Water woes are probably not going to go away, so readup on how to best manage water at this new blog.
- Author: Rachael Long
Guest post from Rachael Long, UC Cooperative Extension Farm Advisor, Yolo County
The Yolo County Flood Control and Water Conservation District (YCFC) is an agency that supplies water to farmers in northern California. The agency is at the forefront of innovative efforts aimed at banking groundwater by diverting flood waters into their unlined canals. This gives flood waters time to infiltrate soils and recharge groundwater.
Using a water right permit that they recently obtained from California's State Water Resources Control Board, flood waters from recent storms are being captured from Cache Creek as it enters the Sacramento Valley. YCFC recently opened their lateral gates, allowing the flood waters to...
Groundwater wells can fail in many ways. Sometimes the water table sinks below the level of the well. Sometimes minerals cause buildup in well systems. And, sometimes, wells get clogged with lots and lots of microbes.
Microbes can form large, jelly-like mats that lead to well failure from what is known as biofouling. Biofouled wells can be both expensive and technically challenging to repair. There are even times that repair is not possible and replacement is the only option. In Washington State, for example, researchers have encountered well pipes completely clogged by mats of bacteria....
California's Sacramento-San Joaquin River Delta region, commonly referred to simply as the Delta, is often described as a unique part of the world. Although it is located between two big urban centers – the greater Sacramento and San Francisco Bay areas – the Delta can feel like another world altogether.
This is something Michelle Leinfelder-Miles, a farm advisor with UC Agriculture and Natural Resources, knows well. She comes from a sixth-generation farming family in San Joaquin County and, after accepting her position several years ago, was happy to return “home”...
The California drought has shined a spotlight on stories of people and communities living without water. Unfortunately, lack of access to clean and affordable water is not a new issue. Water security has been an enduring challenge across the state in wet and dry years alike, particularly for disadvantaged communities. Trying to meet concerns about water availability and affordability with pragmatic action is where things get both complicated and interesting.
One approach that the state has invested a great deal in exploring is known as integrated regional water management. While it is a complex topic, the basic idea is that there are multiple needs for water throughout the...
Street-side stormwater facilities are turning runoff once seen as a nuisance into a resource. Also known as bioretention areas, rain gardens, and bioswales, these small stormwater facilities provide a decentralized approach to alleviating peak stormwater runoff and subsequent flood damages. These are particularly critical functions in cities like San Francisco where the storm and sanitary sewer systems are combined because they help managers to prevent dreaded “combined sewer overflow” events. As a bonus, stormwater facilities have also proved useful in promoting groundwater recharge and filtering pollutants as water percolates through soils.
While street-side facilities are effective in helping to manage...
This is a sad time to be an avocado. Winter's gone and temperatures are just ripe for flowering and the trees are going bust. So much so, that those sad leaves that have accumulated salts over the last year are being dropped and only flowers might be seen, especially on young trees. This is time for a little shot of nitrogen to encourage some new vegetative growth. Not a bunch, but a nudge. Several pounds per acre, something less than 10-15 pounds of N for a mature orchard and even less for a new orchard.
A commonly held belief is that if you apply nitrogen at the wrong time, it will push resources into vegetative growth at the expense of flower and fruit. This is somewhat true for annual plants that get most of their nutrients from outside sources (soil, air, fertilizer, water), but trees have a huge buffer in their storage organs (roots, stems, leaves, etc.). Most growth in trees occurs from this storage source and most importantly from photosynthesis and the sun. The more sun captured the more energy for flowering and fruit production.
So it is this competition for photosynthates that becomes the most limiting factor. When there is not enough to go around, the tree sheds fruit. If you see fruit dropping off a tree after applying a slug of fertilizer, it's a salt effect. Too much salt and it causes a water competition and the tree is stressed. It's not the nitrogen, but too much salt. With fertigation this is not so likely to happen as when dry fertilizers were applied and someone got too aggressive with the application
In fact a dose of nitrogen fertilizer is a good idea at this time when there are lots of flowers. This can encourage a flush of leaves that will protect the fruit that does set from sunburn and damage that would cause fruit to drop. A bit of nitrogen to encourage leaf replacement is a good approach to dealing with persea mite damage that occurred the previous season.
For further reading about the competition between vegetative and reproductive growth as affected by nitrogen (or little affected in fruit trees by nitrogen), D.O. Huett wrote a wonderful review of past research on this topic:
Also, if the trees have really defoliated, it might be time to do some whitewashing, south and west sides of branches, to prevent sunburn.
Avocado defoliated and ones in a balanced bloom
Drought Induced Problems in Our Orchards
Abiotic disorders are plant problems that are non-infective. They are not caused by an organism, but through their damage, they may bring on damage caused by organisms. Think of a tree hit by lightning or a tractor. The damage breaches the protective bark which allows fungi to start working on the damaged area, eventually leading to a decayed trunk. It was the mechanical damage, though that set the process in motion.
Too much or too little water can also predispose a plant to disease. Think of Phytophthora root rot or even asphyxiation that can come from waterlogging or too frequent irrigations.
Salinity Effects from Lack of Water
Lack of water and especially sufficient rainfall can lead to salinity and specific salts like boron, sodium and chloride accumulating in the root zone. This happens from a lack of leaching that removes native soil salts from the root zone or the salts from the previous salt-laden irrigation from the root zone. These salts cause their own kind of damage, but they can also predispose a tree to disorders, disease and invertebrate (insect and mite) damage.
Lack of water and salt accumulation act in a similar fashion. Soil salt acts in competition with roots for water. The more soil salt, the harder a tree needs to pull on water to get what it needs. The first symptom of lack of water or salt accumulation may be an initial dropping of the leaves. If this condition is more persistent, though we start to see what is called “tip burn” or “salt damage”. Southern California is tremendously dependent on rainfall to clean up irrigation salts, and when rain is lacking, irrigation must be relied on to do the leaching
As the lack of leaching advances (lack of rainfall and sufficient irrigation leaching) the canopy thins from leaf drop, exposing fruit to sunburn and fruit shriveling.
Leaf drop and fruit shriveling in avocado.
In the case of sensitive citrus varieties like mandarins, water stress can lead to a pithy core with darker colored seeds, almost as if the fruit had matured too long on the tree.
Total salinity plays an important factor in plant disorder, but also the specific salts. These salts accumulate in the older leaves, and cause characteristic symptoms that are characteristic in most trees. Boron will appear on older leaves, causing an initial terminal yellowing in the leaf that gradually turns to a tip burn.
Often times it is hard to distinguish between chloride, sodium and total salinity damage. It is somewhat a moot point, since the method to control all of them is the same – increased leaching. There is no amendment or fertilizer that can be applied that will correct this problem. The damage symptoms do not go away until the leaf drops and a new one replaces it. By that time hopefully rain and/or a more efficient irrigation program has been put in place.
The Impact of Drought on Nutrient Deficiencies
Salinity and drought stress can also lead to mineral deficiencies. This is either due to the lack of water movement carrying nutrients or to direct completion for nutrients. A common deficiency for drought stressed plants is nitrogen deficiency from lack of water entraining that nutrient into the plant.
This usually starts out in the older tissue and gradually spreads to the younger tissue in more advanced cases.
The salts in the root zone can also lead to competition for uptake of other nutrients like calcium and potassium. Apples and tomatoes are famous for blossom end rot when calcium uptake is low, but we have also seen it in citrus. Low calcium in avocado, and many other fruits, leads to lower shelf life. Sodium and boron accumulation in the root zone can lead to induced calcium deficiencies and increased sodium can also further lead to potassium deficiencies. Leaching can help remove these competitive elements.
Drought Effect on Tree Disease
Drought and salt stress can also lead to disease, but in many cases once the problem has been dealt with the disease symptoms slowly disappear. They are secondary pathogens and unless it is a young tree (under three years of age) or one blighted with a more aggressive disease, the disease condition is not fatal. Often times, in the best of years, on hilly ground these diseases might be seen where water pressure is lowest or there are broken or clogged emitters. The symptoms are many – leaf blights, cankers, dieback, gummosis – but they are all caused by decomposing fungi that are found in the decaying material found in orchards, especially in the naturally occurring avocado mulch or artificially mulched orchards. Many of these fungi are related Botryosphaerias, but we once lumped then all under the fungus Dothiorella. These decay fungi will go to all manner of plant species, from citrus to roses to Brazilian pepper.
Another secondary pathogen that clears up as soon as the stress is relieved is bacterial canker in avocado. These ugly cankers form white crusted circles that ooze sap, but when the tree is healthy again, the cankers dry up with a little bark flap where the canker had been.
Drought Effect on Pests
Water/salt stress also makes trees more susceptible to insect and mite attack. Mites are often predated by predacious mites, and when there are dusty situations, they can't do their jobs efficiently and mites can get out of hand. Mite damage on leaves is often noted in well irrigated orchards along dusty picking rows
Many borers are attracted to water stressed trees and it is possible that the Polyphagous and Kuroshio Shot Hole Borers are more attracted to those trees.
And then we have conditions like Valencia rind stain that also appears in other citrus varieties. We know it will show up in water stressed trees, but we aren't sure what the mechanism that causes this rind breakdown just at color break. Could it be from thrips attracted to the stressed tree or a nutrient imbalance, it's not clear?
Water and salt stress can have all manner of effects on tree growth. It should lead to smaller trees, smaller crops and smaller fruit. The only way to manage this condition is through irrigation management. Using all the tools available, such as CIMIS, soil probes, soil sensors, your eyes, etc. and good quality available water are the way to improve management of the orchard to avoid these problems.
Scroll down for Images
Tip Burn, notice sun burn bottom right hand fruit
Endoxerosis with dried out core
Blossom end rot
Bot gumming in lemon
Black Streak in Avocado
Citrus red mite
Polyphagous Shot Hole Borer damage on avocado
Valencia Rind Stain
Nutrient availability from organic sources has been considered “slow release” by many growers and advisers. This may be true in environments are colder and especially soils are cooler. Organic nutrients are dependent on microbes to break down materials and release those nutrients, and when soils are cold, microbes can't do their thing. Soils in much of agricultural California tend to be warm and lack the freezing conditions that occur in many soils in the continental US. Imagine how much microbial activity occurs in the Mid-West when soils cool down to 32 deg F at a four inch depth and deeper. The top layers of soil are where organic matter accumulates and where most microbial activity occurs. When soils cool below 50 deg F, nitrogen leaching becomes less common, because less activity is occurring which also coincides with much less plant growth.
Soils in coastal California rarely fall below 50 deg F in the surface layers, so microbial activity is ongoing, all year long. So the question is, how “slow acting” are organic fertilizers? A recent study by Tim Hartz, Richard Smith and Mark Gaskell looked at release rates of injectable organic fertilizer and found that much of the nutrient release occurs within about a week after application depending on the formulation and temperature during the study. The results conform to another study that they did where they evaluated the nitrogen release rates of dry formulations of organic fertilizers – compost, manures, feather meal, etc.
Aside from the issues of the higher costs of these materials and their potential clogging, there is the issue of application timing. In the case of avocados and citrus, adequate levels of nitrogen are needed in the trees going into to fruit set in order to optimize set. And then after fruit set, in order to maintain growth into the fast growth period, again nitrogen needs to be adequate. Using organic fertilizers with a rapid conversion to useable forms of nitrogen, means that application timing should coincide with these critical periods in tree phenology or growth cycle.
Using information on organic nutrient management based on work from cold soil climates needs to be carefully evaluated before applying it to California soils. One of the most common problems in organic production is nitrogen management. Part of the problem is the cost of supplemental nitrogen amendments, but also learning to anticipate when that applied nutrient becomes available to the plant. Developing better estimates for local release rates and patterns will better help manage organic nutrient sources.
Summary: Limited soil nitrogen (N) availability is a common problem in organic vegetable production that often necessitates additional N fertilization. The increasing use of drip irrigation has created a demand for liquid organic fertilizers that can be applied with irrigation. The N availability of three liquid organic fertilizers was evaluated in an incubation study and a greenhouse bioassay. Phytamin 801 contained fishery wastes and seabird guano, while Phytamin 421 and Biolyzer were formulated from plant materials. The fertilizers ranged from 26 to 60 g·kg−1 N, 8% to 21% of which was associated with particulate matter large enough to potentially be removed by drip irrigation system filtration. The fertilizers were incubated aerobically in two organically managed soils at constant moisture at 15 and 25 °C, and sampled for mineral N concentration after 1, 2, and 4 weeks. In the greenhouse study, these fertilizers and an inorganic fertilizer (ammonium sulfate) were applied to pots of the two organically managed soils with established fescue (Festuca arundinacea) turf; the N content of clippings was compared with that from unfertilized pots after 2 and 4 weeks of growth. Across soils and incubation temperatures, the N availability from Phytamin 801 ranged from 79% to 93% of the initial N content after 1 week, and 83% to 99% after 4 weeks. The plant-based fertilizers had significantly lower N availability, but after 4 weeks, had 48% to 92% of initial N in mineral form. Soil and incubation temperature had modest but significant effects on fertilizer N availability. Nitrification was rapid, with >90% of mineral N in nitrate form after 1 week of incubation at 25 °C, or 2 weeks at 15 °C. N recovery in fescue clippings 4 weeks after application averaged 60%, 38%, and 36% of initial N content for Phytamin 801, Phytamin 421, and Biolyzer, respectively, equivalent to or better than the N recovery from ammonium sulfate.
- Author: Vanessa Ashworth and Philippe Rolshausen
Department of Botany and Plant Sciences, University of California Riverside.
Evidence of avocado selection by human hand as far back as 8,000 BC is preserved in archaeological sites in Puebla State, Mexico. At the time of European contact, written records indicate that there already existed three distinct types of avocado, each from a separate geographic center of origin. Today, we refer to them as botanical races, and they represent the “primeval soup” that gave rise to modern avocado cultivars. Here is what we know about the three botanical races of avocado, respectively called (1) the West Indian (formerly known also as the South American), (2) the Guatemalan, and (3) the Mexican (also known as the “criollo”): Each exhibits a characteristic suite of traits that includes differences in leaf chemistry (a distinctive anise scent is found only in Mexican race avocados), peel texture and color, fruit oil content, and sources of tolerance (diseases and salinity). The races were domesticated in separate geographic regions, the “West Indian” race in lowland coastal Mesoamerica (possibly Yucatán), the Guatemalan race in upland Guatemala, and the Mexican race in highland Mexico. The Guatemalan and Mexican races remained fairly local, so their names reflect their respective centers of domestication, but the “West Indian” race seems to have been spread far and wide by indigenous cultures in Meso- and South America and was, incorrectly, named for a much later destination. The explorations of the 15th and 16th centuries kicked off the worldwide distribution of (mostly West Indian race) avocados, reaching Spain in the early 17th century, Jamaica in the mid-17th century, and Indonesia by the mid-18th century. It wasn't until the mid- to late 19th century that the three races of avocado found their way to the United States, primarily Florida and California, where they underwent many rounds of selection and hybridization. ‘Hass', the cornerstone of the California avocado industry, was patented in 1935 but its ancestry is unknown. It is considered to be a Mexican x Guatemalan hybrid because its leaves lack the anise scent and its fruits combine the thick, rough skin of the Guatemalan race but the high oil content of the Mexican race.