EC value for fertigation of tomatoes

Jarrod King · May 2, 2017

What EC value would you recommend for continuous drip fertigation over tomatoes growing in very sandy soil?

I don't want to go so high they are burned but I want to explore pretty high level fertilization this way.

http://www.homehydrosystems.com/ph_t...bles_page.html

That chart says 2-5 for hydroponics but says values for soil will be different. How different?

This https://www.nrcs.usda.gov/Internet/F...2p2_053280.pdf says soil levels of >2.5 lead to decreased yield but I don't know how to predict how the fertigation liquid will change the soil saturated paste EC value.

PureHarvest · May 2, 2017

A lot of us use a 3 part mix of 4-18-38 + Calcium Nitrate + Magnesium Sulfate. The label at full strength would be an EC of 2.27. This is for soil-less media though.

https://hydro-gardens.com/product/to...s-bag-4-18-38/

You would have to calculate how many pounds of each element you want to deliver each week and mix accordingly.

I could give you a simplified explanation of this when figuring for one element like N, P, or K, but it would get cumbersome when you look at all the elements in the mix.

This will show you a fertigation schedule for N and K in soil. Go to page F 208. Of course it is all in pound PER ACRE, so we'd have to reduce down to your footprint. Then divide your size by the percentage of the element.
https://cdn.extension.udel.edu/wp-co...5/Tomatoes.pdf

Example you have 1,500 sqft. That is .03 acres (1,500/43,560). When the chart shows, for example, that you want 3.5 lbs of N/acre in week 1, multiply the 3.5 by .03 =.1 lbs of N. BUT not .1 lbs of your fertilizer. That is .1 lbs of actual n. So, .1/the percent N of your fert=actual pounds.
If you used cal nitrate (15% N) it would be .1/.15=.66 lbs of calcium nitrate to deliver .1 lbs of actual N for week one's N needs. You could split this into any number of feedings over the week or do it once.
But then you are missing out on the P, K, Mag, etc.
You could do the 3 part mix mentioned at the top of my post and get all of the needs met, but I'd have to figure out how to tell you on how much you'll need to mix at each feeding per your square footage.
I thought I had seen a soil rec for the Masterblend version of 4-18-38, but can not find that via google right now.

AKmark · May 2, 2017

Your question is almost impossible to determine without a soil sample. As PH mentioned, the 4-18-38, 2.27 recommendation is for soil-less, and I will add that the high EC is for Dutch varieties which can tolerate more N. We get the last 200 PPM with KNO3, heirlooms do not like the high N that comes with getting our EC's to 2.27. With that said, you will most likely fry your soil grown tomatoes with that high od an EC.
I usually use about a half strength (in soil) of the same blend, and it is still too strong for some varieties.

Ricky Shaw · May 2, 2017

mark, might be kind of similar. How'd you feed those potted up plants you half stuck in the ground a couple years ago. And did you cut the bottoms out of those bags? Seemed they did well.

AKmark · May 2, 2017

Quote:

Originally Posted by Ricky Shaw

mark, might be kind of similar. How'd you feed those potted up plants you half stuck in the ground a couple years ago. And did you cut the bottoms out of those bags? Seemed they did well.

I ran those at about 1200PPM, and even that was too much to use all the time. I did cut the bottoms out, and that works great in the north.

PureHarvest · May 3, 2017

Quote:

Originally Posted by AKmark

Your question is almost impossible to determine without a soil sample. As PH mentioned, the 4-18-38, 2.27 recommendation is for soil-less, and I will add that the high EC is for Dutch varieties which can tolerate more N. We get the last 200 PPM with KNO3, heirlooms do not like the high N that comes with getting our EC's to 2.27. With that said, you will most likely fry your soil grown tomatoes with that high od an EC.
I usually use about a half strength (in soil) of the same blend, and it is still too strong for some varieties.

Mark, even though they don't supposedly like it, do you still go with Dutch rates on your heirlooms? I'm sure we've covered this before, but wanted to clarify. I'll be dialing in my injector this weekend, and want to have a plan for how I will step things up once I get through the seedling rate. First blossoms will probably open today.

AKmark · May 3, 2017

Quote:

Originally Posted by PureHarvest

Mark, even though they don't supposedly like it, do you still go with Dutch rates on your heirlooms? I'm sure we've covered this before, but wanted to clarify. I'll be dialing in my injector this weekend, and want to have a plan for how I will step things up once I get through the seedling rate. First blossoms will probably open today.

I have tried it, but they don't yield as well, I run about 1600 as a compromise for now, and that is still too much for some varieties. They get very thick stems/ bully, as a sign.
In the future I am separating some varieties from others, since I am all but done with trying new heirlooms. Try Aker's West Virginia at 1700PPM, that's a conversation piece.

BigVanVader · May 3, 2017

Quote:

Originally Posted by AKmark

I have tried it, but they don't yield as well, I run about 1600 as a compromise for now, and that is still too much for some varieties. They get very thick stems/ bully, as a sign.
In the future I am separating some varieties from others, since I am all but done with trying new heirlooms. Try Aker's West Virginia at 1700PPM, that's a conversation piece.

So I'm doing TTF+Calcium Nitrate in ground, should I just go for 1200 PPM since it is all kinds of heirlooms?

Ricky Shaw · May 3, 2017

It's the measured control of nutrients that's so different about growing soilless in containers vs in-ground. With containers you're feeding continuous, and ideally at rate that's no less or no more than you need to avoid underfeeding or fert build-up. It also makes the assumption that dilution from run-off isn't a factor and the media passes nutrients freely.

I'd imagine it's tough to get that exactness with soil/dirt or in-ground because of differences in compaction, and rain if outside. I'd start at an EC 1000-1200/ mhos 1.0 to 1.2 and monitor new growth and the oldest leaves, they're the first to show.

Jarrod King · May 3, 2017

Thank you so much for all the great answers!

Cole_Robbie · May 3, 2017

One of the other soil variables is humate content. Dark soil, high in organic matter and humates will uptake nutrients faster and do more with less. The easiest soil to dial-in a "perfect" number would be pure sand, like the way a lot of Florida strawberries and tomatoes are grown.

I would guess that perfect number may also vary between tomato varieties, and even with weather. The right number when it's cold and cloudy, I would guess at least, would be different than on a hot sunny day. Very hot weather may also require not fertigating with every single watering, or lowering the dose because you have to give them a lot more water.

AKmark · May 3, 2017

Quote:

Originally Posted by Cole_Robbie

One of the other soil variables is humate content. Dark soil, high in organic matter and humates will uptake nutrients faster and do more with less. The easiest soil to dial-in a "perfect" number would be pure sand, like the way a lot of Florida strawberries and tomatoes are grown.

I would guess that perfect number may also vary between tomato varieties, and even with weather. The right number when it's cold and cloudy, I would guess at least, would be different than on a hot sunny day. Very hot weather may also require not fertigating with every single watering, or lowering the dose because you have to give them a lot more water.

Yes, humic and fulvic are the organic gardeners version of chelated micro elements, that is why they work.

BVV, that is hard to answer, I do suggest caution, then observation, since you understand what a tomato plant should look like.

BigVanVader · May 3, 2017

Ok thanks. I feel like I can use a lot of CaN because soil test said "Before planting, broadcast and work into the soil either 6 lbs calcium nitrate (15.5-0-0) or 3 lbs 34-0-0 per 1,000 square feet (or for each 300 feet of row). Three weeks after appearance of first new leaves, apply four inches from base of the plants, either 10 lbs calcium nitrate (15.5-0-0) or 5 lbs 34-0-0 per 300 feet or row in a continuous band. For organic gardening recommendations, please call the Home and Garden Information Center at 1-888-656-9988 between 9:00 a.m. and 1:00 p.m. during the workweek."

PureHarvest · May 4, 2017

Quote:

Originally Posted by AKmark

I have tried it, but they don't yield as well, I run about 1600 as a compromise for now, and that is still too much for some varieties. They get very thick stems/ bully, as a sign.
In the future I am separating some varieties from others, since I am all but done with trying new heirlooms. Try Aker's West Virginia at 1700PPM, that's a conversation piece.

Thanks Mark.
So the 2nd and final stage of the heirloom schedule leaves off the 1.6 ounces of potassium nitrate and extra ounce of mgso4 in the final mix for Dutch. Do you cut those in half or so to provide some KNO3 and MGSO4 without going above 1600 ppm?

AKmark · May 4, 2017

Quote:

Originally Posted by PureHarvest

Thanks Mark.
So the 2nd and final stage of the heirloom schedule leaves off the 1.6 ounces of potassium nitrate and extra ounce of mgso4 in the final mix for Dutch. Do you cut those in half or so to provide some KNO3 and MGSO4 without going above 1600 ppm?

I use more MgSO4 than recommended, and I trimmed my fert mix back a touch, I have some micro elements that are a bit high, my K and N are both on the safe side, so I use KNO3 at about 1.6. I have extra long days, my mix is going to be slightly different than yours. If I used the recommended MgSo4 I think my plants would die. LOL
Do a leaf sample, you can tailor your mix for your situation with no guessing.

May 2, 2017	#1
Jarrod King Tomatovillian™ Join Date: Feb 2015 Location: Norman, OK Posts: 23	EC value for fertigation of tomatoes What EC value would you recommend for continuous drip fertigation over tomatoes growing in very sandy soil? I don't want to go so high they are burned but I want to explore pretty high level fertilization this way. http://www.homehydrosystems.com/ph_t...bles_page.html That chart says 2-5 for hydroponics but says values for soil will be different. How different? This https://www.nrcs.usda.gov/Internet/F...2p2_053280.pdf says soil levels of >2.5 lead to decreased yield but I don't know how to predict how the fertigation liquid will change the soil saturated paste EC value. Last edited by Jarrod King; May 2, 2017 at 01:15 PM.

May 2, 2017	#2
PureHarvest Tomatovillian™ Join Date: Mar 2014 Location: Mid-Atlantic right on the line of Zone 7a and 7b Posts: 1,369	A lot of us use a 3 part mix of 4-18-38 + Calcium Nitrate + Magnesium Sulfate. The label at full strength would be an EC of 2.27. This is for soil-less media though. https://hydro-gardens.com/product/to...s-bag-4-18-38/ You would have to calculate how many pounds of each element you want to deliver each week and mix accordingly. I could give you a simplified explanation of this when figuring for one element like N, P, or K, but it would get cumbersome when you look at all the elements in the mix. This will show you a fertigation schedule for N and K in soil. Go to page F 208. Of course it is all in pound PER ACRE, so we'd have to reduce down to your footprint. Then divide your size by the percentage of the element. https://cdn.extension.udel.edu/wp-co...5/Tomatoes.pdf Example you have 1,500 sqft. That is .03 acres (1,500/43,560). When the chart shows, for example, that you want 3.5 lbs of N/acre in week 1, multiply the 3.5 by .03 =.1 lbs of N. BUT not .1 lbs of your fertilizer. That is .1 lbs of actual n. So, .1/the percent N of your fert=actual pounds. If you used cal nitrate (15% N) it would be .1/.15=.66 lbs of calcium nitrate to deliver .1 lbs of actual N for week one's N needs. You could split this into any number of feedings over the week or do it once. But then you are missing out on the P, K, Mag, etc. You could do the 3 part mix mentioned at the top of my post and get all of the needs met, but I'd have to figure out how to tell you on how much you'll need to mix at each feeding per your square footage. I thought I had seen a soil rec for the Masterblend version of 4-18-38, but can not find that via google right now. Last edited by PureHarvest; May 2, 2017 at 02:19 PM.

May 3, 2017	#9
Ricky Shaw Tomatovillian™ Join Date: Aug 2015 Location: Zone 6a Denver North Metro Posts: 1,910	It's the measured control of nutrients that's so different about growing soilless in containers vs in-ground. With containers you're feeding continuous, and ideally at rate that's no less or no more than you need to avoid underfeeding or fert build-up. It also makes the assumption that dilution from run-off isn't a factor and the media passes nutrients freely. I'd imagine it's tough to get that exactness with soil/dirt or in-ground because of differences in compaction, and rain if outside. I'd start at an EC 1000-1200/ mhos 1.0 to 1.2 and monitor new growth and the oldest leaves, they're the first to show. Last edited by Ricky Shaw; May 4, 2017 at 08:03 AM.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

May 2, 2017	#3
AKmark Tomatovillian™ Join Date: Jun 2013 Location: Wasilla Alaska Posts: 2,010	Your question is almost impossible to determine without a soil sample. As PH mentioned, the 4-18-38, 2.27 recommendation is for soil-less, and I will add that the high EC is for Dutch varieties which can tolerate more N. We get the last 200 PPM with KNO3, heirlooms do not like the high N that comes with getting our EC's to 2.27. With that said, you will most likely fry your soil grown tomatoes with that high od an EC. I usually use about a half strength (in soil) of the same blend, and it is still too strong for some varieties.

May 3, 2017	#11
Cole_Robbie Tomatovillian™ Join Date: Jun 2012 Location: Illinois, zone 6 Posts: 8,407	One of the other soil variables is humate content. Dark soil, high in organic matter and humates will uptake nutrients faster and do more with less. The easiest soil to dial-in a "perfect" number would be pure sand, like the way a lot of Florida strawberries and tomatoes are grown. I would guess that perfect number may also vary between tomato varieties, and even with weather. The right number when it's cold and cloudy, I would guess at least, would be different than on a hot sunny day. Very hot weather may also require not fertigating with every single watering, or lowering the dose because you have to give them a lot more water.

May 3, 2017	#13
BigVanVader Tomatovillian™ Join Date: Mar 2014 Location: Greenville, South Carolina Posts: 3,099	Ok thanks. I feel like I can use a lot of CaN because soil test said "Before planting, broadcast and work into the soil either 6 lbs calcium nitrate (15.5-0-0) or 3 lbs 34-0-0 per 1,000 square feet (or for each 300 feet of row). Three weeks after appearance of first new leaves, apply four inches from base of the plants, either 10 lbs calcium nitrate (15.5-0-0) or 5 lbs 34-0-0 per 300 feet or row in a continuous band. For organic gardening recommendations, please call the Home and Garden Information Center at 1-888-656-9988 between 9:00 a.m. and 1:00 p.m. during the workweek."