Abstract: In a field experiment in karst cluster-peak depression of karst region, this paper studied the responses of hybrid Napiergrass (Pennisetum purpureum) ‘Guimu1’ to different topdressing rate of fertilizer N. The results indicated that under N topdressing, the plant height, tiller number, hay yield, coarse protein content, and watersoluble sugar content of ‘Guimu1’ were higher than CK. The plant height was significantly higher under high N topdressing; the tiller number and hay yield were significantly higher under medium N topdressing; and the coarse protein and water-soluble sugar contents were significantly higher in all N topdressing treatments then CK. N topdressing was beneficial to the plant growth and nutrient accumulation of ‘Guimu1’, but the annual net income of high N topdressing was lower than that of CK. Among the three topdressing rates of N, only medium rate of N topdressing had a significantly higher annual net income than CK.

Key words: Combined flocculants, Flocculent performance, Wastewater treatment, COD, Turbidity, Environmental safety