Digit grass (Digitaria eriantha spp. eriantha) is a tufted perennial summer-growing grass. Easy to establish, it is adapted to low fertility sandstone, granite and traprock soils of South East Queensland as well as the more fertile, lighter clay and scrub soils on the Darling Downs, the Western Downs and Maranoa. It is unsuited to heavy-cracking alkaline clay soils. Digit grass needs a minimum annual rainfall of 600 mm.
Other attributes of digit grass are its good tolerance of cold and drought. Although the leaves become frosted in winter they remain palatable and green shoots can often be found close to the ground. In lightly frosted areas it will shoot quickly after early spring rain. Digit grass foliage is low in oxalate.
Premier is a variety of digit grass commercially available.
When to sow
Digit grass may be planted from October to late February. If planting in early spring be aware that even though evaporation is lower, weed competition at this time can be detrimental to young pasture seedlings. Mid-summer planting (January to February), when there is a higher probability of receiving consecutive rain days, has the best chance of success. It is also the most likely period to receive good follow-up rain after planting.
Winter legumes can be oversown when the established grass growth has slowed between May and June.
Best results are obtained from a prepared seedbed that has been fallowed for moisture, nitrogen accumulation and weed control. The surface 50 mm should be fine and firm. The chances of successfully establishing a pasture improve if the sub-soil moisture is good at sowing. Depending on soil depth aim for a minimum of 40 cm of wet soil under the seedbed. Rougher seedbeds with less soil disturbance need a higher seeding rate and give less reliable results.
On sandy surfaced soils, good pastures have resulted from broadcasting seed into standing stubble (e.g. oats) followed by grazing. The animals trample the seed into the soil surface.
Sow 1-2 kg/ha of good quality seed.
Legumes for digit grass pasture
On all soils, sow the grass with an adapted legume to add nitrogen to the system e.g. serradella (5 kg/ha podded seed) on sands, sub clover (4 kg/ha) on traprock soils and lucerne (1-2 kg/ha) and/or burr or barrel medics (2-3 kg/ha) on clay soils.
Sowing method and sowing depth
Seed may be broadcast onto the dry seedbed surface or drilled into a dry seedbed with precision planters. The small seed should be within the first 5-10 mm of the soil surface.
Seed and soil contact may be improved on non-crusting soils by rollers or presswheels that will firm the soil around the seed. Be careful if harrowing after sowing that the small pasture seed is not being buried by more than 10 mm of soil or the shoot might not have the energy to emerge.
Digit grass seed is slightly hairy and getting the seed to flow at a steady rate through some planting equipment can be a problem. Mixing seed with superphosphate, or sawdust, will allow it to be planted through the fertiliser box of a combine, or a fertiliser spreader. New seed boxes with better seed handling mechanisms, or pelleting, are methods of improving seed flow.
Sowing dry ensures that pasture seed is in the right position to take advantage of the next rainfall to start germination. The seed must remain in close contact with wet soil for about three days to establish a seedling. Sub-soil moisture will sustain the seedling until follow-up rainfall occurs. This rain will also promote the development of secondary roots. This allows the crown of the establishing grass to develop.
Pasture seed in the bottom of shallow tine furrows or small depressions in more roughly prepared seedbeds are more likely to establish seedlings because they accumulate water and stay wetter for longer after rain.
In situations where establishment is poor, a thin population of digit grass, allowed to seed and given the right weather conditions, will thicken up rapidly.
A soil analysis may indicate major nutrient deficiencies.
A good fallow before planting should release enough nitrogen to allow the grass to establish. Phosphorus superphosphate to the seed bed if soil analysis or past history indicates a phosphorus deficiency. Alternatively on low fertility soils a mixed fertiliser containing nitrogen and phosphorus (e.g. Phosul or MAP-S) could be used at 50-100 kg/ha. Both fertilisers would supply sulfur.
A vigorous legume component will be the best source of nitrogen for the grass in an established dryland pasture as it is usually uneconomic to apply nitrogen fertiliser. Renovation of mature pasture that is showing signs of decline will release nitrogen to rejuvenate the stand for a short time.
Legumes require sulfur and phosphorus for good production. Topdress with 125 kg/ha superphosphate per year if phosphorus is low, applied in early spring to autumn. If only sulfur is deficient, apply gypsum (0.5 t/ha) or elemental sulfur (60 kg/ha) every two to three years.
Weeds can retard the growth of young digit grass seedlings and affect their establishment. Good cultural practices in the season before sowing (pre-cropping or fallow), will help reduce the weed seed population in the prepared pasture seedbed. Slashing or light grazing may reduce weed competition.
After establishment most broadleaved weeds should be suppressed by a dense vigorous pasture growth. Although it is generally impractical to use herbicides for broadleaved weed control, a number are registered for this purpose. Care should be taken in their selection to avoid killing useful pasture legumes. For further information on herbicide selection consult your company agronomist.
Pests and diseases
Although not serious problems, seed heads may be infected by false smut (Ephelis sp.) particularly during prolonged wet periods, and in coastal areas the foliage can be affected by rust (Puccinia oahuensis).
The successful establishment of a pasture will depend on grazing management in the first year. Do not graze until follow-up rainfall allows seedlings to develop a strong root system and set some seed, then graze lightly. Allow the pasture to set seed every second year if possible. Short periods of grazing are preferable to continuous stocking.
Digit grass can be direct headed. Timing of harvest is critical as seed drop occurs very quickly when the crop is ripe. The colour of the seedhead changes from green to grey, and the seed becomes easy to rub from the seedhead. Header yields of up to 300 kg/ha have been achieved from a fertilised, irrigated stand during a summer season.