The researchers studied how different amounts of N,P,K fertilizers in the soil affect the levels of sugar, nitrogen, protein, and nicotine in burley tobacco leaves as they grow. They found that total sugar and reducing sugar increased as the plant grew, while total nitrogen and protein decreased. Increasing N fertilizer led to higher levels of total nitrogen, protein, and nicotine, but lower levels of total sugar and reducing sugar at certain stages. More P fertilizer increased total nitrogen, protein, and nicotine levels, but decreased total sugar and reducing sugar at specific stages. Increasing K fertilizer decreased total nitrogen and nicotine levels. N and K fertilizers had a stronger impact on sugar levels, while N and P fertilizers affected nicotine, nitrogen, and protein levels more.