Successful establishment of tropical perennial grasses in North West NSW

Introduction

Thousands of hectares of tropical grasses have been successfully established   in the North West, however the risk of failure is substantial as indicated by   the results of a series of grass trials involving 51 sites in the northern   cropping belt between 1986 and 1989. A failure rate of 50 % occurred. Besides   low rainfall, the main factors contributing to failure were: weed competition,   low seed quality, and less than ideal seedbed tilth. The failure rate was   reduced to acceptable levels in subsequent trials by attention to these factors.

Tropical species, unlike temperate species are sown when evaporation rates   are high, and when probability of rain is often low (see Figure1). The chances   of adequate moisture being available in the top centimetre or two is much less   than when sowing temperate species in the autumn/winter period.

Additionally, many of these species have low seedling vigour relative to sub   clover, medic or lucerne, and are therefore less forgiving of drying seedbeds,   weed competition and deep sowing.

Despite these differences, the principles of establishment are similar,   however the emphasis on some factors is greater to account for the drier, more   hostile seed bed conditions.

The key to success?

The key to success is to plan pasture programs well. This is essential if you   want to consistently establish good pastures. Successful producers, plan their   overall pasture program 1–2 years ahead.

The most important factors are:

1. Adequate subsoil moisture

Always aim to sow on good subsoil moisture. Ideally, sow shallow into   moisture and firm moist soil around the seed. In the North West, the reality is   that we can often sow on good subsoil moisture, but the seedbed is dry. Rain   following sowing is critical. Ideally, favourable conditions are needed in the   3–4 weeks following emergence to ensure secondary root development. Rolling,   sowing on time and reducing weed competition can make better use of available   moisture. Use a moisture probe to monitor subsoil moisture in the fallow.

2. Effective weed control

Weed competition is a major cause of failure. Most troublesome weeds can be   controlled in the year or two before sowing.

Get to know the paddocks intended for sowing and the weeds that are likely to   establish following sowing. Remember that potential weeds of summer growing   pastures may not be significant weeds in winter crops, and that herbicides for   use in pastures are few. Annual grasses and broadleaf weeds such as rape,   turnip, caltrop, mintweed threaten establishment.

Broadleaved weed herbicides have a role but it is most cost effective to   control weeds in the fallow and in crops before sowing. Prevent annual weeds   seeding the previous summer. Do not sow in spring unless one good germination of   annual weeds is controlled.

3. Good seed quality/treatment

The quality of tropical grass seed can be extremely variable and often   disappointing. Seed dormancy is common. Insist on a recent seed test for purity,   viability, germination and weed contamination (germination percentages in the   order of 40% for tropical grasses are acceptable while 70% is considered very   good). The risk of bringing parthenium weed and other noxious weeds onto your   property in low quality seed can result in enormous ongoing expense.

Inoculate all companion legumes unless you have good evidence that the   correct strain of rhizobia is abundant in the soil. Seed treatment to prevent   seed theft by ants is essential for all surface sown seed. Responses are   unlikely where seed is well covered by soil on farming country.

Nutrient seed coating has not shown any advantage except improved physical   handling of fluffy seeds. Fungicides are unlikely to give a response except for   sowing legumes in cold wet conditions.

4. Shallow sowing depth

These grasses are all sensitive to deep sowing. What is deep? Aim to sow less   than 1.5 cm deep, especially with rhodes grass. Sowing deeper usually results in   poor establishment. Sowing on the surface with a very light coverage with   harrows is adequate.

The better the seedling vigour of the species, the more they will emerge from   deeper sowing (e.g. purple pigeon grass will establish more readily from depth   than Bambatsi panic). Similarly, seedlings emerge better from depth in sandy or   self mulching soils, than in hard setting soils. However, still sow 1.5 cm deep.   Figure 2 shows the effect of deep sowing on emergence of grass seedlings. An   exception is shown in Figure 3 where this trial was on self mulching soil, the   deep mulch offering little resistance on this occasion.

5. Best sowing time

It has been said that 'the best time to sow tropical grasses is just before 2   inches of rain'. This may well be true but difficult to achieve.

Sowing temperature requirements for most summer grasses are similar to   sorghum, minimum temperatures being 130C for buffel, 140C   for rhodes grass, 170C for Bambatsi panic, 250C for purple   pigeon grass, so that germination is unlikely before early October for most of   the region (except for Consol lovegrass).

Based on trials and rainfall probability (Figure 1), the risk of failure can   be reduced by sowing in the late summer/early autumn in the west (e.g. Walgett)   and in either spring or late summer/early autumn in the east of the region (e.g.   Narrabri).

Note that because of the huge variability of rainfall, successful   establishment is possible at any time when temperatures are sufficiently high.   Avoid sowing in mid summer on the plains or hotter parts of the slopes, while in   cooler parts of the slopes (e.g. Coonabarabran, Bingara), with a shorter period   for plants to develop before frost, sowing in mid summer has been reasonably   successful.

With late season sowing, falling temperatures mean that sowing should take   place before the end of February for most of the region, slightly later in the   west and earlier in the cooler areas on the slopes (e,g, Coonabarabran,   Bingara). Producers in the Dubbo/Gilgandra area have successfully sown Pioneer   rhodes grass as late as early March. This timing allows sowing of annual legumes   and Consol lovegrass as well.

Where temperate legumes can't be included at sowing, they need to be added   with the last crop before sowing, or drilled in after the grass has established,   or in the case of sub clover or serradella, surface sown in the autumn after   establishment.

6. Adequate soil fertility

Nutrition is particularly important, especially on previously cropped   country. Soil testing will ascertain if a response is likely to phosphorus (P)   or sulfur (S). S is of particular interest as the continued use of high analysis   (low S) fertilisers, can deplete soil S. When considering the fertiliser option,   allow for the needs of the companion legume.

The use of nitrogenous fertilisers at sowing needs to be assessed in terms of   the economics at the time. While a response on cropping country is very likely,   it may not be economic, especially considering the risk of establishment   failure. On higher rainfall country, a small quantity of N (e.g. 10–15 kg N/ha)   at sowing is adequate to assist establishment, assuming sowing moisture is good   and weeds are under control. Again this may not be economic.

7. Good grazing management

In the establishment year, do not graze until plants have seeded down. The   exceptions are where weed competition is severe, in which case ensure that   grasses are well anchored before grazing. The second exception is where plants   are well advanced for the season with good soil moisture. Light grazing may then   assist tillering.

Management of established pastures is difficult with large paddocks, yet for   high livestock growth rates, these grasses should be kept leafy and legumes must   be kept in the pasture for as long as practical. This ensures grasses remain   vigorous and improves the likelihood of nitrogen being available for following   crops.

Some producers have found that by grazing pastures hard late in summer/early   autumn, to open up the sward, that annual medics establish better. By grazing a   number of paddocks in rotation, say one year in three, medic may become   sufficiently dense to maintain or increase soil nitrogen and promote grass   growth.

Perennial grasses in general benefit from being allowed to seed periodically.   This spelling allows root reserves to be replenished and provides seed for   regeneration.

The ProGraze program available through NSW Agriculture can provide the latest   information on grazing management. It is currently available to producers on the   slopes and some areas of the near plains.

Sowing methods

Commercially, reliability of establishment is higher with conventional   sowing, followed by direct drill and finally aerial sowing into crop or stubble.   The last 2 methods are less forgiving of poor management and climatic   variability, however, results can be highly variable with all methods.

Conventional establishment on cropping country

Seed is often sown the year following cereal harvest. The disadvantage of   sowing into conventionally worked seedbeds is the additional erosion risk with   bare soil being exposed for a long period. The advantages are that of ease and   efficiency of operations such as weed control and sowing.

Except for fluffy seeds (e.g. buffel) traditional sowing machinery such as a   combine with a small seed box with covering harrows has been satisfactory—adding   a bandseeder provides more reliable seed placement. Specialised seeders are   available for sowing fluffy seed. Precision planters have been successful.

Sowing rates for these species will vary from 0.3 to 2.0 kg/ha. Seed size,   seed quality and whether there is more than one variety in the mix will   determine optimum rates. Don't skimp on seed, it is false economy. Conventional   combine row spacings are adequate assuming low seeding rates. Widening rows may   benefit the companion legume and possibly the grass in drier areas but can allow   weed invasion and increase the risk of erosion.

Note that furrow sowing (where seed is directed from the small seeds box down   behind the last row of cultivating tynes with harrows removed) may prove   unsuccessful on self mulching soils. This is because heavy rainfall before   plants are established, can cause seed to be covered by too much soil washing   into the furrow (Figure 4).

The presence of a moderate amount of mulched cereal stubble is unlikely to   cause any problems unless it results in lower seedbed temperatures or excess   seedbed moisture.

Aerial sowing seed onto a worked seedbed followed by harrowing has been   effective in the Coonamble district, replacing the need for sowing equipment and   ensuring timely sowing.

Sowing under a cover crop cannot be recommended. Some success has been   achieved with Consol lovegrass sown early under oats.

Direct Drill

Direct drilling into cropping country has the advantage of dramatically   reducing the erosion potential. Results tend to be less reliable and more   variable compared to conventional sowing. In the case of undisturbed country,   the need to introduce tropical grasses must be balanced against the cost and   potential to improve the existing native pastures by strategic grazing   management. It is most applicable where native perennial grasses have been lost   through cropping or overgrazing.

A range of direct drill machines are available that are effective, some   better than others and some more cost effective than others. Potential exists to   modify existing equipment to achieve acceptable seed placement, as has been done   in other areas of the State, (e.g. small seed boxes on scarifiers etc). Machines   ideally need to be able to prepare a seedbed, place the seed 1.5 cm deep,   fertiliser to similar depth or deeper, cover it, and be able to firm the soil   around the seed (press wheels). On tight soils, a tyne that creates tilth below   the seed will hasten establishment, as it allows more rapid root development.   Additionally, where sowing into crop stubble, the machine must be able to   penetrate and clear stubble effectively.

On heavy clay soils, failures have occurred where low soil moisture and or   drying conditions have been associated with cracking of the soil below the tyne   mark, rapidly drying the root zone.

Machinery developments:

The Department of Land and Water Conservation has developed a very robust   machine ('soil flow seeder') which is currently being   demonstrated in the North West. It is an all purpose machine, suited to sowing   into stubble as well as direct drilling.

CSIRO has developed another very robust machine called a band   seeder (not to be confused with the traditional band seeders). The   machine can spray herbicide, sow seed, cover and press soil around the seed with   trailing press wheels. It has the disadvantage of a wide tyne spacing (1.5 m) as   it was designed to sow trailing legumes.

The crocodile seeder works on the pitting principle. It   scoops out soil and drops the seed into a small pit, the seed is then covered by   varying quantities of soil. Soil cover depends on soil type and speed of   operation. The scooping action kills plant growth in the pit (reducing the need   for herbicide) and water can accumulate in the pit enhancing establishment. It   has the disadvantage of less control over tilth and soil cover, and no ability   to firm soil around seed.

Aerial sowing into crop/stubble

While the advantages of speed, reduced cost, and low erosion risk are   attractive, aerial sowing into undisturbed pasture country is not recommended,   and aerial sowing into standing crop or crop stubble is a technique with an   increased chance of failure compared to conventional or direct drill   establishment.

Commercial experience with aerial sowing into crop or stubble is very   limited, although good results have been achieved north of Goondiwindi, sowing   rhodes grass into cereals on extensive areas of lighter textured soils.

Success is of course dependant on good follow up rain. There is little   likelihood of good subsoil moisture immediately following a crop.

Research at Walgett (NSW Agric) into aerial sowing into stubble on self   mulching soils showed that this is possible provided follow up rainfall   is good and sound guidelines are followed. The chance of receiving good   rain (75 mm over two months) for good establishment is one year in seven.

Commercially, aerial sowing of perennial grasses onto worked seedbeds has   been successful in the Coonamble district. This technique has been used to   establish ground cover to reduce weed invasion. Paddocks are normally worked,   aerially sown and then harrowed. Refer to the principles for conventional sowing   for this technique.

Overcoming seed handling difficulties

Sowing some seed types is difficult due to factors such as inappropriate   machinery and fluffy seed.

QLD DPI agronomists have developed guidelines based on commercial experience   where specialised machinery is unavailable. They are summarised as follows:

To overcome bridging in the seed box (especially buffel, rhodes, creeping   blue grasses)

1. Pellet seed (but increase seed rate to allow for pellet material) OR

2. Mix seed with a carrier such as cracked grain, fertiliser, sawdust, bran   etc.

• If using a combine grain box, try 1 part seed to 3 parts carrier and adjust   rates to suit machine.
• If using a combine fertiliser box, try 1 part seed to 15 parts of   superphosphate with rate set for the fertiliser only.
• If using a spreader (or aerial) check overlap is adequate for even seed   distribution.
• If using sawdust as a carrier (cypress pine preferred) mix at 1:1 to 1:4   seed to sawdust.
• Sow rhodes grass with a carrier through the coarse side or through the   fertiliser box.
• Sow panics, pigeon grass through the fine side of the grain box when mixed   with a carrier or through a small seeds box if available.

Acknowledgements

Research results from W Bellotti, M Campbell, B Haigh and R Freebairn of NSW   Agriculture, F Lambert and A Leys of the University of New England, L Watt of   the Soil Conservation Service, B Radford Qld DPI. Information from P Thompson,   formerly Qld,DPI, I Kelly of Castlereagh Macquarie County Council, R Anderson,   Moree and G O'Brien, Gulargambone.

Related information for establishment of tropical grasses in NW NSW

General:

Pasture Production for Livestock - North West Plains NSW Agric (   booklet)
Pasture Production for Livestock - Northern Slopes and Upper   Hunter, NSW Agric (booklet)

Establishment:

Band Seeders for Pasture Establishment. NSW Agric Agfact   P2.E.1
Inoculating and Pelleting Pasture Legume Seeds (2000) NSW   Agric Agfact P2.2.7
Prime Pastures Guide (   1996 ) NSW Agric Booklet.

Species:

Purple Pigeon Grass, (1986) NSW Agric Agfact P2.5.21
Curly   Mitchell Grass (1992) NSW Agric Agfact P2.5.37
Panic Grasses for   Pastures (1992) NSW Agric Agfact P2.5.35
Consol Lovegrass (1991) NSW Agric Agfact P2.5.33
Rhodes   Grass (1990) NSW Agric Agfact P2.5.31
Medic Pastures (1986) NSW   Agric Agfact P2.5.11
Lucerne for Pasture and Fodder NSW Agric Agfact   P2.2.25
The Buffel Book - a guide to buffel grass pasture development in   Queensland. (1991) by J Cavaye. Department of Primary Industries No. Q   190001
Pasture planner on NSW Agriculture's web site contains short agnotes on all species covered in this agnote.

Management:

Prograze Manual (1995) NSW Agric booklet
Weed control in lucerne and   pasture. NSW Agric booklet

Producer experience:

A number of producers have documented their experiences in pasture sowing in   the North West.
Anderson, Robert (1992) Proc 7th Annual Conference   Grassland Soc of NSW, 40–42
Cull, John (1992) Proc 7th Annual   Conference Grassland Soc. of NSW, 27–29
Simpson, Reg (1992) Proc 7th   Annual Conference Grassland Soc of NSW, 30–32.
Copeland, Jock (1995) Proc 10th Annual Conference Grassland Soc of NSW, 62–65
Price, Hugh   (1995) Proc 10th Annual Conference Grassland Soc of NSW,   66–72
Stephens, Maraun (1995) Proc 10th Annual Conference Grassland Soc   of NSW, 59–61
Wettenhall, John (1991) Proc 6th Annual Conference   Grassland Soc of NSW, 20–23