Posts Tagged: potassium
Fertilizer Remarks.
By Cynthia Kerson, UC Master Gardener of Napa County Recently, my husband asked me what to...
Fertilizer (dreamstime.com)
Organic and synthetic fertilizer (ipm.ucanr.edu)
NPK in short (zone9garden.com)
The goal of proper application--beautiful flowers. (markus-winkler-unsplash)
Slow Spring Growth in Alfalfa Fields
Lately, I have been corresponding with growers and consultants about slow spring growth in their...
Why 'AA' is for Avocado Addict
If you're like most of us, you “go bananas” for a banana for breakfast.
It's healthy, nutritious and packed with potassium.
But wait! You should probably go bananas for another fruit--that pear-shaped avocado. Did you know the avocado provides more potassium than a banana?
It does. A medium-sized banana yields 422 milligrams of potassium, while a medium-sized avocado, a whopping 708 milligrams.
“Eating more unsaturated fats -- as opposed to saturated fats and processed carbohydrate -- is a delicious step we all can take to maximize cardiovascular health,” Adams says. “Avocados are such a delicious way to do that!"
We love our avocados, our veritable green goddess that never disappoints, never deceives, never dissatisfies, whether we “butter” them on toast in the morning for breakfast, or slice or chunk or cube them for our salads at lunch and dinner. Health-conscious folks call them a superfood, and even mash and freeze them to ensure a steady supply in the winter. There's even a website on “50 Things to Love About Fresh Avocados.”
This year, California's 2000 avocado growers anticipate a yield of 374.6 million pounds. That crop forecast, according to Tom Bellamore, president of the California Avocado Commission, is nearly double the yield of the 2017 crop and “despite the ravages of Mother Nature in California's avocado growing regions.”
UC Cooperative Extension adviser and avocado researcher Ben Faber of Ventura and Santa Barbara counties, points out that the avocado is really a fruit, not a vegetable. “The Supreme Court classified the tomato in 1920 or so as a vegetable because that's the way people think of it and it was taxed differently for tariffs. Politics or botany separates a lot of things in our lives.”
“The avocado is an amazing fruit,” Faber says. “It grows on a tree and comes to maturity, reaches certain oil content and a stage at which it will ripen, but it does not ripen on the tree. It needs to be removed from the tree before it will soften. If the fruit is removed before it has reached maturity it will not soften, and will remain rubbery and inedible.”
“One of the problems is that the fruit will hang on the tree for an extended period of time and it is hard to know when they are mature,” Faber points out. “Avocados are not like apricots where you have about two weeks to get the fruit off before it falls off. As the fruit stays on the tree, it gradually develops more and more oil content and has a richer flavor.”
What if the fruit stays on the tree too long? “It can develop an almost rancid flavor,” Faber says. “So it is good to know when the best, acceptable flavor is. Avocado varieties fall into general seasonal periods when they are mature, such as ‘Fuerte' and ‘Bacon' in winter, ‘Hass' in spring/summer, ‘Lamb-Hass' in summer/fall.”
The fruit will typically be ripe in seven to ten days, Faber advises. “If you want to speed things along a bit you can take three or four avocados and place them in a loosely closed paper bag with two or three Red or Golden Delicious apples or ripe kiwifruit. The purpose of the apples or kiwifruit is that these fruit produce a natural plant hormone, ethylene, that will help stimulate the avocado to produce its own ethylene. Apples and kiwifruit are known to produce lots of ethylene. The Delicious apples are varieties that produce more ethylene than other apple varieties. You can keep them even after they are shriveled and they will be producing ethylene.”
Never place your avocados in a plastic bag “unless you keep it open since the fruit needs to breathe during this process,” he says. “Just keep the fruit on your kitchen counter or in a warm place; 68F is the ideal temperature. Lower and higher temperatures both actually slow the process.”
Plant scientists trace the origin of the avocado (Persea americana) to south central Mexico. The avocado belongs to the flowering plant family, Lauraceae. Growers and gardeners glean tips on pest management from the industry and from the UC Statewide Integrated Pest Management Program.
Of the many known varieties, avocados fall into three broad categories based on whether they are of the Mexican, Guatemalan or West Indian races of Persea americana, the avocado species and the crosses that occur between these races. Generally speaking, California varieties have been the result of crossing between the Mexican and Guatemalan races. West Indian race varieties are not common here because of their generally lower cold tolerance.”
Ben Faber, like Linda W. Adams, enjoys avocados. He usually buys them “whenever they are reasonably priced.”
“One of the reasons I do research is that all the downed fruit is not salable because it is against food safety restrictions to introduce it into the food chain and all that fruit either gets eaten by coyotes or me,” he quips, adding “The tree is too big to fit into my backyard.”
Looking for a great recipe? The California Avocado Commission offers many recipes, including what it calls “The Best Guacamole Ever."
Dietitian Adams shares one of her favorites at https://www.delish.com/cooking/recipe-ideas/a19872947/avocado-tomato-salad-recipe/.
Avocado Tomato Salad
Ingredients
1/4 cup extra-virgin olive oil
Juice of 1 lime
1/4 tsp. cumin
Kosher salt
Freshly ground black pepper
3 avocados, cubed
1 pint cherry tomatoes, halved
1 small cucumber, sliced into half moons
1/3 cup corn
1 jalepeño, minced (optional)
2 tbsp. chopped cilantro
Directions
In a small bowl, whisk together olive oil, lime juice, and cumin. Season with salt and pepper.
In a large serving bowl, combine avocados, tomatoes, cucumber, corn, jalapeño, and cilantro. Gently toss with dressing and serve immediately.
Enjoy! The avocado keeps good company!
Now is the Time to Sample Citrus for Nutrients - and Avocados Too
University of California (UC) researchers and private industry consultants have invested much effort in correlating optimal citrus tree growth, fruit quality and yield to concentrations of necessary plant nutrients in citrus (especially orange) leaf tissue. The grower can remove much of the guesswork of fertilization by adhering to UC recommendations of critical levels of nutrients in the tissues of appropriately sampled leaves. Optimal values for elements important in plant nutrition are presented on a dry-weight basis in Table 1. Adding them in appropriate rates by broadcasting to the soil, fertigating through the irrigation system or spraying them foliarly may correct concentrations of nutrients in the deficient or low range. Compared to the cost of fertilizers, and the loss of fruit yield and quality that can occur as a result of nutrient deficiencies or excesses, leaf tissue analysis is a bargain. At a minimum, the grower should monitor the nitrogen status of the grove through tissue sampling on an annual basis.
Leaves of the spring flush are sampled during the time period from about August 15 through October 15. Pick healthy, undamaged leaves that are 4-6 months old on non-fruiting branches. Select leaves that reflect the average size leaf for the spring flush and do not pick the terminal leaf of a branch. Typically 75 to 100 leaves from a uniform 20- acre block of citrus are sufficient for testing. Generally, the sampler will walk diagonally across the area to be sampled, and randomly pick leaves, one per tree. Leaves should be taken so that the final sample includes roughly the same number of leaves from each of the four quadrants of the tree canopy. Values in Table 1 will not reflect the nutritional status of the orchard if these sampling guidelines are not followed. Typically, citrus is able to store considerable quantities of nutrients in the tree. Sampling leaves from trees more frequently than once a year in the fall is usually unnecessary. A single annual sample in the fall provides ample time for detecting and correcting developing deficiencies.
Table 1. Mineral nutrition standards for leaves from mature orange trees based on dry-weight concentration of elements in 4 to 7 month old spring flush leaves from non-fruiting branch terminals.
element |
unit |
deficiency |
low |
optimum |
high |
excess |
|
|
|
|
|
|
|
N |
% |
2.2 |
2.2-2.4 |
2.5-2.7 |
2.7-2.8 |
3.0 |
P |
% |
0.9 |
0.9-0.11 |
0.12-0.16 |
0.17-0.29 |
0.3 |
K (Calif.*) |
% |
0.40 |
0.40-0.69 |
0.70-1.09 |
1.1-2.0 |
2.3 |
K (Florida*) |
% |
0.7 |
0.7-1.1 |
1.2-1.7 |
1.8-2.3 |
2.4 |
Ca |
% |
1.5 |
1.6-2.9 |
3.0-5.5 |
5.6-6.9 |
7.0 |
Mg |
% |
0.16 |
0.16-0.25 |
0.26-0.6 |
0.7-1.1 |
1.2 |
S |
% |
0.14 |
0.14-0.19 |
0.2-0.3 |
0.4-0.5 |
0.6 |
Cl |
% |
? |
? |
<0.03 |
0.4-0.6 |
0.7 |
Na |
% |
? |
? |
<0.16 |
0.17-0.24 |
0.25 |
B |
ppm |
21 |
21-30 |
31-100 |
101.260 |
260 |
Fe |
ppm |
36 |
36-59 |
60-120 |
130-200 |
250? |
Mn |
ppm |
16 |
16-24 |
25-200 |
300-500? |
1000 |
Zn |
ppm |
16 |
16-24 |
25-100 |
110-200 |
300 |
Cu |
ppm |
3.6 |
3.6-4.9 |
5 - 16 |
17-22? |
22 |
*California and Florida recommendations for K are sufficiently different that they are presented separately. The California standards are based on production of table navels and Valencias, and those for Florida were developed primarily for juice oranges like Valencia.
The sampled leaves should be placed in a paper bag, and protected from excessive heat (like in a hot trunk or cab) during the day. If possible, find a laboratory that will wash the leaves as part of their procedure instead of requiring the sampler to do this. Leaf samples can be held in the refrigerator (not the freezer) overnight. Leaves should be taken to the lab for washing and analysis as quickly as is feasible.
Often separate samples are taken within a block if areas exist that appear to have special nutrient problems. The temptation encountered in sampling areas with weak trees is to take the worst looking, most severely chlorotic or necrotic leaves on the tree. Selecting this type of leaf may be counter-productive in that the tree may have already reabsorbed most of the nutrients from these leaves before they were sampled. A leaf-tissue analysis based on leaves like this often results in a report of general starvation, and the true cause of the tree decline if the result of a single nutritional deficiency may not be obvious. Often in weak areas, it is beneficial to sample normal appearing or slightly affected leaves. If the problem is a deficiency, the nutrient will, generally, be deficient in the healthy-looking tissue as well.
Groves of early navels that are not normally treated with copper and lime as a fungicide should include an analysis for copper. Copper deficiency is a real possibility on trees growing in sandy, organic, or calcareous soils. For later harvested varieties, leaves should be sampled before fall fungicidal or nutritional sprays are applied because nutrients adhering to the exterior of leaves will give an inaccurate picture of the actual nutritional status of the tree.
Usually leaf samples taken from trees deficient in nitrogen will overestimate the true quantity of nitrogen storage in the trees. Trees deficient in nitrogen typically rob nitrogen from older leaves to use in the production of new leaves. Frequently, by the time fall leaf samples are collected in nitrogen deficient groves, these spent spring flush leaves have already fallen. Nitrogen deficient trees typically have thin-looking canopies as a result of this physiological response. Since the spring flush leaves are no longer present on the tree in the fall when leaves are sampled, younger leaves are often taken by mistake for analysis. These leaves are higher in nitrogen than the now missing spring flush leaves would have been and provide an inaccurately higher nitrogen status in the grove than actually exists.
Critical levels for leaf-nitrogen for some varieties of citrus, like the grapefruits, pummelos, pummelo x grapefruit hybrids and the mandarins, have not been investigated as well as those for oranges. However, the mineral nutrient requirements of most citrus varieties are probably similar to those for sweet oranges presented in Table 1, except for lemons, where the recommended nitrogen dry-weight percentage is in the range of 2.2- 2.4%.
A complete soil sample in conjunction with the leaf sample can provide valuable information on the native fertility of the soil with respect to some mineral nutrients and information on how best to amend the soil if necessary to improve uptake of fertilizers and improve water infiltration.
P.S. from Ben Faber
What has been said here about citrus is also generally true for avocado, although the nitrogen sufficiency levels are lower than for citrus. For a more detailed discussion see: http://www.californiaavocadogrowers.com/sites/default/files/documents/11-Final-Report-Issued-Giving-Tools-for-Fertilization-and-Salinity-Management-Winter-2016.pdf
Photo: Nitrogen deficient avocado leaf
nitrogen avocado
Potassium and Disease in Berries
Continuing on with my perusal of the relation of fertility and plant disease out of the excellent “Mineral Nutrition and Plant Disease” by looking at potassium (K) this week. For the record, while I do a lot of reading in this area lately, don't get the impression that this is all I read about! For example I recently finished reading “The Iliad” written by the poet Homer (not in the original Greek though).
There is actually not that much to say about the relationship of potassium and plant disease. The only thing that came out of this chapter that could be relevant to us berry people is that K fertilization has been shown to reduce the severity of vascular wilts in several crop plants caused by Verticillium, but only in situations when it is deficient in the soil. When K is sufficient (something around 200 ppm K and above) in the soil, the disease mitigation benefit of potassium additions is not realized. Too, the effectiveness of the K additions is going to depend on the host plant resistance to the disease, as well as the amount of disease inoculum in the soil.
Bottom line is I'm not seeing a lot for us here. Most of our soils on the Central Coast are close to 200 ppm K or well above (see the link to an excellent survey in the Salinas Valley below), so a benefit in the way of vascular disease resistance through the use of more potassium fertilizer doesn't seem to hold a lot of promise.
//ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=6029