| Qilian Mountain is an important ecological safety barrier in western China.Due to the in-fluence of natural and human factors,the grassland in Qilian Mountains has been seriously de-graded in recent years,which further aggravates the contradiction between grass and livestock,and seriously affects the sustainable development of grass husbandry,local ecological environ-ment and social economy.Forage plants are the primary productivity of grazing system and the main nutrient source of livestock.The spatiotemporal differentiation of forage grass resources exacerbates the contradiction between supply and demand of forage and livestock in the region.Therefore,making clear species,distribution,yield and nutrition of forage resources,clarifying the temporal and spatial dynamic characteristics of forage resources,revealing the feeding preference mechanism of grazing livestock to different forage resources,optimizing allocation of forage grass and livestock and the regional spatiotemporal differentiation of grassland re-sources achieved the regional balance of forage and livestock.In this study,a typical natural grazing system in the Jinqianghe basin of the Eastern Qilian Mountains was selected to study the species,distribution,yield and forage value of forage grass in different topography,and the spatiotemporal differentiation of mineral elements in soil-grass-livestock system.And hetero-geneity of forage grass under topographic distribution were studied.Based on this,the regener-ation of forage grass in the growing season and the natural loss of forage grass in the cold sea-son were considered,and the monthly theoretical carrying of the study area was calculated.At the same time,the monthly balance of dry matter,nutrition and energy of grass and livestock under three levels of physiological maintenance,normal growth and quality production was an-alyzed.The main results are as follows:1)There were 116 species of herbaceous plants belonging to 86 genera and 32 families in the Jinqianghe basin,and the number of species in terrace(64 species)>half shady slope(53species)>shady slope(47 species)>riparian zones(43 species)>half sunny slope(40 spe-cies)>sunny slope(37 species).Shannon index,Patrick index and Simpson index were highest in half shady slope,and lowest in sunny slope.Pielou index was the highest on shady slope and lowest in half sunny slope.The total biomass of forage grass decreased first,then increased and then decreased with the increase of month,with the highest biomass in terrace and the lowest biomass in shady slope.2)The crude protein,crude fat and crude ash content,relative feeding value and metabo-lizable energy of forage grass were highest in July.Comprehensive analysis of TOPSIS model showed that the nutritional quality of gramineae was highest in shady slope,the nutritional quality of sedge and legumes were highest in terrace,the nutritional quality of forbs and whole community were highest in the sunny slope.The metabolizable energy of forage grass commu-nity was highest in terrace,riparian zones,shady slope and half shady slope.3)The mineral elements content of soil,forage grass and livestock serum increased firstly and then decreased with the increase of the month,and reached the maximum in September,July and July,respectively.The contents of total potassium,sodium,calcium,iron,manganese,copper and zinc of soil were the highest in sunny slope and half sunny slope.And the contents of total phosphorus,calcium,manganese and magnesium,copper and zinc of forage grass were higher in shady slope and half shady slope.In addition,the soil and forage grass were deficient in calcium,magnesium,copper and zinc in winter and spring,and livestock was deficient in phosphorus and sodium all year round,magnesium and cobalt in winter and spring.4)Food preference of Tibetan sheep in gramineae,cyperaceae,forbs and community were stronger in sunny slope,while food preference of yak in gramineae,legumes,forbs and com-munity were stronger in the terrace.The piecewise structural equation showed that topography indirectly affected the food preference index of Tibetan sheep through affecting the contents of forage grass crude ash and crude protein,functional group indirectly positively affected the food preference of Tibetan sheep through affecting forage grass crude protein contents and rela-tive feeding value,and the interactions between topography and functional group mainly af-fected the food preference index of Tibetan sheep through affecting forage grass crude ash and potassium contents.Topography indirectly affected food preference of yak through affecting forage grass crude ash and potassium contents,functional group indirectly positively affected the food preference of yak through affecting the forage grass crude protein contents and relative feeding value,and the interactions between topography and functional group mainly affected the food preference of yak through affecting forage grass crude ash and crude fibre contents.5)The total area of grassland in the study area was 510.41×106 m~2,and the stocking rate of the study area in 2019 was 89030.3 sheep units.When livestock was kept in subsistence,the dry matter,nutrition and energy of grass between forage grass and livestock in the study area were balanced.In terms of dry matter balanced,the overloading rates were 12.5%and 31%when livestock was kept in normal growth and high quality production.The dry matter defi-ciency was 2278.7 t in May when livestock was kept in normal growth,dry matter deficiency were 1566 t and 6017.9 t in March and May when livestock was kept in high quality production.In terms of nutrition balanced,the overloading rates were 16%and 32.8%when livestock keep in normal growth and high quality production.The crude protein deficiency were 189.7 t and235.5 t in April and May when livestock kept in normal livestock growth,crude protein defi-ciency were 3.2 t,379.3 t and 379.3 t in March,April and May when livestock kept in high quality production.In terms of energy balanced,the overloading rates were 17.8%and 33.6%when livestock was kept in normal growth and high quality production.The metabolic energy deficiency was 13.21×10~6 MJ and 38.01×10~6 MJ in May when livestock keep in normal live-stock growth and high quality production.In conclusion,the spatiotemporal differentiation of forage grass resource in Jinqianghe ba-sin was significant,and the supply and demand of dry matter,nutrition,energy and mineral el-ements of forage and livestock were unbalanced from March to May.Different topography of yield,nutrition,energy,mineral elements,and livestock food preference of forage grass should be fully considered in future grassland grazing management,effective combination and man-agement of different topography grassland would maintain the grassland ecological balance and improve the effective utilization of grassland resources.Meantime,reducing livestock,increas-ing grass and improving efficiency were suggested to achieve the monthly balance between supply and demand of grass and livestock in this area:1)speeding up the turnover rate with selling lambs and older livestock in autumn and reducing the number of livestock in cold sea-son.When livestock in the Jinqianghe basin of eastern Qilian Mountains kept in normal growth and high quality production,livestock should be reduced by 9874.51 sheep units and 19062.93sheep units to maintain dry matter balance,respectively,and livestock should be reduced by12259.7 sheep units and 21991.2 sheep units to maintain nutrition balanced,respectively,and livestock should be reduced by 12259.7 sheep units and 21991.2 sheep units to maintain energy balanced,respectively.2)adjusting the herd structure with increasing the proportion of breeding female animals;3)establishing high quality and high yield artificial grassland in the area with superior hydrothermal conditions to provide supplementary forage in the cold season.4)changing the traditional extensive supplementary feeding method with simple processing such as cutting and rubbing of supplementary feeding grass,and adopting feeding trough to improve the utilization rate of supplementary feeding grass. |
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