Abstract:

Euchlaena mexicana is one of forage crops with high yield and high quality, which has been introduced from Japan since 1979. In forage cultivation, mass nitrogen fertilizer are generally applied in order to gain high yield, but over-use of nitrogen will reduce the quality of forage crops, and cause negative effects to the environment as well. A micro-plot experiment was carried out to study the effects of nitrogen application on nitrate (NO₃^--N) accumulation and yield of E. mexicana. In this experiment, four treatments induced two levels of nitrogen rate (the middle level of 300 kg/ha and the high level of 600 kg/ha), and two modes of nitrogen application (all nitrogen applied as basic fertilizer, and another applied averagely at three times). During the whole growth season, the plants were mowed three times on August 10^th (H₁), September 11^th (H₂) and October 12^th (H₃), respectively, and the plant height was about 110 cm at every harvest stage. Nitrogen fertilizer was applied as dressing at H₁ and H₂ after mowing. The NO₃^--N concentrations of the newly leaves, fully expanded leaves, old leaves, stalks and roots were determined. The results showed that the NO₃^--N concentration was high in the newly leaves, low in the fully expanded leaves and middle in the old leaves. The concentrations of NO₃^--N in both stalks and roots were lower than those in all the leaves on H₁ and in newly leaves on H₂, but higher than those in all leaves on H₃. With the increase of harvest times, the concentration of NO₃^--N was decreased in all leaves. However, the concentrations of NO₃^--N in stalks and roots were decreased on H₂ and increased on H₃. The treatment of high nitrogen and applied averagely three times led to NO₃^--N accumulation largely in the same type of leaves. In the treatment of N_2-3 (600 kg/ha averagely applied three times), the NO₃^--N concentration of the newly leaves was 92.66 mg/g, which was the highest in the three types of leaves on H₂, and was still lower than the potential toxicosis dose for animals. With the increase of nitrogen rate, the nitrogen utilization efficiency (NUE) reduced, but the dry matter yield and crude protein yield of high nitrogen treatment (600 kg/ha, applied as basic fertilizer) were significantly higher than that of any other treatment. It comes to a conclusion in E. mexicana production practice, high basic nitrogen fertilizer may tend to high forage yield and be safe to livestocks.

Key words: Euchlaena mexicana, Nitrogen rate, Mode of nitrogen application, Nitrate, Yield