| South China Karst is one of the four major ecologically fragile areas in China.The South Karst,centered on the Guizhou Plateau,is the largest and most concentrated area of karst distribution in China.The Party Central Committee and the State Council have attached great importance to the comprehensive control project of rocky desertification in karst areas andmade important instructions on many occasions.The development of ecological animal husbandry in karst areas is one of the important measures to take into account the regional economic development and ecological security,and is an important part of the rocky desertification control model and technical system.To study the circulation mechanism of mineral elements in karst rocky desertification environment in soil-grass-livestock ecosystem and clarify the migration-enrichment law between various elements is a necessary condition for maintaining the healthy development of ecological animal husbandry,which is of great significance to alleviate the contradiction between ecological protection and production development.According to the theories of geography,ecology,pedology,plant nutrition and animal nutrition,aiming at the problems and scientific and technological needs of poor soil,serious grassland degradation,low forage quality and extensive breeding methods in karst rocky desertification areas,Bijie Salaxi,Guanling-Zhenfeng Huajiang and Shibing karst are selected as the study areas in Guizhou plateau mountainous areas representing the main karst habitat types in southern China.From 2019 to 2022,based on the investigation of the background value of soil mineral elements,we carried out the grass and livestock mineral element circulation experiment and beef cattle healthy breeding experiment.Through the processing of the experimental data,we analyzed the change characteristics and mutual relationship of mineral element content in soil,pasture and beef cattle ecosystem during the succession of different levels of rocky desertification,and clarified the coupling mechanism between grass and livestock mineral element circulation and beef cattle healthy breeding.This paper revealed the factors affecting the change of mineral elements in the ecosystem,screens and innovates the direct and indirect supplementary feeding technology of mineral elements,integrated the optimal regulation technology of mineral elements,and carries out application demonstration and verification,in order to provide scientific and technological reference for promoting the development of ecological animal husbandry in Karst areas.（1）In karst rocky desertification areas,the content of mineral elements in soil varied greatly among different regions,and some elements may not meet the nutritional needs of plant growth and development:compared to the background value of Chinese soil,the average contents of P,Fe,Cu,Mn,Zn and Cr in the soil of Salaxi demonstration area in Bijie were higher,while the contents of Ca,K,Se and Mo were lower;The average contents of Ca,P,Fe,Cu,Mn,Zn and Cr in the soil of Guanling-Zhenfeng Huajiang demonstration area were higher,while the contents of K,Se and Mo were lower;The average contents of P,Mn and Zn in the soil of Shibing karst demonstration area were higher,the difference of Se content was small,while the contents of Ca,K,Fe,Cu,Mo and Cr were lower.Soil is the central reservoir of mineral elements.The lack of a mineral element in soil may reduce the content of the mineral element in forage,and then affect the health of livestock.Evaluating the content of soil mineral elements is the premise of precision fertilization or improvement measures,which is conducive to the sustainable development of grassland industry.（2）The content of mineral elements in soil and forage varied with the growth period of forage.Except Se,other elements in soil and forage in karst rocky desertification area can meet the nutritional needs of beef cattle:with the growth period,the content of Ca in the above-ground part of Dactylis glomerata was relatively stable,while the contents of K,Fe,Zn,Cu,Se,Mo and Cr changed significantly in different growth periods（P<0.05）;Ca,K,Fe,Zn,Cu,Se,Mo and Cr in the upper part of Pennisetum hydridum showed different regular changes with the change of growth period（P<0.05）;The content of some mineral elements in the above-ground part of Lolium perenne also had similar changes with the growth period.Moreover,there were great differences in the content of the same element among different forages.Only Se element was in critical deficiency state in Dactylis glomerata grassland,Lolium perenne grassland and Lolium perenne grassland,which may lead to the decrease of Se content in forages and indirectly lead to Se deficiency in animals.Similar to the content of elements in soil,it was found that except Se,other elements in Dactylis glomerata,Lolium perenne and Lolium perenne could meet the nutritional needs of beef cattle.The content of mineral elements in soil and forage varied with the growth period of forage,which affected the circulation efficiency of mineral elements between soil and forage,and finally led to the fluctuation of mineral element content of beef cattle with time.Reveal the change law of mineral element content in forage,which is convenient for targeted supplementary feeding and realize the healthy development of livestock.（3）The correlation of mineral elements between forage and beef cattle hair was clarified:during feeding,there was a correlation between the elements Ca,K,Zn and Cu in the hair of Dactylis glomerata and Weining cattle,but it was not significant（P>0.05）;There was a significant correlation between Lolium perenne and Ca in the hair of Guanling cattle（P<0.05）,and there was a very significant correlation between Zn（P<0.01）,but there was no significant correlation between Se,Mo and Cr（P>0.05）;There was a significant correlation between Lolium perenne and Ca and Se in Liping cattle hair（P<0.05）,but there was no significant correlation between elements Fe,Zn,Cu and Mo（P>0.05）.Some mineral elements had a certain correlation between forage and beef cattle hair.Therefore,the mineral element analysis in forage can be used to measure the nutritional level of mineral elements in beef cattle hair.By analyzing the relationship of mineral element content between grass and livestock,it was helpful to evaluate the nutritional level of livestock and provide scientific basis for mineral element supplement.（4）The coupling mechanism between the cycling of grass and livestock mineral elements in karst rocky desertification environment and the healthy breeding of beef cattle was revealed:by comparing the serum biochemical indexes of the control group and the experimental group before and after the test,it was found that the addition of selenium enriched yeast in the basic diet effectively increased the contents of whole blood selenium,serum GSH-Px,SOD and MDA of Weining cattle,Guanling cattle and Liping cattle.Although there were some interspecific differences in the test effect,the content of whole blood selenium was higher than the critical value of selenium deficiency of beef cattle.Applying the organic fertilizer made of beef manure in the experimental group,the physical and chemical properties of grassland soil were significantly or extremely significantly higher than those in the control group;The contents of biomass and nutrients（CP,Ash,EE,CF,Se）in the above-ground part of Dactylis glomerata,Lolium perenne and Lolium perenne grassland were significantly or very significantly higher than those in the control group,but the content of Se in soil and forage was lower than the nutritional needs of beef cattle.Understanding the coupling mechanism between grass livestock mineral element cycle and healthy beef cattle breeding is not only the basic content of protecting the healthy development of soil-grass-livestock ecosystem,but also an important premise to adjust the mineral element level of livestock through human interference.（5）The key technologies suitable for the nutrient cycling of grass and livestock and the healthy breeding of beef cattle in karst rocky desertification were put forward,and the achievements were demonstrated and verified:according to the existing technologies of karst rocky desertification grass and livestock nutrient element circulation and healthy beef cattle breeding in Bijie Salaxi demonstration area,Guanling-Zhenfeng Huajiang demonstration area and Shibing karst demonstration area,compound fertilizer technology and supplementary feeding improvement technology were put forward.Since the start of the experiment,about 14.12hm~2 of high-quality artificial grassland with both ecological protection and economic development has been built in Bijie Salaxi demonstration area,about 10.04 hm~2 of high-quality artificial grassland with both ecological protection and economic development has been built in Guanling-Zhenfeng Huajiang demonstration area,and about 7.75 hm~2 of high-quality artificial grassland with both ecological protection and economic development has been built in Shibing demonstration area,with obvious demonstration effect.In the selection of fertilization and supplementary feeding modes,it is still necessary to strengthen the suitability analysis.According to the characteristics of planting and feeding in different regions,the selection according to local conditions,and the integration and innovation of technologies should be strengthened. |
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