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Understanding the effects of different levels of nitrogen fertilizer applications on soil respiration rates and soil biochemical properties is of great importance for providing a theoretical basis for accurate assessments of the soil respiration intensity and carbon recycling in grassland ecosystems. A field experiment was performed from April 2017 to March 2018, in which four different levels of nitrogen applications were investigated, including 0 kg·hm -2 (N0), 60 kg·hm -2 (N1), 120 kg·hm -2 (N2), and 180 kg·hm -2 (N3). The seasonal changes in the soil respiration rate, soil temperature, and soil moisture in the alfalfa grassland under different levels of nitrogen applications were observed, and soil biochemical characteristics were observed after each harvest in the growing season. The results showed that soil respiration rate of the alfalfa grassland displayed significant seasonal variation under different nitrogen levels. In particular, the soil respiration rate reached a peak during the last 10-day period of July and then decreased to the minimum in mid-December. During the growing season of alfalfa, the soil respiration rate of the alfalfa grassland increased with the increases in the nitrogen application rate. The mean soil respiration rates of the N1, N2, and N3 treatments were 0.97, 1.04, and 1.07 g·(m 2 ·h) -1 , respectively, and these values were 10.2%, 18.2%, and 21.6% greater than that of N0[0.88 g·(m 2 ·h) -1 ], respectively. The results from ANOVA testing indicated that nitrogen applications had no significant effect on the soil respiration rate during the non-growing season of alfalfa ( P> 0.05). According to the statistical analysis, the soil respiration rate had a significant exponential positive relationship with soil temperature during the growing season, non-growing season, and entire year of alfalfa grassland observations under different nitrogen application rates ( P <0.01); the coefficients of determination were ranked as follows:growing season (0.46-0.62) < non-growing season (0.66-0.76) < whole year (0.80-0.86). Soil temperature ( T ) and soil moisture ( W ) interacted with each other and ultimately affected the soil respiration ( R S ), and by using a two-factor linear model of soil temperature and soil moisture, a better fit was obtained for the change in the soil respiration rate. Both of the two factors explained 68%-80% of the variation in the seasonal soil respiratory rate during the growing season of alfalfa. Nitrogen fertilization decreased the soil pH and available phosphorus content (AP) to varying degrees, but it increased the available potassium (AK), soil organic matter (SOM), and soil urease (URE) and invertase activity (INV). Total nitrogen (TN) and available nitrogen (AN) showed different trends under different nitrogen levels. The TN and AN contents increased considerably in soils; however, when the nitrogen rate was higher than N2 (120 kg·hm -2 ), TN and AN decreased with the increases in the nitrogen application rate. According to the correlation matrix analysis between soil respiration and soil biochemical properties during the growth period of alfalfa, data showed that the soil respiration rate (RS) was significantly and negatively correlated with soil pH ( P <0.01), and it was significantly and positively correlated with soil TN and URE ( P <0.01). Simultaneously, there was a significant positive correlation between the soil respiration rate ( R S ) and SOM ( P <0.05), and there was a significant negative correlation with INV ( P <0.05). The soil nutrient and enzyme activities of the alfalfa grassland explained the variations in the soil respiration rate under different nitrogen application levels to varying degrees.

Field plot experiment was carried out during May 2012 to June 2014 to investigate the impacts of nitrogen fertilizations on the emissions of nitrous oxide (N 2 O) and methane (CH 4 ) from alfalfa field as well as the dry matter yield and soil nitrate contents. Five treatments including CK, urea (100 kg N·hm -2 , CF), urea (100 kg N·hm -2 ) + dairy cattle manure (60 kg N·hm -2 ) (DM 1 ), urea (100 kg N·hm -2 )+ digestate (60 kg N·hm -2 ) (DT) and reduced urea (40 kg N·hm -2 )+ dairy cattle manure (60 kg N·hm -2 ) (DM 2 ) were conducted. Results indicated that in comparison with CK, CF, DM 1 , DT and DM 2 treatments significantly increased the dry matter yields of alfalfa by 44.2%, 38.9%, 56.3% and 30.6%, and increased the N 2 O emissions by 52.2%,89.1%, 133.7% and 59.4%, respectively, whereas the oxidation of atmospheric CH 4 was reduced to different extents by these N management practices. The losses of N 2 O-N originated from urea and dairy cattle manure N accounted for 0.25%-0.28% of their inputs, whereas a greater va-lue of 0.64% was observed for digestate N. Applying urea or organic N to alfalfa field could significantly increase the dry matter yield without significant NO 3 - -N leaching, however, it would lead to higher net CO 2-equivalent emissions of producing 1 t dry matter of alfalfa.

This paper investigated soil moisture in alfalfa (Medicago sativa) cropland with different growth years (1, 3, 8, 12 and 14 years) and discussed the optimum growth years of alfalfa on the Loess Plateau of central Gansu. The results showed that the soil moisture along 0-300 cm soil profile of alfalfa croplands with different growth years was obviously lower than that of the local soil stable moisture. The soil water contents in croplands with alfalfa that had grown for 12 and 14 years were only 9.2% and 7.1% of local soil stable moisture, respectively, which were even lower than the lower limit of alfalfa growth. The average soil dryness indexes along 0-300 cm soil profile in 1, 3, 8, 12 and 14 years alfalfa croplands were 125.4%, 30.5%, 18.4%, -34.2% and -83.3% respectively. The results indicated that soil dryness occurred to varying degrees with different growth years except croplands with alfalfa grown for 1 year. With the increase of growth years of alfalfa, the soil dryness intensity increased and the soil dryness rate decreased. According to the soil moisture and alfalfa productivity results in this study, it could be concluded that the optimum growth years of alfalfa are 8-10 years in semiarid areas of the Loess Plateau.

Based on a long-term rotation and fertilization experiment in Changwu, Shaanxi, China, we determined the enzymatic activities and nutrients in soils after 27 years continuous cropping of alfalfa and wheat, respectively. The activities of invertase, urease and phosphatase were not affected by fertilization treatment within each cropping system, but they were significantly higher in the alfalfa continuous cropping system than in the wheat continuous cropping system under each fertilization treatment. The activity of hydrogen peroxidase was not affected by the type of cropping system or fertilization treatment. Across the cropping systems, the activities of soil urease, phosphatase and hydrogen peroxidase were higher while soil invertase activity was lower in N, P and manure (NPM) combined treatment compared with the other fertilization treatments. The accumulations of soil organic matter, total nitrogen and available nitrogen were greater in the alfalfa cropping system than in the wheat continuous cropping system, and the NPM treatment could improve the soil fertility.

In order to provide scientific basis for inter-planting alfalfa in abandoned farmland, a shading experiment was conducted to simulate the effects of different light intensities on the aboveground biomass, the contents of carbon, nitrogen, phosphorus and potassium, and the stoichiometric characteristics of alfalfa under the plantation. The results showed that the aboveground biomass of alfalfa correlated significantly with the light intensity, and shading treatment reduced the aboveground biomass of alfalfa significantly. The aboveground alfalfa tissues under the 62% shading treatment had the highest contents of carbon, nitrogen and phosphorus, which was 373.73, 34.38 and 5.47 g · kg(-1), respectively, and significantly higher than those of the control. However, shading treatments had no significant effect on the potassium content of aboveground part. The C/N ratio in aboveground tissues under the 72% shading treatment was significantly higher than that of the control, but no significant differences among other treatments were found. The ratios of N/P and C/P in aboveground tissues showed a tendency that decreased firstly and then increased with the increase of light intensity.

A field experiment with complete random design was conducted to investigate the effects of different mulching materials [common plastic film (CMR), biodegradable mulch film (BMR), and soil crust (SR)] and different ratios of furrow to ridge (60 cm:30 cm, 60 cm:45 cm, and 60 cm:60 cm) on the runoff efficiency, soil water storage, soil water content, and hay yield and water use efficiency of alfalfa in semiarid areas of the Loess Plateau. The runoff efficiency in treatments SR, BMR, and CMR was 32.0%, 90.7%, and 96.4%, respectively. In the early growth period of alfalfa (from April to June) , the soil water storage between the treatments had no significant difference, but in the late growth period (from July to September), the soil water storage in CMR and BMR was significantly higher than that in SR. The soil water storage in SR was significantly higher than that in traditional planting (TP). At budding stage, the soil water storage in TP, SR, BMR, and CMR was 223.27, 248.56, and 277. 81, and 284.16 mm, respectively. In the whole growth period, the hay yield of alfalfa in TP, SR, BMR, and CMR was 4112.1, 3397.5, 4317.8, and 4523.8 kg x hm(-2), and the water use efficiency was 11.08, 10.48, 14.56, and 14.95 kg x mm(-1) x hm(-2), respectively. The ratio of furrow to ridge had no significant effects on the water use efficiency in the same treatments. When the ratio of furrow to ridge was 60 cm:44 cm, the hay yield in CMR and BMR reached the maximum.

Soil samples were collected from the fields planted with alfalfa for different years in the hilly region of southern Ningxia, and the technique of synchrotron radiation-fourier transform infrared spectroscopy (SR-FTIR) was adopted to study the characters of soil organic carbon (SOC) functional groups in different sizes of soil aggregates. Planting alfalfa changed the contents of SOC functional groups and their distribution in soil aggregates. With the increasing year of planting alfalfa, the SOC content, percentage of macro-aggregates (> 0.25 mm), aggregates stability, and relative content of SOC saturated alkyl all increased, and the saturated alkyl was mainly distributed in 0.25-1 mm aggregates. However, the relative contents of SOC aliphatic-C and alcohol-C decreased with the increase of soil aggregate size. The increased aliphatic-C and alcohol-C were mainly distributed in macro-aggregates, whereas the aromatic-C was mainly distributed in < 0.25 mm aggregates. The variation range of the relative contents of the functional groups in macro-aggregates was larger than that in < 0.25 mm aggregates, showing that the SOC stability in micro-aggregates was higher than that in macro-aggregates. Continuous planting of alfalfa made the increment of SOC easily oxidizable functional groups (aliphatic-C and alcohol-C) be larger than that of aromatic-C and the chemical stability of SOC increased, with the best effect observed in 8-year planting. The aliphatic-C, alcohol-C, and saturated alkyl in SOC had higher percentages, their variation was most active, and had great contribution to the increase of SOC content.

In order to explore the regulation approaches for improving the salt-tolerance of alfalfa, the seedlings of Medicago sativa L. cv. Gannong No. 4 were taken to study their growth and nitrogen metabolism under salt stress as affected by NO-donor SNP, NO-scavenger c-PTIO, and sodium ferrocyanide (a SNP analogue with NO not released). Exogenous NO could obviously alleviate the inhibition effects of salt stress on the seedling growth and photosynthesis via increasing plant dry matter and leaf chlorophyll content, net photosynthesis rate, transpiration rate, and soluble protein content. Exogenous NO enhanced the activities of leaf nitrate reductase, glutamine synthetase, and glutamate-oxoglutarate aminotransferase, restrained the activities of protease and glutamate dehydrogenase, decreased the free amino acid content, and improved the nitrate content and ammonium assimilation under salt stress. Applying sodium ferrocyanide did not show any alleviation effect on the seedling growth and nitrogen metabolism under salt stress. As a NO-scavenger, c-PTIO inhibited the growth and nitrogen metabolism under salt stress, but the inhibition effect could be mitigated by supplementing SNP. It was suggested that exogenous and endogenous NO were involved in the regulation of alfalfa nitrogen metabolism under salt stress.

A field experiment was conducted to study the remediation of agricultural soils polluted with polychlorinated biphenyls (PCBs) by several ecological controlling measures. After sequential stages of liming, plowing, planting alfalfa and paddy, a significant part of PCBs was removed from the soil, with an average removal rate of 86.9%. The treatment also decreased the toxic equivalency of dioxin-like PCBs in soil. Analysis of PCB congener composition showed that at stages of liming, plowing and alfalfa planting, the low-chlorinated biphenyls were removed; whereas at the stage of paddy planting, the high-chlorinated biphenyls were degraded. The ecological controlling measures had little influence on the microbial communities in soil. The results suggest that ecological control techniques could be widely applied in the remediation of agricultural soils with PCBs contamination.

In order to elucidate the toxic mechanisms of Trifolium repens, Festuca arundinacea and Medicago sativa under chromium [Cr (VI)] stress, provide a theoretic foundation for phytoremediation of Cr-contaminated soil, pot experiment was conducted to investigate the effects of Cr(VI) on plant growth, physiological characteristics, Cr accumulation and distribution in three herbaceous plants. Soil sample was treated by adding K2Cr2O7 with the Cr(VI) concentration of 0, 100, 200, 300 and 400 mg x kg(-1), respectively. The results indicated that the average tolerance indices of T. repens, F. arundinacea and M. sativa were 62.5, 48.3 and 36.33, respectively. Compared with control group, contents of chlorophyll, the activity of superoxide dismutase(SOD) and peroxidase (POD) were 57.14%, 51.51%, 35.76% and 63.27%, 52.96%, 41.36% in T. repens, and F. arundinacea, respectively, but M. sativa died in 400 mg x kg(-1) Cr(VI) treatment. The plant height, root length, dry mass of roots and shoots decreased under Cr(VI) stress in three herbaceous plants, and M. sativa > F. arundinacea > T. repens, however, the content of malonyldialdehyde (MDA) increased compared to the control, and the variation range of M. sativa was the highest, while T. repens was the smallest among them. The tolerance of Cr( VI) was T. repens > F. arundinacea > M. sativa. Cr mainly distributed in cell wall and then in the cytoplasm, and less distributed in the mitochondrion and chloroplast in leaves of three herbaceous plants, whereas the content of chlorophyll, MDA, the activity of SOD and POD correlated well with Cr accumulation in the mitochondrion and chloroplast. Cr concentration in the subcellular of leaves increased with the adding Cr(VI) concentration,and M. sativa > F. arundinacea > T. repens. In comparison with T. repens, F. arundinacea, Cr concentration in the leaves of M. sativa was the maximal, i.e. 51.44 mg x kg(-1), and the proportions in the mitochondrion (18.04%) and chloroplast (19.09%) were also higher in 300 mg x kg(-1) Cr(VI). The average accumulation factors of shoots/roots were 1.22/1.54, 1.16/1.44 and 1.26/1.62, while the average translocation factors were 0.78, 0.78 and 0.74 in T. repens, F. arundinacea and M. sativa, respectively. The results suggest that T. repens and F. arundinacea are promising for the phytoremediation of Cr-contaminated soil.

The present study proposes a new approach to producing accurate estimates of fall dormancy (FD) in alfalfa in a rapid manner. Using near infrared spectroscopy, the approach produces results fast without causing damage to samples. Near infrared reflectance spectroscopy was applied to measuring the spectra of samples. Then principal component analysis (PCA) was conducted on the measurements. The top ten principal components were selected based on their cumulative contribution rates to build a support vector machine (SVM) model. Detailed analysis and discussions were conducted over their parameter and kernel classifications. The experiment found that when c = 0.339 2 and g = 32, the accuracy of the predictions of the test set can reach 98.182%. Therefore the approach can estimate the FD in alfalfa in a rapid and accurate manner. Moreover, it was compared with other approaches such as principal component regression, partial least squares regression, BP neural networks, and LVQ neural networks. The comparisons have shown that the PCA-SVM model can effectively address the small-sample-size problem and avoid local minimum.

Soil physicochemical properties play an important role in the efficiency of phytoremediation and soil arability after phytoremediation. Soil pot experiments were conducted to investigate the dynamic changes of physicochemical properties in phenanthrene (a representative of polycyclic aromatic hydrocarbons)-contaminated soil under wheat and clover intercropping. The results showed that plants improved the pH values of phenanthrene-polluted soil with a maximum variation pH of 0.61. The difference in pH between wheat/clover intercropping and wheat/clover single cropping was not significant. Soil organic matter, total nitrogen, available nitrogen, total phosphorus, available phosphorus, cation exchange capacity and available potassium decreased over the experiment period due to biodecomposition and plant root absorption. The intercropping of wheat and alfalfa accelerated the consumption of the above-mentioned nutrients. And the decrease percentages ranged from 5.24% to 57.85%, more than those of wheat or alfalfa only planted with decrease percentages between 6.29% and 39.09%. In particular, soil available nitrogen and availiable phosphorus decreased more than the other nutrients with a maximum reduction percentage of 57.85%. Therefore, the application of nitrogen and phosphorus must be paid more attention during phytoremediation of polycyclic aromatic hydrocarbon-contaminated soil in the wheat and alfalfa intercropping system.

With the combination of field survey and EPIC modeling, this paper simulated the restoration effect of soil moisture in different alfalfa (Medicago sativa)-grain rotation systems in semi-arid and drought-prone regions of Loess Plateau. In perennial alfalfa field and in grain crop field after alfalfa, the correlation coefficients between the simulated and observed values of soil moisture content in 0-10 m layer were larger than 0.9 (P < 0.01), and their relative root mean square errors were between 0.05 and 0.16, with the relative errors less than 10%. The dynamic changes of the simulated soil moisture contents in different soil layers were consistent with those of the observed values. In the study regions, it was difficult for the restoration of soil moisture in the deep soil layers of alfalfa field. During the cultivation of alfalfa, the soil moisture content in the layers at 8-10 m depth should not be less than 5.7%. Considering the sustainable development of agricultural production, the appropriate cultivation duration of alfalfa should be 4-6 years and no more than 8 years. For the restoration of soil moisture after alfalfa cultivation in the study regions, the rotation system potato (Solanum tuberosum) --> potato --> spring wheat (Triticum aestivum) could be adopted, and alfalfa could be cultivated again after 32-33 years.

By the soil respiration system, the characteristics of soil respiration were investigated to explore the correlations between soil respiration and soil temperature, soil water and soil nutrient under different land use patterns in the water-wind erosion crisscross region of the Loess Plateau. The results indicated that the seasonal changing characteristics of soil respiration were distinguished significantly among different vegetations, and soil water content and temperature were the main influencing factors. Soil respiration seasonal changing ranges, such as bare land, crop land, Medicago sativa land, Caragana korshinskii land, abandoned wild grass land, Stipa bungeana land, wild grass land, degraded Medicago sativa land, sloping Medicago sativa land, sloping abandoned wild grass land, sloping crop land and terraced crop land, were 0.32-0.82, 0.41-2.83, 0.74-2.81, 0.76-3.07, 0.67-2.79, 0.51-2.12, 0.56-2.05, 0.59-1.66, 0.42-2.09, 0.31-1.86, 0.32-1.93 and 0.41-3.17 micromol x (m2 x s)(-1). Comparing seasonal changing magnitudes of soil respiration, crop land was the biggest (167% - 203%), abandoned wild grass land (117% -154%), Caragana korshinskii land (134%), Stipa bungeana land (129%), Medicago sativa land (119%-120%) and bare land (94%) followed crop land. The smallest was degraded Medicago sativa land (92%). Bare land and degraded Medicago sativa land had small seasonal variation during the study period. Monthly average values of soil carbon flux (soil respiration) of Medicago sativa land and Caragana korshinskii land were maximal, but the maximum values under crop land were observed in July and August. Besides Q10 of crop land was also maximal, which reached 1.86. There were significant correlations between soil respiration and soil organic matter and available K. Moreover, soil respiration was affected by soil organic matter and total nitrogen in July and August when the water and heat condition were plentiful, but soil ammonium nitrogen had negative impact on soil respiration in the seasons when water and heat were not optimal.

A pot experiment was conducted to study the effects of irrigation with regenerated water on the growth, nutrient uptake, and quality of alfalfa. Four treatments were installed, i.e., irrigation with fresh water (Q), irrigation with regenerated water (Z), mixed irrigation with regenerated water and fresh water (Z + Q), and rotational irrigation with regenerated water and fresh water (Z/Q). Comparing with treatment Q, treatment Z increased the stem length, lateral branch number, and plant biomass significantly, but decreased leaf area. Treatments Z, Z + Q, and Z/Q increased plant soluble protein content by 78.43%, 83.68% and 72.53%, respectively, but treatment Z decreased plant soluble sugar content. Treatment Z increased plant Ca and Mg contents by 27.78% and 26.61%, and treatments Z and Z + Q decreased plant Fe content by 28.71% and 10.09%, respectively. Treatments Z, Z + Q, and Z/Q increased the cadmium content in above-ground part of alfalfa by 98.6%, 89.5%, and 59.0%, respectively, but the cadmium and lead contents were still lower than the thresholds of National Sanitation Standard (GB 13078-2001). It was suggested that regenerated water could be used as a source of irrigation water in alfalfa growth, but its long-term effect should be concerned.

By the method of hand-sorting, and using the indices individual number, group number, and biodiversity, the changes in the soil macrofaunal community under the grassland restoration from cropland in Wuchuan County, Inner Mongolia were investigated. A total of 1479 soil macrofauna belonging to 3 classes, 7 orders and 41 families were captured. After the grassland restoration from cropland, the group number, individual number, and biomass of soil macrofauna all had an increasing trend, and the biodiversity of soil macrofaunal community reflected by D(Ma) and DG increased significantly. However, due to the short term of cropland rehabilitation, the Shannon-Wiener index H' and the Pielou evenness index E of the soil microfaunal community in grassland were not higher than those in cropland. Different soil macrofaunal groups had different responses to the grassland restoration from cropland. The preferable approaches for the grassland restoration from cropland were planting Medicago sativa or planting Medicago sativa + Artemisia sp.

Based on GIS techniques, the interpolation maps of Therioaphis trifolii population on the arable lands in Yuanzhou District of Guyuan City in different periods were overlapped with the ecological regionalization map and digital altitude map, aimed to analyze the relations of T. trifolii population density with its ecological environment and geographical distribution. In the study area, the occurrence and distribution of T. trifolii had close relations with climate, geomorphology, and altitude. The suitable habitat of T. trifolii in the District was located in the semi-arid plain area and semi-arid holly area at the altitude 1440-2000 m, while the most possible occurrence area was the semi-arid plain at the altitude 1600-1800 m. By combining the suitable habitat with the interpolation maps of T. trifolii population in different periods, the spatial dynamics of T. trifolii population in variety of ecological areas could be analyzed quantitatively.

A pot experiment was conducted to study the effects of cadmium (Cd) stress on the soil-plant system under Brassica juncea-alfalfa intercropping, and to evaluate the Cd feed safety of alfalfa. Comparing with monoculture, when the soil Cd content was in the range of 0.37-20.37 mg x kg(-1), intercropping decreased the B. juncea biomass by 0.4%-11.8% while increased the alfalfa biomass by 55.3%-70.0%. Soil available Cd was mainly determined by soil total Cd and plant species, and less affected by planting pattern. Comparing with monoculture, when the soil Cd content was in the range of 0.37-5.37 mg x kg(-1), intercropping increased the Cd content in above-ground part of B. juncea by 14.5%, but decreased the Cd content in above-ground part of alfalfa by 57.1%. The Cd contents in the above-ground parts of alfalfa under monoculture and intercropping were 0.21 and 0.09 mg x kg(-1), respectively, neither of them being over the feed safety standard (0.5 mg x kg(-1)). When the soil Cd content was in the range of 10.37-20.37 mg x kg(-1), though the Cd contents of mono-cultured and intercropped alfalfa were both over the standard, the Cd contents in the above-ground parts of alfalfa and B. juncea under intercropping were decreased by 2.8%-48.3% and 1.1%-48.6%, respectively. Under both monoculture and intercropping, the Cd transport coefficient of B. juncea was far greater than that of alfalfa.

By the method of cross correlation coefficient in geo-statistics, this paper studied the soil hydraulic properties and their influences on soil water distribution under four land uses, i.e., farmland, waste-grassland, forestland, and alfalfa land in Liudaogou watershed of Loess Plateau. The results showed that farmland soil and waste-grassland soil had the similar physical characteristics, as did forestland soil and alfalfa land soil. For any given soil suction, farmland soil had the highest water content, while forestland soil had the lowest one. The opposite was observed for the saturated hydraulic conductivity of soil water. In forestland and alfalfa land, soil water content increased with increasing depth during water consumption period, but decreased with soil depth at any other time. The influence range of saturated hydraulic conductivity on soil water content depended on soil water condition. During the compensation period of soil water, the influenced lag distance of saturated hydraulic conductivity to water content was 0-40 cm, and that of water content to saturated hydraulic conductivity was 0-50 cm; while during the stable period of soil water, the influenced lag distances of saturated hydraulic conductivity and water content were both 0-60 cm. There were positive correlations between the two properties under all land uses during these two periods. During water consumption period, saturated hydraulic conductivity was positively correlated with soil water content in farmland and waste-grassland. The influence range of saturated hydraulic conductivity to water content was about 0-80 cm, while that of water content to saturated hydraulic conductivity was 0-60 cm. However, negative correlation was observed in forestland and alfalfa land, and the influence ranges were also about 0-60 cm.

Leaf concentration in alfalfa is an important factor affecting the nutritive value, forage intake and digestibility. Estimates of leaf concentrations commonly used currently involve a labor intensive process of hand separating leaf and stem fractions. In the present study, a total of 41 artificial alfalfa samples were mixed with different leaf concentrations ranging from 15% to 55%. The object was to develop 3 calibrations for predicting alfalfa leaf concentrations using 15, 25 and 35 calibrated samples by near infrared reflectance spectroscopy. The root mean square error of prediction(RMSEP)was 1.02, 1.97 and 0.51, respectively. External validation had a coefficient of determination (r2) ranging from 0.79 8 to 0.998 9. The ratio of performance to standard deviation (RPD) varied from 2.85 to 25.93. The results showed that 15 samples could develop accurate NIRS model of alfalfa leaf concentrations; the calibration equations got better accuracy with the increase in calibrated samples numbers from 15 to 35.

Based on model validation and database establishment, the dynamic changes of water potential productivity, available water amount in 0-10 m soil layer, and moisture distribution in soil profiles on the alfalfa grasslands at Changwu of semi-humid area, Guyuan of semi-arid area, and Haiyuan of semi-arid prone drought area on Loess Plateau were simulated with WinEPIC model in a 20-30 years period. The results showed that the simulated water potential productivity of alfalfa grasslands at Changwu, Guyuan and Haiyuan fluctuated but declined with precipitation, and the mean value was 8.81, 3.83 and 2.48 t x hm(-2), respectively. The simulated monthly available water amount in 0-10 m soil layer also declined obviously but with fluctuation. On the 4-8 years old alfalfa grasslands, soil desiccation was quite serious, and soil available water amount fluctuated at low level with precipitation for a long period. With the increasing year of alfalfa growth, the thickness and distribution depth of desiccated soil layer increased gradually, and the duration for the desiccated soil depth over 10 m was 6 years at Changwu, 6 years at Guyuan, and 4 years at Haiyuan. After then, the soil layer beneath rainfall infiltration depth lasted permanently in a desiccated status. The reasonable duration for water sustainable use on alfalfa grasslands was 8-10 years on semi-humid area, 6-8 years on semi-arid years, and 4-6 years on semi-arid prone drought area.

Pot experiment was used to investigate phytoremediation of phenanthrene-contaminated soil with alfalfa (Medicago sativa L.). Results indicated that phenanthrene had inhibitive effect on alfalfa growth, and higher phenanthrene concentration seriously prevent alfalfa growth. When the concentration was 445.22 mg/kg, the shoot and root biomasses were only 57.31% and 31.20% of control respectively. Alfalfa significantly promoted phenanthrene degradation in the soil. After 60 days, 85.68%-91.40% and 75.25%-86.61% of spiked phenanthrene disappeared from the rhizosphere and non-rhizosphere soils respectively. And the average removal ratio of phenanthrene in rhizosphere soils was 6.33% higher than that in non-rhizoshpere soils. The residual concentration of phenanthrene in the rhizosphere was lower than that in the non-rhizosphere but the dehydrogenase activity was on the contrary. With phenanthrene concentration increase the removal ratio and dehydrogenase activity decreased. A positive correlation was observed between the soil dehydrogenase activity and the removal ratio of phenanthrene in both the rhizosphere and non-rhizosphere soils. Therefore the presence of alfalfa roots was effective in promoting the phytoremediation of phenanthrene.

Vegetation recovery and reconstruction is the key of ecosystem restoration in the North Loess Plateau. With the Liudaogou catchment of Shenmu County, Shaanxi Province as test area, this paper studied the dynamics of the plant diversity of artificial alfalfa (Medicago sativa) grassland during its degradation process. The results showed that the degradation process of the grassland could be divided into three stages, i.e., artificial alfalfa grassland stage (1-6 yrs), transitional stage from artificial to natural grassland (6-10 yrs), and secondary natural grassland stage dominated by Stipa bungeana ( >10 yrs). In the whole degradation process from 1-to 30-yrs, 32 species belonging to 13 families and 28 genera were found, of which, 90% appeared in the initial 6-yrs. The dynamics of accumulatively appeared family, genus, and species in the vegetation succession process were well described by logarithmic function. During the process of community succession, the species richness (Gleason index and Margalef index),plant diversity (Shannon-Wiener index), and Pielou evenness index were changed with a similar tendency, i.e., increased more rapidly at the first stage, and the climax phase appeared in the second stage. The plant diversity and evenness decreased slightly, and gradually became stable later. Planting alfalfa could markedly accelerate the natural vegetation succession process in the forest-steppe ecotone of Loess Plateau, mainly due to the intensive soil water consumption of artificial grassland, which accelerated the process of soil aridification. To develop artificial grasslands in the Loess Plateau is an optimal joint between accelerating natural vegetation recovery and increasing farmers' income by stockbreeding, and is also a favorable paradigm both for the ecological and for the economic benefits in the eco-environmental construction in West China.

In the semi-arid area of Loess Plateau, seasonal drought often occurs during the vegetative stage of grass plants, leading to the subsequent serious reduction of their yield. Aimed to study the responses of the seedlings growth and water use of two perennial leguminous grasses Medicago sativa and Astragalus adsurgens to different soil moisture regimes, a pot experiment was installed with five treatments, i.e., adequate water supply (HW), moderate water stress (LW), soil drying gradually from HW (DHW) and LW (DLW), and refilling water to LW after soil drying from LW (RWL). The results showed that under HW, the seedlings of both M. sativa and A. adsurgens had the highest biomass and transpiration water use efficiency (TWUE), and M. sativa had a significantly higher biomass than A. adsurgens (P < 0.05). When the soil moisture content declined, M. sativa had a higher reduction rate in biomass and TWUE than A. adsurgens, and after the soil moisture regime changed from LW and DLW to RWL, the biomass of M. sativa and A. adsurgens was reduced by 47.8% and 27.9%, respectively, as compared to LW (P < 0.05). At the same time, the root/shoot ratio (R/S) of M. sativa and its water consumption per unit root increased significantly, while the TWUE decreased significantly (P < 0.05); but for A. adsurgens, its R/S decreased significantly (P < 0.05), while the TWUE and the water consumption per unit root had no significant change.

Pasture-crop rotation is regarded as a key planting system in the semiarid area of China's Loess Plateau. This paper studied the dynamics of soil nitrogen, phosphorus and organic matter within the two years of alfalfa-crop rotation. The results showed that in comparing with continuous alfalfa planting, alfalfa-crop rotation induced a decline of soil total nitrogen and organic matter contents by 5.4% and 19.5%, and 46.8% and 28.2%, respectively, in the first and second year, but no significant difference was found in soil total phosphorus. Soil nutrient availability was improved due to the rotation. In the first and second year of rotation, soil nitrate nitrogen and available phosphorus contents increased by 15.5% and 159.1%, and 44.5% and 48.0%, respectively. Planting spring wheat could maintain soil fertility, the second was fallow and planting potato, while planting corn accelerated the depletion of soil total nitrogen, organic matter and available phosphorus. As a result, in the alfalfa-crop rotation, planting spring wheat could be more available to the maintenance of soil fertility.

This paper studied the dynamics of alfalfa growth and its relation with the excessive depletion and resumption of soil water in loess hilly and gully region. The results showed that alfalfa could grow in this region for 10 years, being most flourishing at the forth and fifth year, but declined gradually because of the excessive depletion of soil water. From 0 to 35 cm above ground, the stem biomass was higher than the leaf biomass, and the ratio of stem to leaf was 1.7:1; at 40 cm above ground, the biomass of stem and leaf was equal; and from 45 to 90 cm above ground, the leaf biomass was higher than the stem biomass, with the ratio of leaf to stem 1.42:1. The soil dry layer was not distinct in first two years of alfalfa growth, but getting thicker with time, being from 110 cm in third year to 260 cm in seventh year, with a 4.6%-6.2% of soil water content. It took 5 years for the natural resumption of soil water in degraded alfalfa grassland, and soil water content was increased with time.

The protoplast fusion was induced between Astragalus adsurgens Pall and Agrobacterium rhizogenes-transformed cell line of Medicago Sativa L. by use of PEG method. Putative somatic hybrid cells were selected based on the observation that only intergeneric hybrid cells continued to divide on the DPD medium without any phytohormone while the cells and clusters derived from parental cells did not survive further. After being cultured, the somatic hybrid calli were obtained. Although both of the parental calli were not capable of regenerating , one of the hydrid cell lines recovered the differentiation ability and produced small shoots. Characterizations of the hybrid calli were carried out by examination of chromsome number, opine synthetase assay, isoenzyme and RAPD analyses.

Based on the theories of accumulated temperature and on the physio-ecological characteristics of Medicago sativa, a simulation model for its growth under soil water stress in arid sandy region was developed. The model was mainly composed of four modules: the stage module of growth, the dynamic module of leaf area index, the accumulated module of dry matter, and the distributive module of dry matter. After simulating and calculating, the model could be used to predict the growing progress and dynamic changes of leaf area and yield for herbage in sandy region. The result shows that the application of the model to production is usually effective.