Modeling grass yields in Qinghai Province,China,based on MODIS NDVI data--an empirical comparison

Qinghai Province is one of the four largest pastoral regions in China.Timely monitoring of grass growth and accurate estimation of grass yields are essential for its ecological protection and sustainable development.To estimate grass yields in Qinghai,we used the normalized difference vegetation index(NDVI)time-series data derived from the Moderate-resolution Imaging Spectroradiometer(MODIS)and a pre-existing grassland type map.We developed five estimation approaches to quantify the overall accuracy by combining four data pre-processing techniques(original,Savitzky-Golay(SG),Asymmetry Gaussian(AG)and Double Logistic(DL)),three metrics derived from NDVI time series(VImax,VIseason and VImean)and four fitting functions(linear,second-degree polynomial,power function,and exponential function).The five approaches were investigated in terms of overall accuracy based on 556 ground survey samples in 2016.After assessment and evaluation,we applied the best estimation model in each approach to map the fresh grass yields over the entire Qinghai Province in 2016.Results indicated that:1)For sample estimation,the crossvalidated overall accuracies increased with the increasing flexibility in the chosen fitting variables,and the best estimation accuracy was obtained by the so called“fully flexible model”with R2 of 0.57 and RMSE of 1140 kg/ha.2)Exponential models generally outperformed linear and power models.3)Although overall similar,strong local discrepancies were identified between the grass yield maps derived from the five approaches.In particular,the two most flexible modeling approaches were too sensitive to errors in the pre-existing grassland type map.This led to locally strong overestimations in the modeled grass yields.

Effects of Planting Density and Row Spacing on Grass Yield of Forage Sweet Sorghum(Sorghum bicolor [L.]Moench)

[Objective] The aim was to explore high-yielding cultivation techniques for forage sweet sorghum. [Method[ The effects of planting density and row spacing on plant productivity and grass yield of forage sweet sorghum （Sorghum bicolor （L.） Moench） were compared using split-plot design and LSD method of IBMSPSSStatis- ticsv22. [Result]The planting density and row spacing had important influence on the plant productivity and yield of forage sweet sorghum. The optimum planting density- row spacing combination for plant productivity of forage sweet sorghum was A1B,, i. e., planting density of 75 000 plants/hm2 and row spacing of 40 cm, and the opti- mum combination for yield of forage sweet sorghum was A2B,, i.e., planting density of 225 000 plants/hm2 and row spacing of 40 cm. [Conclusion] This study will pro- vide theoretical basis and technical support for the production practice of forage sweet sorghum.

Study on the Relationship of Seedling Density and Line Spacing to Leaf-stem Ratio, DW/FW Ratio and Grass Yield of Forage Sweet Sorghum

[ Objectives ] The aim was to optimize the configuration of seedling density and line spacing of forage sweet sorghum （ Sorghum blcolor （ L. ） Moench） and explore its high-yield cultivation techniques. [ Methods] Effects of such two influencing factors as line spacing and seedling density on the leaf-stem ratio, DW/FW ratio and grass yield of forage sweet sorghum were analyzed by using split-plot experiment design experiment method and LSD method of IBM. SPSS. Statis- tics. v22 stati, stics software. [ Results ~ Seedling density and line spacing had no obvious effect on the leaf-stem ratio and DW/FW ratio of forage sweet sorghum but had obvious influences on the grass yield. Moreover, the optimal combination of seedling density and line spacing for high yield of forage sweet sorghum was A2 B4, that is, seedling density was 225 000 plants/hm2, and line spacing was 40 cm. [ Conclusions] The results provided a theoretical basis and technical support for high-yield cultivation techniques of forage sweet sorghum.

Adaptability Comparison of Chinese Milk Vetch (Astragalus sinicus) Varieties for Double-rice Cropping System in Hunan

Five Chinese milk vetch（Astragalus sinicus） varieties were selected to make a comparison in order to screen effective varieties which could suit for the double-rice cropping system of Hunan Province. The results showed that the growth period of Xiangzi 2 is shorter than that of Xiangfei 2, Xiangfei 3 and Yujiangdaye,and is similar to that of Xinyang Chinese milk vetch. The full-bloom stage of Xiangzi 2 is also similar to Xinyang variety and obviously earlier than that of the other three varieties. The fresh grass yield of Xiangzi 2 in full-bloom stage is 23 842.5kg/hm^2, which increases by 39.9% compared with Xinyang variety. Nitrogen content in the fresh grass of Xiangzi 2 is higher than that of the other four varieties. In conclusion, Xiangzi 2 is an extremely early-blossoming and early-maturing Chinese milk vetch variety with moderate fresh grass yield, high nutrient contents, stable characters and wide adaptability. So, Xiangzi 2 is suitable for planting in double-rice cropping region in Hunan Province and other same latitude regions which have similar ecological conditions.

Effects of grazing intensity to water source on grassland condition, yield and nutritional content of selected grass species in Northwest Ethiopia

Background:Savanna grasslands are globally important ecosystems consisting of one of the most extensive grazing lands with unique biodiversity.The objectives of the study were to assess the effect of grazing intensity on grassland ecosystem condition,herbaceous plant biomass production,and nutritional content of selected grass species.Methods:The study was conducted at Chagni Ranch,Northwest Ethiopia.Four transects to water source point at regular intervals of 20m between sampling plots along transects were used for data collection.The distance between the four transects was 200m in radius.Data were collected on grass composition,basal cover,litter cover,number of seedlings,and age distribution of dominant grasses(i.e.,young,medium,or old in terms of stage of maturity),soil condition in terms of soil compaction,and soil erosion linked to the effects of trampling by grazing animals along transects(hereafter referred to as transect)to water source point.The total sample size for grass species was 160 plots.The grassland ecosystem condition,herbaceous biomass,and grass nutritional content were used as response variables linked to transect from water source point.The effects of transect on grassland ecosystem condition scores and grass nutritional content were analyzed using the analysis of variance(ANOVA).Results:Grassland condition factors like grass composition,basal cover,litter cover,age distribution of dominant grasses,and soil condition were significantly(P<0.05)higher for the furthest transect to water source point than nearest transect.Out of the 28 identified herbaceous species,grasses accounted for 64.3%of the herbaceous community.Within grass species,about 55.6%were highly desirable in terms of palatability and grazing value(as most palatable species are susceptible to heavy grazing intensity).The results showed a significantly(P<0.05)higher proportion of perennial grasses at the furthest transect to water source point than nearest transect.The dry matter yield at the furthest transect(TD4)and third transect(TD3)were significantly(P<0.05)higher than the nearest transect to water source point(i.e.,the first transect(TD1)and second transect(TD2)).Ash,neutral detergent fiber,acid detergent fiber,and acid detergent lignin contents of Cynodon dactylon,Sporobolus pyramidalis,and Digitaria ternata were significantly(P<0.05)higher at the furthest transect to water source point than nearest transect.Grazing intensity had no significant effect on the crude protein content of Cynodon dactylon and Sporobolus pyramidalis at different transects.Conclusions:The results showed that the furthest transect to water source point were in good condition.Grass biomass production and the nutritional contents of grasses were higher for the furthest transect to water source point.The results suggested that increased grazing intensity towards water source point greatly reduced the abundance of desirable perennial grasses and the sustainability of grassland for livestock production.

Spatial non-stationary characteristics between temperate grasslands based on a mixed geographically weighted regression model

Spatial models are effective in obtaining local details on grassland biomass,and their accuracy has important practical significance for the stable management of grasses and livestock.To this end,the present study utilized measured quadrat data of grass yield across different regions in the main growing season of temperate grasslands in Ningxia of China(August 2020),combined with hydrometeorology,elevation,net primary productivity(NPP),and other auxiliary data over the same period.Accordingly,non-stationary characteristics of the spatial scale,and the effects of influencing factors on grass yield were analyzed using a mixed geographically weighted regression(MGWR)model.The results showed that the model was suitable for correlation analysis.The spatial scale of ratio resident-area index(PRI)was the largest,followed by the digital elevation model,NPP,distance from gully,distance from river,average July rainfall,and daily temperature range;whereas the spatial scales of night light,distance from roads,and relative humidity(RH)were the most limited.All influencing factors maintained positive and negative effects on grass yield,save for the strictly negative effect of RH.The regression results revealed a multiscale differential spatial response regularity of different influencing factors on grass yield.Regression parameters revealed that the results of Ordinary least squares(OLS)(Adjusted R^(2)=0.642)and geographically weighted regression(GWR)(Adjusted R^(2)=0.797)models were worse than those of MGWR(Adjusted R^(2)=0.889)models.Based on the results of the RMSE and radius index,the simulation effect also was MGWR>GWR>OLS models.Ultimately,the MGWR model held the strongest prediction performance(R^(2)=0.8306).Spatially,the grass yield was high in the south and west,and low in the north and east of the study area.The results of this study provide a new technical support for rapid and accurate estimation of grassland yield to dynamically adjust grazing decision in the semi-arid loess hilly region.