Abstract: In this paper,a field experiment was conducted on a red soil of South China to study the effects of applying selenium fertilizer on the growth,forage quality and nitrogen-fixing ability of Chamaecrista rotundifolia. The results showed that applying 75,150,225 and 300 g Se·hm^-2 could increase the plant height,branch number,dry root weight and dry forage yield by 0.3%～6.2%,65.1%～79.5%,155%～252% and 30.6%～54.1%,respectively. The total nitrogen,total phosphorus and total potassium contents of plant were increased by 21.79%～41.46%,20.74%～34.67% and 34.3%～62.4%, respectively,and the raw protein,raw fat,raw fiber and amino acid contents were increased by 21.79%～41.46%,1.4%～89.6%,34.1%～56.6% and 6.33%～63.24%,respectively. Among the 4 doses,150 g Se·hm^-2 was the most effective and suitable application amount. The selenium content in plant after applying 300 g Se·hm^-2（S4） was 0.695 mg·kg^-1,with an increase of 0.658 mg·kg^-1 compared to no selenium fertilization. There was a significantly positive correlation between plant selenium content and applied selenium (R²=0.9666**). The root nodule weight,number and nitrogenase activity in treatment 150 g Se·hm^-2（S2） were respectively 131.7%, 114.3% and 1 417.9% higher than those of no selenium fertilization. The correlation between applied selenium and nitrogenase activity was also significant (R²=0.9606*).

Key words: Cotton, Compound population, Cropping pattern, LAI, Leaf area duration