有机培肥土壤对优势流中养分淋失的影响

为研究有机培肥对土壤优势流中养分淋失的影响,采用原状土柱模拟淋溶的方法,对土壤优势流中养分淋失的情况进行研究.结果表明,土壤经有机培肥后,明显降低了优势流中各种养分的淋失速度,从而使养分的淋失总量减少,为未施秸秆处理的1/3左右.有机培肥土壤对于淋溶液中养分浓度的影响表现为,在淋溶液中养分浓度总体降低的同时,各种养分的浓度降低的幅度又有所不同,其中对水溶性K和铵离子的效果最明显,而对硝态氮（NO-3-N）保持作用则相对差些.上述结果说明,有机培肥对减少土壤优势流造成的土壤养分淋失以及降低地下水污染都有一定的作用.     

Soil organic‐C accumulation and N availability under improved pastures established in Mediterranean oak woodlands

Long‐term effects of improved pasture establishment (with high proportion of legumes) on soil organic‐C status and N availability in Mediterranean cork oak (Quercus suber L.) woodlands were assessed. Soils were sampled beneath scattered crowns and in open areas, considering two systems: unmanaged and managed woodlands where improved pastures were installed 26 and 32 years ago. Total and labile C and N pools were measured and C and N mineralization were determined over 24 weeks laboratory incubation. Soils under improved pastures showed higher organic‐C, total‐N and net N mineralization than those under unmanaged pasture, mainly when established beneath trees. Potentially mineralizable C, C mineralization rate and microbial C were not statistically different between the unmanaged and improved pasture sites, but were higher closer to the tree than in the open area (1.8, 1.2 and 1.2 times, respectively). The qCO₂ was higher in improved pastures (1.7 times). Labile pool of C and N extracted with hot water increased under improved pasture (3.4 and 1.7 times, respectively). Results indicate that soil quality amelioration by improved pastures is stronger in the presence of oak trees. Management systems that favour oak tree maintenance and regeneration should be taken into account to reverse soil degradation.     

Driving forces of soil organic matter change in Jiangsu Province of China

Soil organic matter (SOM) is a key property determining soil functions and a major form of carbon stored in soil. Understanding the spatial and temporal variability of SOM and the driving forces responsible for spatial and temporal changes is important to assess regional soil quality and carbon sequestration potential and, particularly, to establish better practices for land use and management. We evaluated the spatio‐temporal change in SOM content from 1979–1982 to 2006 and its driving forces in Jiangsu Province, East China, using geostatistics. The results showed that mean SOM content increased from 16.60 ± 8.50 to 18.31 ± 8.32 g/kg over a 26‐yr period. The maps of SOM generated by ordinary kriging represented the increasing trend from north to south across the province in the two periods. The level of SOM in 1979–1982 affected the pattern of change: the SOM increasing in areas initially with a small content while decreasing in areas having a large content. The map of SOM change showed that the rate of increase decreased from north to south within the province. Increased fertilizer application promoted crop production with more residual biomass being retained in the soil, which resulted in increased SOM content. Land use changes to paddy, upland or forest improved SOM content, whereas abandoning land reduced SOM content.     

Is Discrimination of 13C in Potato Leaflets and Tubers an Appropriate Trait to Describe Genotype Responses to Restrictive and Well‐Watered Conditions?

Selection for drought tolerance entails prioritizing plant traits that integrate critical physiological processes occurring during crop growth. Discrimination against ¹³C (?) in leaflets (?_leaflet) and tubers (?_tuber) was compared under two water regimes in two potato‐improved varieties selected to maintain yield under drought conditions (Unica and Sarnav) and one drought susceptible European cultivar (Désirée). In the control treatment, soil water content was kept at field capacity over the whole growth cycle, while in the drought treatment water supply was restricted after tuber initiation (50 % of field capacity). Gas exchange and N content per unit leaf area (N_area) as well as ? were assessed at different stages. Sarnav showed the highest tuber yield in both water conditions, suggesting that yield in the water restriction treatment was largely driven by yield potential in this genotype. Higher stomatal conductance (g_s) and N_area and lower ?_leaflet in well‐watered Sarnav suggested higher photosynthetic capacity. Under water restriction, Sarnav maintained higher g_s indicating that carbon diffusion was a key factor for biomass accumulation under water restriction. Our results suggest the use of ? determined after tuber initiation as an indirect selection indicator for tuber yield under both well‐watered and restricted soil water availability conditions.     

广东三岭山森林公园主要人工林碳汇功能及其经济价值评价

本文以广东三岭山森林公园的马尾松、尾叶桉、大叶相思人工林为研究对象，研究对比它们的碳储量和碳汇经济价值，为评价广东的3个优势造林树种的碳汇能力及为广东的造林选择提供依据。结果表明：3种人工林树种单位碳储量由大到小排列次序为：尾叶桉(166.89 t·hm-2)＞大叶相思(128.72 t·hm-2)＞马尾松(70.12 t·hm-2)。3种人工林平均碳汇经济价值按大小排列次序为：尾叶桉(45611.04元·hm-2)＞大叶相思(35179.18元·hm-2)＞马尾松(19163.80元·hm-2)。尾叶桉是这3种人工林中碳储量的主要部分，对广东三岭森林公园发挥着巨大的碳汇功能并具有强大的碳汇经济价值。因此，可以考虑在广东省碳汇造林时选择尾叶桉种植。     

Late nitrogen fertilization affects carbohydrate mobilization in wheat

An experiment was carried out to determine how the late application of nitrogen (N) fertilizer affects the use of pre‐anthesis carbon reserves during the grain‐filling period of pot‐grown wheat with no water shortage. Increasing doses (equivalent to 0, 140, and 180 kg N ha^–1) of N fertilizer were applied, either in two amendments (stages GS20 and GS30) or in three amendments (stages GS20, GS30, and GS37, according to Zadoks scale). The management of fertilizer by combining an increased N rate with late N application was able to stimulate canopy development, to raise photosynthetic capacity and carbohydrate accumulation during the vegetative stages, and to increase grain yield. Based on the dynamics of carbohydrate accumulation in the ear, three phases were differentiated during the grain‐filling period, whose temporary pattern remained stable regardless of the fertilizer management. The net remobilization of carbohydrates started 12 d after anthesis from the leaves and 28 d after anthesis from roots and stems. The increase of the N dose with late N application allowed on one hand a lower use of the pre‐anthesis carbon reserves in favor of greater de novo photosynthesis during the grain‐filling period, and on the other hand greater relative contribution of the leaf and ear C reserves to remobilization towards the grain. Further splitting the dose increased only the relative contribution of ear C reserves. The stem contribution seemed to be independent of N applied whereas the root contribution tended to diminish with late N application.     

Enhancement of Germination and Growth of Slickspot Peppergrass in a New Medium with Two Compost Organic Fractions

Slickspot peppergrass (Lepidium papilliferum) is an herbaceous biennal or possibly perennial “rare” endemic plant of the southwestern Idaho high desert listed as a threatened species. This plant establishes perennial seed banks, with seeds remaining dormant and viable for several years. This study aimed to enhance the germination and early growth of this plant by adopting a new medium, a nutrient-enriched agar solution, also added with humic acid (HA) and water-extractable organic matter (WEOM) fractions isolated from a green compost (GC) and a mixed compost (MC). The germination percentage of slickspot peppergrass in this new medium was much greater than that obtained in previous studies. Further, the addition of GC-HA in the medium enhanced significantly the germination and early growth of this plant. The addition of GC-WEOM and MC-WEOM were beneficial only on plant growth for at least 7 months.     

Sulfur content of plant material: A comparison of methods of oxidation prior to determination

Abstract

Procedures for S determination involving digestion of plant material with HNO₃/HClO₄ mixtures gave lower values than those using oxygen flask combustion. Tests on a range of S compounds showed that the HNO₃/HClO₄ procedure underestimated S present in methionine, cysteine and glutathione but S in sulfate and the glucosinolate, sinigrin, was not underestimated.

Low recoveries using HNO₃/HClO₄ digestion procedures can be due both to incomplete oxidation of certain compounds and to gaseous losses during the vigorous boiling stage of digestion.     

Organic Chemical Characterization of Decomposing Plant Litter: A Comparison of Methods

There are two common methods to characterize organic chemical composition of decomposing plant litter, a forest products method and a forage fiber method. These methods divide litter into a few fractions based on extractions using different solvents. In this study, equivalencies were established between the fractions of the methods. Some of the equivalencies were based on similarities in the fractionation methods, whereas some were estimated empirically. The equivalencies gave similar chemical composition for different litter types as measurements. The results were also comparable to, or for certain fractions even better than, those obtained using earlier conversion equations. The equivalencies established are suitable for converting the forage fiber fractions to the forest products fractions in litter decomposition studies. Thus, they increase possibilities to exchange data on litter chemical characteristics across the methods in decomposition studies.     

有机与无机肥料对山地梨枣品质的影响

设置不同无机肥料(氮肥、磷肥、钾肥和氮磷钾混合肥施用)、不同有机肥(沼肥和腐熟油渣肥)和不施肥(对照),研究不同施肥方法对梨枣的水分含量,总糖、可溶性固形物、还原型抗坏血酸和总抗坏血酸、质构特性以及有机酸的影响。结果表明:肥料对梨枣的水分含量没有显著性影响,显著降低了梨枣的苹果酸,柠檬酸和有机酸总含量。有机肥沼肥和腐熟油渣肥可显著提高梨枣的果皮果肉硬度和咀嚼性以及可溶性固形物、总糖含量、抗坏血酸含量,酒石酸含量却显著降低。无机肥料氮肥、磷肥、钾肥中,钾肥有利于梨枣的可溶性固形物、总糖、抗坏血酸,苹果酸和柠檬酸的含量积累,而酒石酸含量却减少。表明增施有机肥和钾肥有利于山地梨枣品质的提高。