Arbuscular mycorrhizal fungi in northern Greece and influence of soil resources on their colonization

Abundance of arbuscular mycorrhizal fungi (AMF) in the roots of plant species was assessed in two areas in Greece in a 4-year study (2004–2007). The field experiment was conducted in a mountainous and herbaceous grassland in Greece in which both nitrogen (N)- and phosphorus (P)-limited plant community productivity. In 2006, data were also collected from a pot experiment in which 14 herbaceous plant species were grown as monocultures in P-limited soil. A factorial design of two levels of N and P was established in the mountainous field to test plant response to nutrient additions with respect to AMF colonization levels. Effects of fungicides were also investigated over year in the pot experiment and over three years in the field experiment. In addition, the effect of irrigation on AMF colonization was determined in a 1-year field study. Measurements included estimating the level of plant species specific hyphal colonization of roots according to the McGonicle et al. [McGonigle, T.P., Miller, M.H., Evans, D.G., Fairchild, D.L., Swan, J.A., 1990. A new method which gives an objective measure of colonization of roots by vesicular–arbuscular mycorrhizal fungi. New Phytol. 115, 495–501] method. AMF colonization was highest in the leguminous species, intermediate in the forbs and lowest in the grasses. AMF responses to N and P additions were not uniform. P addition in the field experiment increased the colonization level of the high P demanding annual forb (non-leguminous dicot) Galium lucidum, decreased hyphal abundance of the forb Plantago lanceolata and the grass Agrostis capillaris, and appeared to have a negligible effect on the forb Prunella vulgaris and on leguminous species. Effects of N addition were influenced by P addition and were only significant in plots not enriched with P where N addition increased the AMF colonization. Irrigation increased colonization of the tested species A. capillaris and P. lanceolata but only significantly increased that of P. lanceolata. There was interannual variation in the effects of fungicides on AMF colonization, which was partly due to differences in the active ingredient and formulation used. Among the tested species, A. capillaris was the most susceptible to fungicides.     

Influence of topographic and edaphic factors on vulnerability to soil degradation due to cattle grazing in humid tropical mountains in northern Honduras

Low altitude humid tropical mountains in Central America have experienced a process of livestock expansion during recent decades. However, the use of sloping areas for cattle grazing may lead to significant soil degradation and therefore we examined the influence of the slope gradient on soil degradation in pastures in a humid tropical mountainous area in northern Honduras. Understanding this relationship permits estimates of the physical carrying capacity of the soil, which in turn may help to improve livestock use within the study area. Variables examined included soil bulk density, texture, organic matter content and consistency as well as visual indicators of soil and vegetation degradation. There is a significant positive correlation between the bulk density as a proxy for soil degradation and slope gradient. Furthermore, it was found that when soils are water-saturated grazing leads to severe degradation. Together with visual indicators, these data show that paddocks with slopes less than 30% have a carrying capacity between 900 and 1900 Animal Units (AU) ha^− 1 year^− 1 and many are currently underutilized. Paddocks with slopes between 30 and 50% have a carrying capacity between 400 and 600 AU ha^− 1 year^− 1. Paddocks with slopes over 50% have the lowest carrying capacity: less than 200 AU ha^− 1 year^− 1. The latter are frequently over-used; most of them show clear signs of soil and vegetation degradation. Land use in these areas needs to change or their grazing management needs to be reorganized to adjust actual stocking rate to physical carrying capacity of the soils to prevent further degradation.     

Effect of Combined Use of Organic and Inorganic Sources of Nutrients on Sunflower Yield,Soil Fertility,and Overall Soil Quality in Rainfed Alfisol

Abstract

To study the response of inorganic and organic nitrogen (N) sources both alone and in conjunction and their influence on soil quality, a field experiment was conducted during kharif and rabi seasons using sunflower (MSFH‐8) as test crop. The experimental site soil was Typic Haplustalf situated at Hayatnagar Research Farm of Central Research Institute of Dryland Agriculture, Hyderabad, India, at 17° 18′ N latitude, 78° 36′ E longitude. The experiment design was a simple randomized block design with 11 treatments replicated four times. Among all the treatments, vermicompost (VC)+Fert at 25+25 kg N ha^?1 recorded the highest grain yields of 1878 and 2160 kg ha^?1 during both kharif and rabi seasons, respectively, which were 43.9 and 85.1% higher than their respective control plots. Apparent N recovery varied from as little as 38.30% (FYM at 50 kg N ha^?1) to 62.16 (25 kg N ha^?1) during kharif and 49.65 (75 kg ha^?1) to 83.28% (VC+Fert at 25+25 kg N ha^?1) during rabi season. Conjunctive nutrient treatments proved quite superior to other set of treatments in improving the uptake of N, phosphorus (P), potassium (K), sulfur (S), and micronutrients in sunflower and their buildup in the soil. Highest relative soil quality indexes (RSQI) were observed under VC+Fert at 25+25 kg N ha^?1 (1.00) followed by VC+Gly at 25+25 kg N ha^?1 (0.87). Considering the yield and relative soil quality indices (RSQI), conjunctive applications of VC with either inorganic fertilizer, FYM, or Gly at 25+25 kg N ha^?1 could be a successful and sustainable soil nutrient management practice in semi‐arid tropical Alfisols. Besides this, the fertilizer N demand could be reduced up to 50%.     

短期放牧对高寒草甸表层土壤入渗和水分保持能力的影响

为深入揭示短期放牧对高寒草甸生态系统地表水文过程的影响机理,基于5个放牧强度(A:2.75只羊/hm~2;B:3.64只羊/hm~2;C:4.35只羊/hm~2;D:4.76只羊/hm~2;E:5.20只羊/hm~2)的3a控制放牧试验,对比研究了表层土壤(0—10cm)物理性状、入渗过程、土壤水分特征曲线及持水和供水能力对放牧强度的响应。结果表明:C处理的土壤初始含水量显著高于D、E处理,但各放牧强度的土壤容重和4个孔隙指标无显著变化;放牧改变了土壤入渗过程,随放牧强度增加,B与C处理入渗较好,D与E处理入渗较差;Gardner模型适用于放牧强度的土壤水分特征曲线拟合,相关系数均达极显著水平,且表征土壤持水性能的a值与低中吸力段含水量表明B与C处理的持水能力高于其它处理;100kPa吸力下比水容量显示,A、B和C处理较D与E处理提高了土壤供水能力。总之,合理放牧强度短期内有利于保存高寒草甸土壤含水量,增强土壤导水性和持水能力,保证土壤有效供水,降低高寒草甸生态系统的退化风险。