The effect of nitrogen fertilizer application rate on chlorophyll fluorescence characteristics and dry matter accumulation of switchgrass (Panicum virgatum) is of great significance for the improvement of light use efficiency and biomass yield of switchgrass in saline-alkali land. In this research, the patterns of variation in chlorophyll fluorescence parameters and dry matter accumulation in switchgrass were studied in field conditions with a range of nitrogen application treatments: no nitrogen (0 kg·ha^-1, N₀), low nitrogen application (60 kg·ha^-1, N₆₀), medium nitrogen application (120 kg·ha^-1, N₁₂₀) and high nitrogen application (240 kg·ha^-1, N₂₄₀), and the comprehensive effect of nitrogen application on chlorophyll fluorescence and dry matter accumulation in switchgrass was evaluated using a multivariate Grey relational analysis procedure. It was found that: under N₆₀, N₁₂₀ and N₂₄₀ treatments, the PSⅡ maximum photochemical efficiency (F_v/F_m), PSⅡ actual photochemical quantum efficiency (Φ_PSⅡ), potential activity (F_v/F_o), photochemical quenching (qP), non photochemical quenching (NPQ) and biomass yield were significantly higher, and the heat dissipation of quantum ratio (F_o/F_m) was significantly lower than for the N₀ treatment during the flowering and seed maturation stages of switchgrass development. During the flowering period of switchgrass, the PSⅡ potential activity (F_v/F_o) was initially increased and subsequently decreased across the range of nitrogen application rates, with a maximum observed value of 3.13 at N₁₂₀ (increased 16.26% compared with N₀). The effect of nitrogen application rate on dry matter accumulation differed between the crop growth stages. Dry matter accumulation was high during jointing and booting periods, reached its maximum at the seed filling stage, and decreased slightly thereafter. The maximum observed dry matter accumulation (378.13 g·hole^-1) occurred under the N₂₄₀ treatment during the post-flowering stage and was, respectively, 24.33%, 20.09% and 7.24% higher than that of the N₀, N₆₀ and N₁₂₀ treatments. Grey relational analysis showed that the association between the weighted correlation index and the ideal fertilization level was the highest under the N₂₄₀ treatment. In summary, the N₂₄₀ treatment in this study in the Yinbei saline-alkali area of Ningxia optimized the photochemical activity of PSⅡ and dry matter accumulation of switchgrass.

Understanding of the transformations and recycling processes of carbon, nitrogen and phosphorus in the soil rhizosphere is fundamental to solving the problems currently limiting the sustainable utilization of grassland agricultural ecosystems and improving grassland productivity. Rhizosphere processes in grassland can reflect the soil carbon, nitrogen and phosphorus nutrient turnover rates, affect the competition for and capture of nutrients by plants and soil microorganisms, and also determine the nutrient balance of each component in the rhizosphere microenvironment. Compared with crop systems, the coupling between carbon, nitrogen and phosphorus in grassland is stronger. Therefore, the structure and function of rhizosphere micro-ecosystems play an important role in maintaining nutrient transformation and circulation. Many literature reports indicate that the critical factor that regulates the rhizosphere microenvironment is the key substance of the plant and soil for material exchange and information transmission. The root exudates and rhizosphere exudates are also the key substances that mediate rhizosphere microorganisms and enzyme activities. When the grassland environment changes, the rhizosphere exudates, rhizosphere enzyme activities, and the composition and diversity of rhizosphere soil microorganisms will also change fundamentally, which will cause a change of supply and availability of soil nutrients, and in turn will affect grassland productivity and utilization efficiency of nutrients. So, further research on the regulation mechanism of nutrient cycling in grassland rhizosphere process is very important for revealing the distribution and utilization of nutrients and nutrient exchanges between grassland plants and microorganisms. This article reviews the mechanisms and interactions involving rhizosphere exudates, rhizosphere enzymes, and rhizosphere microorganisms involved in nutrient cycling, summarizes the mechanisms of grassland rhizosphere processes contributing to nutrient cycling and provides a perspective for consideration when formulating future research on rhizosphere microdomains in grassland ecosystems.

This study explored the effects of fence enclosure on community composition and niche characteristics in temperate meadow steppe. The indexes Levins niche breadth, Pianka niche overlap and species diversity were used to evaluate the degree of resource utilization by species and the intensity of interspecific competition inside and outside the enclosure. It was found that: the fencing enclosure significantly promoted vegetation restoration of degraded grassland. The aboveground biomass and belowground biomass in the enclosure treatments were enhanced by 255.06% and 51.06%, respectively. The species diversity and richness were enhanced in fenced enclosures by 10.36% and 10.34%, respectively. The two species with the highest niche breadth in enclosures were Iris ventricosa and Leymus chinensis, with values of 0.921 and 0.873, respectively. In comparison, the two species with the highest niche breadth in the freely grazed grassland were Taraxacum mongolicum and Carex duriuscula, with values of 0.912 and 0.791, respectively. Our results clearly show that enclosure by fencing is an efficient restoration measure that not only promotes species diversity but also improves grassland productivity. Compared with free grazing, fencing enclosure increases the overall niche overlap value and inter-species competition of plant communities and their component plant populations.

The amounts of nitrogen, phosphorus and potassium applied and the ratio of legume to grass in mixed sowings are key factors affecting the yield and fertilizer use efficiency of mixed grassland. The forage yield and utilization efficiency of nitrogen, phosphorus and potassium under different application ratios of those nutrients were analyzed to provide a scientific basis to manage cultivation of mixed grass-legume grassland for high yield. Field experiments were conducted on mixed swards of alfalfa and smooth brome. The experiment comprised two row configurations (legume:grass inter-row pattern 2:2 and 1:2) and seven nitrogen, phosphorus and potassium combinations: N₂₈₀P₁₅₀K₀ (A₁), N₃₅₀P₁₀₀K₃₆₀ (A₂), N₁₄₀P₃₀₀K₃₀₀(A₃), N₄₂₀P₂₅₀K₁₂₀ (A₄), N₇₀P₅₀K₆₀ (A₅), N₂₁₀P₀K₂₄₀ (A₆) and N₀P₂₀₀K₁₈₀ (A₇), where subscripts after each element indicate the application rate as kg·ha^-1 N, P₂O₅, and K₂O, respectively. The highest value for annual total yield of mixed legume-grass forage (11.68 t DM·ha^-1) occurred in the A₂ treatment, and yield in this treatment was significantly higher than in other treatments (P<0.01). Alfalfa yield in the A₂ treatment was 8.60 t DM·ha^-1, and it was significantly higher than A₁, A₅, A₆ and A₇ treatments (P<0.01). Grass yield in the A₁ treatment was 3.80 t DM·ha^-1, and it was significantly higher than in other treatments (P<0.01). Yields of grass and grass-legume forage were lowest in the zero nitrogen treatment, A₇. The combined grass-legume yield was significantly related to the rate of N fertilizer. Both combined grass-legume yield and alfalfa yield displayed a N×K interaction (P<0.05). The NPK partial productivity, and uptake efficiency of grass, alfalfa and grass-legume forage all showed a downward trend with increase in NPK level, and the A₅ treatment was significantly superior to other treatments (P<0.01). The nitrogen utilization efficiency of alfalfa decreased significantly in the zero potassium (A₁) and low potassium (A₅) treatments, and the potassium utilization efficiency of grass, alfalfa and grass-legume forage decreased significantly in the zero phosphorus (A₆) and high phosphorus (A₃) treatments. The annual total yield of alfalfa and legume-grass forage in the 2:2 row configuration were significantly higher than in the 1:2 configuration, with extreme significance (P<0.01). Also, the partial productivity, uptake rate and uptake efficiency of alfalfa NPK, and partial productivity of NPK, N uptake rate and N uptake efficiency of grass-legume forage in the 2:2 row configuration mixture were significantly higher than in the 1:2 configuration with extreme significance (P<0.01), and the partial productivity, uptake amount and absorption efficiency of grass NPK were significantly lower in the 2:2 than in the 1:2 configuration with extreme significance (P<0.01). Considering forage yield and nutrient utilization efficiency, alfalfa-smooth brome mixed sowing in a 2:2 row configuration, and fertilizer application of 140 kg·ha^-1 N, 100 kg·ha^-1 P₂O₅, and 120 kg·ha^-1 K₂O can be recommended, based on these results.

The objective of this study was to evaluate the effects drinking water temperature on production performance, apparent digestibility of nutrients and blood biochemical parameters in fattening sheep in winter, and rumen structure was also observed using a microscope. Information on the ideal temperature of drinking water for fattening sheep might well lead to improved production efficiencies through mechanisms such as alleviation of cold stress. A flock of 135 healthy fattening sheep with similar weight were randomly assigned into three groups, with drinking water supplied at 2, 8 and 20 ℃ for the respective groups. Each treatment contained three pens (15 sheep·pen^-1). The experiment duration was 28 days. It was found that: 1) Compared with the 2 ℃ group, the 8 and 20 ℃ groups had increased daily water consumption (P<0.05). Although there was no statistical difference (P>0.05) in daily feed intake and daily gain between any of the groups, the feed conversion efficiency in the 20 ℃ group was higher than that in 2 ℃ group (P<0.05). 2) There was a difference (P<0.01) between groups in the serum glucose (GLU) contents. The GLU content in 8 and 20 ℃ groups was 1.39 and 1.14 times higher, respectively, than that in the 2 ℃ group, and the 20 ℃ group had decreased the serum cholesterol (P<0.05). The serum urea nitrogen, total protein and serum hormone (triiodothyronine, thyroxine and growth hormone) contents did not differ between groups (P>0.05). 3) The length, width, and surface area of rumen papilla in the 20 ℃ group were increased (P<0.05) compared with the 2 and 8 ℃ groups. The group drinking water at 20 ℃ had reduced rumen muscle layer thickness (P<0.05) and increased submucosal thickness (P<0.05). However, there was no difference (P>0.05) in thickness of mucosal epithelium among groups. 4) With increase in drinking water temperature, the apparent digestibility of crude fat, neutral detergent fiber (NDF) and phosphorus (P) increased (P<0.05), especially P and NDF, while the digestibility of other nutrients did not differ between treatment groups (P>0.05). The results showed that drinking warm water improved the feed conversion efficiency of fattening sheep. In addition, drinking warm water may improve rumen function and promote the digestion and absorption of nutrients.

In this research two experiments were conducted to investigate the effects of slope and cultivation system on soil erosion control. In Experiment 1, a completely random design was used to study the runoff efficiency and the rainfall threshold to produce runoff for ridges along different slopes (0°, 5° and 10°). In Experiment 2, a split-plot design with slope (5° and 10°) as the main plot factor and tillage method (traditional planting, open ridging and tied-ridging) as the split-plot treatment was adopted to study the effect of tied-ridging rainwater harvesting on soil moisture, runoff, sediment yield, nutrient loss, alfalfa fodder yield and water use efficiency (WUE). The mean runoff efficiencies for ridges along slopes of 0°, 5° and 10° were 88.2%, 91.1% and 92.7%, respectively. The threshold precipitation to produce runoff for the respective treatments was 1.55, 1.33 and 1.00 mm, respectively. Compared with traditional planting, the decreases in runoff, runoff efficiency, sediment yield, total nitrogen loss, total phosphorus loss and organic matter loss for open ridging were 62.3%-67.9%, 51.0%-54.5%, 95.6%-96.4%, 95.3%-96.2%, 95.3%-96.1% and 94.1%-95.6%, respectively, whereas the corresponding decreases for tied-ridging were 76.4%-79.9%, 67.8%-68.2%, 98.4%, 98.1%-98.2%, 98.2% and 97.8%-97.9%, respectively. The open ridging and tied-ridging increased shallow-layer (0-60 cm) soil moisture. The increase in alfalfa forage yield and WUE for open ridging were 40.3%-50.4% and 4.4-11.5 kg·ha^-1·mm^-1, respectively. The corresponding increases for tied-ridging were 16.0%-18.7% and 2.0-5.3 kg·ha^-1·mm^-1. The runoff, runoff efficiency, sediment yield, total nitrogen loss, total phosphorus loss and organic matter loss for the 10° slope were 1.44, 1.40, 2.34, 2.24, 2.39 and 1.97 times greater than those for the 5° slope. Lastly, average soil water storage, alfalfa fodder yield and WUE for the 5° slope were 1.05, 1.28, and 1.41 times greater than those for the 10° slope. Tied-ridging rainwater harvesting was particularly beneficial for reducing runoff, sediment yield and nutrient loss. Open-ridging was offered particular effects on increase of alfalfa fodder yield and WUE.

This research explored the physiological leaf response mechanisms of sugar beet to re-watering after drought with a focus on photosynthetic physiological traits and photo-responsive parameters. Two cultivars with different drought resistance, ‘XJT9907’ (a drought sensitive type) and ‘XJT9916’ (a drought tolerant type) were studied. A controlled water deficit was imposed on plants in the leafy growth stage, whereby soil moisture content was allowed to fall to 45%-50% of field water holding capacity for 7 days, then irrigation water was added to raise soil moisture to 70%-75% of the field water holding capacity for 48 hours. At this point, the photosynthetic physiological parameters of leaves were determined, and nonlinear regression used to fit sigmoid curves for the relationship between net photosynthetic rate of leaves and light intensity. It was found that drought stress during the leafy growth stage of sugar beet development significantly reduced the SPAD value, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), and transpiration rate (T_r) of both sugar beet varieties. After re-watering, the SPAD value, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i) and transpiration rate (T_r) of sugar beet leaves under drought stress treatments all improved. The values of physiological parameters for drought tolerant XJT9916 were significantly higher than those of drought sensitive XJT9907, although none of the values exceeded those of plants with a normal level of water supply, indicating a degree of compensation effect. After the re-watering treatment, the maximum net photosynthetic rates (P_nmax) of XJT9916 and XJT9907 varieties were, respectively, 6.2% and 17.1% lower than the control, and the apparent quantum efficiency (AQY) was, respectively, 6.5% and 12.2% lower than the control. Similarly, comparing drought tolerant and drought sensitive varieties to control plants. respiration rates (Rd) were, respectively, 19.1% and 14.9% lower than the control, light saturation points (LSP) were 19.6% and 14.1% lower than the control, while the light compensation points (LCP) were, respectively, 15.4% and 17.6% (P<0.05) higher than the control. For the drought sensitive variety, the light energy utilization interval was comparatively narrow, and the light energy utilization efficiency was reduced. Taken together, the results show that when the soil moisture content is 45%-50% of the field water holding capacity during the sugar beet leafy growth period, the photosynthetic potential of sugar beet leaves is not realized, the photosynthetic capacity of the leaves is weakened and cannot be restored to normal levels after re-watering. The drought-tolerant sugar beet variety XJT9916 has strong photosynthetic recovery ability in the context of re-watering after drought.