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Interesting. My immediate question was about nitrogen. Did you do any soil testing before and after?

Nice video well documented but long to get through

I don't use urea fertilizer, I only use sulfate of ammonia because of the same problem you had with it. Urea has twice the nitrogen of sulfate of ammonia and it is easy to kill plants with it. If you use sulfate of ammonia or a complete synthetic fertilizer with much lower nitrogen like a 14-14-14 or 10-20-20 plus micros. Your results may have been different. Nitrogen fertilizer needs to be divided, you cannot use nitrogen only as a starter fertilizer. Try banding fertilizer instead of broadcasting. The mulch will tie up less fertilizer and the fertilizer will be delivered at the root zone where the plants need it. Nitrogen side dressing are better banded and mixed with a filler like compost so you don't have to much in any one place or hit the plants with it as it will burn.

Some of the wood chips did not look very fresh. Wood chips that decompose faster when tilled in or are partially decomposed work better than fresher harder wood. Wood that is resistant to decomposition, likewise does not cause that much of a problem either. It can takes years to breakdown some wood chips and since they are resistant they don't use up a lot of nitrogen at a fast rate. Faster decomposing chips do benefit from extra nitrogen, but you need to wait about 6-8 weeks before you plant your main crop and I still would use a starter fertilizer. Organic works when you have a lot of organic matter in the soil and a good soil web built. Synthetic works if you pick the right ones. There are synthetic fertilizers with slow N. If you have a good organic base with compost and a soil test, you should be able to fertilize without over fertilizing.

In your field tests, the broccoli responded noticeably to the applications of liquid fertilizer, which means they responding to the fast nitrogen. Nitrogen need to be delivered at the right time and at the right rate for the plants to thrive and not get burned.

When you repeat your study, it would be better to refine the variables. It was initially a study about wood chips, but you also had used different fertilizers both synthetic and organic. You used fertilizers in different forms, and as you realized, weather and temperature also made a difference. I think you also made mistakes when applying the fertilizer. Urea is a difficult fertilizer to use since it is so high in nitrogen. You need to be more precise than a "smidgen". Temperature makes a big difference in how plants grow but also in the activity of the microbes in the soil. Warmer soil temperatures will have greater activity and faster decomposition than colder soils. There were really too many variables to consider, temperature, different fertilizers and forms of fertilization, even different kinds of wood chips. There are too many variables to draw conclusions about the main premise which was about wood chips.

40 years ago about 1980 I got saw dust from lumber yard then tilled that into my garden in Sept. Spring garden started out good then very quick plants turned yellow and everything died.

It took 2 years to get the soil back to normal so plants will grow. Few years later I put saw dust down the center of the rows making sure to keep saw dust 12" from all plants about a month later plants started turning yellow. I removed all the saw dust plants continued to turn yellow and die.

About 10 years later I tried wood chips with the same results garden plants turned yellow and died.

Then I learned if I compose wood chips in a pile 3 years while adding ammonium nitrate the wood chips cause less low nitrogen problems in the garden. No problems with plants that don't need very much nitrogen. Corn still does not like these wood chips plants turned yellow very slow.

I learned hard wood chips from oak trees decomposes slower than pine wood chips. Oak is less of a nitrogen problem in the garden than pine.

I learned plants that need lots of nitrogen like corn suffer and die sooner than plants that don't need much nitrogen.

1990 I met a gardener in town he had 7 piles of composting wood chips in his back yard. Tree removal services chip trees and haul it away, he had a truck load of wood chips dumped in the very rear of his back yard every year. He marked each pile with the Date it was dumped there. After 7 years the 7 years old pile of compose wood chips went into has garden and was replaced with a new pile of fresh cut wood chips. Great idea if you have a place for 7 piles of wood chips in your yard.

Urea is a slow release nitrogen it is not a nitrogen that plants can use. Urea is dependent on calcium in the soil to slowly convert to a different type nitrogen plants can use. If I add calcium to my garden soil Urea with convert to a different nitrogen very fast in only 2 days then it produces too much nitrogen and kills plants.

I watch YouTube garden videos many of the best gardens that grow the best crops soil looks like it is all composted wood chips. Everyone says, compose wood chips in a pile 3 years before putting it in the garden.

Today I got a truck load of 2 year old composted wood chips. I am going to put this on my potato row next spring after mud is dried up enough to till the garden.

I actually grew right in top soil and manure that was on top of wood chips in my hugelkultur bed with no problem
It was the first year hugelkultur too.

1st layer, logs


2nd layer, sticks and smaller branches


3rd layer, existing clay soil.


4th layer, wood chips


5th layer, black kow manure


6th layer, top soil


This is two months later


And another bed that was done very similar


I really did not know about nitrogen tie up when I did these beds and the reason I put wood chips/mulch down on the branches was to hold the manure and top soil in place to be able to plant immediately, also all the wood was about a year old and still not seasoned.

2nd bed but no wood chips/mulch until the end of season.
logs


shrub


logs


clay soil


composted manure


2 months later



this one didn't get wood-chip mulch until fall/winter prep



To be honest I didn't notice any deficiency so I'm not sure what was going on. Both beds were built and planted immediately following the build. Could it be that they were bagged chips/mulch?
Anyhow I don't use bagged stuff anymore and have been using double ground mulch
I did do my fruit trees, ornamental tree and one of the hugelkultur beds in single ground wood chips.

Hugelkultur usually does not use fresh cut wood, but wood that is partially decomposed. It has a head start being colonized with the decomposing organisms. You added manure and topsoil on the wood chips and it looked like a hefty amount of composted manure, that would have given the bed a nitrogen boost. Wood that decays slowly won't tie up as much nitrogen as wood that decays very fast.
If you fertilized your beds with fish emulsion or compost tea or any nitrogenous fertilizer, there was probably sufficient nitrogen to support both the plants and the decomposers and would be a reasonable explanation for why you did not have a problem with nitrogen being tied up.

You also planted sunflowers in the bed. If your initial plantings were legumes or plants with low nitrogen requirements, they would not have needed that much nitrogen. Something like corn would have needed more nitrogen.