Part of my work has come to include substrate production of caneberries. Some of these are easy since they are pest management issues which don't vary that much from field problems, but others, like the nutritional situation depicted below, are far more complex.

A couple of things going on in this field, which are raspberries being grown in substrate under macro-tunnels.  First, the very young leaves have a light yellow cast (see photo one below) to them and second the older leaves are seeming to have some difficulty (see second picture below), again becoming a sterner sort of yellow.  I don't worry as much about the older leaves as I do the newer ones, which after all represent the future of the plant.

As you know, I'm not making any call without doing some thorough sampling.  In this case, we took multiple samples of the younger leaves demonstrating the lighter shade of yellow and the same for the older yellowed leaves. To set the baseline, adult normal leaves (those surrounding the yellow leaves in the first picture below) were also sampled in multiple.

An important comment.  We are sampling leaves of 3 different ages, and we should be aware that this is going to distort some of the concentrations.  For example N, P, and K as plant mobile will by default trend higher in younger leaves, and nutrients such as Ca and B are going to trend higher in the older. 

And sure enough in perusing the analysis below, N,P and K are higher in our newest leaves and lowest in the older, with the adult leaves in between.  Likewise, Ca and B are very much higher in the oldest leaves than the other two age leaves, and as a matter of fact in the newest leaves these two nutrients are lower than what one normally would see recommended.  

Moving on however to the levels of iron things get a bit more interesting.  While it is highly accumulated in the oldest leaves, it is far less so in the youngest at 4x less, and 3x in the normal adult leaves.  Calcium shows a similar pattern of concentration, but the visual symptoms are nothing like what we know calcium deficiency to look like.  Iron deficiency, on the other hand, usually described as chlorosis of one type of another, as a matter of fact does.  In addition, we know that nitrogen can accentuate iron deficiencies because of growth promotion.

The older leaves turning yellow?  It seems to me they are just old leaves, might be some dieback being pushed by high tunnel heat but nothing that excites a lot of attention.

In other words, it looks like the plant is outgrowing its ability to pull up iron for the moment.  Given that we've had (still in October of all things!) some pretty hot plant growth weather, once the weather cools down a lot of this should disappear.

My advice to the grower is watch this one, I'm not sure yet concrete action is merited yet, best to see if once the plant slows down in its growth and nitrogen accumulation these symptoms subside.

Mark here.  The video by Dr. Eric Brennan concerning the sustainability problems of using what is essentially repackaged synthetic nitrogen in organic agriculture that I posted a few weeks ago has sparked a lot of discussion in my social circles, most recently for me at a dinner with a big ag company and a local PCA specializing in organic consultation.  These conversations turn around the same point that reader Thomas Flewell (Thom - note you got your byline!) brings up below.  Best to go to the expert on this very subject so I asked Dr. Brennan if couldn't answer the question for all of us, and he graciously accepted my invitation to do so.

Follow along below:

Thomas Flewell: Preface-  As the world population approaches 9 billion within the next 100 years, it is clear that organic farming will not serve up enough food for everyone.  
Dr Brennan's reasoning toward the use of synthetic nitrogen in organic farming is persuasive but I see an error of omission. Dr Brennan failed to note that manure derived fertilizer will be produced whether or not it is used for agriculture. Cows poop. Chickens poop. Pigs poop. Goats poop. All god's creatures poop. And none of them are raised only to produce fertilizer. So the energy to produce argument seems weak. Also, while manures are used as pre-plant fertilizer and in some instances as a top dress or side dress for crops, fish fertilizers are also used. I have had very good results with a hydrolyzed (not emulsified) fish fertilizer with a very low N analysis. Perhaps just an academic point.  

Eric Brennan:

Hi Thomas,

Thanks for your interest in my ‘repackaged' synthetic nitrogen video and for your comments on it. I've heard others raise similar questions after seeing my video. I'm working on an opinion paper that will provide more details on the arguments that I raise in the video, and hopefully will bolster my arguments with citations, and examples that I was able to fit into the video. But in the meantime here are some ideas to consider and some articles to help with that.

I agree on the value and importance of recycling nutrients from manure and animal slaughter by-products; to my knowledge slaughter by-products are more important than manure in high-value organic crops California. However, I imagine that rendering process (extraction, grinding, heating, pressing, etc.) to convert this material into pelleted fertilizers takes a fair bit of energy to ensure that the material is safe to use, and easy to handle and apply. And transporting this bulky material to where it's used is also energy-intensive. Consider an organic system in a place like my home state of Hawai'i where there is relatively limited animal production. Think of the energy costs to move organic fertilizer made of chicken manure, meat, bone, and feather meal all the way from California, for use on an organic farm in Hawai'i! To me, this seems like a relatively inefficient way to get N in these systems.

Ideally these animal production by-products could be used in organic and conventional systems near to where they are produced and in systems that need the full suite of nutrients they contain; even better would be for the nutrients in these materials to return to the systems that produced the feed for these animals. But having to rely heavily or almost exclusively on this type of fertilizer material (as in often the case in organic vegetable production in many regions) for nutrients like nitrogen (N) can be problematic and quite expensive. As I mentioned in the video, one problem is that N in many of these ‘repackaged' synthetic N fertilizers often come with excessive amounts of phosphorous (P) that far exceed what is being removed from the soil in crop yields. I became well aware of this issue of excessive P inputs in my research when I collaborated with researchers from Stanford and UC Davis to calculate P budgets (P inputs versus P outputs) in two long-term organic studies in California. This is described in detail in the a few publications like this one available here. To improve our P budgets in our long-term study in Salinas we switched from using pre-plant fertilizers with a 4-4-2 analysis to an pre-plant with a 8-1-1 analysis which was more expensive per unit of N; from what I've seen with pelleted organic fertilizers, unfortunately the materials with lower P or no P have a higher per unit cost for N. Switching to 8-1-1 helped with our P budgets, but we still were applying more P than needed when we added yard-waste compost to these systems. This improvement in our P budget is very obvious in figure 2B in of the paper note above that shows a big decline from 2007 to 2008 in the P balance. This also highlights the importance using cover crops to add carbon back to the soil, rather than over relying on compost which can add too much P. Carbon added by cover crops represents ‘on-farm carbon production' that doesn't add P, but just recycles what's already in the soil to produce the organic matter. Furthermore, organic matter inputs from cover crops appear to be a more important driver of soil health improvement than organic matter from compost. Here's our recent paper that describes that issue

Getting back to the P budget issue, during 8 years of our long-term trial on high-value vegetable production, we added more than 400 lbs of P per acre than was needed to replace what was removed in exported yields !   It's important to highlight that unlike N that we can capture out the air with biological N fixation (using legumes) and by synthetic fixation (using the Haber-Bosch process), P is a limited, mined nutrient, and there is considerable concern about the worlds dwindling P reserves; this highlights why we should only apply P when needed. Here's a link to another paper from our long-term study that provides some information the biological N fixation potential from legume-cereal cover crop mixture in these systems. While legumes do fix N in these systems, this is limited by their ability to complete with non-legumes likes cereals that provide other important services like nitrogen scavenging from previous vegetable crops, … and there can be other challenges with legume-cereal cover crops that I highlighted in this video Are legume-cereal cover crops a good fit for organic vegetable production?

Another issue to consider with organic soil fertility management that is relevant to the arguments in my ‘repackaged' synthetic N video is the total supply of manure and slaughter by-product based fertilizers available in a region like California. I don't know the extent of this supply, but it seems likely that as organic agriculture acreage grows here and uses more of these organic fertilizers, this supply of fertilizer will become more and more limited unless animal production (that relies primarily on feed grown synthetic N) increases. This is concerning because the science of climate change indicates the need for people in regions like the U.S., with excessive protein consumption, to reduce consumption of animal products. This important dietary shift to less meat consumption would likely reduce the amount of manure and slaughter by-products available for recycling as fertilizers. Furthermore, relying on fish as source of N for organic agriculture could overtax the world's oceans that are already over fished in many regions. Perhaps I'm wrong, but I don't believe there is a sound scientific basis for a total ban on the use of pure synthetic nitrogen in organic agriculture. That's why I argued for what I call ‘SPorganic' (i.e., scientifically progressive organic) agriculture that would allow the careful use of synthetic N in it's pure form, rather than only in the ‘repackaged' synthetic forms that are currently allowed in organic systems. However, I believe that limiting the use of N inputs (from ‘repackaged' and pure synthetic forms) and greater adoption of best-management practices like cover cropping, make scientific sense. ‘Enriching the Earth' by Vaclav Smil is a book that I highly recommend for additional reading on the complex issue of nitrogen in agriculture and how the Haber-Bosch process has transformed our lives and accounts for at least 40% of the world's dietary protein. Here's link to an entertaining RadioLab podcast on the Haber-Bosch story that you might also enjoy.

My N video was first presented along with 10 other 5 minute videos at a 2016 symposium that I helped organize at the American Society of Agronomy conference; here' a link to the 11 videos. One of my intentions with my N video was to start a conversation around a complex issue that I believe limits the sustainability of organic systems like those that I work with in California. Thanks for joining that conversation.

Take care, Eric Brennan

Mark here - thanks Thom and Eric for a most informative exchange - really appreciate it!!

">

Should we be able to use synthetic fertilizers in organic agriculture since the organic ones we can use in these systems are repackaged synthetics anyway? This was discussed at a really great lunch meeting today with scientists and growers (THANK YOU Mark C.!), and it's something that is really thought provoking.  Watch the video (it's only 5 min), Dr. Brennan can explain way better than I can.  Give it some thought.

H/T Eric Brennan.

Comments welcome.

Below is a look at what happens to a soil following application of mustard seed meal (MSM) at 1.5 T per acre and mustard seed meal (again 1.5 T per acre) + crab meal (500# per acre) as separate treatments two weeks after fumigation with Ally 33  (67% AITC, 33% chloropicrin applied at 340# per acre on Oct 7).

Grower standard was methyl bromide/chloropicrin applied at 350# per acre. Planting took place Nov 3.

A soil sample taken on Nov 7 did not show differences in soil aspects analyzed between any of the treatments, although ammonium - N concentrations were surprisingly high (30 ppm and up) and nitrate - N numbers tended to be quite low (6 ppm and below).

Remarkably, look what has happened in the 4 weeks since that sample.  Bear in mind that the grower has since sprinkled overhead several times and we had a good amount of rain as well.  Commenting continues below the tables.

Unless otherwise indicated, units are in ppm of dry soil.

 Table 1A. Soil analysis from December 7, 2016

*Student's T-Test; different from grower standard at 5% level of significance.

Table 1B. Soil analysis from December 7, 2016 

*Student's T-Test, different from grower standard at 5% level of significance.

 One sees immediately that the pH has fallen, even significantly, in plots treated with mustard seed meal and mustard seed meal + crab meal.  This is not surprising, since in the month's time since the initial sample on Nov 7, the ammonium has clearly nitrified (releasing 2 H⁺ ions per molecule, in turn acidifying the soil) creating a big pool of nitrates which have gone up significantly over the grower standard.

EC has gone up a bit due to the higher nitrates (NOT because of sodium or chloride), and interestingly levels of manganese (Mn) a mineral sensitive to acidification apparently, have soared in both MSM treated plots.  Levels of available potassium (K) have gone up significantly also in MSM treated plots.

Quite interesting on the whole.  By the way, a soil report like this makes for pretty good reading, and outside of the EC which is for the time being a little high in the MSM plots, all the other numbers are right where I like to see them.

Stay tuned on this one; we are following all of this trial through the season.