MNPP Estimation And Forage-livestock Balance Characteristics Of Temperate Grassland In Semi-arid Loess Hilly Region

Climate change and human activities have had an important impact on the grassland ecosystem in China,especially in the semi-arid ecologically fragile areas in China.As an important basic means of production for traditional animal husbandry,natural grassland is an important link in the ecological chain of grassland ecosystem.The estimation and prediction of its primary production is the key to determine the reasonable livestock carrying capacity.Yuanzhou district is the largest temperate grassland area in Ningxia.The typical semi-agricultural and semi pastoral area has been damaged to varying degrees since the 1930s.The policy of returning farmland to forest and grassland has been gradually implemented.The "grazing prohibition and house feeding" has become the main animal husbandry mode of the temperate grassland in the semi-arid loess hilly region.After more than 20 years of implementation of the grassland management measures of "returning farmland to forest and Grassland",the grassland ecological environment has been greatly improved.All grasslands have not been developed and utilized,and the cultivated land has been gradually withdrawn.The sources of livestock ration supply are shrinking day by day,and the phenomenon of people and livestock competing for food still exists for a long time.It is questionable to dynamically adjust the grassland management policies to alleviate the pressure of farmers’ livestock feeding on forage grass.It is particularly important to reevaluate the balance between grass and livestock on temperate grasslands,It is a scientific question that must be answered to dynamically adjust grassland management policies.On the premise that the State advocates the development of ecological animal husbandry,it is necessary to coordinate the rational allocation of all natural grassland and artificial grassland resources related to animal husbandry,so as to promote the healthy and sustainable development of modern ecological animal husbandry.By revealing the occurrence mechanism of influencing factors of forage-livestock balance,this study,taking 2020 as the time section,analyzes the influencing factors of primary production of temperate grassland,constructs a prediction and analysis model of grass yield and nutrition,analyzes the allocation characteristics of different forage resources and their yield per unit area and nutrition carrying capacity in typical villages,and finally realizes the scale transformation of forage-livestock balance relationship among counties,villages and farmers,So as to realize the identification of influencing factors of forage-livestock balance in the temperate grassland in the semi-arid loess hilly region,provide technical support for the rapid,accurate,efficient and nondestructive estimation of the livestock carrying capacity of the temperate grassland,and also provide scientific basis for the government to comprehensively formulate animal husbandry development policies and dynamically adjust grassland management policies.The main achievements are as follows:(1)Based on CASA model,the monthly NPP of Yuanzhou District in 2020 was estimated.The results showed that the grassland MNPP mainly accumulated from May to October,and the annual grassland NPP fluctuated from.36.16 to 881.00 g·Cm-2·a-1.In order to further improve the estimation accuracy,the independent variables are set as pressure(PS),temperature(T),water vapor pressure(HPA),humidity(Rhu),sunshine hours(HR),solar radiation(SOL),normalized vegetation index(NDVI),wind speed(WS),rainfall(P)and other related meteorological factors.The correlation analysis results show that the above meteorological factors are related to grassland MNPP(p<0.01).Considering the spatio-temporal uncertainty between grassland MNPP and meteorological factors,a spatio-temporal change estimation model of grassland MNPP based on the spatio-temporal geographically and temporally weighted regression(GTWR)algorithm is established.The results well describe the spatio-temporal non-stationary characteristics of grassland MNPP change and its influencing factors.Compared with the algorithm estimation results of OLS,GWR and TWR models,the adjustment R2 of GTWR model reaches 0.974,which shows the advantages of GTWR model in improving the estimation of grassland MNPP and realizing the visualization of grassland MNPP spatial and temporal distribution.The calculation results are basically consistent with the estimation results of CASA model,and more details are shown on this basis.(2)Based on the measured quadrat data of grass yield in different regions during the main growing season of temperate grassland in August 2020,combined with the hydrometeorology,digital terrain,NPP and other auxiliary data in the same period in the study area,a grass yield estimation model based on the mixed geographically weighted regression model(MGWR)algorithm is proposed,and a new functional relationship between grass yield and its influencing factors is constructed,The spatial non-stationary characteristics of grass yield between the action scale and effect and the influencing factors were described.The results show that the RMSE and radius indexes are 92.6180 and 39.0543 respectively,and the simulation effect is the best.In terms of prediction performance,the MGWR model algorithm has the best prediction performance,and the fitting degree R2 reaches 0.8306.The grass yield in the study area shows a spatial distribution pattern of high in the South and low in the north,high in the West and low in the East.It is a potential model to fit the relationship between grass yield and influencing factors,providing a more real and effective description of the spatial process;In terms of the action scale,the impervious surface index(PRI)has the largest action scale,followed by elevation(DEM),net primary production capacity(NPP),distance from gully(DS),distance from river(DR),average rainfall in July(AJR)and daily temperature range(DTR),and the action scales of night light(NL),distance from road(DP)and relative humidity(RH)are the most limited;In terms of the effect,except for the negative effect of RH,other influencing factors have both positive and negative effects on the grass yield.(3)Grey relation analysis model(GRAM)is introduced and nine NIRS models of conventional nutrients are constructed.The determination coefficients(1-VR)of DM,ADF,CP and NDF are 0.948,0.900,0.962 and 0.917,and the relative analysis errors(RPDCV)of cross validation are greater than 3.Therefore,it can be used to predict the near-infrared calibration model of temperate grassland;While ADL,ash and Ca cross verify that the relative analysis error(RPDCV)is less than 3 and greater than 2.5,indicating that the calibration model needs to further increase the sample size to improve the prediction accuracy;The relative analysis error(RPDCV)of EE and P is less than 2.5,indicating that their calibration models can not be used to predict the near-infrared calibration model of temperate grassland for the time being.The results of spatial heterogeneity analysis of nutrient content show that Pengbao Village(γi=0.7192)has higher nutritional value,and 18 villages have good nutritional value,the rest are mostly villages with medium nutritional value,and 29 villages have poor nutritional value,showing a spatial pattern of high in the north and low in the south.The regions with higher nutritional value are concentrated in the central and northern regions.(4)In Baihe Village,the output of natural forage was low and the planting area of artificial forage was small,but the output of CP and EE per unit area was higher than that of natural forage;VFA content indicates that different types of forage resources can improve the production performance of livestock.The ratio of B to C in Baihe Village indicates that the energy utilization efficiency of Artificial Forage is higher than that of natural forage,and the carrying capacity of DCP and ME(8.59 SU·hm-2 and 9.10 SU·hm-2)are higher than that of different types of forage;Caichuan village is located at the foot of Yunwu Mountain.Due to the high yield of natural forage grass,the high planting area of artificial forage grass and the large amount of idle cultivated land,its nutrient carrying capacity(5.55 SU·hm-2 and 3.24 SU·hm-2)is greater than that of natural forage grass.The nutrient carrying capacity of natural forage grass(2.69 SU·hm-2 and 1.41 SU·hm-2)is higher than that of Baihe Village(2.51 SU·hm-2 and 0.95 SU·hm-2);The output of natural forage grass in different regions of Huangbao village varies greatly,and its average output is larger than that of Baihe Village and Caichuan village,but there is no large spatial heterogeneity in the output of forage grass in Caichuan village.As a village located in Liupan Mountain area,it has obvious advantages in the output of natural forage grass.At the same time,the planting area of artificial forage grass is large,but the land is tight.The results show that the advantages of Artificial Forage Grass in livestock carrying capacity are obvious,as high as 13.17 SU·hm-2,It is the village with the largest livestock carrying capacity in all typical villages.The CP output required by herbivores is superior in artificial forages,which can carry 23.41 SU·hm-2 livestock carrying capacity.It is the forage type with the strongest livestock carrying capacity in all typical villages.From the perspective of different detection methods,.the nutritional value of natural forage grass in typical villages was tested in conjunction with dairy one Ruminant Nutrition Laboratory of the United States.The fitting results showed that the fitting accuracy of DM and Ca in the three typical villages was high,that of NDF and CP in Baihe Village and Huangbao Village was high,that of ADF in Baihe Village was high,and that of Caichuan village needed to add more samples to improve the prediction accuracy of nutritional content.(5)At present,Yuanzhou district can carry 1576200 sheep units in general,which is in a serious overload state;In typical villages,the 8107.59 sheep unit in Baihe Village is at the level of slight overload,while the 14938.72 sheep unit and 10221.86 sheep unit in Caichuan village and Huangbao village are at the level of extreme overload in varying degrees,and the forage yield can not meet the current breeding scale for the time being;At the household scale,the typical peasant households in Baihe Village carrying 4284.01 sheep units are at the serious overload level,the typical peasant households in Caichuan village carrying 13837.66 sheep units are at the forage-livestock balance level,and the typical peasant households in Huangbao village carrying 9612.78 sheep units are at the overload level.Based on the above results and the correlation analysis of influencing factors,the mechanism of influencing factors on forage-livestock balance in temperate grassland in semi-arid loess hilly region was put forward.It was suggested that five measures should be taken to manage forage-livestock balance,such as dynamically adjusting animal husbandry policies,promoting the construction of animal husbandry infomatization,improving the planting quality of forage grass,promoting the modernization of animal husbandry and enriching the structure of livestock species.