WHILE there is a big role for newer annual legumes such as serradella and biserrula, it is important not to underestimate the value of sub clover, a species first recognised as useful around 1900. It remains for many situations a tough and productive legume. It is grown on millions of hectares with many varieties for different environments.
Despite drought conditions over three years from 2017 through to summer 2020, with almost no seed set for three consecutive springs, commonly sub clover pastures regenerated strongly this past autumn with excellent growth and seed set. A big reason for such persistence has been the development and growing of varieties with good levels of "hard" seed. Also important for long term persistence has been the release and growing of varieties that are early to flower and set seed.
A sub clover's endearing feature, and not shared by most other winter legumes, is its ability to set seed when grazed close to the soil surface, a common occurrence in years with dry late winter/springs. Many varieties flower via runners creeping across the soil and bury a good proportion of their seed. This allows seed set in tough conditions with a good level of seed survival despite tough conditions. In contrast aerial only seeding species commonly fail to set seed under these grazing conditions.
"Hard" seed means once a reasonable seed set has occurred, some survive for years should droughts occur or after a cropping phase where clover plants are killed via weed control herbicide strategies. Some "hard" seed remains "hard" for at least several years with good reestablishment if seeding has not occurred for some years.
Early maturing varieties, while not as productive as longer season varieties in good years, commonly can set at least some seed in all but the toughest of drought years (like 2019 for many areas). This year early maturing varieties for example were flowering from around mid-July onwards and in areas where the season cut out early, for example as has occurred around Boggabri, good seed set has occurred.
Extra early flowering may not be an enduring feature for colder tableland environments because of coldness at flowering, but "hard" seed and at least mid-season maturity combine well for long term persistence. In slopes and plains areas early maturity has also been more important when growing winter legumes with tropical and temperate perennial grasses. These perennials commonly add to spring moisture stress with early flowering and seed set more critical for reliable seeding.
Many other aspects are important for persistence and productivity of winter legumes, including sub clover. Correction of soil deficiencies is clearly critical with many trials conducted by various research bodies like NSW DPI, CSIRO, and universities like New England, over the past 70 years, highlighting this need.
Research has shown that while correcting soil deficiencies is important, this does not necessarily mean high fertiliser rates or fertiliser required every year. Soil phosphorus and sulphur levels for example can build via fertiliser application, often to above levels requiring fertiliser. Periodic monitoring of soil fertility via soil testing is important for repeat fertiliser decisions. Good fertiliser decisions also depend on products with sufficient levels of needed elements in an available form, or a form likely to be available in reasonable time. Strong research supports these views.
Sub clover suits a wide range of soils, generally with pH from around 4.8 (where aluminium toxicity is not excessive) to 6.5, with some varieties (Brachycalycinum sub species) growing well on higher pH soils. Other varieties (Yaninnicum sub species) suit soils prone to waterlogging.
While bloat commonly occurs on sub clover dominant pastures in lush conditions, it is generally not considered as bloaty as species like white clover and lucerne. Like most pasture species it has its share of detrimental aspects like susceptibility to some diseases like root rots and various viruses. It also does not root as deeply or as fast as species like serradella and biserrula. But for my money sub clover is worth including as a vital part in many pasture situations.
Next week: Big Narrabri investment linked to crop research outcomes.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email firstname.lastname@example.org or contact 0428 752 149.