Abstract: In this study, we monitored fine root turnover and root distribution characteristics of three alfalfa varieties (WL343HQ, WL363HQ, and WL366HQ) to determine the relationship between these characteristics and hay yield. The three alfalfa varieties were from the Oasis Region of Northern Xinjiang. Fine root production and mortality of the three alfalfa species were monitored using minirhizotrons to clarify the dynamic characteristics of fine root turnover and characteristics in different soil layers. The total fine root standing crop of the three alfalfa species reached their maximum values on July 21 (0.294, 0.861, and 0.568 cm·cm^-3 in WL343HQ, WL363HQ, and WL366HQ, respectively). In WL343HQ, WL363HQ, and WL366HQ, fine root production had two, three, and two peaks, and fine root mortality had two, two and three peaks, respectively. The maximum fine root crop of alfalfa occurred during the period July 6 to July 21. The cultivars were ranked, from largest fine root crop to smallest, as follows: WL363HQ (0.455 cm·cm^-3)>WL366HQ (0.260 cm·cm^-3)>WL343HQ (0.116 cm·cm^-3). The maximum mortality of alfalfa fine roots occurred at different times in the three cultivars. Fine root growth and death occurred at different stages, and the size of the fine root standing crop was lower during the cutting period than during the unprocessed period. This result indicates that cutting can reduce the growth of alfalfa fine roots and reduce the fine root standing crop. The soil layers were ranked, from most fine roots of the three alfalfa species to least, as follows: 0-20 cm>20-40 cm>40-60 cm. The fine root turnover rates of WL343HQ, WL363HQ, and WL366HQ were 1.566, 1.973, and 1.859 yr^-1, respectively, and there was no significant difference among them (P>0.05). In correlation analyses, the total hay yield of alfalfa was significantly positively correlated with annual fine root mortality (P<0.01), and the maximum annual standing crop of fine roots was significantly positively correlated with annual fine root production. The results indicated that fine root mortality in alfalfa affects the growth and development of above-ground parts and the hay yield. The fine root standing crop, production quantity, and hay yield were higher in WL363HQ than in WL343HQ and WL366HQ, indicating that WL363HQ performs better in local areas and is more suitable for local cultivation.

Key words: fine root standing crop, fine root production, fine root mortality, alfalfa, fine root turnover