The Gordon Gnohm

Play along at home, read Future Farmer in The Braidwood Bugle every Wednesday. 

Passive Land Hydration Pt 3 Contour Trench

Keylines furrows, as discussed previously, are a great start to harvesting water for your paddock. Hydration is great for the landscape but there is limited benefit to the broader ecosystem. The evolution of PA Yeomans work is to turn the keyline furrow into a small contour trench for harvesting and holding Skywater. 

The use of a contour trench has been popularised by many humans across the globe, and none more than Peter Andrews OAM. Peter is one of a growing list of Australians focussed on improving Australian Farmscapes starting with hydration.

If you want to upset his gentle soul, try calling his contour trenches a Swale. I did, and I was schooled. He is of course correct; a contour trench is not a Swale. A contour trench is a simple structure, easily constructed by digging a shallow trench. The spoils of the trench are added to the downhill side. 

The structure will become covered in grass, freed from the seed bank already in the soil. As the contour trench is the lowest point in the paddock, the trench will stay damp, and reeds will appear. The reeds produce biomass very quickly sequestering carbon and stabilising the soil. The expanding biodiversity creates specialised habitat and new critters move in.

Standing Water

Water is the source of all life and holding it in your paddock has many benefits. Once a waterway is formed, critters will collaborate to make good use of the space. You will hear the frogs first. They will use the full trench as a tadpole nursery. The water in the trench may stay long enough for the tadpoles to become frogs and they will live happily in the reeds, grass and soft earth until more rain comes. 

If the trench empties the tadpoles will not survive. They will become easy food for birds, ants, yabbies etc. It’s a bit gruesome, but the decaying bodies will also add to the nutrient load in the contour trench. I have heard of farmers using prawns and fish in this way to great effect on their soil and ecosystem.

An abundance of benefit is served up after the rain. The watering hole provides food and safe haven, bringing more critters to your paddock party. 

The next to arrive in summer will be the dragon flies. A male dragonfly requires around 10m of water edge to call his own, for mating rights. He will defend this territory against other males like the Red Baron. The aerial display is worthy of a cuppa. The female lays her eggs in the water, on reeds, ensuring future generations for you. 

The most amazing thing about dragonflies is their appetite for mosquitoes. Not much can match a mosquito in the air like a dragonfly. Again, it’s amazing to watch, and super beneficial to the ecosystem. Dragonflies eat them during the day and at night microbats will feast.

That’s a lot going on in your paddock, with the provision of standing water, occasionally throughout the year. Birds will frequent the seasonal watering hole. Birds love to eat bugs. Bugs in the paddock are often pests if their numbers are left unchecked. Birds eating bugs also leave nutrients when they arrive and when they depart. Win, win, win.

Of course, the standing water will soak and provide useful hydration to your soil, microbes and grass roots, long after the rain event has passed. The pasture downhill will become lush as a result. Stock feeding on this grass will fare better and you will start to see an improvement in your Soil Moisture Deficit (Grassland SDI) during dry times.

Excess Water

In times of significant rainfall, excess water needs a way out. Overflow of the trench can be directed as with the Yeoman method. This spillway will find its way downhill into the next contour trench via a path on the ridge or through scrub/reeds. There is also an opinion that the trench should overflow across the top of the mound.  

Over the Top

The idea is to overflow water across the mound evenly. Dropping sediment/nutrient in the grass on the way downhill, as nature intended. Ultimately reducing erosion that can sometimes occur from endpoint overflows.

I have found that keeping the top of the mound level, takes a lot of work before grasses take over. Even the slightest dip will allow the initial overflow an easy path to erode before the rest of the mound overflows. In one significant rain event a slight dip in my mound ended up as a spillway a meter wide. It is now stabilised with a grass covering and is the permanent spillway. 

Best Use

I find this method of passive land hydration very effective for harnessing runoff to fill dams. Running contour trenches as dam wings out into the landscape. Collecting water from afar to feed the empty dam. Conversely these wings also preform the overflow function, taking excess water out into the landscape for hydration purposes.

This Week

As summer fades there are spaces opening in the garden for winter plantings. My potatoes are ready, but I’m only grabbing tonights tucker. Storing them in the ground until new planting requires the garden space. Starting with the volunteers from last year there will be potatoes for months.

All the corn is gone. The stalks have been placed on top of the garden bed where they were harvested. A simple mulch returning the nutrients directly back the soil it grew from. Cutting the stalks up into small pieces will assist them to break down faster. Running them through a shredder would be ideal if you have one.

Pumpkins have produced very well and as the stalks on top of the fruit start to brown, its time to harvest pumpkins for storing. If the stalk stays green, it will not store well. The green stalk will be the first spot to start rotting when left on the shelf.

Trees will have dropped most fruit by now, so it’s a good time to give your trees a summer prune, while the sap still flows. You can do a final hedge trim for the season, as the foliage will still have time to fill in before growth slows.

It appears the Autumn effect has arrived early this year. My Virginia Creeper has changed colour already. Some of my Trident Maples are starting to change colour. My neighbour’s Grapevine was the first sign. Its anyones guess, but trees are the best tell. 

Usually, the Poplars outside The Showground are a great indicator of the onset of Autumn. They are now changing. The Ornamental Pear near the Bedervale gate is turning as are the Hawthorns on Bombay Rd. Bye Bye Summer.

Stay Awesome.

The Gordon Gnohm

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