Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

麻栎林龄对土壤水稳性团聚体及其有机碳含量的影响

为了解林龄对土壤团聚体及其有机碳含量的影响,探求各级团聚体中碳含量与团聚体稳定性之间的关系,以17、26和65 a的麻栎人工林为对象,研究了林地0～40 cm土壤水稳性团聚体组成、团聚体水稳定性以及各级团聚体有机碳含量的变化规律和相互关系。结果表明:①林龄对土壤团聚体组成及其水稳定性影响显著,影响效果随林龄增加而增强,随土层加深而减弱;②林龄对土壤团聚体有机碳含量影响显著,影响程度随林龄增加而增强;③0.25 mm土壤团聚体有机碳含量与各级土壤有机碳含量密切相关,也是影响团聚体水稳定性的主要因素。     

Water management options based on rainfall analysis for rainfed maize (Zea mays L.) production in Rushinga district, Zimbabwe

Maize (Zea mays L.), the dominant and staple food crop in Southern and Eastern Africa, is preferred to the drought-tolerant sorghum and pearl millet even in semi-arid areas. In semi-arid areas production of maize is constrained by droughts and poor rainfall distribution. The best way to grow crops in these areas is through irrigation, but limited areal extent, increasing water scarcity, and prohibitive development costs limit the feasibility of irrigation. Therefore, there is need for a policy shift towards other viable options. This paper presents daily rainfall analysis from Rushinga district, a semi-arid location in Northern Zimbabwe. The purpose of the rainfall analysis was to assess opportunities and limitations for rainfed maize production using 25 years of data. Data was analysed using a variety of statistical methods that include trend analysis, t-test for independent samples, rank-based frequency analysis, Spearman's correlation coefficient and Mann-Whitney's U test. The results showed no evidence of change in rainfall pattern. The mean seasonal rainfall was 631 mm with a standard deviation (SD) of 175 mm. December, January and February consistently remained the major rainfall months. The results depicted high inter-annual variability for both annual and seasonal rainfall totals, a high incidence of droughts ≥3 out of every 10 years and ≥1 wet year in 10 years. Using the planting criteria recommended in Zimbabwe, most of the plantings would occur from the third decade of November with the mode being the first decade of December. This predisposes the rainfall to high evaporation and runoff losses especially in December when the crop is still in its initial stage of growth. On average 5 to more than 20 days dry spells occupy 56% of the rainy season. Seasonal rainfall exhibited negative correlation (P < 0.001; R = −0.746) with cumulative dry spell length, and wet years were free from dry spells exceeding 20 days. The most common dry spells (6-10 days), are in the range in which irrigated crops survive on available soil water. Therefore, they can be mitigated by in situ rainwater harvesting (RWH) and water conservation. The potential evapotranspiration of a 140-day maize crop was estimated to be 540 mm. Consequently, short season maize cultivars that mature in less than 140 days could be grown successfully in this area in all but drought years. However, sustainable maize production can only be achieved with careful management of the soil as a medium for storing water, which is essential for buffering against dry spells. To this end soil restorative farming systems are recommended such as conservation farming, in situ RWH techniques for dry spell mitigation and a cropping system that includes drought-tolerant cereal crops as for example sorghum and pearl millet, and perennial carbohydrate sources as for example cassava to provide stable crop yields.     

三种土壤改良基质对农田栽培人参产量及质量的影响

目的通过配施发酵玉米秸秆粉、EM菌、硅藻土3种物质改良农田土壤栽培人参。方法通过正交实验设计,研究土壤改良剂对人参产量及质量的影响。结果3种物质施入后,3年生人参根长、根粗和根重分别提高0-28．85％、7．20％-60．58％和1．99％-86．54％;同时,存苗率提高0-15．36％、产量提高6．56％-67．21％,而发病率则降低3．77％-43．46％。此外,人参总皂苷含量提高3．18％-57．67％,主要单体皂苷Rg1、Re、Rb1分别提高4．72％～66．92％、7．50％-33．75％、7．22％-72．01％。极差分析表明。3种改良基质对人参产量及质量响应顺序为：EM菌〉发酵玉米秸秆粉〉硅藻土。结论通过农田土壤改良,促进了人参根系的生长,提高了产量及有效成分含量,改善了人参品质。     

稻田墒情的实时监测方案

稻田墒情监测是区域土壤墒情监测的组成部分和重要内容,但目前尚未有比较成熟的监测方案。围绕土壤含水量监测和田面水层监测2个关键环节,提出了一套稻田墒情实时监测方案。该方案能够满足田面有水层与无水层不断交替的墒情监测要求,具有一定的可操作性,可供实际工作借鉴。     

全球气候变化对松嫩草原土壤水分和生产力影响的研究

本文首先模拟计算松嫩草原土壤水量平衡,并结合未来气候情景估算松嫩草原土壤水分的变化。最后,在土壤水分研究的基础上,初步评估全球气候变化对松嫩草原生产力的影响。     

百草枯对土壤微生物影响的研究

研究了5种不同浓度百草枯对土壤微生物种群数量及土壤中细菌、放线菌和真菌生长速率的影响。结果表明,百草枯对土壤微生物的种群数量及土壤细菌、放线菌和真菌生长速率均具有一定的抑制作用,且随药剂浓度升高逐渐增强。加药后2～7d,对细菌种群抑制率为13.3%～100%,抑菌圈直径达0.07～0.93cm;对放线菌种群抑制率为8.6%～100%,抑菌圈直径达0～3.00cm;对真菌种群抑制率为7.6%～100%,生长速率的抑制率达1.4%～77.3%。抑制作用随加药时间延长又逐渐减弱。     

腐植酸复混肥对葡萄养分吸收利用的影响

为明确不同腐植酸复混肥施用量,对葡萄生长及土壤养分的影响,采取以二年生葡萄幼树进行盆栽试验。结果表明,与等养分无机化肥相比,腐植酸复合肥明显提高了葡萄植株对N、P、K肥的利用率,使土壤中的N素释放减缓,P的移动性和K的含量有较明显提高,并使土壤中有机质含量有增加的趋势。     

Changes in net N mineralization rates and soil N and P pools in a pine forest wildfire chronosequence

The concern that climate change may increase fire frequency and intensity has recently heightened the interest in the effects of wildfires on ecosystem functioning. Although short-term fire effects on forest soils are well known, less information can be found on the long-term effects of wildfires on soil fertility. Our objective was to study the 17-year effect of wildfires on forest net mineralization rates and extractable inorganic nitrogen (N) and phosphorus (P) concentrations. We hypothesize that (1) burned forest stands should exhibit lower net mineralization rates than unburned ones; (2) these differences would be greatest during the growing season; (3) differences between soil variables might also be observed among plots from different years since the last fire; and (4) due to fire-resistant geochemical processes controlling P availability, this nutrient should recover faster than N. We used a wildfire chronosequence of natural and unmanaged Pinus canariensis forests in La Palma Island (Canary Islands). Soil samples were collected during winter and spring at 22 burned and unburned plots. We found significantly higher values for net N mineralization and extractable N pools in unburned plots. These differences were higher for the winter sampling date than for the spring sampling date. Unlike extractable N and N mineralization rates, extractable P levels of burned plots exhibited a gradual recovery over time after an initial decrease. These results demonstrate that P. canariensis forest soils showed low resilience after wildfires, especially for N, and that this disturbance might induce long-term changes in ecosystem functioning.     

黄河三角洲盐生植被演替对土壤真菌碳源代谢多样性的影响

探究土壤真菌碳源代谢水平与盐生植被演替之间的关系,是理清生态系统的内部结构和功能变化的重要步骤。采用Biolog-FF微孔板培养法,结合土壤理化性质分析,研究黄河三角洲地区不同盐生植被下土壤真菌的碳源代谢活性特征。结果表明,在0~20cm土层,每孔平均吸光值(Average well color development,AWCD值)表现为白茅罗布麻柽柳马绊草光板地,20~40cm土层则表现为白茅马绊草柽柳罗布麻光板地,即随盐生植被正向演替,土壤真菌碳源代谢活性显著提高(P0.05);各样地土壤真菌群落的香农-威尔指数H、丰富度指数S和辛普森指数D按演替顺序均有显著提高,同一样地不同土层中,除马绊草群落,其余样地的3种指数均表现为0~20 cm20~40cm,说明盐生植被正向演替过程改善了土壤中真菌的多样性和丰富度,提高了群落中常见物种的优势度。土壤理化性质与土壤真菌吸光值、真菌多样性指数相关性分析结果表明,全氮、碱解氮、土壤有机质、磷酸酶和过氧化氢酶显著促进了土壤真菌的碳源代谢活性,土壤含盐量则显著抑制真菌的碳源代谢活性(P0.05);土壤主成分分析表明,纤维醇、鸟氨酸和D-甘露醇等是0~20 cm土层下土壤真菌利用的主要碳源,D-山梨醇、丙三醇和L-天冬氨酸等则是20~40 cm土层下土壤真菌利用的主要碳源,表明糖类、醇类和酸类是控制土壤真菌碳源代谢发生差异的主要碳源。土壤真菌碳源代谢水平与盐生植被演替关系的结果为黄河三角洲的生态恢复和利用奠定了理论基础。