i reuse all the time and have never had a bad result, like another user posted ...farmers dont throw away fields!!
1: after harvest i let the soil completely dry out,......bone dry
2 : then i break it up and take out the thick and long roots
3: i then repot and water with a double dosage of veg nutrient (currently canna vega) ((4ml per 1 litre, and ill use 1.5 litres water)
4: i will repeat step 3 upto 3 times for 1 week letting soil completely dry each time
5: after the soil is completely dry after week 1 the soil is good to go...
ive used this method a long time, the soil seems to be perfect for either veg or flower. i never get any issues at all, and ive never noticed a drop in yeild. (and yes i have compared)
to answer other posts i read in this thread.....some people dont have the choice but to reuse soil....its too easy to say "oh a bag of soil is so cheap theres no point using old soil"...but some ppl live in a block of flats (i dont btw) and transporting dirt around like its trash isnt possible at all!