The first Chestnut Irrigation Design post was all about our orchard's soil types, expected crop ET, and the general irrigation system we were going to install in light of those two factors. This post will cover some updates to that general design and details on how the system works now that's its in place.
Updates to the Design
Here's the original design sketch.
Here's the design as it is installed today.
The main changes from the initial design are:
- We broke the East side of the orchard into two zones, adding the small SE zone (shown in grey in the map above). Doing so required adding another valve, filter, & submain, but the soils in that corner of the orchard are very different from those on the rest of the East Block. Having that corner be its own block, will allow us to irrigate based on what the trees in that soil needs, vs. what the rest of the East Block needs.
- We increased the size of the mainline from 3" to 4" and the first couple hundred feet of the East Block submain to 3" instead of 2". This increased the cost, but reduces the friction loss as water flows through the pipe which will allow us to irrigate more of the orchard in a single set when the trees are mature.
- We increased the size of the pump that drives the system from 300 GPM to 400 GPM. Like #2 above, this increased the cost but will allow us to irrigate the whole orchard in a single set when the trees are little. It may be enough to irrigate the whole orchard in a single set at maturity too. We'll see.
Drip & Emitters
Why would a pump be able to irrigate the whole orchard in a single set now, but may not be able to at maturity? Great question!
It's because we're going to add drip emitters over time. The trees are small right now, with roots that only extend a few inches laterally from their trunk. They only need water on their roots, so there is no need to waste water irrigating other parts of the rows where the trees won't be able to reach the water.
As the trees mature, we'll add additional emitters on to the drip lines to increase both the amount of water that is distributed per hour and the area around each trees that receives water.
Valve Setup & Controls
The core of the whole system is at the center of the orchard where the mainline connects to each of the submains. Each submain has the following in this order starting from the mainline tee and shown in the image below:
- 2" Pressure reducing valve
- 2" Screen filter
- Small port with on/off for future fertilizer injection
- Pressure gauge to read the post-filter pressure
The wires running from the valve and pressure gauge are to enable the whole system to be monitored and controlled via my phone or computer via WiseConn.
WiseConn's has a whole suite of irrigation, weather, and soil monitoring hardware and software that is serving as the irrigation management system for the orchard. The main elements that we're using are:
Soil moisture and temperature probes in each irrigation zone. This give us a reading on how much water is in the soil profile every few inches all the way down to around 3ft. Below is a screenshot of a real-time reading of one of the probes.
Each line in the chart represents a different soil depth. The thin vertical line is test irrigation that we ran. It was too short to have an impact on soil moisture, but in the future we'll see the irrigation start and the % soil moisture rise at each level down the profiles as the water percolates through the soil.
The spike in soil moisture near the end of the graph is due to a ~0.25" rain event. The probe shows that the rain significantly increased moisture at 4" and 8" deep and a little at 12" deep, but had little impact beyond that. These probes also capture soil temperature and the software allows us to place any kind of notifications or limits we'd like prompt us to irrigate if things are too dry.
A weather station to give real-time and historic on-farm weather data. Below is a screenshot of some of the basic data that the weather station captures.
The middle "Rainfall / ETO" is the most useful as we go through the summer and want to irrigate to keep up with the tree's water demand. There is another view of this same chart in Drop Control that adds in irrigation water that has been applied. That allows us to see if rain + irrigation = the orchard's evapotranspiration (ET).
Controllers & pressure gauges on each of the valves that allow us to schedule, turn on/off irrigations, and confirm if the set is running. The soil probes and weather stations tell us what's going on in the field, the equipment at the valve lets us doing something about it.
Each zone has it's own controller that opens and closes the valve based on a signal from WiseConn's Drop Control App and a pressure sensor after the valve to confirm if water is flowing. This allows us to start or stop irrigations in each zone without being physically at the valves as well as schedule them for future dates based on the soil moisture and weather readings. If a valve is open, but the pressure sensor is not reading >5 PSI in the submain in that valve's zone, we know there is something wrong (like a major leak) and the software will not count the time the valve is open as an irrigation event.
Below is a view of the drop control app showing historic irrigations by zone and buttons to graphical data & to schedule an irrigation. 
Finally, less real-time useful but more valuable for long-term monitoring is the 1-2x per week satellite imagery and NDVI. NDVI stands for Normalized Difference Vegetation Index, which is a fancy way of saying "a way to see which areas of your orchard are more & less vigorous." Below is what this analysis looks like of our orchard's largest irrigation block. Since the trees are so small, the analysis is picking up on the cover crop's vigor, not the chestnut's, but when the tree's have a larger canopy, the satellite will be reading them, not the ground cover.
I suspect, however, that the NDVI of the trees won't be wholly different. The worst soils on the farm are in the north, which is already showing a less healthy cover crop on NDVI. My guess is that the trees in that same northern edge will struggle more than those in the richer soils to the south and therefore NDVI analysis of the trees will map pretty well onto this one.