Trees don't care about evapotranspiration..

True. But we certainly do.. It tells us when and how much to water our farm.

We can determine optimum time and amount of water to irrigate the orchard by tracking how much water is lost from the soil via evapotranspiration (the loss of moisture in the soil thru evaporation + the loss of water thru tree transpiration).

Here's an example. For almond orchards, we strive to maintain soil moisture level of 4-5 ft deep. But to keep it simple, consider this:

Let's say you measured soil moisture level at the end of Sunday to be 1 inch. And say, you can only tolerate half-inch depletion.

Monday ET = 0.15 inches --> 0.15'' of top soil lost moisture --> ok
Tuesday ET = 0.20 inches --> 0.35'' of top soil is dry --> ok
Wednes  ET = 0.15 inches --> 0.50'' of top soil is dry --> ok
Thurs     ET =  0.20 inches --> 0.70'' of top soil is dry --> NOT ok --> IRRIGATE NOW.

You get the idea..

How do we get daily ET numbers? It's calculated from daily satellite and weather data (temp, humidity, wind) and the type of crop (ground cover) at the farm. I find that different sources provide slightly different numbers. This ET number can be different for different parts of your farm based on soil type differences.

Alternative to doing this calculation is to install ground sensors to measure soil moisture up to several feet (like we did at Carpenter ranch). Based on the readings from these sensors, you can make irrigation decisions.

What exactly is evapotranspiration?

"Evapo what?." That's my reaction when I first heard that word.

Simply put, it is the amount of water vapor released into atmosphere by soil and plants on any given day.

Evapotranspiration = Evaporation from Soil + Transpiration from Plants

Evaporation: On average, water is evaporated across the earth's surface at the rate of 1/8th inch each day. At tropics, more evaporation occurs. At cooler areas, less so.

Transpiration: Transpiration is vaporization of the liquid water in the plant. Plants have small openings (called "stoma") in the underside of leaves that release water vapor into atmosphere. Read my previous post for more info on this.

If the crop is smaller (like strawberries), water is predominantly lost by the soil evaporation.
If the crop is alfalfa or well-developed almond orchard with full canopy, then transpiration becomes the main component of evapotranspiration.

Transpiration: How do plants release water into the air?

This is how transpiration happens:

• When sunlight falls on a leaf, its radiant energy excites the water molecules in the leaf. 
• The H2O molecules heat up, and they start bouncing around and eventually come up to the surface of the leaf. 
• When they absorb even more energy, bonds between adjacent H2O molecules break, turn into water vapor and evaporate into the atmosphere. 

Transpiration also cools plants, enables flow of nutrients and water from roots to shoots. The more water transpires from leaves, the more water is sucked in from the ground via roots by capillary action.

Potassium.. Where art thou?

Potassium is the third major plant and crop food, after nitrogen and phosphorus. Potash is important for agriculture because it improves water retention (because it regulates opening and closing of pores on leaves) and disease resistance of crop too.

Anyway, despite applying potassium annually at Carpenter the leaf tests and visual symptoms indicate that we continue to be deficient in this important nutrient. We have had decent crops and each crop removes a lot of potassium. So we need to increase the amount we apply to compensate for the amount being removed.

Our plan is to purchase two truckloads of potassium fertilizer this year for Carpenter (instead of the usual one), and one for Whitmore (half for the Candycots, the other half for the almonds).  We will begin to apply it as soon as the soil is dry enough to do so. If it stops raining for an extended period of time (10 days) we will be able to apply all of the potassium at both ranches before the end of December.

Uh ho.. Ranch house has some interesting guests..

Douglas (the tenant) alerted us to the presence of some insects which he thought might be termites in the kitchen skylight of the ranch home at Whitmore. When Lane looked at it with him, he found some shed wings and a neat pile of frass (insect poop). Lane declared it was that of drywood termites.

Later, Clark Pest Control  confirmed the presence of drywood termites in the rafters of the house. It appears to be a limited infestation, but they could not access and inspect all parts of the attic. They did not find any subterranean termites or other problems under the house. They recommended fumigation of the house.

Sri Ahobila Jeeyar Swamiji visits the orchard just after the harvest.

Irrational fear of chemicals

I know it's a touchy topic. Pesticides. Some say we are  dousing our farms and orchards with dangerous chemicals and that it will lead to silent spring.

First of all, we do not _douse_ our orchards with pesticides. Many people throw fertilizers and pesticides into the same bucket. Fertilizers are like vitamin supplements. Pesticides are like anti-biotics. We only use pesticides if and when needed.

Second of all, I, maybe, understand people's concerns about pesticide residues on fruits like apple and grapes. But, we grow almonds, which are inside a hard-shell, which in turn is inside a thick hull.

Finally, some people just don't like the word "chemical." The notion that chemicals are a distinct group of modern evils invading our food supply is ludicrous.

Every physical thing is exclusively made of chemicals.

No food or medicine can be "chemical free." The only thing that is chemical free is a perfect vacuum and perhaps those tiny spaces between atoms.

But any object sold to you is chemicals (unless, of course, it is a big box of nothing in which case it is probably not worth your money- also you should discard the box- it's jam packed with chemicals).

• We take from nature both the life saving penicillin and the dangerous anthrax..

• We make in laboratories the life saving insulin and BPA.

• Then there's a world of neutral:
• the delicious potato and it's poisonous leaves
• pesticides which help provide more people with affordable produce but with unknown effects on people and the environment. 
• the polymers which keep lettuce fresher reducing wasted food but end up in landfills failing to rot away.

Interesting stuff..