A study looked at how not tilling the soil and using organic manure affects soil fertility in rice and wheat fields over 14 years. They found that not tilling the soil for 14 years increased the levels of organic carbon, nitrogen, and available nitrogen in the top 5 cm of soil. Water-stable aggregates, which help soil structure, also increased. The best fertilization treatments for soil fertility were pig manure, straw, green manure, chemical fertilizer, and no fertilizer in that order.