An evolving view of plant nutrition

One of the hallmarks of science is that our view of the world evolves and changes as new evidence comes to light.  When I was a grade-schooler following the Apollo missions, for example, I knew all the planets in order from Mercury to Pluto and how many moons each one had; Jupiter was the champ with 12.  Today, Jupiter has as many as 63 moons depending on who’s counting.  And Pluto, let’s not even go there.   Likewise, our view of plant science has changed over the years.  As I’ve mentioned before, when I took introductory Botany as an undergrad thirty-some years ago we learned that there were 16 essential plant nutrient elements.  Since then we’ve learned that nickel is also essential at least for some plants.

 

If you took your plant science more than 10 years ago, you also learned that nitrogen is taken up from the soil as either ammonium or nitrate.  This view is now being revised due largely to evidence from the ecological literature.  Ecologists have found that in northern boreal regions where soil temperatures are cold and mineralization and nitrification rates are low, plants will take up intact amino acids from the soil (Nashholm and Persson, 2001; Kielland et al., 2006).  Recent studies have extended these observations to temperate forests (Gallet-Budynek et al., 2009) and horticultural crops. (Ge et al., 2009), indicating that a range of plants may be able to derive a portion of their N requirements directly from organic sources.

 

So what does this have to do with the Garden Professors and the science of landscape horticulture?  First off, this is pretty cool stuff and certainly will cause a lot of re-evaluation of some established paradigms.  From an applied perspective, fertilizing with amino acids and related organic source has some potential benefits.  In warm, well-aerated soils, nitrate-N predominates.  When plants take up nitrate, it must be reduced via nitrate reductase and nitrite reductase before it can be assimilated into amino acids.  These steps require metabolic energy.  In theory, amino acids could bypass the reduction and assimilation processes and provide a more efficient means of fertilization.  At this point, most of the scientific focus is on quantifying how much organic N can be directly taken up from the soil.  Evaluating efficiency of uptake and utilization is a couple steps down the road.  Amino acid fertilization could potentially provide another benefit over nitrate fertilization by reducing nitrate leaching.

 

Of course there’s a potential downside as well.  A quick Google search of ‘amino acid fertilizer’ reveals sites shilling all manner of concoctions for fertilizing plants; many of dubious value.  One of the first sites I hit proclaims that, unlike inorganic fertilizers, their product provides the 70 elements needed for plant growth.  Seventy?!  Well that’s close to seventeen.   Point is be prepared for an ever increasing barrage of claims about organic fertilizers.  There is no doubt that compost and similar organic sources can provide essential plant nutrients and effective fertilizer sources.  As always, however, be skeptical of spectacular claims and secret, proprietary ingredients and pay close attention to the cost of amino acids compared to conventional fertilizers.  There is some science here; clearly many plants have the capacity to take up amino acids directly.  Beyond that we’ve still got a lot to learn.

 

Gallet-Budynek, A., E. Brzostek, V.L. Rodgers, J.M. Talbot, S. Hyzy, and A.C. Finzi. 2009. Intact amino acid uptake by northern hardwood and conifer trees. Oecologia 160:129–138.

 

Ge, T., S. Song, P. Roberts, D.L. Jones, D. Huang, and K. Iwasaki. 2009. Amino acids as a nitrogen source for tomato seedlings: The use of dual-labeled (13C, 15N) glycine to test for direct uptake by tomato seedlings. Environmental and Experimental Botany. Volume 66: 357-361.

 

Kielland K, J. McFarland, and K. Olson. 2006. Amino acid uptake in deciduous and coniferous taiga ecosystems. Plant Soil 288:297–307.

 

T. Näsholm and J. Persson.  2001. Plant acquisition of organic nitrogen in boreal forests, Physiol. Plant 111: 419–426.

Atrazine, The news, And the reality

A paper was recently published in the Proceedings of the National Academy of Sciences which discussed the dangers of one of the most commonly used weed killers in the United States, atrazine.  This paper was written by Tyrone Hayes and colleagues and was immediately embraced by the media because it showed something scary (which the media loves — in case you were wondering).  In a nutshell this study showed that frogs were changed from males to females when they were exposed to relatively small amounts of the herbicide atrazine.  The next day in class I had a student come up to me and ask me about it and what I thought.  I gave him my short answer (class was about to start).  Here’s the longer one, but first I want to present you with some notes which will be important as we proceed.

Science does not provide values, instead it is a tool to use with your own personal value system.  Some people may put a high value on cheaper production of important food crops such as corn, while others may put a high value the absence of potentially dangerous chemicals.  That doesn’t matter to science.  Remember that — science doesn’t give a poop what you care about.  Furthermore, science doesn’t care what past experiments have found — what one researcher finds another may not find.  Who knows why?  That’s just the way things happen.  On with the story.

Atrazine has been around since 1959.  It’s a preemergent herbicide (which means that it kills weed seeds as they germinate) used on a variety of crops, but most frequently on corn.  One of the advantages of atrazine is that it works extremely well in no-till growing systems which are used to reduce erosion.  Another advantage of atrazine is that it’s cheap.  Generally atrazine is considered to have a low toxicity (lower than caffeine for example).  Additionally, though there is some data out there showing that it may cause cancer, this is grossly outweighed by data demonstrating that it isn’t carcinogenic.  But there is data showing that atrazine is a hormone disruptor potentially affecting such hormones as estrogen and testosterone — and this effect is generally considered real — in other words not many scientists dispute it.

Over the years this hormone effect has been seen as a Bad Thing, but not bad enough to warrant banning this useful herbicide.  Then along came Tyrone Hayes — and he started looking at how atrazine affected frogs — despite the recent news surge he has been doing this work for a long time (about 10 years) and has published much of that work.  In a nutshell he is showing that atrazine, and to some extent other chemicals, cause hormone problems in frogs, particularly male frogs.  Sex change and/or hermaphroditic frogs ensue!  Unfortunately (or fortunately depending on how you look at it) other researchers have not been able to show the same things — at least not it the dramatic way that Dr. Hayes has (I’m not implying that they haven’t found problems with atrazine — they have — Dr. Hayes findings just tend to be more dramatic.  Speaking of which, if you ever have the opportunity to see Dr. Hayes give a talk GO!  He is an amazing public speaker and his slides and words make his findings even more dramatic).  There is little to no direct evidence that hormone disruption caused by atrazine is currently affecting humans though many news sources are trying to draw that link.  Indirect evidence is pretty weak too — but not nonexistent.  The European Union banned atrazine in 2001.  Should we follow?

My value judgement follows — yours might be — in fact it probably should be — different.

Here’s what I think.  Ban atrazine, or at least regulate it more tightly.  Why?  Because there are many weeds resistant to it (that’s what happens to old herbicides…). Because there are options which are safer for our ecology (though they are somewhat more expensive). Because this stuff is showing up in groundwater at rates higher than what we’d like to see, and these concentrations will probably continue to rise — a direct result of using the stuff for so many years.  Look, we don’t need to cut farmers off from this stuff right now, lets start a phase-out program and get rid of it over the next five years.  Why not?  If we NEEDED it to produce crops I’d probably be on the other side of the issue, but we don’t, so I reside firmly on the “let’s be cautious about this” side.

Art, Science, and Faith

First of all, who we are and what we do.  All of the Garden Professors are in the business of the science of Horticulture.  What’s Horticulture?  The standard definition of Horticulture is the art and science of tending a garden.  Horticulture is clearly more than science but science is the foundation and underpinning.   For anyone that needs convincing that Horticulture is an art as much as a science I suggest the following exercise.  Go to a major research university and wander through their Botany or Plant Biology greenhouses. Observe the plants.  They look like crap.  The people working there are on the cutting edge of plant science; they sequence genes, they elucidate biochemical pathways but they can’t grow a plant to save their lives.   Now wander through the Horticulture greenhouse; plants are thriving, flowers are blooming.  What’s the difference?  The horticulturalists not only have the science, they have the art.  There is no denying that art and intuition play a role in growing plants, especially in ornamental horticulture where we deal with hundreds of species and cultivars, each with its own subtleties and nuances.  But as educators, especially public funded educators, how do we teach intuition?   It’s very difficult.  What we teach are principles developed through systematic scientific inquiry.  How do we know there are 17 essential elements needed for plant growth?  Repeated experiments over the years.  And our knowledge continues to evolve based on the scientific method.  I’m old enough that I learned 16 essential elements as an undergrad; the need for nickel by some plants had not yet been established.  As extension educators our role is to disseminate science-based information.  For some of us that phrase is even in our job description.  We can try to impart our experience and intuition but it’s a difficult thing.

It can be especially difficult when we deal with alternative systems for which a long-term knowledge base may be lacking.  Despite perceptions to the contrary, we are not apologists for the status quo.  Overuse and misuse of pesticides and fertilizers are rampant, especially in ornamental horticulture.  A lot of our current research and extension programming deals with reducing water and nutrient usage to reduce run-off and to reduce leaching.  I spend a lot of time telling growers things they don’t really want to hear.  How do we know growers are potentially impacting water resources? Because we and others have done the scientific research.  We’ve set out plots, we’ve fertilized, we’ve sampled leachate, we’ve measured run-off.  And we’ve conducted extension programs teaching growers that they can back off fertilization and irrigation rates without reducing crop growth.

Where we get concerned is that some assume or take on faith that because a nutrient source is ‘organic’ or ‘natural’ it’s automatically better or safer for the environment.  Is the nitrate from Chilean nitrate less likely to cause blue baby syndrome then nitrate from ammonium nitrate?   Dr. Corey Reams developed his principles as revealed to him through divine revelation.  Unfortunately most of us are not blessed with such experiences.  Instead we rely on systematic scientific investigation to develop knowledge that we share with our clients.  Personally I do not believe that faith and science are mutually exclusive.  Some of the most brilliant scientists I have met in my career have been people of deep and abiding faith.  But we need to keep each in its context.  Science is knowledge gained through systematic inquiry.  Faith is a belief system.  The central tenets of most Christian denominations are stated in the Nicene Creed which begins, “We believe in one God…”  Note it doesn’t start “We know…” or “We can prove…”  In their liturgy Catholics, “proclaim the mystery of faith; Christ has died, Christ is risen, Christ will come again.”  Not only can they not prove these things they celebrate the fact that it’s a mystery.  Faith does not demand proof.  Science does.

The No-Work Garden Book

Occasionally one of the GPs will blog about a book that’s particulary good – or not.  I was given a copy of Ruth Stout’s No-Work Garden Book a few years ago and frankly hadn’t given much more than a passing glance.  But last week I thumbed through it and was immediately struck by the quality of science this self-taught gardener brought to her writing.

Much of Ruth’s gardening practices included the use of organic mulch on vegetable gardens, and she regularly wrote to scientists to ask for their interpretation of “expert” advice.  Here’s an excerpt from a letter written 50 years ago by Dr. Arthur Pratt from Cornell:

“Yes, leaves, hay, straw, etc. that are not decayed or that are only partially decayed will rob the soil of nitrogen if they are mixed into the soil. But when used on top the way you use them, I have never seen a nitrogen shortage as a result of the mulch.”

So, we’ve known for at least 50 years that organic mulches don’t cause nitrogen deficiencies.  Why does this misconception persist, especially for woody mulches?

Ruth also challenged the use of plastic mulches, then relatively new to the garden product market.  She understood the benefits of a no-till approach to maintaining healthy soils.  She has a whole chapter entitled “Make Mine More Mulch.”

So here’s to Ruth Stout, the original “Mulch Queen.”

Packing Pearls

Yes, not my day to post, but I just received an email with a link to a new product called Packing Pearls.  These are polystyrene balls that fill the bottom of large containers so they aren’t so heavy.  They are promoted as “improving water drainage and oxygen flow.”  You can find a link here

The “pearls” are separated from the soil and plant roots with a pot liner (composition unknown).  We’re told that the roots can’t grow through the pot liner.  So now my question:  can a material that “improves water drainage and oxygen flow” be impervious to root growth?  Doesn’t it sound as though you’d be waterlogging the soil by installing this liner?

I honestly don’t know the answers to these questions, and the web site is not detailed (nor does it contain any links to research).  The emailed advertisement states “Tests show that flowering plants bloom two to three months longer when grown in containers with a base of Packing Pearls. Plants are also visibly healthier and hardier.”

Anyone used this system before?

Peanuts

I’m not from the South, and so I can’t call myself a Southerner like Holly can, but I did spend 6 years in Georgia.  There are lots of things about it which I miss: winters which are more like a Minnesota fall, the almost disgustingly friendly people (OK, there was that one time that I was chased by a guy with an SKS assault rifle — but that was an exception — generally Southerners are the nicest people you could ever want to meet), and, especially, the food.  I love okra, I love grits, I love country fried steak, I love mustard greens, collard greens, fried catfish, sweet tea (which is starting to become popular here) etc. And for those of you thinking well shoot, you can get that at your nearest Cracker Barrel (which I frequent) — IT JUST ISN’T THE SAME.  One of the foods which I miss the most though — one that hasn’t found its way to Minnesota yet — is the boiled peanut.  For those of you who don’t know what a boiled peanut is, it’s a little piece of heaven that has been boiled in a tub of hot salt water for a long time so that, when you break open the peanut’s shell, now the texture of watery cardboard, the seeds inside are soft, warm and, you guessed it, salty.  So, why am I telling you this?  Because I can’t suppress my excitement any longer.  Tom Michaels. a good friend of mine who is a transplant from a Canadian University where he worked on bean breeding, and I recently were talking about boiled peanuts and he told me that he has a peanut variety which will grow here in Minnesota without too much trouble and which is can be used to make hot boiled peanuts.  So I’m in the process of finding excuses to plant this critter — I’m going to plant it between rows of trees, in grass plots, in vegetable gardens — and then I’m gonna harvest them all and make hot boiled peanuts through the entire winter next year!

International Ag Labs – who are they and what do they do?

Last week I posted a short message about this company, asking you to do a little homework.  Bryn, CP, and Karen all have teased out some details that agree with my skepticism on how reliable this company is for soil testing and analysis.  (See last Wednesday’s post and comments if you haven’t read them already.)

To back up a little bit, I received an email from LB last week, along with the attached soil test, analysis and recommendations. LB intends to do some “market gardening” and here are his questions:

1. Is there anything to this perspective? Understanding your soil and rl37 (a “Jack of all trades” product).

2. I “get” that I should not willy nilly spread compost over everything, but what in the attached recommendation (based on the soil analysis) should I follow (Note: Crescendo and Stimulate are no longer offered, but there are lots of other interesting products here.)

3. Have you read any peer reviewed research that supports their “High Brix” market garden approach that uses sugar content and refractive index to supposedly correlate to improved flavor and higher nutrient content in selected vegetables?  I have heard of chefs using this to evaluate certain produce (carrots and tomatoes) in the market but nothing in a peer reviewed journal.”

Take a look at the linked report from IAL (from the second paragraph).  This is a confusing analysis, as it combines traditional ppm measures with pounds/acre.  (My understanding is that you can divide this latter number by 2 to get ppm.)  However, pounds/acre only represents a portion of what’s actually available in the soil.  It’s not an indication of how much, if any, of these nutrients to add.  (If you’ve never seen U. Mass Amherst’s soil testing lab, take a look at their webpage, especially their fact sheets related to soil testing.)

What irks me is the recommendations (which are in the first table in the attached document).  I’m not even sure of the rate – I assume it’s per acre, but who knows? And what is the purpose of all this stuff?

This company is heavily used by many people, including researchers (if you Google the name of the company along with site:.edu, you’ll find reference to articles and university reports that use their services.

Let’s have some discussion on this.  I’m certainly not an expert on performing soil tests, but I’ve had enough of them done that I have a pretty good idea how to interpret them and their recommendations.

Cool tree App for i-Phone users

I’m preparing to give my Woody Plant Physiology students their first opportunity to flaunt their new-found knowledge (aka Exam one) so only time for a short post.

As my fellow Garden Professors are aware, I am among the least tech-savvy people roaming the halls of academia these days and was long ago declared roadkill on the information superhighway.  However, I recently found out about a new App for the i-phone that could lure me back into the 21st century.


Programmer Brett Camper has developed an i-Phone app called ‘Trees Near You’.  The App is based on a street tree inventory for the City of New York and allows users to view maps of over 500,000 street trees.  For each tree users can look up info about individual trees including their size and estimated environmental and economic benefits based on energy savings and storm water retention.   The App also links to Wikipedia pages that provide more info on the tree’s botanical characteristics.  For more info, including a QuickTime movie demo, go to: http://www.treesnearyou.com/


While it may be easy to quibble with particular estimates of tree values or a particular bit of info from Wiki, there is no arguing this is pretty cool stuff.  Hopefully other App writers will be inspired and Trees Near You-type Apps will start appearing for other cities.  This is a great educational tool and a great way for urban and community forestry programs to promote the value of trees where we live.

Native vs. introduced species – the discussion continues

I was asked earlier today to comment on the Garden Rant blog regarding the issue of nonnative plants and insect survival, specifically in reference to Dr. Tallamy’s research.  Though I haven’t read his popular book (Bringing Nature Home), I did read one of his most recent papers (DW Tallamy and KJ Shropshire, 2009.  Ranking lepidopteran use of native versus introduced plants, Conservation Biology 23(4): 941-947).  The authors argue that lepidopterans prefer native to alien species for egg laying.  A serious problem I see in this paper is that the authors are literally comparing apples to oranges.  They do not compare effects among species in the same genus (the reasoning is there aren’t enough publications to look at), but among genera.  Thus, they lump at least 179 “alien” woody species into “native” woody genera and compare those to woody genera that are completely alien.  There are only 112 species in the latter.

I would bet that if he separated out these 179 woody species and added them to the alien genera list his findings would be quite different.

Comments?

So much for my happy summer vacation

It figures.  After I write a happy post I get an email question that brings me back to reality.  I plan on sharing a little more about the question – and my answer – with you later, but I’m going to give you some homework.  Let’s see what you can find out about these topics:

International Ag Labs

High Brix Gardens

Reams’ Biological Theory of Ionization

Hint: they are all interrelated.  Post your comments on the blog and let’s see where we go with the discussion.