Tuesday, January 23, 2007

Why didn't we get runoff ?

The recent high rainfalls of between 50 and 75mm locally didn't produce much runoff-why ? Mainly because the falls were generally of quite low intensity- even statisically for this time of year . Dry soils too of course , but in summer some soils will run . High runoff periods for most slopes are rare ( occuring only about 3 times in an average year on wet loam to clays soils in areas between 700- 1000mm total per year. .
However ,you can get a lot higher runoff and erosion with summer rain because the intensities are usually higher when soils are drier , but effect is over small areas. The worst kind around here for big areas are associated with easterlies - Either way , care should be taken at this time of year both to avoid cultivating steep slopes intensively or to align tracks with more care/ crossings than often seems necesary . for some ideas click here

Saturday, January 20, 2007

The taproot -not better , but very handy !

So what a plant survive the drought. Deep roots,a tap root ,top feeders , or all three . The answer looking at bare ground oocupied by plantain is all three clearly .
( jan20th 2007) Its been very dry . . Most Trees control the water balance of an area the radius length of their height .they mostly rely on surface roots. Plants like the plantain control much more than their height and keep growing inspite of dry surface soils because of the enormously tough and deep tap root (shown - goes down 800mm here ) linked with leaf area control when surface moisture is high - never one nor the other with switching taps and survival .Plants are better designed than we think! Let's face it, they cope better than we think they should with what appears to be impossible odds ! why don't their leaves just shrivel up in the sun like everything else does?

How do plants cope with these very dry and hot conditions ?

The last 6mths, surface soil water balances are impossible for shallow plant roots to get moisture Except those like the ones shown here that extarct just a little from the clays below ( in otways region clay subsoils predominate so there is enough moisture there to keep plants ticking away ). These skeleton weed and plantain plants in the park at Colac have obvoiusly the best of all worlds
( like anything that still has leaves on at this time of year .)
--leaf stomata that close water traffic on wilting.
--leaf and stem structure that avoids the leaves cooking under the sun
--ability to direct condensation into/onto plant in mornings
--very deep tap root ( both plants shown ) they even beat kikuyu which is the plant to kill right now if you haven't done it earlier .Gotta be some good come outta the drought . More ideas here