Irrigation/Fertigation on terraces with digestate

Heyo!

I did a search and couldn't find anything related, nor do I actually know which forum this best fits in...

But -

We've recently bought an acre of land in rural Taranaki, New Zealand.  It had a pretty steep hill, mostly north facing.  We've done our earthworks, cut a building pad and 4 additional terraces plus a couple of ponds - one with a trickle of a spring at the bottom which is gaining steam now that our autumn rains have started.

There was a pre-existing house bus on the property which is where we're currently living and will continue to for at least the next few years.  

Two of my next projects coincide and that's what I'm here for.

I've got a plant/tree order that I'm about to place any day now, AND it's time to get our anaerobic digester set up.  I'm planning on irrigating/fertilizing with the overflow and digestate from our anaerobic digester which will be continuously fed from our black water tank as well as kitchen scraps and trimmings, clippings, and more persistent weeds (convovulous and blackberry are awful things around here).

What I'm hoping to do is run some 19mm (3/4") alkathene pipe that I'll punch holes into and just let that irrigation take care of itself.  My questions are, though, will it be sufficient to run that drip line on top of the ground and mulch over top of it or am I seriously better off burying it into a shallow gravel pit?  

Also, my husband and I are of differing opinions about how much pipe we actually need to run - I reckon it needs to snake all the way along the terraces either in a single continuous system (though I have no idea will it all drip out in the top, will it rush to the bottom, or will it distribute evenly) or in zones which, say, get fed independently one day a week (though I don't love the implied human intervention for this). He reckons if we just run it along the edge of the top pad, the water and nutrients will slowly distribute throughout the soil and eventually just saturate the landscape.  Thoughts?

Definitely would love to hear your ideas/experiences/thoughts/feedback.

Thanks team!

I let my digestate run into a sump from which I pump out to whatever plant is being spoilt. A french drain leads out of the sump and into a trench along which some roses and hibiscus have been growing happily for years. So both systems work.

I think the advantage of building in some space for human intervention is you never know which plant needs spoiling. New fruit trees, for instance, really benefit from this precious resource. So don't lock yourself out of options.

How the water behaves will depend on the type of pipe you use and the volume of water. It sounds like you are planning to have a fairly passive trickle running into a pipe with holes drilled in it? In that scenario I would expect that most of the liquid would seep through the first holes. If it was pumped out in a greater volume then the liquid would flow out through the holes at lower elevation faster than those at higher elevations. I would think that having zones would give you more control, especially if you use a pump to move the liquid

Thanks team!  Gives me some good stuff to think about.  We ended up emptying our black water tank and have decided to put this off until Spring so we're not fighting against nature to get it established and insulated in time.

You want to get pressure compensated drip emmiters /drip pipe.
This is the easiest way to evenly distribute the water, but most need at least 0.5bar (5 metres in height difference) to work.

Furthermore you loose pressure trough the supply pipe, the bigger the pipe in diameter, the less pressure you loose. There are online calculators for this.