Florida Citrus OHS/APS News

The fertilization and irrigation programs for Open Hydroponics Systems begin their life each year with an “Orchard Information Master”.  It’s basically a collection of the information needed to determine how much fertilizer to apply, the ratio of the different components of the fertilizer, and the basic irrigation program.

Here’s this year’s Orchard Master web page for our Rock Bottom grove: http://www.arapahocitrus.com/files/rockbottom/master

You’ll see that there are a number of items on the download list.  The Orchard Information Master itself is the controlling document, and the other items are necessary to provide the details and general idea of the condition and size of the trees.  We gather and record all this information for each irrigation zone in a grove, then send it to Japie Kruger so he can build the programs.

If you download and open the Orchard Information Master file, you’ll see that it opens to the Metric tab.  To see the same information in pounds, gallons, boxes, acres, etc., just click on the next tab to the left down on the bottom.  When Japie builds the programs, he actually does it in metric units since it’s so much simpler — kilograms and liters are easier to work with than pounds and gallons when building formulas with percentages and ratios.  Not to worry, though — when the programs are finished, we just convert everything back into English units so that the grove managers can set up the Netafim NMC controllers to run the systems.

The Orchard Information Master is broken down by irrigation zones.  The flows, tree characteristics, and leaf, soil, and water analysis are all required to complete the form.  It takes a fair amount of work to pull it all together, but the nice thing is that you only have to do it once a year.

Perhaps the most important, yet most confusing, concept is the “% Canopy Coverage”.  All the programs are first built as if the trees were fully mature and grown to the point where they fill the space allotted to them.  For smaller trees, though, this would result in too much water and fertilizer.  So, the % Canopy Coverage is estimated, and the amounts of water and fertilizer are reduced by that percentage.  For example a block of trees with 70% canopy coverage would receive 70% of the water and fertilizer required for a full size tree.

The Orchard Information Master provides the pieces of the puzzle necessary to build the water and fertilization program for the year.  The program becomes the basic operating schedule for each day of a month.  Then, we fine-tune things as necessary based on the weather conditions and other factors.  You can’t skip steps — the everything has to move through the process the same way every year.

More on Orchard Information Masters in later blog posts.

Pete

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