Why did my crops do worse after amending my soil?

I have a clayey loam soil and I made mini hugels, adding:

Sand
Compost
Grass clippings (had some ponderosa needles mixed in)

I mixed these into the soil I had in a wheelbarrow and put that on top of apple and maple wood logs at the bottom layer, and covered my mounds with a straw (brome grass) mulch. I seeded into the top of the mounds the day I mounded.

That's it, didn't change anything else, and my crops did far worse this year than last. Any suggestions would be much appreciated... What happened here?

Fundamentally, I disagree with digging low quality organics into the soil. To become hummus and give back to your plants they need to suck in everything that life needs- nitrogen, phosphorous, potassium and the rest. They will give it back when they become hummus but until then they will out compete your plants. This stuff may help your mychorizia but until that develops its also a nutrient vacuum.  Amendments to me means something else- ashes, composted compost , manure epsum salt et al. This is a long term development that you did, not expected to do well at first and not worth doing in my climate and soil.

Xanther, I too have some really poor clay soil  to which I have been adding compost, leaf mould, and grass clippings. I didn't see much improvement in the soil until I added some rabbit manure. That's when I really started seeing a big difference in appearance and tilth. I have also incorporated some chop & drop Comfrey and the worms seem to like it a lot.   I would suggest you add some manure and see if things improve

Give it a year.

I would imagine that those green grass clippings went anaerobic on you --- stinky and oxygen deprived.  That feeds all the wrong kinds of microbes and kills a lot of the good ones.  Too many greens buried under the soil can lead to pockets of methane.  If that's what happened, no wonder your garden was funky.  Methane blocks plants from getting CO2 or O2.  Too much methane (natural gas) is a bad thing.  So between the methane and the lack of oxygen, that's a lousy environment for soil microbes, plant roots, and even earthworms.  You might have created a dead zone in your root zone.  

Also, fresh grass clippings would temporarally tie up the nitrogen in the root zone, if your plants were growing down into the grass you buried.  Grass clippings are 4% N, but that's not enough to offset what is taking place as they decompose.  Couple that with the pine needles, and you probably shocked the system and it was too soon to plant in that soil.

You'll do a lot better to just pile those pine needles and grass clippings around the base of your plants next year --- don't till them in.  Mulch with them—don't use them as soil amendments.  

By next year, things should be much better.  Live and learn, right?  Those buried apple and maple logs should have a healthy fungal network starting to break down the wood fiber.  Maybe try a cover crop now and see if you can get it to grow before the growing season comes to an end.  Clover, vetch, or some such.  Many seed companies offer a cool season cover crop mix.  Get some and seed your bed again.  By next spring, the microbial community in the soil will have recovered, and hopefully, you'll have a healthy fungal community as well.

sounds to me like you put carbon into the soil but not enough nitrogen takes a lot of it to make up for carbon.It takes nitrogen to brake down the carbon .

An addition
https://permies.com/t/58634/soil/urban-myth-woodchips-nitrogen
good no best post about nitrogen  

Xanther Hayman wrote:I have a clayey loam soil and I made mini hugels, adding:

Sand
Compost
Grass clippings (had some ponderosa needles mixed in)

I mixed these into the soil I had in a wheelbarrow and put that on top of apple and maple wood logs at the bottom layer, and covered my mounds with a straw (brome grass) mulch. I seeded into the top of the mounds the day I mounded.

That's it, didn't change anything else, and my crops did far worse this year than last. Any suggestions would be much appreciated... What happened here?

hau Xanther,  

Some questions first; were the logs you used already decomposing or were these newly cut?  
New cut logs take quite a while to start really adsorbing water, it is usually best to use partially decomposed logs for hugel mounds since they are prepared to soak up water and release it for roots to suck up.

How much (quantity) compost and grass clippings did you mix into the soil?
When you are building a hugel with "dirt" VRS "soil", the dirt will need a ratio of 3:1 (compost/clippings : dirt).

Sand, when added to clay tends to turn to a concrete, if there isn't enough humus to bind with the fine clay particles.  When loose clay particles meet sand grains, they encapsulate those sand grains, this allows clay to bind to clay which is what happens when you are making pottery.

You mention that crops did worse this year, did these crops do well in the hugel last year?  

Now to some solutions;

continue to add humus to the mound(s), digging some into the topping layer will help faster.
Making compost or manure tea and watering the hugel(s) with that will help a lot with friability and it will provide nutrients as it conditions the topping soil.
you are doing good to keep the mound mulched, but it might need even more.
Find some locally growing mushrooms and poke some holes down to the logs, chop up the mushrooms, mix with chlorine free water and pour this mix down the holes. This will get some hyphae spores down to those logs and help them decompose faster.
While you are pouring the mushroom mix down the holes, spread some over the soil too, this will help plant roots with nutrient uptake and they will be able to adsorb water better too.

hope this helps,  please keep us informed on your progress.

Redhawk

A few points;

As others said, burying grass clipping can create all kinds of weird compounds; methane, alcohol, hydrogen sulfide, even formaldehyde type compounds. In general, burying green material is a bad idea.

Wood, pine needles, etc. need nitrogen to break down.

Finally, adding sand to clay is a bad idea; that is a good way to make adobe bricks, but a bad way to make garden soil.

But as others said, probably no permanent damage is done, and things will go better next year, with some added nitrogen.