Exceptional growth after summer dry

Soil matters
with Peter Burton
Functional Fertiliser Ltd

In nature, there’s always a trade. When summer pasture growth has been limited by lack of moisture, after rain arrives compensatory growth can be expected.

During early-autumn soil temperatures remain high, sunshine hours are adequate and there’s an abundance of nutrient available for plant uptake once litter, dung, and old root has been digested.

Two lots of rain are required to spark strong autumn growth. The first starts the process of bacterial and fungal growth in the soil. 

Dryness and heat significantly reduce beneficial soil populations during summer and for rapid recovery it’s essential that populations rebuild as everything entering a plant is subject to natural biological processes.

The build-up of microbial populations along with the degradation of organic matter provides the unmistakeable earthy smell that permeates land immediately after a dry summer.  

However, it is the second rain – which often arrives ten to 14 days after the first rain – that sparks rapid plant growth. Growth rates during the following 30 days may be every bit as strong as growth in October.

Why growth slows

The reason growth slows with the approach of winter is fewer and less direct sunshine hours along with a corresponding drop in soil temperatures. Keeping a log of daily soil temperatures allows accurate growth predictions through until the slow growth period arrives with soil temperatures reaching 10 degrees Celsius.

Should enough rain not arrive until conditions are too cool for compensatory growth it will be deferred to spring, however it will arrive.

In cooler areas of the country Easter is often regarded as the cut-off date for strong growth.  If it hasn’t arrived by then it’s not until soil temperatures reach 10 degrees Celsius again in late-winter that fears of it never arriving start to dissipate.

And application of nitrogen will have little if any positive effect on total autumn and winter growth. The long-term trial work by research institutes all comes to much the same conclusion – that the application of nitrogen to permanent pastures is seldom worthwhile.

This is due to the well-documented lag-effect that follows a nitrogen application. Applying more N to overcome the lag effect simply defers the time when natural systems recover from unnatural stimulus.

That nature always has the last say is something all of us should be mindful of, if we wish to generate our income from land long-term.

There’s an old saying about burning the candle at both ends. Eventually there’s some unpleasant consequences, and continually stimulating pasture growth and depriving it of its rest and recovery periods results in a number of outcomes.


Spring growth declines and there are any number of long-term silage contractors that will attest to that, along with recorded growth figures from throughout the country.

Summer growth becomes highly dependent on regular rainfall and even when abundant there’s not the bulk of pasture required, and greater inputs of supplementary feed are required. Pest and weed pressure steadily increase and the number of seasons before total pasture renewal is required lessen.

Functional Fertiliser clients have pastures that haven’t been resown in more than 20 years, although they may have been renovated by undersowing at some stage. These pastures regularly grow more than 18 tonne DM/ha and contain a wide range of pasture species.

Applied nutrient mixes contain the required phosphorus, potassium and sulphur based on standard removal calculations.

Typically, 200kg/ha of calcium is applied annually with a mix of soft carbons containing a wide range of selected beneficial fungi and bacteria. The activity of these ensure carbon is sequestered and nitrate N losses to groundwater are reduced by up to 70 per cent compared to high N input properties.

Autumn, with an abundance of natural nitrogen, is the ideal time to reduce reliance on applied N and shift to a more productive, lower-cost, environmentally sustainable system.        

For more information, call Peter on 0800 843 809


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