The researchers studied how different levels of nitrogen affect the growth and nitrogen metabolism of peanuts. They looked at the protein and amino acid content in different parts of the plant, as well as the activity of key enzymes involved in nitrogen metabolism. They found that increasing nitrogen levels led to higher protein and amino acid content, as well as increased enzyme activity. However, excessive nitrogen could have negative effects on certain enzyme activities. The best nitrogen level for peanut growth was determined to be 90 N kg·hm–2.