We just moved to Texas and I built some raised garden boxes. I purchased some premium garden soil. When I did a soil test in my vegetable garden it turned out to be not so premium. The texture is good not too sandy and not too hard but it has no nutrients in the soil. Ph 7.5, nitrogen and phosphorous were both so low they didn't read on the chart. Potash read low to very low. What can I add to improve the soil that wouldn't break me. I have about 320 square feet of raised garden space.