Richard, I have seen this happen many times. seen where a ditch was dug to lay a cable and things flourished for a while. You went the extra step and added to the clay and indeed you see it did wonders. Around here to build up the soil, I use green manure crops. I can build a lot of ground fairly cheep and can see dramatic results like you posted. I like to use soy beans for a summer crop. Any legume will do for they get there nitrogen from the air mainly, and in turn when plowing them under, you are adding nitrogen to the soil. If you were to plant something else other then a legume, the plant has to take its nitrogen out of the soil. And when you plow it back under, you are just returning the nitrogen back to the soil and not adding any. As well the green manure is adding organic matter into the soil which is essential for a healthy soil.
For a winter crop I try to use winter rye for it just puts so much bio mass in the soil with its green growth above and the intense root system below ground. The two pictures are actually the same piece of ground with beans planted and worked in last summer and autumn, and the rye went in last fall and was plowed under this spring. I have not a picture, but some rye was planted beside where the beans were and like your artichokes, the results were night and day. This garden is now my tomato patch and am hoping the extra effort pays off.
