The researchers tested different combinations of organic and synthetic nitrogen fertilizers to improve rice grain filling and quality. They found that using a mix of poultry or cattle manure with chemical fertilizers increased the activity of enzymes involved in starch metabolism, leading to higher grain yield and better quality. The combined treatments also resulted in increased expression of genes related to starch synthesis, further enhancing grain filling. Overall, the study suggests that a 30% organic nitrogen and 70% synthetic nitrogen combination is effective in boosting rice production and quality while minimizing environmental impact.