 below shows nutrient removal rates for various products and the Image 1 shows Hummer MaxP® tall fescue direct drilled after maize silage was harvested. The light green strip had no starter fertiliser and the rest of the paddock had 200kg/ha of DAP.

 

Table 3. Typical nutrient removal rates (kg/ha of nutrient removed per tonne harvested or per 1,000L of milk produced)
Image 1. Hummer MaxP® tall fescue direct drilled after maize silage was harvested.

 

  • The use of the correct fertiliser at planting down the seeding tube will increase DM (drymatter) production usually by double compared with broadcasting the same fertiliser. Therefore placing fertiliser with the seed is critical.

 

  • Applying Nitrogen to a pasture is the most cost effective way to fill your feed gap. On average there will be at least 10kg’s of drymatter produced for every 1kg of nitrogen applied. So 50 kg/ha of urea equates to 23kg N/ha and this will grow approximately 230 kgs DM/ha additional feed (depending on base soil fertility and timing of urea application).

 

 

Grazing of all new pastures should not commence until all plants are well anchored. This can be tested by using the ‘pluck method’. If leaves snap off and roots remain anchored, when plucked then the grass is ready for grazing. If the roots pull out when plucked then the grass is not ready for grazing.



Key tips:

 

  • Graze very lightly, with a light stock class like lambs or calves and only when it passes the ‘pull test’. The pull test is when you can pull upwards on the grass and the leaf breaks without pulling the plant out of the ground. These light grazings will promote tillering, which increases ground cover and plant strength. Examples of the pull test are shown in the Images 2 & 3 below.

 

  • Do not let your perennial pastures get out of control as you quickly lose quality, plant density, legume content and production. Grazing management is one of the key tools in your control, so make sure you get it right.

 

 

Image 2. Pluck test failed
Image 3. Pluck test passed

 

Persistence and productivity rely on the plants ability to produce carbohydrates via photosynthesis. For most plants, the first leaf is produced by drawing on carbohydrates stored in the base of the plant and roots. This first leaf will start photosynthesising carbohydrates to produce the second leaf and then both leaves create the third leaf. After the third leaf, the plant will replenish carbohydrates to the roots and begin tillering (see below Diagram 1). 

Diagram 1. Leaf growth and water soluble carbohydrate levels of a ryegrass tiller following defoliation
Diagram 1. Leaf growth and water soluble carbohydrate levels of a ryegrass tiller following defoliation (adapted from Donaghy, 1998)

 

A ryegrass plant does not support a fourth true leaf (unlike cocksfoot and phalaris). For productive grazing,  it is recommended to graze most grasses at their second to third true leaf stage. Grazing before this stage can stress the plant and potentially lead to plant losses, but grazing after the third leaf can result in low quality feed, wastage and aerial tillering. It is important to note that the speed of leaf stage is greatly driven by temperature, moisture availability and fertility. For example, the slowest growth of most grasses occurs during the winter and summer months.



Persistence heavily relies on the ability of a plant to replenish root reserves. Under intensive, continual or set-stock grazing practices, leaves are always being consumed meaning root reserves struggle to be replenished and the roots are often shallow and easily pulled out.

 

Rotationally grazing by moving animals off the pasture to maintain a residual of 4-6 cm (1,500-1,600 kg DM/ha) is strongly recommended for most grass species. This will result in a strong recovery from grazing and will aid in replenishing root carbohydrates.

 

Over summer and long dry periods, it is recommended to spell dryland pastures, particularly perennial ryegrass, as continual grazing of the “green pick” from summer rains etc. can severely stress plants and result in pasture death.

 

For more information about fertiliser for new pastures or grazing management, please contact our DLF Seeds Sales Agronomist or your trusted farm advisor.



References
Incitec Pivot, 2011. http://www.incitecpivotfertilisers.com.au
NSWDPI, 2006, http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0008/166562/Fertilisers-for-pastures.pdf
University of Georgia, http://extension.uga.edu/publications/detail.cfm?number=B1346
AusWest & SPS Pasture Reference Guide, 2022

 

Share this page