Effect Of Different Mowing Initial Time And Frequency On Dry Matter Yield,Nutritive Value And Regrowth Of Leymus Chinensis In Northeast China

Grassland is one of the most important renewable natural resources,which provides the necessary means of production and living for human survival and development.Mowing is one of the common ways of grassland utilization.Different types of grassland have different suitable mowing regime.Although the growth of forage is seasonally affected by temperature and precipitation,suitable mowing regime can break the physiological cycle of Leymus chinensis,stimulate more tillers of L.chinensis,and change the direction of nutrient precipitation in order to obtain high yield and nutritive value which increase the grassland utilization efficiency Therefore,scientific and reasonable mowing regime are of great significance for the sustainable utilization of grassland.Taking L.chinensis community as the research object at Ecological Research Station for Grassland Farming,Changling Chinese Academy of Sciences,three experiments were conducted to study the effects of different mowing time and frequency on the yield,nutritive value and regrowth of L.chinensis,in order to explore suitable mowing regime in this area.The results show that:（1）From May 15,the DM yield and the accumulated yield of L.chinensis were only38.8 and 121.8 g.m^-2,which were significantly lower than those in June 1（P<0.05）.After mowing from June 1,the DM yield of L.chinensis was higher,and the regrowth yield was significantly higher than that of other treatments（except May 15）.With the delay of mowing initial time,crude protein（CP）content of L.chinensis showed a significant decreased trend,and after June 15,CP content decreased to less than 7.5%（P<0.05）,while neutral detergent fiber（NDF）increased more than 66.2%.In mid-August 2017,the DM yield of different treatments with different mowing initial was determined.The results showed that the DM yield of L.chinensis was the highest on September 30,and there was no significant difference among other treatments（except for cutting on May 15 and June15）.（2）Mowing 1-2 times yearly had significantly negative effects on the DM yield and nutritive value of L.chinensis.Mowing three times yearly increased the annual yield of L.chinensis by 16%compared with mowing once yearly,and was significantly higher than other treatments（P<0.05）.After mowing more than three times yearly,the DM yield of L.chinensis decreased significantly with the increase of mowing frequency（P<0.05）,with a decrease of 7 and 23%respectively.The CP content increased significantly（P<0.05）and the NDF and ADF content decreased significantly（P<0.05）from 1^st to 4^th cut in mowing four times a yearly.The change trend of contents of CP,NDF and ADF were the same among the mowing five times yearly,but the CP content among each cut in mowing five times yearly was generally higher and NDF and ADF contents were generally lower than that of each cut in mowing five times yearly.（3）The yield of L.chinensis treated with mowing in jointing stage（MJS）was the lowest,and significantly lower than that of other treatments（P<0.05）.The DM yield of L.chinensis treated with mowing in flowering stage（MFS）was the highest,significantly higher than that of other treatments（P<0.05）.The net photosynthetic rate,stomatal conductance and transpiration rate of L.chinensis treated with MJS and mowing in heading stage（MHS）were higher than those of control group,but there was no significant difference,both of which were significantly lower than those of MFS treatment（P<0.05）.The intercellular CO₂ concentration of each mowing treatment was significantly higher than that of the control group,and the highest concentration of intercellular CO₂ was found in MFS treatment.Different treatments of L.chinensis had no significant effect on water use efficiency.（4）The regrowth ability of L.chinensis decreased significantly under 30-days mowing interval（MTD）.The DM yield of L.chinensis in the 2^nd and 3^rd cut was only around 60%of that in the 1^st.After the 3^rd cut,the DM yield of L.chinensis decreased significantly again（P<0.05）,and the DM yield of L.chinensis in the 4^th and the 5^th cut decreased to the lowest for 12.6 and 11.7 g.m^-2,respectively.The DM yield of L.chinensis decreased significantly（P<0.05）from 1^st cut to 4^th cut under 40-days mowing interval（MFD）.From the 2^nd to the 4^th cut,the DM yield decreased from 74%to 16%compared with that in the1^st cut.The DM yield of L.chinensis in 2^nd cut in mowing interval between two heading stages（MHS）and 60-days mowing interval（MSD）was regenerated and significantly higher than that of 1^st cut（P<0.05）.From the total yield of L.chinensis,MHS and MSD treatments had the highest total yield,while MFD treatment had the lowest total yield.The work concluded that:1)L.chinensis had an optimal nutritive value if the first cut was conducted on^June 1,which preserved its ability to recover and regrow;2)The optimal mowing frequency of L.chinensis is three times yearly,which the total DM yield,total nutrient yield and nutritive value in each cut can be optimized.