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.

KOM活化堆土壤改良剂改良盐碱土壤的效果与分析

在盐碱较重的40hm2农田上施入KOM制剂，施入量为60kg·hm2，兑水800—1000倍，1个月后分别试验地和对照取样，对土壤物理性质和化学性质进行测试分析，8月上旬对作物长势进行调查测试。调查结果表明：在种植农作物的土壤中施人KOM，通过0．5cm、1．0cm、2．0cm、3．0cm、10．0cm孔径筛的土粒的百分率分别为对照的6．0倍、4．3倍、4．5倍、3．8倍和1．8倍；土壤有机质、水解氮、有效磷和速效钾的含量分别为对照的1．4倍、1．5倍、8．9倍和4．2倍；菜豆豆荚的平均长度16cm左右，而对照不足10cm。在草地施入KOM（在顶极群落羊草未形成的前提下），优势草层高度和草覆盖度分别提高了5个和14个百分点，丰富度指数和多样性指数分别是对照的2．2倍和4．0倍。在苏打盐碱土上施入KOM活化堆土壤改良剂，可显著改善土壤的理化性质，提高土地生产力。

A study of parameter uncertainties causing uncertainties in modeling a grassland ecosystem using the conditional nonlinear optimal perturbation method

In this paper, we apply the approach of conditional nonlinear optimal perturbation related to the parameter(CNOP-P)to study parameter uncertainties that lead to the stability(maintenance or degradation) of a grassland ecosystem. The maintenance of the grassland ecosystem refers to the unchanged or increased quantity of living biomass and wilted biomass in the ecosystem,and the degradation of the grassland ecosystem refers to the reduction in the quantity of living biomass and wilted biomass or its transformation into a desert ecosystem. Based on a theoretical five-variable grassland ecosystem model, 32 physical model parameters are selected for numerical experiments. Two types of parameter uncertainties could be obtained. The first type of parameter uncertainty is the linear combination of each parameter uncertainty that is computed using the CNOP-P method. The second type is the parameter uncertainty from multi-parameter optimization using the CNOP-P method. The results show that for the 32 model parameters, at a given optimization time and with greater parameter uncertainty, the patterns of the two types of parameter uncertainties are different. The different patterns represent physical processes of soil wetness. This implies that the variations in soil wetness(surface layer and root zone) are the primary reasons for uncertainty in the maintenance or degradation of grassland ecosystems, especially for the soil moisture of the surface layer. The above results show that the CNOP-P method is a useful tool for discussing the abovementioned problems.

生物质调理剂对川西北高寒草地沙化土壤养分和微生物群落特征的影响

将农牧废弃物进行资源化处置制成生物质调理剂,用于沙化土壤改良是目前川西北沙化草地生态治理的有效途径之一。为了阐明不同原料调理剂在川西北高寒沙化草地上的实际应用效果,本研究以不施用调理剂为对照(CK),设置施用量均为12 t·hm^(-2)的菌渣(JZ)、秸秆(JG)和生物炭(SWT)3种调理剂,分析了调理剂施用对土壤养分和微生物群落特征及其相互关系的影响。结果表明:与对照相比,各种生物质调理剂均显著增加了土壤速效养分和活性有机碳含量,增幅在23.0%~521.6%,其中施用秸秆调理剂(JG)的效果最佳,增幅为65.1%~521.6%。因生物质调理剂只在第一年施入,第二年的土壤速效养分和活性有机碳含量均较第一年整体下降了4.5%~92.3%,而土壤有机碳含量和微生物生物量碳均较第一年整体上升了5.6%~458.0%。生物质调理剂改变了微生物属水平优势菌属的相对丰度,其中,JG处理对细菌菌群的影响较大,JG和JZ处理对真菌菌群的影响较大。与CK相比,JG处理显著降低了土壤细菌和真菌的多样性,其中,Shannon指数显著降低了2.9%和31.8%,而Simpson指数显著提高了175.0%和320.9%。冗余分析显示,土壤速效养分和活性有机碳含量是影响微生物群落组成的重要因素,其中,土壤硝态氮含量和微生物生物量碳对细菌群落组成的影响较大,共解释了65.9%的群落变化,土壤速效钾含量和微生物生物量碳对真菌群落组成的影响较大,共解释了83.2%的群落变化。综合比较,秸秆调理剂能显著增加土壤速效养分和活性有机碳含量,有利于有益细菌和真菌微生物菌属的生长,可以作为提升川西北地区高寒草地沙化土壤质量的推广措施。