A field experiment study was conducted in Bashang Plateau in North China in 2008 to determine the effect of three first cutting dates on the growth and water use efficiency(WUE) of Siberian wildrye(Elymus sibiricus L.) in the agropastoral ecotone of North China(APENC).The experiment was conducted in a split plot design with three replications with water supply regime as the main plot treatment and first cutting date as the subplot treatment.Two water supply regimes were used,which included rain-fed treatment as control(CK) and a single irrigation and straw mulch treatment(W).Three first cutting date treatments were conducted at early heading stage on July 1(E),at late heading stage on July 12(L),and at flowering stage on July 27(F),respectively.The results showed that the forage yield and WUE were the lowest at early heading stage harvest,while the highest at flowering stage either in CK or W treatment.Under combined CK and W treatments,average forage yields of the F subplots were 2 900 and 6 703 kg ha-1,and the values of WUE were 0.82 and 2.28 kg m-3,respectively.Under the CK treatment,forage yields of the E and L subplots were 43.8 and 41.9% lower than the F subplots,and their values of WUE were 46.2 and 50.3% lower than F,respectively.Under the W treatment,the forage yields of the E and L subplots were 74.9 and 61.6% lower,and their values of WUE were 78.1 and 63.3% lower,respectively,as compared with F subplots.Therefore,earlier first cutting did not increase the regrowth of Siberian wildrye and improve the mismatch between rainy season and the period of high growth potential of the grass in the semiarid APENC.
