Suitability of lucerne cultivars, with respect to root development, to semi arid conditions in west China

New Zealand Journal of Agricultural Research ISSN: 8-833 (Print) 75-8775 (Online) Journal homepage: https://www.tandfonline.com/loi/tnza Suitability of lucerne cultivars, with respect to root development, to semi arid conditions in west China Guo Zheng Gang, Liu Hui Xia, Wang Yan Rong, Wang Suo Min & Cheng Guo Dong To cite this article: Guo Zheng Gang, Liu Hui Xia, Wang Yan Rong, Wang Suo Min & Cheng Guo Dong (4) Suitability of lucerne cultivars, with respect to root development, to semi arid conditions in west China, New Zealand Journal of Agricultural Research, 47:, 5-59, DOI:.8/8833.4.95357 To link to this article: https://doi.org/.8/8833.4.95357 Published online: 7 Mar. Submit your article to this journal Article views: 9 Citing articles: 6 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalinformation?journalcode=tnza

New Zealand Journal of Agricultural Research, 4, Vol. 47Guoetal. SuitabilityoflucernetodroughtinwestChina: 5 5-59 8-833/4/47-5 The Royal Society of New Zealand 4 Suitability of lucerne cultivars, with respect to root development, to semi-arid conditions in west China GUO ZHENG GANG, LIU HUI XIA WANG YAN RONG WANG SUO MIN CHENG GUO DONG Key Laboratory of Grassland Agro-Ecosystem Ministry of Agriculture College of Pastoral Agricultural Science and Technology Lanzhou University P.O. Box 6 Lanzhou City, 73, PR of China email: zhenggangguo@hotmail.com State Key Laboratory of Frozen Soil Engineering Cold and Arid Regions Environmental and Engineering Research Institute The Chinese Academy of Sciences Lanzhou City, 73, PR China Root biomass and fine root volume were also significantly different between the eight cultivars, and the increase in the rate of development of fine root volume and root biomass in the cultivars and 'Amerigraze4+Z' was significantly faster than those of the other six cultivars, indicating that and 'Amerigraze4+Z' were better adapted to semi-arid conditions. Fine root volume and root biomass of all cultivars decreased with depth, except for those of and 'Amerigraze4+Z' where fine root volume and root biomass at -3 cm depth was greater than that at - cm. Using secondary roots, taproot length, fine root volume, and root biomass as analysis factors, cluster analysis results suggested that and 'Amerigraze4+Z' are suitable for sowing in the semi-arid and arid conditions of west China due to their strong root development. Keywords suitability; root development; lucerne cultivars; semi-arid condition; cluster analysis Abstract Lucerne root growth not only affects the ability of lucerne cultivars to assist soil conservation, but is the primary pathway for the plants to absorb water and nutrients. Therefore, the study of root development is important for assessing the suitability of lucerne cultivars to semi-arid environments. A field experiment was conducted during - in the semi-arid and arid region of west China to study the suitability of one local and seven introduced lucerne (Medicago sativa) cultivars by comparing their root development. The total number of secondary roots and taproot length were significantly different between lucerne cultivars after only one dry season. Sixty-five percent of secondary roots were present during vegetative growth, and 4% of secondary roots arose within the - cm depth. A33; Online publication date 6 February 4 Received 7 January 3; accepted 4 October 3 INTRODUCTION Lucerne (Medicago sativa) is a drought-hardy, perennial legume which produces high-quality forage (McCallum et al. ). Because of its high crude protein content, lucerne is widely used to establish pasture, not only in China but throughout the world (Li 984). Compared with cropland, lucerne pasture has been shown to decrease runoff by 94% and soil erosion by 89% (Liu 99). In recent years, establishing lucerne pastures has increasingly played a major role in improving the ecological environment and animal production in China (Wang 988; Chen et al. 99; Guo & Zhang ). There are many native and introduced lucerne cultivars in China (Wu et al. 99), but some cultivars introduced from abroad or other climatic regions are not suitable for the semi-arid conditions in west China (Ren & Hou ). Selecting the welladapted cultivars is essential, but can be problematic for rural farmers.

5 New Zealand Journal of Agricultural Research, 4, Vol. 47 The above-ground yield of different lucerne cultivars has been widely studied (Wu & Zhang 988; Zhang & Li 99; Eagleton et al. 99; Peterson et al.99; Li & Zhu 993; Saeed & El- Nadi 997), and studies indicate that herbage yield differs between cultivars (Hong et al. 987; Chen et al. 99). Below-ground growth, however, remains poorly understood. Roots not only affect the ability of cultivars to decrease soil erosion, but are key organs by which plants absorb and store nutrients (Za 987; Zhao et al. 99), and are the primary pathways for water and nutrient uptake. Moreover, root biomass in lucerne is often greater than aboveground biomass, and annual carbon and nutrient inputs to the soil from fine roots frequently equals or exceeds those extracted from leaves (Jackson et al. 997). Therefore, it is important to study root development in lucerne cultivars, as a means of assessing their suitability (Wang 99). Numerous studies on lucerne root growth carried out under irrigated conditions, pot experiments, and high rainfall field sites (Frosheiser & Barnes 973; McIntosh & Miller 98; Viands 988; Ma et al. 999; Bai et al. ) have indicated that root development differs between lucerne cultivars. However, few studies have been carried out in semiarid field conditions without irrigation. As irrigation is unavailable in large regions in west China due to topography (Guo et al. 3), this study plays an important role in lucerne research. Root development is an important indicator for estimating suitability to drought resistance (Lu 99; Ren 998), and can therefore be used to evaluate suitability of lucerne cultivars to semi-arid conditions when irrigation is unavailable. Generally, strong root development is a characteristic of lucerne cultivars adapted to dryland conditions (Guo et al. ), and this trait can be used to select adapted cultivars for establishing pasture in semi-arid and arid regions of west China. A field study was undertaken in the semi-arid and arid regions of Gansu province to analyse root development and assess the suitability of seven introduced and one local lucerne cultivars. The suitability of the eight lucerne cultivars was evaluated over years, using taproot length, secondary root, fine root volume, and root biomass measurements. The study results would be useful for selecting well-adapted lucerne cultivars to semi-arid conditions of west China. MATERIALS AND METHODS Experiment site description and treatments The field experiment was carried out during - at Jiuhuagou Basin (4 45 E and 35 54 3 N) at an elevation of 7 m in the hill and valley region of Gansu province of west China. This semi-arid region is characterised by its seasonality, and receives a 3-month high rainfall season followed by a 9-month dry season. Mean annual rainfall is 38 mm, over the past years (374 mm in ), of which 78% occurs from July to September. The mean annual evaporation is 55 mm. Soils at the experimental site are derived from a parent material consisting of silt deposited in the middle Pleistocene period (Dai & Zhang 99). The principal soil type is sienna, and has a loose texture which is prone to water erosion. To select the best adapted lucerne cultivars for these conditions, seven introduced cultivars (,,, and from the Netherlands; and 'Goldenempress' from Canada; and 'Amerigraze4+Z' from the Table Secondary roots of eight lucerne cultivars at each growth stage (roots/plant). Data are actual counts of secondary roots; within a column, numbers with the same letter are not significantly different (P =.5). in Branching Growing stage in Budding Peak Maturity 'Amerigraze4+Z' 'Goldenempress' 8 b 5 c 4c 7b IP 5 c 8 b 8 b b 7 c 5 c 9c 3 a 7c IP b b 7c 6 c b 4 a 8 c b b b 7c 6 c b 4 a 8 c b b

Guo et al. Suitability of lucerne to drought in west China 53 United States) and one local lucerne cultivar () were chosen. The experimental design was a randomised block with four replicates. Each cultivar was sown in m plots with.5 m buffer strips between plots. The experimental blocks were sown on June, by drilling to a depth of 3 cm, and using a row spacing of cm. The seeding rate was 4 kg/ha. Superphosphate was applied at 45 kg/ha. Root sampling Secondary root and taproot length was determined as described by Guo et al. (). Briefly, 5 plants from each plot were selected randomly, height, number of tillers, and canopy (area in space occupied by the plant canopy) measured, and the mean values were recorded. Ten representative plants were selected for each plot at each time of sampling. These plants were close to the mean values for tiller numbers and canopy area, and within mm of the mean plant height. After the above-ground growth was harvested, soil was excavated from a 5 cm radius around each representative plant in cm depth intervals with a spade. Secondary roots were counted and recorded at each layer. A secondary root was defined as a root with a diameter larger than mm. Taproot length was defined as the maximum depth at which the taproot had a diameter greater than mm. Stratified sampling was used to collect root biomass and fine root volume data. Within each plot, four quadrats (5 cm 5 cm) were selected randomly. After the above-ground biomass was harvested, soil in the quadrats was sampled at cm depth increments, using a spade. Each soil sample was sieved through a.5 mm mesh screen to catch and retain roots. Washed roots (after impurities in root sample had been removed) were placed in labelled plastic cups with water and refrigerated. Coarse roots ( mm diameter) and fine roots (< mm) were then separated from soil debris for each washed sample. Coarse roots were placed in labelled plastic bags and stored in the refrigerator at 4 C. Fine roots were placed in a measuring cylinder with a recorded volume of water. After the fine roots had been completely submerged for min, the Table Vertical distribution of secondary roots among eight lucerne cultivars at maturity in (roots/plant). Data are actual counts of secondary roots; within a column, numbers with the same letter are not significantly different (P =.5). - - Soil depth -3 (cm) 3-4 4-5 'Amerigraze4+Z' 'Goldenempress' 3 3 3 5 ab 3 bc 3 bc 4 ab 6 a 4ab 5 ab 6 a b b b b 4 a b 4 a b - - Table 3 Taproot length of eight lucerne cultivars at each growing stage (mm). Within a column, numbers with the same letter are not significantly different (P =.5). in Branching Budding Growing stage in Peak Maturity 5 7 8 8 9 6 'Amerigraze4+Z' 8 'Goldenempress' 6 8 9 3 4 3 9 36 b 8 c 6 c 36 b 5 a 9 c 49 a 36 b 47 b 35 c 3 c 47 b 66 a 36 c 6 a 43 b 59 b 44 c 38 c 6 b 84 a 46 c 75 a 56 b 74 b 57 c 47 c 83 b a 59 c 99 a 7 b

54 New Zealand Journal of Agricultural Research, 4, Vol. 47 water volume was recorded again and the increase (ml) of water was assumed to be the volume of fineroots (cm 3 ) (Za 987). Coarse and fine roots for each sample were enclosed in weighed filter paper, placed into labelled coin envelopes, and dried at 8-9 C for 48 h. Dried coarse and fine roots were removed from the filter paper and weighed to the nearest. g. The mean value of the four quadrats was considered as one plot for statistical analysis. All sampling was performed on 3 September at the beginning, 9 April at branching, 9 June at budding, July at the beginning, 4 August at peak, and 5 September at maturity. Statistical analysis Root data from field and laboratory measurements were analysed for variance of taproot length, number of secondary roots, fine root volume and root biomass between cultivars. Cluster analysis was used to assess the suitability of each lucerne cultivar using secondary root number, taproot length, fine root volume, and root biomass as analysis factors. RESULTS Secondary roots and their vertical distribution This study indicated that the total number of secondary roots differed significantly (P <.5) between lucerne cultivars (Table ) following budding in. had greater ability than the other seven cultivars to produce secondary roots after years. The number of secondary roots at the branching stage in as a percentage of the number at maturity in that year did not differ significantly between cultivars, and was below %. This was similar to the percentage recorded at the beginning of in, and shows that no secondary root growth occurred in winter. However, by the budding stage in the proportion of secondary roots was over 5% of total secondary root development. After peak, no secondary roots grew from the taproot for any cultivar. This result indicated that approximately 65% of secondary roots were produced during vegetative growth, which demonstrated that secondary root Table 4 Fine root volume of eight lucerne cultivars at each growth stage (mm 3 /.5 m 3 ). Within a column, numbers with the same letter are not significantly different (P =.5). Beginning in Branching Budding Growing stage in Beginning Peak Maturity ' Amerigraze4+Z' 'Goldenempress' 364 b 459 b 39 b 4 b 3 46 a 59 b 6 a 493 b 466 b 64 b 485 b 55 b 6 4 a 638 b 3 a 64 b 4 55 b 44 b 98 b 7 4 b 35 69 a 59 b 3 38 a 8 46 b 4 87 b 4 58 c 3 88 c 35 7 b 55 67 a 6 44 c 5 9 a 35 56 b 55 9 b 4 77c 33 3c 5 3 b 8 86 a 39 97c 7 9 a 56 53 b 75 84 b 56 4 c 46 34 c 68 3 b 5 36 a 5 56 c 9 46 a 68 5 b Table 5 Vertical distribution of fine root volume of eight lucerne cultivars at maturity in (mm 3 /.5 m 3 ). Within a column, numbers with the same letter are not significantly different (P =.5). - - Soil depth (cm) -3 3-4 4-5 >5 ' Amerigraze4+Z' 'Goldenempress' 5 8 b 55 bc 8 5 c 4 9 b 33 3 a 3 bc 8 5 a 3 bc 54 a 4 4 c 7 c 8 76 b 4 8 a 3 7 c 8 b 8 b 6 3 b c 78 c 3 7 b 6 4 a 78 c 4 a 5 b 78 b 5 c 47 c 68 b 7 a 38 c 7 a 77 b 387c 4c 347c 348c 75 a 8c 89 a 46 b 3 6 3 7 36

Guo et al. Suitability of lucerne to drought in west China 55 growth occurred mainly in the dry season of the study region. After years, over 4% of secondary roots developed from the taproot in the - cm layer, while no secondary roots developed below 5 cm depth (Table ). Table also shows that the main difference between cultivars occurred at the - cm and -3 cm layers. Secondary roots in and were closer to surface, with all secondary roots in the -3 cm layer. was the only cultivar to have secondary roots in the 4-5 cm layer. Taproot growth Taproot length did not differ significantly between cultivars in, but significant differences occurred after budding in (Table 3). Taproots of and 'Amerigraze4+Z' were longer than those of other cultivars after years because their growth rate was faster during the branching to budding stage in the dry season. The seasonality of rainfall contributed to the variation of taproot growth in lucerne cultivars. The high rainfall period in July at the experimental site provided favourable conditions for root growth. The high rainfall from July to September in and in the winter seasons did not affect taproot growth because taproot length was not significantly different between lucerne cultivars at these times. But significant differences between the cultivars in taproot growth occurred during the dry season (April-late June in ). with strong drought resistance maintained more rapid root growth during the dry season, whereas cultivars with weak drought resistance were affected by the dry season, consequentially slowing the growth rate. In contrast to other cultivars, 'Amerigraze4+Z' and demonstrated drought resistance. Fine root volume and its vertical distribution Fine root volume was significantly different (P <.5) between lucerne cultivars (Table 4). The fine root volume of and 'Amerigraze4+Z' was significantly greater than those of the other cultivars over years. While there was no difference between the other six lucerne cultivars in, fine Table 6 Root biomass in eight lucerne cultivars at each growing stage (g/.5 m 3 ). Within a column, numbers with the same letter are not significantly different (P =.5). in Branching Budding Growing stage in Peak Maturity 5.8 b 6.63 b 5.6 b 5.4 b 5.6 a 6.5 b 'Amerigraze4+Z'.67 a 'Goldenempress' 6.3 b 6.83 b 7. b 6.53 b 7. b 8.46 a 8.63 b 4.89 a 8.5 b.98 b.58 c.46 c 8.4 b 4.46 a 4. c 3.3 a 7.83 b 44.87 b 5.39 c 3.99 c 38.35 b 64.87 a.63 c 54.33 a 4.74 b 6.59 b 36.58 c 7.46 c 55. b 87. a 4.88 c 76.66 a 58.7 b 83.5 b 5.46 c 38.5 c 73.8 b 3.5 a 54.3 c 97.5 a 7.5 b Table 7 Vertical distribution of root biomass of eight lucerne cultivars at maturity in (g/.5 m 3 ). Within a column, numbers with the same letter are not significantly different (P =.5). - - Soil -3 depth (cm) 3-4 4-5 >5 ' Amerigraze4+Z' 'Goldenempress'.56 b 4.3 c.93 c 6.45 a 37.4 b 4.7 c 7.33 a 9.8 b 8.48 a 3.57 b.67 b.5 a.37 a 4.3 b 7.7 a 9.5 a 6.7 b.75 c 7.99 c 4.73 b 3.4 a.9 c 4.4 a 4.7 b.57 b 7.87 c 5.5 c 7.56 c 4.33 a 7.65 c 5.95 a 9.45 b 9.4 a 3.3 b.9 c 3.59 b 9.44 a 5.53 b 9.4 a 4.3 b 5.6(6.) a.(.) b.69(.8) c.8(. ) c.56(.) b.4(.) c.8(.9) b 3.53(5.) b

56 New Zealand Journal of Agricultural Research, 4, Vol. 47 Distance > f Fig. Cluster analysis on root development of eight lucerne cultivars in semi-arid conditions. DF, ; AQ, ; GE, 'Goldenempress'; ST, ; DB, ; LD, lucerne; SD, ; AG, 'Amerigraze4+Z'. 4 root volumes of,, and 'Goldenempress' were greater than that produced by,, and from the beginning of in, suggesting that the dry season has an affect on fine root growth. This study showed that 7% of the fine roots developed at -3 cm depth, and fewer than 6% were at below 5 cm (Table 5). Fine root volume was greatest at - cm. Two distribution patterns of fine roots in the soil also were observed in this experiment. The fine root volume of most cultivars decreased with depth, but and 'Amerigraze4+Z' had a greater volume at -3 cm than at - cm. The depth at which secondary roots arose from taproot greatly affected the fine root distribution in the soil. For 'Amerigraze4+Z' and, secondary roots grew from the taproot 7-9 cm below the surface and thus increased fine roots at -3 cm. Root biomass and its vertical distribution Root biomass differed significantly (P <.5) between the eight lucerne cultivars (Table 6). Root biomass of and 'Amerigraze4+Z' was greater than those of the other six cultivars at each growing stage. Root biomass was not significantly different between the other six cultivars from to the budding in, but significant difference did occur from the beginning of in, demonstrating that healthy root growth in,, and required more rainfall than,, and 'Goldenempress' in dry seasons. This indicated that the dry season affected the accumulation of root biomass in lucerne cultivars with weak drought resistance. The vertical distribution of root biomass at maturity in was analysed to better understand the ability of lucerne cultivars to grow deeper into the soil. Root biomass at -3 cm accounted for 7% of the total root biomass, but below 5 cm there was less than 6% of the roots (Table 7). Root biomass was greatest at - cm in all cultivars, but the proportion of roots in this horizon differed significantly (P <.5) between cultivars. There were two vertical distribution patterns of root biomass. One type was found in the root biomass of,,,, and 'Goldenempress', which decreased with depth. The other type was the pattern for and 'Amerigraze4+Z', which decreased from - cm depth to - cm depth, before increasing in the - cm to -3 cm depths, and finally decreasing below 3 cm. For 'Amerigraze4+Z' and, the root biomass at -3 cm was greater than at - cm. Evaluation of suitability among eight lucerne cultivars to dry conditions Space Complete Euclidean Distance was applied to analyse the suitability of each lucerne cultivar to dry conditions by taking secondary root amount, fine root volume, root biomass, and taproot length as analysis factors. Lucerne cultivars were classified into three groups using the Euclidean Distance of 4: Group : and 'Amerigraze4+Z'; Group : 'Goldenempress',, and ; and Group 3:,, and (Fig. ). Using the Euclidean Distance of 6, the eight Lucerne cultivars were classified into two groups: Group : and 'Amerigraze4+Z'; Group : 'Goldenempress',,,,, and.

Guo et al. Suitability of lucerne to drought in west China 57 DISCUSSION Secondary root and taproot growth Deeper taproots are a common strategy for resource acquisition in 5 different species of plants (Casper & Jackson 997) and are especially important in the semi-arid regions when upper soil layers dry out easily. The results of this study demonstrate that taproot lengths of several lucerne cultivars were not significantly different under moist conditions, but are significantly different after a dry season without irrigation. After one dry season, taproot growth in 'Amerigraze4+Z' and was faster than in the six other cultivars. Longer taproots provide plants with more opportunities to develop secondary roots, particularly in deeper soils. The taproot is important for producing secondary roots. The longer the taproot is, the more potential opportunities there are for developing secondary roots to a greater depth in the soil. Secondary roots are closely related to soil water and nutrient uptake by lucerne (Guo et al. ), and are also related to the drought resistance of lucerne cultivars. This study showed that the secondary root numbers were not significantly different between lucerne cultivars after year. After years, however, differences occurred, demonstrating that seasonality of rainfall in the study region affected the development of secondary roots, as this significant difference was observed only during the dry season. McIntosh & Miller (98) and Ma et al. (999) reported that secondary roots in the lucerne cultivars were significantly different in pot experiments after only 3 months. In the two pot experiments, taproots were destroyed to stimulate secondary root development (Ma et al. 998), which could have potentially made the secondary root growth different between lucerne cultivars. Secondary roots developed mainly during the vegetative period in this study. Further, the ability to produce secondary roots was reduced when lucerne entered into the reproductive stage, because water and nutrients acquired by the root system are needed to satisfy the reproductive needs of plants. Previous studies have indicated that secondary roots in lucerne grow mainly from the top cm of the taproot in regions receiving 5 mm of rainfall (Za 987). Similar results were obtained in the pot experiments (Ma et al. 999; Bai et al. ). In this study, however, 4% of secondary roots grew at - cm depth. The distribution of soil water content is the key to secondary root distribution (Guo et al. ). Soil water content at - cm depth was sufficient in the pot experiments and in high rainfall regions with regular rainfall to give more opportunities for secondary roots to grow. In semi-arid regions, rainfall is insufficient and moisture is unable to penetrate below 3 cm depth, while water in the - cm horizon evaporates easily. Few secondary roots were present in the - cm depth, but many were present at - cm depth. This would be advantageous for lucerne to extract water stored deeper in the soil profile. This appears to be an adaptive mechanism for lucerne to tolerant dry conditions. For drought-resistant cultivars, both taproot and secondary root growth were relatively high in the dry season. For cultivars with little drought resistance, taproot growth increased only when there was good rainfall. Because of their taproot and secondary root growth, 'Amerigraze4+Z' and should have better drought resistance than the other lucerne cultivars. Fine root volume and root biomass in lucerne cultivars Fine root volume reflects the ability of plants to compete for soil water and nutrients (Zhang et al. 995). The greater the fine root volume of lucerne is, the more soil water and nutrients the plant is able to extract (Wang 99; Zhao et al. 99). Root biomass is the consequence of the interaction between many ecological and agricultural factors and reflects the relative productivity and suitability of plants in a given environment (Guo et al. ). This study shows that both fine root volume and root biomass were significantly different between lucerne cultivars, similar to the results obtained from a pot experiment by Ma et al. (999) and a field study in eastern China by Bai et al. (). The difference in root volume and biomass suggests that the ability to absorb soil water and nutrients is different between the eight lucerne cultivars. The fine root volume of 'Amerigraze4+Z' and was significantly greater than those of the six other cultivars, indicating that 'Amerigraze4+Z' and can absorb and utilise more soil water and nutrients than the other six cultivars under similar dry conditions. This study showed that drought stress affected the rate of fine root volume and root biomass, which increased faster in 'Amerigraze4+Z' and than the other cultivars during the dry season, indicating that they have a greater drought resistance. The fine root volume and root biomass increase of, 'Sitel, and were slower than those of 'Goldenempress',, and,

58 New Zealand Journal of Agricultural Research, 4, Vol. 47 providing further evidence that dry season performance was the key to selecting well-adapted legumes. Lucerne cultivars are suitable for sowing in the semi-arid and arid environments only if they have healthy root development or if the dry season does not significantly restrict their root development. Comparing the traits of root biomass and fine root volume in the different soil layers is the key to understanding the ability of different cultivars to take up soil water and nutrients in deeper soil profiles. Two different distribution patterns have been described in the soil profile at maturity in. One pattern was that fine root volume and root biomass decreased with depth, similar to that reported from Cicer milkvetchin and other legume studies (Za 987; Wang 99). The other was that fine root volume and root biomass at - cm depth was smaller than that at -3 cm depth. The fine root volume and biomass of 'Amerigraze4+Z' and belonged to the latter group, which showed that they can absorb more soil water and nutrients from deep within the soil than other cultivars under dry conditions, allowing them to grow successfully in semi-arid and arid regions of west China. Suitability of cultivars Suitability of lucerne varieties is the basis for introducing them from their original places of development to the semi-arid conditions in western China. The results of the cluster analysis were consistent with field observations where, in root growth, 'Amerigraze4+Z' and were best, 'Goldenempress',, and were good, and,, and were poor. The cluster analysis showed that and 'Amerigraze4+Z' were the best adapted cultivars for sowing in the semi-arid hill and valley regions of Loess Plateau, China. CONCLUSION This study showed that ability to develop secondary roots, taproot, fine root volume, and root biomass was different between one local and seven introduced lucerne cultivars. In this field experiment, 'Amerigraze4+Z', from America, and, from the Netherlands, had stronger root development than six other cultivars, implying that they have better dry season resistance. This study suggests that the cultivars 'Amerigraze4+Z' and are suitable for sowing in the semi-arid of west China. ACKNOWLEDGMENT The research was supported in part by the National Key Basic Research Special Foundation Project of China (G86), the Australian Centre of International Agriculture Research Project in China (AS/998/6), and the National S & T Key Project of China (BA9A8). The introduced cultivars were provided by China Western Pratacultural Engineeing Company, and the local cultivar was provided by Gansu Grassland Ecological Research Institute. REFERENCES Bai Wenming; Zuo Qiang; Huang Yuanfang : Effect of water supply on root growth and water uptake of lucerne in Wulanbuhe sandy region. Acta Phyoecological Sinica 5: 35-4. Casper, B. B.; Jackson, R. B. : Plant competition underground. Annual Review of Ecology and Systematics 3: 4-7. Chen Wen; Li Qi; Zhang Xiaohu 99: The existing limiting factors for lucerne (Medicago sativa) production, and solutions with the emphasis of cultivar, soil phosphorus and cutting management in the Qingyang loess plateau area, Gansu province, China. In: Ren, J. Z. ed. Proceedings of the International Conference on Farming System on the Loess Plateau of China. Lanzhou, Gansu Science and Technology Press. Pp. 3-8. Dai Xuerong; Zhang Linyuan 99: On the formation and evolution of the Loess Plateau in China. In: Ren J. Z. ed. Proceedings of the International Conference on Farming System on the Loess Plateau of China. Lanzhou, Gansu Science and Technology Press. Pp. 8-8. Eagleton, G. E.; Zhang Xiaohu; Chen Wen 99: Lessons from on-farm experimentation into the nutritional requirements of lucerne in eastern Gansu, China. In: Ren J. Z. ed. Proceedings of the International Conference on Farming System on the Loess Plateau of China. Lanzhou, Gansu Science and Technology Press. Pp. 94-98. Frosheiser, F. I.; Barnes, D. K. 973: Field and greenhouse selection for PRR resistance in lucerne. Crop Science 3: 735-738. Guo Zhenggang; Zhang Zihe : Preliminary probe into compatibility of vegetation construction and pasture agro-ecosystem in Gansu loess plateau. Journal of Lanzhou University (Natural Sciences) 37 (Supp.): 84-9. Guo Zhenggang; Zhang Zihe; Hou Fujiang; Xiao Jinyu; Lu Ni : Study on root system development ability of several lucerne cultivars in hills and valleys of loess plateau. Chinese Journal of Applied Ecology 3: 7-.

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