Brix over time

[Frosti]

I've been looking into the weather data for my area and I found something peculiar.
The data I've looked at is from a weather station about 25 km (15 miles) away from my growing location.

For comparison's sake I averaged the brix values from the three plants with the most data points (5-24, 17-24, and 18-24)

The sweetness of the fruits generally doesn't change instantaneously but rather gradually.
So it was not surprising to find that the correlation between the sweetness and any weather metric averaged over a certain time period was higher than the correlation between the sweetness and raw data points for a weather metric.

The metric with the highest absolute correlation to brix turned out to be the average daily rainfall over the last 42 days.
The correlation coefficient is +0.83

real_avg_brix_F3_avg_rainfall_42d_20250106.png

Average daily hours of full sun over the last 70 days with a correlation coefficient of -0.79:

real_avg_brix_F3_avg_sunshine_h_70d_20250106.png

Average daily minimum air temperature at ground level over the last 77 days with a correlation coefficient of -0.77:

real_avg_brix_F3_avg_min_air_temp_ground_77d_20250106.png

it seems my tomatoes don't like nice weather?
Jokes aside, I believe this is a case of correlation != causation. Since all of the tomato plants were grown in containers they had to be watered by hand, which was not recorded at all. Some rain reached the plants so in weeks with cloudy weather and a bit of rain multiple days could go by without hand watering, while there were also days with scorching sun where watering even once a day seemed not enough. Of course hand watering flooded the plants with a lot a water, instead of the slow water feeding rain causes, which decreased the sweetness.

At least that's how I interpret this. Any thoughts?

[Uncle_Feist]

On brix.
I was able to not only see but also taste the improvement in fruit flavor and quality years ago by using high quality nitrate nitrogen fertilizers in my mater and melon crops, especially by using KN03. I discontinued cheaper ammoniacal and urea sources of N and have never looked back. Another thing I learned quite by accident, was that sulphur boosted sugars and overall flavor. I'm blessed to have a sulphur spring that I use as a source for irrigation water, but the same thing can be accomplished by feeding epsom salt.

Here is an article discussing how crop nutrition affects fruit flavor. There are related articles at the bottom of the page.
https://www.yara.us/crop-nutrition/toma ... 20of%204.5.

[Frosti]

Hmm, nutrition is another thing I haven't recorded systematically... thanks for the link!

What high quality nitrogen fertilizer are you using in particular?

[MrBig46]

On brix.
I was able to not only see but also taste the improvement in fruit flavor and quality years ago by using high quality nitrate nitrogen fertilizers in my mater and melon crops, especially by using KN03. I discontinued cheaper ammoniacal and urea sources of N and have never looked back. Another thing I learned quite by accident, was that sulphur boosted sugars and overall flavor. I'm blessed to have a sulphur spring that I use as a source for irrigation water, but the same thing can be accomplished by feeding epsom salt.

Here is an article discussing how crop nutrition affects fruit flavor. There are related articles at the bottom of the page.
https://www.yara.us/crop-nutrition/toma ... 20of%204.5.

Thanks for the link to that interesting article.
Vladimír

[MrBig46]

"it seems my tomatoes don't like nice weather?" Yes, that is a true statement, even with evidence. With tomatoes it is like this: When the weather is nice, tomatoes grow quickly and also need a lot of water for that growth (frequent watering). The sugars and all the important substances for taste are then diluted in these tomatoes and the tomatoes lose their taste.

There are two tricks to growing sweeter tomatoes:
raise the EC and keep the potassium-to-nitrogen ratio high. EC stands for electrical conductivity. Distilled water doesn’t conduct electricity; it has an EC of about zero. But the higher the concentration of minerals in the water, the more it conducts electricity, and the higher the EC. There is a direct relationship between the EC and the sugar content of the fruit. Higher EC equals more sugar. When you raise the EC by adding more minerals, the nutrient solution becomes “saltier” and the roots have more difficulty taking up water. So the sugars, organic acids, and vitamins condense and accumulate in the fruit. In fact, if you raise the EC high enough, you can actually double the lycopene (red pigment) content of the tomato, making it all red! The fruit may be a little smaller, but it is packed with nutrients and flavor.
Another trick is to increase the potassium to nitrate ratio in the nutrient solution. Potassium is a catalyst for carbohydrate metabolism in the plant, while nitrate to nitrogen depletes sugars in favor of vegetative growth. So, if you want to grow sweeter tomatoes, make sure the potassium:nitrate ratio is at least two to one. Again, during heavy budding and flowering, plants can significantly reduce potassium levels in the nutrient solution and create a potassium deficiency. If tomatoes are potassium deficient, the fruit will be watery, low in sugar, and have poor shelf life. So during the generative phase, I like to top up the supply with potassium whenever I add water between tank changes. Keeping potassium levels high ensures that I am consistently growing the best of the best! Water-soluble potassium sulfate is a great aid for growing sweeter tomatoes. Make sure you are using a pure, high-quality potassium supplement with a fine particle size (<0.015 mm). Fine particles dissolve faster and are better suited for irrigation or foliar spraying. Potassium sulfate will also help raise EC without adding additional nitrate nitrogen! How high is too high when raising EC? This depends on the plant and environmental conditions. If the leaves start to curl slightly, it is usually fine, but if the leaves start to curl and turn brown at the edges, it is too high. Stress is good, but too much stress will land you in the hospital! Gradually increase EC with potassium supplements until you find the ideal dose for the sweetest fruit.
I read somewhere that the optimal conductivity for tomatoes should be somewhere around 4mS (source some Spanish website). Last year I set up an experiment to test this theory, but in the end I abandoned it due to my health problems. I have an EC meter, but I don't know if I'll ever get around to it. I chose potassium salt KCl as the fertilizer. Adding a certain amount of this salt to each watering will probably be beyond my son's capabilities.
Vladimír

[bower]

So, the observations about potassium and sweetness could help to explain Frosti's results, insofar as high temperatures can affect the plant's ability to absorb potassium.
Potassium is a bit of a 'goldilocks' in its own right.
https://extension.umd.edu/resource/toma ... tassium-0/
I had some better references to this when I had ripening issues a few years ago, but don't have them at hand. Failure to take up potassium can happen in multiple conditions: too much sun, not enough sun, high temp, low temp, etc.

[Frosti]

So, the observations about potassium and sweetness could help to explain Frosti's results, insofar as high temperatures can affect the plant's ability to absorb potassium.
Potassium is a bit of a 'goldilocks' in its own right.
https://extension.umd.edu/resource/toma ... tassium-0/
I had some better references to this when I had ripening issues a few years ago, but don't have them at hand. Failure to take up potassium can happen in multiple conditions: too much sun, not enough sun, high temp, low temp, etc.

The tomatoes were in pots in a paved card next to a south facing wall. So yes, temperatures could habe played a huge (indirect) role

[Frosti]

"it seems my tomatoes don't like nice weather?" Yes, that is a true statement, even with evidence. With tomatoes it is like this: When the weather is nice, tomatoes grow quickly and also need a lot of water for that growth (frequent watering). The sugars and all the important substances for taste are then diluted in these tomatoes and the tomatoes lose their taste.

There are two tricks to growing sweeter tomatoes:
raise the EC and keep the potassium-to-nitrogen ratio high. EC stands for electrical conductivity. Distilled water doesn’t conduct electricity; it has an EC of about zero. But the higher the concentration of minerals in the water, the more it conducts electricity, and the higher the EC. There is a direct relationship between the EC and the sugar content of the fruit. Higher EC equals more sugar. When you raise the EC by adding more minerals, the nutrient solution becomes “saltier” and the roots have more difficulty taking up water. So the sugars, organic acids, and vitamins condense and accumulate in the fruit. In fact, if you raise the EC high enough, you can actually double the lycopene (red pigment) content of the tomato, making it all red! The fruit may be a little smaller, but it is packed with nutrients and flavor.
Another trick is to increase the potassium to nitrate ratio in the nutrient solution. Potassium is a catalyst for carbohydrate metabolism in the plant, while nitrate to nitrogen depletes sugars in favor of vegetative growth. So, if you want to grow sweeter tomatoes, make sure the potassium:nitrate ratio is at least two to one. Again, during heavy budding and flowering, plants can significantly reduce potassium levels in the nutrient solution and create a potassium deficiency. If tomatoes are potassium deficient, the fruit will be watery, low in sugar, and have poor shelf life. So during the generative phase, I like to top up the supply with potassium whenever I add water between tank changes. Keeping potassium levels high ensures that I am consistently growing the best of the best! Water-soluble potassium sulfate is a great aid for growing sweeter tomatoes. Make sure you are using a pure, high-quality potassium supplement with a fine particle size (<0.015 mm). Fine particles dissolve faster and are better suited for irrigation or foliar spraying. Potassium sulfate will also help raise EC without adding additional nitrate nitrogen! How high is too high when raising EC? This depends on the plant and environmental conditions. If the leaves start to curl slightly, it is usually fine, but if the leaves start to curl and turn brown at the edges, it is too high. Stress is good, but too much stress will land you in the hospital! Gradually increase EC with potassium supplements until you find the ideal dose for the sweetest fruit.
I read somewhere that the optimal conductivity for tomatoes should be somewhere around 4mS (source some Spanish website). Last year I set up an experiment to test this theory, but in the end I abandoned it due to my health problems. I have an EC meter, but I don't know if I'll ever get around to it. I chose potassium salt KCl as the fertilizer. Adding a certain amount of this salt to each watering will probably be beyond my son's capabilities.
Vladimír

very fascinating insight, thank you so much! I'm pretty sure I'll have to read this post many times

[MrBig46]

I just want to point out that I am not the author of the text. I have it translated into Czech and downloaded to my computer. I only know that the original text was English, I don't know the website anymore. So this is a back translation from Czech to English.
Vladimír

[Uncle_Feist]

Hmm, nutrition is another thing I haven't recorded systematically... thanks for the link!

What high quality nitrogen fertilizer are you using in particular?

Mainly potassium nitrate,(13.7-0-46) but I also use some calcium nitrate. (15.5-0-0)

[Frosti]

I just want to point out that I am not the author of the text. I have it translated into Czech and downloaded to my computer. I only know that the original text was English, I don't know the website anymore. So this is a back translation from Czech to English.
Vladimír

No worries, this isn't academia

[MrBig46]

I think that using nitrogen fertilizers is not good for increasing sweetness, see the article: "nitrates deplete sugars in favor of vegetative growth". Everyone has to decide if they want sweeter tomatoes or a high yield.
Vladimír

[Uncle_Feist]

I think that using nitrogen fertilizers is not good for increasing sweetness, see the article: "nitrates deplete sugars in favor of vegetative growth". Everyone has to decide if they want sweeter tomatoes or a high yield.
Vladimír

Overuse of ammoniacal or urea forms of nitrogen maybe, but that has not been my finding over the years using nitrate forms of nitrogen. A healthy, and well fed crop has always yielded more and better flavored fruit for me.

"K plays a crucial role in various physiological processes, including sugar metabolism. N on the other hand, is a primary component of amino acids, proteins, and nucleic acids, all of which are involved in sugar metabolism. Studies have shown that the combined application of K and N promotes sugar synthesis and accumulation in plants. An integrative effect of N and K helps increase plant growth and development which ultimately improves the sugar contents specifically Sucrose contents in plants."

[MrBig46]

"An integrative effect of N and K helps increase plant growth and development"
I read it like this:
The combination of N and K certainly supports plant growth. If Google translates it correctly for me, it is not about tomato fruits, but about plants in general. But for that growth, nice weather and a lot of water are also needed. Then the question remains whether the ratio of sugars to water will change and how. In my opinion, if I were to assume that the same reaction to K and N will be in the fruits, then the fruits will certainly be watery with a lower Brix.
Vladimír

[MrBig46]

Measuring Brix in cherry tomatoes is not a problem. The tomato is cut open, the liquid is squeezed out and placed on the surface of the refractometer. If I want to measure Brix in steaks, it is not so simple. Steaks usually have juicy meat and a small number of locules filled with seeds and juice. Obtaining a sample corresponding to the whole tomato for measurement is a problem. I see a possibility in that part of the tomato can be frozen in the freezer, which will suspend all enzymatic and other processes. After thawing, it should be possible to simply squeeze out the liquid, which would then be measured for Brix.
I did an experiment. I squeezed out the liquid from a purchased Roma tomato, measured the sweetness - Brix 5. I put the juice in the freezer for 24 hours, then thawed it in the microwave for 30 seconds, immediately after that I measured the sweetness - Brix 5. Conclusion - freezing does not affect the sweetness.
Vladimír

[Frosti]

Nice, good to know!

[MrBig46]

The taste of a tomato is determined by sweetness, various aromatic substances and also acids. If I succeed in my intended project of measuring the sweetness (Brix) of individual Dwarfs, I would like to expand it to measuring their pH (acidity).
Vladimír

[Frosti]

true, how do you plan on measuring the acidity? Any experience with any of the available devices? If there's one that's easy and quick to clean, I might just get one for myself as well

[MrBig46]

I bought an electronic pH meter online. It cost me about 500 CZK (20 US dollars), including calibration solutions. Range from 0 to 14 pH. In the range of 3 to 7 pH, it should be accurate, with a deviation of */- 0.1 pH. I already measured with it last year, but I had a problem preparing samples. This year I want to take advantage of the freezing and I have already thought about how to take a sample from large beefsteak tomatoes so that it corresponds to the whole tomato (just like for measuring Brix and pH).
Vladimír

[Harry Cabluck]

Vladimir, Wishing you a comfortable and successful recovery! Have enjoyed reading about your use of measuring devices and also importance of potassium in feeding tomatoes.