Soil Test for Tomato Bed: Question

GaryStPaul · June 23, 2012

I've decided to do what I've never done but always intended to do, namely have my soil tested by the University of Minnesota agricultural extension dept. They have a home vegetable garden test for $15, which evaluates soil fertility (NPK), pH, and percentage of organic matter. For $5 extra, they'll also do a "soluble salt test," which analyzes for "problems due to excessive salts or fertilizer materials." Any of you with experience here: Do you think the soluble salts test would be worth doing? One of the questions on the form is: what plants are you growing, so I assume they'll take that into account when making their recommendations.

I'm growing 90 tomatoes this year, 28 in-ground. It's soil from this bed I'll be sending in. The proximate reason for this is that, while healthy, these 28 plants seem to be lagging behind (based mainly on height) plants I gave to friends which have grown a good foot higher, though the fact that they were planted out 7 days earlier than mine may help to account for the difference. I grow tomatoes in this bed year after year, amending the soil with fresh compost each year (and this year with additional topsoil from raised beds elsewhere on my property). I don't really know if anything is "wrong," but I assume the soil test will help me assess that. I planted out on May 16; as of today most of the in-ground plants average 32" or so.

Thanks in advance for any advice or suggestions.

Gary

PaulF · June 23, 2012

From what I understand about soluble salts in Minnesota, western Mn. would have more of a problem than St. Paul. That being said, if your garden has contact with deicing salts, high levels of fertilizer, excessive pet urine or other similar urine or feces you may have a salt problem. High salt levels will retard growth and reduces the plant's ability to take up water.

I think the solution is to flush out the soil (I don't know exactly how to do this) with good clean water. Soil tests taken now would give you things to do for next year rather than this year. Adding N, P or K can be done with a side dressing. It sounds like you all the right things for your garden and it is doubtful there is a problem. For peace of mind it is only a few more dollars to see about soluble salt.

Remember, the extension people are more the experts particularly in your area and the above is just my opinion.

GaryStPaul · June 24, 2012

Thanks, Paul. You're right: for five bucks more I might learn something useful.

fortyonenorth · June 24, 2012

Gary,

If you haven't tested your soil previously--or if it's been a number of years--I would highly recommend getting a test that includes the major cations (calcium, magnesium, etc.) and micronutrients, in addition to NPK, %OM, and pH. Here's why.

First, nitrogen is almost impossible to determine with any certainty because it is so dynamic in the soil. Most labs don't even report it. It's prone to volatilization, leaching and can vary based on environmental factors such as temperature and moisture.

Second, manures and composts are good sources of phosphorus and potassium. So, if you've been adding these regularly, they probably aren't a limiting factor for you.

Third, knowing the absolute and relative levels of the major cations (especially calcium and magnesium) in your soil is critical. Among other factors, this information will help to determine what type of lime to add, if indeed you need to lime at all.

Finally, necessary nutrients such as boron, copper, zinc, manganese are deficient in many soils. Maintaining their levels will help optimize yield, quality and disease resistance.

If the UM Ag Ext. offers a more thorough test that includes this information, I'd opt for that. If not, choose a private lab such as Logan Labs or Spectrum Analytics. I use Logan's "standard soil test" and have been very happy with it. It costs $20 and provide all the info you need. For an extra $30 you can have your test evaluated by an agronomist. Or, if you decide to go this route, I'd be happy to interpret the results and provide recommendations. I'm not an expert, but I've been using Logan for a number of years and I'm acquainted with translating their test results into real-world applications.

Good luck!

June 23, 2012	#1
GaryStPaul Tomatovillian™ Join Date: Mar 2008 Location: St Paul, MN Posts: 158	Soil Test for Tomato Bed: Question I've decided to do what I've never done but always intended to do, namely have my soil tested by the University of Minnesota agricultural extension dept. They have a home vegetable garden test for $15, which evaluates soil fertility (NPK), pH, and percentage of organic matter. For $5 extra, they'll also do a "soluble salt test," which analyzes for "problems due to excessive salts or fertilizer materials." Any of you with experience here: Do you think the soluble salts test would be worth doing? One of the questions on the form is: what plants are you growing, so I assume they'll take that into account when making their recommendations. I'm growing 90 tomatoes this year, 28 in-ground. It's soil from this bed I'll be sending in. The proximate reason for this is that, while healthy, these 28 plants seem to be lagging behind (based mainly on height) plants I gave to friends which have grown a good foot higher, though the fact that they were planted out 7 days earlier than mine may help to account for the difference. I grow tomatoes in this bed year after year, amending the soil with fresh compost each year (and this year with additional topsoil from raised beds elsewhere on my property). I don't really know if anything is "wrong," but I assume the soil test will help me assess that. I planted out on May 16; as of today most of the in-ground plants average 32" or so. Thanks in advance for any advice or suggestions. Gary

June 23, 2012	#2
PaulF Tomatovillian™ Join Date: Jan 2006 Location: Brownville, Ne Posts: 3,292	From what I understand about soluble salts in Minnesota, western Mn. would have more of a problem than St. Paul. That being said, if your garden has contact with deicing salts, high levels of fertilizer, excessive pet urine or other similar urine or feces you may have a salt problem. High salt levels will retard growth and reduces the plant's ability to take up water. I think the solution is to flush out the soil (I don't know exactly how to do this) with good clean water. Soil tests taken now would give you things to do for next year rather than this year. Adding N, P or K can be done with a side dressing. It sounds like you all the right things for your garden and it is doubtful there is a problem. For peace of mind it is only a few more dollars to see about soluble salt. Remember, the extension people are more the experts particularly in your area and the above is just my opinion. __________________ there's two things money can't buy; true love and home grown tomatoes.

June 24, 2012	#3
GaryStPaul Tomatovillian™ Join Date: Mar 2008 Location: St Paul, MN Posts: 158	Thanks, Paul. You're right: for five bucks more I might learn something useful.

June 24, 2012	#4
fortyonenorth Tomatovillian™ Join Date: Jan 2010 Location: NW Indiana Posts: 1,150	Gary, If you haven't tested your soil previously--or if it's been a number of years--I would highly recommend getting a test that includes the major cations (calcium, magnesium, etc.) and micronutrients, in addition to NPK, %OM, and pH. Here's why. First, nitrogen is almost impossible to determine with any certainty because it is so dynamic in the soil. Most labs don't even report it. It's prone to volatilization, leaching and can vary based on environmental factors such as temperature and moisture. Second, manures and composts are good sources of phosphorus and potassium. So, if you've been adding these regularly, they probably aren't a limiting factor for you. Third, knowing the absolute and relative levels of the major cations (especially calcium and magnesium) in your soil is critical. Among other factors, this information will help to determine what type of lime to add, if indeed you need to lime at all. Finally, necessary nutrients such as boron, copper, zinc, manganese are deficient in many soils. Maintaining their levels will help optimize yield, quality and disease resistance. If the UM Ag Ext. offers a more thorough test that includes this information, I'd opt for that. If not, choose a private lab such as Logan Labs or Spectrum Analytics. I use Logan's "standard soil test" and have been very happy with it. It costs $20 and provide all the info you need. For an extra $30 you can have your test evaluated by an agronomist. Or, if you decide to go this route, I'd be happy to interpret the results and provide recommendations. I'm not an expert, but I've been using Logan for a number of years and I'm acquainted with translating their test results into real-world applications. Good luck!