Thursday, August 30, 2012

Successfully Establishing Turfgrass is Best Done by Mowing Higher

Cut high to help turfgrass establish seems to be the rule.

The most resilient turf has deep roots that can reach the deep water in the soil profile. New turf must be watered regularly until the deep roots develop, but regular watering discourages the turf from rooting deeply, because the turf gets all the water it needs at the surface. All the while, you’re wasting water.
So what can you, as the turf manager or home grower, do to speed up the deep rooting and so minimise the irrigation?
Researchers at the Texas A&M University, North Carolina State University and the University of Florida asked this question. To answer it, they grew plugs of turf (couch, zoysia grass, bahia grass and buffalo grass) in tall clear tubes, and tested combinations of nitrogen (N) fertiliser and mowing height. Two rates of N approximated the lower and higher ends of the normal recommended range. Two cutting heights (which depended on species) represented heavy and light mowing.
Two conclusions were evident:
  • The higher N rate encouraged faster rooting.
  • The higher cutting height encouraged better rooting.
Cutting height had no effect on the rate of root growth, although it had a big effect on root mass: the low cut greatly reduced root mass.
Bahia grass achieved the best root growth (depth and mass) in the high N, high cut combination. But Zoysia grass did best in the low N, high cut combination. The results depended as much on the species as on the treatments.
Overall, maintaining a high cutting height did far more to encourage rooting than applying high N fertiliser. The authors recommended that turf managers cut establishing turf to the highest height recommended for the species.
This is especially relevant for zoysia grass, where we are already recommending half of the nitrogen rates that appear on most fertiliser bags.  Zoysia does not respond to high nitrogen particularly well, as it is naturally a slower growing grass.  We would suggest a cut height of around 45 -50mm initially, reducing to the more conventional cut height of around 20 - 25mm.

For Bahia grass, a high cut is 65 -75mm, and low cut 35mm, with commercial operators using 45mm.  For Bahia, one might need to also temper cut height and frequency with a need to remove seed heads, which direct fertilisers into reproduction, which is not needed during estabishment.

This also fits well with convention that says that a higher cut height during stress periods is beneficial - for this you could interpret stress as high temperatures and low water availability eg September - mid December in north Australia.

[partially sourced from SESL Newsletter September 2012]  

Further reading
Wherley BG et al. 2011. Nitrogen and cutting height influence root development during warm-season turfgrass sod establishment. Agronomy Journal 103: 1629–1634.

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