How do each of the sub clover varieties fit in different climates and soil types

Sub clover is the basis of many pastures, particularly where winter rainfall is dominant. Their prostrate growth habit and ability to bury seeds allow sub clovers to self-regenerate each year and remain productive for many years in mixed pasture situations. Within the sub clover species, there are 3 sub-categories and a range in maturity lengths with the differences allowing each sub clover category to be suitable to a range of  climatic conditions and soil types.

The three subcategories of sub clover are Subterranean, Yanninicum and Brachycalycinum. Each subcategory is adapted to different soil types, making them suitable and more persistent in different areas.


The most common of the subcategories are Subterranean species, which are suitable for acidic to neutral soils. The Subterraneum varieties are black seeded and prefer free-draining soils. Subterraneum sub clovers have the largest range in maturity length and generally have higher levels of hard seed compared to varieties in the other subcategories.


The second subcategory of sub clover is the Yanninicum (commonly known as Yannis). These have a yellow seed and are also adapted to slightly acidic to neutral soils. Yanninicum species are adapted to heavier soils and waterlogged conditions during winter. In areas that can be seasonally waterlogged, the Yanninicum category is likely to produce more dry matter than other categories of sub clover.


Brachycalycinum species are the final subcategory of sub clover. The “brachys” are adapted to neutral to alkaline soil types and therefore are not as productive in acidic soils compared to the subterranean and yannis. Brachys are incapable of burying their burrs as well as other subcategories and therefore are more persistent in soils where they can drop burrs into soil cracks. Brachys can have black or yellow seeds.


In summary, selecting a subcatgeory that is suitable for the soil type they are sown into aids in persistence and production of the sub clover within that pasture zone.

Flowering time index at Wagga Wagga, NSW (Source: NSW Government Department of Primary Industries website)

Sub clovers are annuals and grow during autumn, winter and spring. There is a wide range of maturity between varieties, ranging from 85 days to 150 days from germination to flowering. See table below for examples of different varieties and their maturity window. 


Maturity length influences the climate zones in which each variety is most suited too. Generally, the earlier maturing that the sub clover is, the lower amount of rainfall is required to allow the plant to flower and set seeds. From the start of flowering, it takes approximately 6 weeks for sub clovers to mature a viable seed. Seed set is key to maintaining a productive sub clover pasture.

 

Grazing management plays a role in the amount of seed set, but the main driver is matching maturity of the sub clover variety with the environment it is grown in. In marginal areas (<500mm rainfall) with short springs, an early season sub clover such as Izmir or Urana is most suitable.

 

Whereas, in areas with more reliable spring rainfall (>600mm rainfall), a late maturing variety such as Coolamon or Leura are more productive options. Picking a variety that will flower and set seed before moisture runs out is essential for seedling recruitment in following years.

 

Sub clovers have varying levels of hard seed content in seed that is produced. It is a general rule that the level of hard seed decreases with increasing length of maturity. ie short-season varieties have high levels (25-65%) of hard seed, while late season varieties have low levels (5-40%). The hard coat of clovers will prevent the seed from germinating on the first rainfall event. In marginal areas where false starts can occur, having a bank of hard seeded clover is vital to maintain persistence of sub clover in the pasture. 


Sub clover is adapted to many different rainfall zones and soil types. Therefore, there is a suitable variety for most situations. Please get in contact with your local territory manager for advice about which variety is best suited to your conditions.

 

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