Hi Daniele, I’m not qualified to offer tech advice but have fixed this myself on small scale by drenching and working the top 50 – 80mm soil with a rake (not the best I know, but it works). I then sow a thick green manure crop into this wet soil and cover with a 50/50 mix of lucerne / wheat chaff about 5 mm thick, as “sunscreen”. The green manure is knocked down at around 500 high and heavily mulched. When I plant into it 4 weeks later, all is good. My other thought would be to add clay (pref kaolinite) or biochar. I live in Western Australia where we have sandy soils and plenty of heat. I also use drip irrigation which seems to promote surface hydrophobia if mulch is not thick enough (80mm+). Hope this helps in some way. Good luck.