Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: drought

A More Water Efficient Avocado?

Here's a pretty technical report of water efficiency in avocado - the amount of water it takes to make fruit.  It looks like there might be some varieties that could produce more fruit with less water. It's a promising start to selecting a tree that could produce under the increasing drought conditions found in avocado growing areas.

 

Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars

Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.

 

Read the article:

https://www.sciencedirect.com/science/article/pii/S0167880918301828

avocado fruit
avocado fruit

Posted on Wednesday, June 20, 2018 at 6:24 AM
Tags: drought (41), production (10), salinity (13), water (49), water use efficiency (1), WUE (1)

Another Victim of Drought Stress

So, this image comes across with the question of what is going on. It's a grapefruit, but what is going on with the leaves? It's happening to two grapefruit side by side or two different ages. It's not affecting other citrus nearby, and not a grapefruit several hundred feet away. Nothing like insect damage. It's not a nutrient deficiency because it's not following a clear pattern. It doesn't look like a chimera, which is common in citrus, because it's only a few outer leaves. It doesn't fit the pattern of an herbicide. It wouldn't be a contact or a drift spray because is both veinal and interveinal, and not strongly one or the other, so it's not consistent with a soil-applied herbicide either.

 

A plant pathologist and an herbologist (weed specialist) both asked if there had been a change in light -Different light exposure or more drought stress. Was a nearby tree removed or somehow the tree got more exposure than previously? Citrus Specialist, Peggy Mauk, nailed it, though.  She said this type of coloration is characteristic of ‘Star Ruby' grapefruit when it is water stressed. And this can occur when the tree is more exposed to wind or light which is what happened here when a nearby hedge was pruned. The other citrus being less affected by such obvious symptoms, although probably stressed, as well.

 

 

citrus leaf clearing 2
citrus leaf clearing 2

Posted on Wednesday, February 28, 2018 at 5:34 AM
Tags: chimera (3), citrus (339), drought (41), grapefruit (27), herbicide (11), star ruby (1), stress (10)

What Damaged the Citrus this Winter? Frost? Herbicide?

Something hit the citrus trees of Riverside in late December 2017. Some vandal spraying herbicide? It was too widespread. It was all over town, orchards and backyards. It was on the north and east sides of trees. It didn't happen in Ventura or Santa Barbara. It probably happened to a lot of other plant species, but our correspondent had eyes only for citrus.

It sure looks like it could have been a cold, freezing wind, but on closer consultation with our Citrus Specialist, Peggy Mauk who also directs the Agricultural Operations at UC Riverside – it was the demon wind. The Satan Wind. The Santa Ana that dried out the trees that had not gotten sufficient water to cool themselves and had dried out on the windward side of the tree and orchard. Burned, in effect. This is the side of the orchard that dries out the most. It's what's called the “clothes line” effect. The margins that dry first because of the greater exposure to wind, sun and usually lower humidity. In this case, way lower. And by the time the damage was noticed a week later, the winds had been forgotten. Expect more water stress in our future.                        

citrus dieback 2
citrus dieback 2

citrus santa ana damage 1
citrus santa ana damage 1

Posted on Thursday, February 22, 2018 at 5:17 AM
Tags: citrus (339), drought (41), heat (6), lemon (100), navel (11), orange (69), Santa Ana (1), stress (10), wind (5)

Soil Moisture Sensor Selection is Confusing

So, every few weeks the question comes up of whether to install soil moisture meters which leads to the question of which to buy and install or have installed.  And then come the questions of what do the readings mean and why aren't the readings consistent.  Or maybe this question arrives after the grower has installed the sensors or system and the values don't conform to a known or knowable pattern.

The first question to the grower is why they want to install soil moisture sensors or a system.  Everyone has a different answer which I've always found interesting.  Usually it boils down to having more or better information, although it's hard to beat a good old soil auger.  Which takes time and labor.

So once that is cleared up, it comes down to what area they want to monitor.  Is it an acre, 10 acres, 50 acres, 100 acres, 200 acres, 1,000 etc.? What are the different irrigation blocks, soil types, aspects?  How complex is the area that is to be monitored?  Do they need one monitoring site or many? Can the information be gathered in the field, or does it need to be accessed from a distance? Linked by hardwire, infrared, cell phone, wifi, satellite, etc.?

Then the question is does the grower do the installation or is it done by a company?  And then whatever the case is, who maintains the system and for that matter, who maintains the information?  What software is used and who interprets it? 

And what sensors are being used: tension, electrical resistance, conductance, capacitance, electromagnetic…….? The list seems to go on and there are no models and brands coming out on a regular basis.  And how reliable are the sensors? What's their lifespan? And what are they measuring and in what units?  How affected are the readings by salinity and what soil volume are they measuring? And how important is their placement? 

This last point is so often overlooked. The sensor needs to be in the active root zone where water is being taken up.  Not where it's convenient to read, not where the plants cant use the water.  Placement is so often overlooked.

And then how much do you want to spend?  $100 per installation, $1000?  With a monthly or yearly maintenance fee or none?  Who responds when there are problems?

Wow, so yeah, there are lots of questions.  Here's a chart that might help categorize some of the questions:

Method

Cost

Ease of use

Accuracy

Reliability

Salt-affected

Stationary

Gypsum block

  L

     H

   H

   H

     L

  YES

Tensiometer

  L

     M

   H

   M

     L

  YES

Portable tensiometer

  M

     M

   H

   M

     L

  NO

Solid-state tensiometer

  M

     H

   H

   H

     L

  YES

Time domain reflectometer

  H

     M

   H

   H

    M

  BOTH

Neutron probe

  H

     L

   H

   H

     L

  YES

Feel (soil probe)

  L

     H

   H

   H

     L

  NO

Gravimetric (oven)

  L

     M

   H

   H

     L

  NO

Conductance

  L

     H

   M

   M

     H

  BOTH

Capacitance

  M

     H

   M

   H

     M

  BOTH

H, high; M, medium; L, low

 

And the good Almond Doctor might help some more:

http://thealmonddoctor.com/2015/07/10/soil-moisture-sensing-systems/

 

And maybe some of these publications can help sort out what questions to ask

http://calag.ucanr.edu/Archive/?article=ca.v054n03p38

http://calag.ucanr.edu/Archive/?article=ca.v054n03p47 

http://anrcatalog.ucanr.edu/Details.aspx?itemNo=21635

Khaled Bali, our Irrigation Specialist at Kearney Research and Education Center near Fresno, is part of a group in the process of evaluating different types and models of soil moisture sensors.  He should have a publication that can more accurately sort through the many sensor choices that are available at this time.  But in time, there should be more models on the market and new update will be necessary.

The question, though, is to ask yourself how irrigation is being done and how it can be improved.  The basics of design, maintenance, distribution uniformity and how scheduling is being currently done – when and how much to apply. Definitely, soil moisture sensors can help, but you gotta know how to use them and maintain them, just like the whole irrigation system. 

A grower who uses tensiometers told me that people think of soil sensors as though they were reading a book. Something cut and dried.  A simple plot line that you follow. Irrigation is not a book.  There are many other subplots to irrigation than just reading the digital face.  Looking at the weather, evapotranspiration, the tree, how fast the moisture is depleted, how deep the moisture is being pulled from all contribute to the "sensors" used to irrigate.  Use them all.   Even though this grower has irrigators on 250 acres of trees, he also checks the orchard tensiometers at least once a week on his own to confirm all of his senses.

tensiometer2
tensiometer2

cimis
cimis

Posted on Tuesday, September 5, 2017 at 6:57 AM
Tags: delta (2), drought (41), echo (1), hobo (1), irrigation (80), irrigation scheduling (3), irrometer (2), scheduling (11), sensors (2), soil moisture equipment (1), water (49), watermark (1)

Earthworms, Soil Productivity, Citrus and Avocado

There are 4,000 species of earthworms grouped into five families and distributed all over the world. Some grow uo to 3 feet long, while others are only a few tenths of inches. We call them nightcrawlers, field worms, manure worms, red worms and some people call them little diggers.

In California, we have some native species of earthworms, but in many cases non-native introduced species have come to dominate. The predominant native species belong to the Argilophilus and Diplocardia while many of the non-native are of European in origin in the Lumbricidae family. Many of these non-natives were probably introduced by settlers bringing plants from home, which had soil containing the worms. A survey of California earthworms by the US Forest Service can be found at:

https://www.fs.fed.us/psw/publications/documents/psw_gtr142/psw_gtr142.pdf

This is a wonderful description of earthworm biology and their occurrence in the landscape.

When digging in citrus orchards, it is common to find earthworms in the wetted mulch under tree canopies. Many of our citrus orchards were initially established by “balled and burlap” nursery trees that brought worms along with the soil. In the case of many avocado orchards, on the other hand, it can be rare to find earthworms in orchards. Most avocado orchards have been established since the 1970s when potting mixes and plastic liners were the standard practice and worms were not part of the planting media. Even though there is a thick leaf mulch in avocado orchards, the worms have not been introduced, and it is rare to find them.

Numerous investigators have pointed out the beneficial effects of earthworms on soil properties. One of the first of these observers was Charles Darwin who published Earthworms and Vegetable Mould in 1881. He remarked on the great quantity of soil the worms can move in a year. He estimated that the earthworms in some of his pastures could form a new layer of soil 7 inches thick in thirty years, or that they brought up about 20 tons of soil per acre, enough to form a layer 0.2-inch-deep each year.

Earthworms, where they flourish, are important agents in mixing the dead surface litter with the main body of the soil. They drag the leaves and other litter down into their burrows where soil microorganisms also begin digesting the material. Some earthworms can burrow as deeply as 5 to 6 feet, but most concentrate in the top 6 to 8 inches of soil.

The worm subsists on organic matter such as leaves and dead roots near the soil surface. The earthworm ingests soil particles along with the organic matter and grinds up the organic matter in a gizzard just as a chicken does. This is excreted in what we call worm casts. The castings differ chemically from the rest of the soil, as they are richer in nitrogen, potassium and other mineral constituents.

Castings are a natural by-product of worms. When added to normal soils in gardens or lawns, they provide the same kinds of benefits as other bulky organic fertilizers. Castings today are not commonly used as fertilizer by commercial plant growers because of their cost relative to other fertilizers. However, castings are used by some organic growers and are sold commercially as a soil amendment or planting medium for ornamental plants grown in pots.

The physical soil churning process also has several important effects:

-Organic residues are more rapidly degraded with the release of elements such as nitrogen, sulfur and other nutrients.

-Some of the inorganic soil minerals tend to be solubilized by the digestive process.

-Extensive burrowing improves soil aeration.

-Burrowing can improve water penetration into soils

-The earthworm carries surface nutrients from the soil surface and imports them into the root zone of the plant.

Although earthworms are considered beneficial to soil productivity, few valid studies have been made to determine whether their presence will significantly improve plant growth. This may seem odd since many of us have learned from childhood that worms are good. It is something like the chicken and the egg analogy. The conditions that are conducive to earthworms are also ideal for plants. Both plants and worms need temperatures between 60 and 100 degrees F for good growth; both need water, but not too much or little; they both require oxygen for respiration; and they do not like soils that are too acid or basic or too salty. By correcting soil conditions that are unfavorable for one will also improve the outlook for the other. The earthworm is a natural component of the soil population. If the soil is properly managed this natural population will thrive. In this sense, the presence or absence or earthworms can be an indicator of the "fertility" of one's soil.

earthworm
earthworm

Posted on Friday, April 28, 2017 at 11:01 AM
Tags: biology (1), drought (41), earthworms (2), fertility (2), fertilizers (6), fuerte (1), grapefruit (27), Hass (4), irrigation (80), leaves (3), lemon (100), mandarin (68), mold (1), mulch (15), nutrients (21), organic matter (7), ornage (4), pollution (1), salinity (13), soil (25), water (49), worms (3)

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