How to boost spring pasture growth

COLD HARD FACT: Frost affects spring growth in pastures. PHOTO/MARK MITCHELL

Spring pasture is often the most valuable feed you will produce all year as it is typically a pinch point on the calendar for many farms.

Typically, whether providing extra feed for lambing ewes or finishing cattle, increasing the amount of quality pasture early in the season fetches good returns.

Ewes fed well during lactation will produce more milk, meaning more lambs can be drafted on the truck at weaning, when returns are highest and the total amount of dry matter consumed is least.

A good rule of thumb is to time spring nitrogen applications three weeks before lambing or calving, as this should when spring pasture growth typically kicks in.

High country or cold inland valleys, where lambing/calving occurs before this growth, would do better with an autumn application when soil temperatures are still conducive to growth.

Cattle will also benefit from more feed during this period allowing more weight to be added before the schedule starts to drop or pasture quality declines in early summer.

Soil temperature

Farmers often lament the slowness of spring growth but long-term climate records show that this is often very consistent year-on-year.

While there is nothing we can do to change this, it is good to know when soil temperatures start to lift where you live.

Generally, soil temperatures peak in late summer and are often lowest about the time lambing and calving are starting.

Frost has a big effect on soil temperature.

Farmers often say they need rain in the spring to get things moving when, in reality, it is the lack of frost, rather than the moisture that is needed.

Also, irrigated areas with wet soil are slower to heat than dry soil.

The temptation to irrigate should be resisted as long as possible to allow soil to warm up.

Nitrogen

The nitrate and ammonium which is plant available is the next biggest driver of spring growth.

Most N found in soil is 'organic N' stored in the organic compounds generated by animal returns and breaking-down plant material.

It is this N that requires 'bugs' in the soil to convert it to the mineral form mentioned above.

These bugs require warm temperatures to perform this at the required rate for rapid pasture growth.

Applying fertiliser N as urea or ammonium-sulphate (Ammo), when soil temperatures are increasing in the spring, will dramatically lift pasture growth rates.

I recommend applying a minimum of 30kgN/ha (65kg Urea/ha) to the warmer parts of your property when soil temperatures are 5C and rising.

Sulphur

Sulphate-sulphur is the last of the trifecta to ensure maximum spring growth.

The major pool of soil sulphur (S) is also stored in organic matter and can be available in limited quantities in spring.

Measure this through soil tests that show the sulphate-sulphur level.

Levels will be good if an S fertiliser has been applied in autumn, or the winter has been dry with limited drainage.