Tropical perennial grasses like Premier digit and bambatsi panic have been universally acclaimed these past few months for their ability to survive drought then rapidly provide summer and autumn feed once rains began.
Even during the drought, especially on lighter soils, they commonly provided useful feed from occasional even relatively low rain.
But it is important to appreciate that even a great pasture plant, whether a tropical grass, temperate perennial like phalaris or even lucerne, growing in their respective suitable environments, quality of feed relates to soil fertility. Persistence and productivity also relate closely to grazing management. If soil fertility is neglected, it leads to a gradual decline in productivity and feed quality.
Take this past autumn. We, via our near neighbour and hay contractor Sam and Megan Clifton, harvested 6.2t/ha hay off two Premier digit grass paddocks. Hay quality was excellent with protein around 12 per cent (good for a grass cut when flowering). That amount of hay, not fed back to these paddocks, remove around 120kg/ha nitrogen, 12kg/ha of sulphur and phosphorus and 25kg/ha potassium.
Paddocks grazed return most of the nutrients used to grow the pasture via dung, urine and trampling. However, depending on stocking rate and enterprise type some nutrient removal occurs. A steer fattening enterprise running around 7.0 dry sheep equivalents/ha, remove, over the year, via sale animals around 11kg/ha nitrogen, 3.0kg phosphorus, 1.0kg sulphur and 1.0kg/ha potassium. Over time that amounts to a considerable amount of nutrients.
In a perennial grass pasture if legumes are an integral part, they can supply most of the nitrogen requirements via rhizobia root bacteria. Around 25kg/ha nitrogen is fixed by legumes per 1.0t/ha legume drymatter production.
If legumes are not an integral part of a pasture, one needs to evaluate the feasibility of adding nitrogen via fertiliser. Because the last three years were drought or semi drought conditions for many properties, including our own, we have routinely applied 100kg/ha urea each spring and feel it has been highly economical. With this year developing into a possible excellent winter legume season, there is a good chance they will supply enough nitrogen for next spring, summer, autumn tropical grass growth.
Phosphorus and sulphur levels need careful watching if good quality and good quantities of pasture, regardless of species, need to be maintained or improved. Both elements are deficient across NSW, and adjoining states, in many soils. Legumes fail to thrive and build soil nitrogen if these deficiencies are not addressed. Grasses also need adequate soil phosphorus levels for efficient production. Grasses also require an adequate sulphur level for good growth and quality.
A recent Cumnock field day looked at tropical grass pastures on David and Christine Weston's property. LLS livestock officer Brett Littler and agronomist Phil Cranney sampled it as well as native grasses including Warrego and annual grasses like liverseed. Protein levels were outstanding for grasses, from 17pc to 23pc metabolizable energy (prediction of energy). These tests are a sound way to evaluate pasture quality and likely animal performance. If low soil fertility values generally fall accordingly.
Like all pasture types, including temperate perennials, feed quality of tropical grasses declines as plants mature and develop stems and heads. However, a tropical like Premier, during its growing season of eight to 10 months (depending on temperature) commonly responds with new leaves every time it rains, despite being in head. In March to May this year we had paddocks of digit in head but at plant base was a mass of new and green leaves of good grazing quality.
Grazing management has also been an important part of pasture growth following for many the breaking of the drought. Where reasonable ground cover was retained plants have tended to survive better and capture storm rains more effectively. Where perennials were given ample opportunity to build good root reserves leading into the drought their survival has generally been better and production regrowth far faster. As an observation careful choice of variety has also been critical.
Next week. Monitor crop diseases carefully.
- Bob Freebairn,agricultural consultant Coonabarabran based. Email firstname.lastname@example.org 0428 752 149.