Many years ago I took on an allotment that had recently been opened. One man had rented the plot before me, and given up. I thought I would try the old trick, grow potatoes. The soil was terrible, no life in it. I put in one row of potatoes and soon realised that something needed to be done. I had access to an animal breeding unit where the animals were kept on sawdust. By the time I got it, it was urine sodden with a whole range of different animal faeces. I spread this out and put in another three rows of potatoes. The first row of potatoes produced about the same number of potatoes as I had planted. The other three were amazing. I decided to spread sawdust over the rest of the plot and leave it for the winter. This plot was full of couch grass and I found that by spreading the sawdust over the ground a couple of inched deep the couch grass quickly grew through it, but what amazed me was that all the roots came up the to sawdust and were easily removed. It shouldn't be too difficult to get some sawdust and soak it in liquid manure and leave it over winter as a mulch, and then dig it in as a fertiliser. You are not left with anything to get rid of afterwards.