There’s two parts to OHS/APS — “Open Field Hydroponics Systems” (OHS), which is the fertilizer and water management, and ”Advanced Production Systems” (APS), which is the high density planting.  The goal of OHS is to use a drip irrigation system to apply a nutrient solution to clusters of roots under the emitters all day long to create a stress-free environment — unless you want to stress the trees for some reason, in which case the dense roots will dry out the soil under the emitters in less than a day even if there’s good soil moisture around them.

Roots just under the soil surface below drip emitter - click to enlarge

One thing is really backwards from everything we’ve tried to do for years.  You want the roots to be as close to the surface of the soil as possible — no more trying to get them to grow down deep.

The pictures show how shallow the roots are in the soil — we just brushed some soil away under an emitter in the one picture, and then dug out a fistful right where the picture was taken to show how dense the roots become under the emitters. 

Root density management is the single thing that makes OHS different from any other irrigation management system.  Instead of relying on the soil to store and release nutrients and water on demand, OHS serves them directly to these masses of roots under each emitter.  It is a very dynamic system that changes rapidly, which is why we dare plant trees so close — we have control over their growth, fruit production, and fruit quality because of the root clusters that you don’t have when the soil texture and chemistry is dominant, as is the case with microsprinklers and conventional drip.

Density of roots under drip emitter i click to enlarge

This is much higher density than we see under conventional drip systems in Florida.  You can only achieve this kind of root density with high frequency pulses with a nutrient solution — plain water alone won’t do it, and most drip systems have been operated with longer application times than what we’re doing in OHS.

Actually, though, we don’t manage the water to achieve this effect — we manage air.  Each pulse can only be long enough to apply some water with fertilizer without creating an oxygen-deficient environment that would suffocate the roots. 

Closeup of root density - click to enlarge

The length of each pulse, then, is based on how quickly the soil under the emitters becomes saturated during an irrigation application, so we apply for a short period, then wait long enough for air to re-enter the root ball before applying the next pulse.

Pete