Friday, January 8, 2016

Remote high tunnel watering

Controlled production environments as we well know, offer a wealth of benefits, particularly in temperate zones. Essentially all environmental conditions are manipulatable (light, irrigation, atmospheric conditions, etc.) to best facilitate growth and development of plant material, and many of these parameters can be automated under growers discretion. Unfortunately, many of these amenities aren’t available to me, both from a financial standing, but even more so by lack of driving forces. One being electricity, and the second being  running water, which despite a high tunnels many advantages, can be difficult to achieve if it resides in a remote area. as per my situation.

Fortunately, I technically have the ability to procure electricity for the high tunnel, however it would require >200 ft. of extension/power cable, but isn’t necessary. Water, which is imperative, would require > 300 ft. of hose/pipe and burial below the frost line for functionality in the winter. Neither implementations are needed at this point, not for a basic small tunnel with rather minimal demand in winter.

 

Initial watering of delicate seedlings in plastic mulch was rather easy by hand, however now that they’re becoming juveniles with a significant canopy, overhead watering is essentially ineffective. The romaine lettuce bed will eventually present the same problem. Fortunately drip line was installed between each row of plants to negotiate this issue. However, the drip line (12” emmiter spacing) used was leftover from prior field applications, I would have preffered a 6” spacing given the close proximity of the tunnel plants. I suppose the clay dominant soil is good in this case as water will spread more horizontally than vertically, as well as reasonable organic matter content. Root growth will also develop towards the wet spots. If every other plant develops twice the size of the plants between them, then it’s evident that my prediction was inaccurate.

 

Essentially, irrigation is achieved by simply transporting a few vessels of water over to the tunnel and dropping the pump.

The reservoir must be large enough to accommodate both the pump as well as sufficient water. The pump is a simple water transfer pump, completely submersible, and runs off a removable rechargeable battery. It produces the appropriate pressure and flow rate to feed the demand of the drip lines without the need of an inline pressure regulator or relief valve/outlet. No need for an inline filter either, as the water used is town tap.

Potential alternatives:

Solar powered water pump. They can be found both as a kit, or can be fabricated as needed to meet ones needs. Aside from higher cost of these options, more importantly is reliability. Battery charging can significantly vary based on light conditions especially in the significantly short days of the winter. Indoor panels will receive less light by reduction from the plastic (double poly means even further reduction), and supplemental light deflection from frost/snow/dew. Panels placed outside the tunnel can be more efficient, considering they are not covered in snow. More panels can be implemented to compensate for the reduced efficiency, however that entails >$$$. A second prominent issue, during the winter months, is battery inefficiency from low temperatures. Loss of stored charge and significant reduced efficiency can render it useless. I suppose the battery can be buried, however I don’t plan on burying a lead-acid cube; especially in a food production facility that’s on certified organic land. All these issues were avoided by utilizing the cheap, easy to use, transportable, rechargeable battery pump.

An alternative automated irrigation consideration is overhead sprinklers.
Reasons why these weren’t used:

1. Soil seed bank is ridiculously high (this is the first year the field is in agricultural use, previously natural pasture). I don’t want to further encourage their growth at this point. I do wish I had the time to run a stale seed bed previous to planting.

2. There is no reason to water foliage (unless you’re going to eat it), for a multitude of reasons, but especially on leaf crops in an enclosed environment.

3. Residual water occupying above ground irrigation lines will inevitably freeze during the winter rendering them useless. I suppose a battery powered air pump can be briefly run on the system to clear the lines after watering. None the less, I’ve yet to have issues with buried drip lines under plastic mulch.

 

For the time being, this practice has treated me well, and I hope it continues to do so. My only concern is residual water in drip lines freezing. Time will tell.

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