Well-managed grazing critical for legume set

Well-managed grazing critical for legume set


On Farm
It's a different spring this year, with many areas experiencing extreme dryness. Like many new winter legume species, gland (pictured above, last year) is an aerial seeder and, when building the soil seed bank, demands care.

It's a different spring this year, with many areas experiencing extreme dryness. Like many new winter legume species, gland (pictured above, last year) is an aerial seeder and, when building the soil seed bank, demands care.

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Late winter and spring is when various grazing management techniques can significantly bolster seed reserves

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PROVIDED one is not in full drought (and several areas are), late winter spring grazing management is a vital aspect for either improving or maintaining good annual pasture legume content.

This especially applies to legume species that are aerial seeders.

Species such as serradella, biserrula, gland, woolly pod vetch, rose, arrowleaf and gland clover, as well as barrel medic slot directly into this category. 

When grazing pressure exceeds growth rates of these plants during flowering and seed development stages, invariably all or most flowers and developing seed pods are eaten.

As spring warms and as soils dry out there is commonly little opportunity for them to develop new flowers and seed pods. 

In contrast species like sub clover, especially the common subterraneum sub species group (eg Dalkeith variety) as well as the yaninnicum sub species group (eg Riverina variety) flower low to the ground and bury a lot of their developing seed.

Dry springs with relatively hard grazing can still result in seed set that commonly replaces or even exceeds prior soil seed reserves.

Monitoring soil seed levels of annual legumes is important to assess appropriate grazing management for a given paddock.

For example, if high seed set occurred last year in a given paddock or number of paddocks, as a consequence of a good season and grazing that allowed for good seed set, soil seed reserves are likely to be excellent.

Provided the main legume varieties are “hard” seeded types it is not critical that they be managed carefully this late winter spring.

In contrast a paddock that may be a new sowing this season after a cropping phase where soil seed reserves were likely to be very low, allowing for good seed set is paramount.

Also paddocks in their early years of legume upgrading, be they native grass, tropical grass or temperate perennial based, also require extra grazing care to ensure a continual build-up of soil seed levels.

One legume plant can extend over one metre diameter if lightly or not grazed, given reasonable soil moisture, and set hundreds if not thousands of seeds.

Even a light establishment can quickly develop into a good density stand given care with grazing, plus at least a reasonable season. 

“Hard” seed levels of a legume variety is a critical aspect for long-term persistence where it is inevitable droughts will occur and seed set will be negligible or non-existent in some years.

“Hard” seed means a proportion of the seed (from non-existent to as much as 90 per cent, depending on species and individual variety) will last in the ground for commonly several years, with germinal seed becoming available each year and depending on species often for several years where seed soil levels were good.

Where possible no grazing in the late winter/spring for new establishments is ideal and will encourage maximum seed set in the first year, especially if the season is on the dry side.

Once seed set has occurred and matured, grazing is then possible.

Stock actually help spread hard seed varieties via trampling and what passes through them.

Health of the pasture as well as rainfall is critical for level of seed set.

Occasionally seed set in the establishment year will fail because of drought and that will have occurred in some areas this year.

Retrying next year will be important if that happens to be the case on your place.

If soil deficiencies are not addressed and, or if, inappropriate species or varieties are chosen, then no matter how good your grazing management is, success will be poor. 

Next week. Cotton’s great success with proactive breeding

  • Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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