Thanks for the reply.
I guess I should have specified what I want to do with this land in the original post.
I would like to get this land producing for me as quickly as possible. I want to grow a wide variety of vegetables, lots of tomatoes, cucumbers, zucchini, peppers & chili's, beans, corn etc.
Identifying the plants has proven to be a bit difficult because nobody around the area remembers what was planted there originally, and there is a major information vacuum in Japan about gardening, people just don't seem to know nor care.
From what I can see there are some plants which seem to indicate high nitrogen in the soil in certain spots, but besides that I'm not sure.
Waiting a year to see the natural cycle of things is unfortunately a luxury I don't have, I would like to get this land producing food for my table as quickly as possible, and the land needs to be brought into a relatively presentable state. At the moment it's turning into a jungle and is becoming a nuisance to the surrounding houses due to the wildlife coming from it. Part of the rental agreement I signed is to make sure it doesn't stay like that, permaculture is OK but it can't be a wilderness reserve.
The current state of the land is as shown in the first picture. The second picture was taken many years ago. It does not look like that now. The current plants growing on the land are completely wild and I can only identify a few of them, but they seem to be mostly weeds. That's my big concern. What is the best way to get control of these and get vegetables and herbs growing as quickly as possible?