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 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:
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.
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.
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.
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.
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.
Advantages and disadvantages of the two sowing windows
Spring sowing (east of region)
Late summer sowing (either east or west of region)
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.
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.
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.
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 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.
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.
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.
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.
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.
Pasture Production for Livestock - North West Plains NSW Agric ( booklet)
Pasture Production for Livestock - Northern Slopes and Upper Hunter, NSW Agric (booklet)
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.
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.
Prograze Manual (1995) NSW Agric booklet
Weed control in lucerne and pasture. NSW Agric booklet
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
Pasture improvement may be associated with an increase in the incidence of certain livestock health disorders. Livestock and production losses from some disorders is possible. Management may need to be modified to minimise risk. Consult your veterinarian or adviser when planning pasture improvement.
The Native Vegetation Conservation Act (1997) restricts some pasture improvement practices where existing pasture contains native species. Inquire through your office of the Department of Land and Water Conservation for further details.