磷与镉对不同类型耕型红壤有机氮矿化的影响

采用室内培养,设磷处理浓度为0、0.1、0.3和0.5 g/kg,镉处理浓度为0、0.5和1.0 mg/kg,研究磷、镉单独处理及磷、镉共同处理对湖南省4种典型母质(第四纪红土、花岗岩风化物、石灰岩风化物和板岩风化物)发育的耕型红壤有机氮矿化的影响.结果表明:培养2~8周的耕型第四纪红土红壤氮矿化量均值随磷添加量增加而先增加后减小,且在添加0.1 g/kg 磷时土壤的氮矿化量最大,其余红壤氮矿化量均随磷添加量的增加而增加;添加镉对耕型第四纪红土红壤和耕型石灰岩红壤氮矿化有抑制作用,最大降幅分别为4.98 mg/kg 和6.53 mg/kg;磷、镉共同处理,除耕型第四纪红土红壤外,对其余红壤氮矿化均表现为促进作用,且不同红壤氮矿化量存在差异;添加0.3 g/kg 和0.5 g/kg 磷对轻度镉污染红壤的有机氮矿化效果最好     

农田土壤温室气体排放研究进展(英文)

[目的]对农田土壤温室气体排放的研究进展进行综述。[方法]根据近几年国内外相关文献,对农田土壤中CO2、CH4和N2O的产生机理、排放特征及其主要影响因素进行归纳。[结果]土壤中温室气体CO2、CH4和N2O的产生和排放过程,是陆地生态系统碳氮循环的重要过程,是土壤碳氮库的重要输出途径,在全球碳氮循环中起到很重要作用,对其展开研究有利于减少其排放温室气体的量以及增大其吸收温室气体的能力,从而更有效地实现温室气体的减排。[结论]该研究有助于对温室气体排放规律和影响因素的正确了解,从而对温室气体减排以及研究气候变化提供理论依据。     

干旱区绿洲农田土壤污染生态补偿标准测算——以白银、金昌市郊农业区为例

文中基于环境价值评估法(CVM)为干旱区绿洲农田土壤重金属污染防治生态补偿政策进行了计量经济学的模型分析,测算了农户对当地实施生态补偿的受偿意愿。在382个调查样本中,91.79%的受访村民认为所在地目前土壤污染问题十分严重并已造成了食用人群健康风险,制定合理的生态补偿标准是保障生态修复工程的核心因素。受偿意愿调查结果显示,干旱区绿洲农田受重金属污染的农户的年平均受偿意愿(MWPA)在746.45-862.73元/hm2之间,影响该数额的主要因素为农户家庭人口、户均耕地面积以及农户受教育程度。该结果说明受访农户提出的受偿意愿是以当地种植基本粮食作物的年收入840元/亩为基础的,但未包括当地农业生产的生态效益损失和对人群健康影响的损失,且受经济欠发达地区农户年均收入较低和信息获取渠道缺乏的影响,当地农户受偿意愿低于其他地区生态补偿受偿意愿。     

Influence of Aluminum Hydroxide on Potassium Release from Two Colombian Soils

Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K₂O, respectively. They were used either untreated or prepared by adding AlCl₃ and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH₄OAc at pH 7.0 and 10 mM CaCl₂ at pH 5.8 for 120 h at 6 mL h^?1 to examine the release of Kex and Knex. In the untreated soils, NH₄ ⁺ and Ca²⁺ released the same amounts of Kex from Caribia, whereas NH₄ ⁺ released about twice as much Kex as Ca²⁺ from High Terrace. This study proposes that the small ionic size of NH₄ ⁺ (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca²⁺ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca²⁺ caused Knex to be released from Caribia with no release by NH₄ ⁺. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca²⁺ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl₃ which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH₄ salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.     

Molybdenum and Copper Uptake by Forage Grasses and Legumes Grown on a Metal‐Contaminated Sludge Site

Abstract

Wastes applied to agricultural land can contain significant concentrations of bioavailable molybdenum (Mo). Because Mo uptake by forage crops could lead to hypocuprosis in ruminants, more knowledge is needed about which crops are most efficient in accumulating Mo. At an old sewage sludge‐amended site, the concentrations of Mo, copper (Cu), and several other trace metals were measured in various grass species. Generally, the grasses grown on the sludge site contained higher Mo concentrations than the same species grown on a nearby control site. However, because Cu concentrations were also higher in the sludge‐grown grasses, Cu:Mo ratios in the grasses were frequently higher on the sludge site. In contrast, all legumes tested (alfalfa, birdsfoot trefoil, red clover, pea), as well as canola and beets, had lower Cu:Mo ratios when grown on the sludge site. Sulfur concentrations in the two crops analyzed for this element (canola and pea) were higher on the sludge site than the control. It is concluded that Mo, Cu, and sulfur (S) bioavailability remains elevated in the soil several decades after sewage sludge application.     

Zinc Deficiency in Rainfed Wheat in Pakistan: Magnitude,Spatial Variability,Management, and Plant Analysis Diagnostic Norms

Abstract

Zinc (Zn) deficiency is a widespread micronutrient disorder in crops grown in calcareous soils; therefore, we conducted a nutrient indexing of farmer‐grown rainfed wheat (Triticum aestivum, cv. Pak‐81) in 1.82 Mha Potohar plateau of Pakistan by sampling up to 30 cm tall whole shoots and associated soils. The crop was Zn deficient in more than 80% of the sampled fields, and a good agreement existed between plant Zn concentration and surface soil AB‐DTPA Zn content (r=0.52; p≤0.01). Contour maps of the sampled areas, prepared by geostatistical analysis techniques and computer graphics, delineated areas of Zn deficiency and, thus, would help focus future research and development. In two field experiments on rainfed wheat grown in alkaline Zn‐deficient Typic Haplustalfs (AB‐DTPA Zn, 0.49–0.52 mg kg^?1), soil‐applied Zn increased grain yield up to 12% over control. Fertilizer requirement for near‐maximum wheat grain yield was 2.0 kg Zn ha^?1, with a VCR of 4∶1. Zinc content in mature grain was a good indicator of soil Zn availability status, and plant tissue critical Zn concentration ranges appear to be 16–20 mg kg^?1 in young whole shoots, 12–16 mg kg^?1 in flag leaves, and 20–24 mg Zn kg^?1 in mature grains.     

Factors Influencing the Dissolution of Phosphate Rock in a Range of High P‐Fixing Soils from Cameroon

Abstract

A laboratory incubation experiment was conducted to evaluate the soil factors that influence the dissolution of two phosphate rocks (PRs) of different reactivity (Gafsa, GPR, reactive PR; and Togo‐Hahotoe, HPR, low reactivity PR) in seven agricultural soils from Cameroon having variable phosphorus (P)‐sorption capacities, organic carbon (C) contents, and exchangeable acidities. Ground PR was mixed with the soils at a rate of 500 mg P kg^?1 soil and incubated at 30°C for 85 days. Dissolution of the PRs was determined at various intervals using the ΔNaOH‐P method (the difference of the amount of P extracted by 0.5 M NaOH between the PR‐treated soils and the control). Between 4 and 27% of HPR and 33 and 50% of GPR were dissolved in the soils. Calcium (Ca) saturation of cation exchange sites and proton supply strongly affected PR dissolution in these soils. Acid soils with pH‐(H₂O)<5 (NKL, ODJ, NSM, MTF) dissolved more phosphate rock than those with pH‐(H₂O)>5 (DSC, FGT, BAF). However, the lack of a sufficient Ca sink in the former constrained the dissolution of both PRs. The dissolution of GPR in the slightly acidic soils was limited by increase in Ca saturation and that of HPR was constrained by limited supply in protons. Generally, the dissolution of GPR was higher than that of HPR for each soil. The kinetics of dissolution of PR in the soils was best described by the power function equation P=At^B. More efficient use of PR in these soils can be achieved by raising the soil cation exchange capacity, thereby increasing the Ca sink size. This could be done by amending such soils with organic materials.     

Analysis of Phosphate Rock Dissolution Determining Factors Using Principal Component Analysis in Some Acid Indonesian Soils

Abstract

Dissolution of phosphate rock (PR) materials and its subsequent phosphorus (P) availability to plants depend upon soil characteristics, PR characteristics, type of crops, and environmental conditions. Agronomic effectiveness of the PR sources has frequently been investigated in the field or in the greenhouse. This is time consuming and not cost‐effective. Therefore, identification of the soil characteristics influencing the dissolution of PR is very important for direct application of P sources. The principal component analysis was used to summarize the characteristics of acid soils in an incubation system into a number of factors that may affect PR dissolution. Three major factors were selected in this study: 1) soil texture, 2) soil acidity, and 3) fertilization. Using the scores of the individual factors as independent variables, a stepwise regression analysis was performed to derive a PR dissolution function. The coefficient of determination (R²) reached 0.91**, and the magnitude of the different factors affect PR dissolution following the order of soil texture (54%)>soil acidity (43%)>fertilizer (3%). Fertilizer was not significant as a PR dissolution factor.     

Predicting Maize Yield,Nutrient Concentration,and Uptake in Phosphorus- and Potassium-Fertilized Soils: Pressurized Hot Water and Other Alternatives to Mehlich I Extraction in Guatemala Soils

Abstract

Poor accessibility and cost of soil testing reduce effectiveness of fertilizer use on small‐scale subsistence farms, and inadequate funding promotes adoption of soil tests in developing countries with minimal validation. For example, Mehlich I extraction of phosphorus (P) currently used extensively in Guatemala may not be suitable for Guatemala's broad range of soils. At least four alternatives are available but relatively untested [Bray 1, Mehlich III, Olsen, and pressurized hot water (PHW)]. Pressurized hot water is relatively simple and inexpensive but is not yet tested against other extraction methods under variable P or potassium (K) fertilization levels. To determine whether PHW‐extracted nutrients could be used to predict maize yield and nutrient concentration and uptake, soil, plant tissue and grain samples were obtained from a multiple‐site field study, and calibration studies were conducted using five rates of P and three rates of K on soils incubated without plants or cropped with maize in greenhouse and field conditions. In the multiple‐site field study, maize yield related significantly to PHW‐extractable P (r²=0.36) and to leaf P concentration (r²=0.23), but Mehlich I–extractable P did not. In the two soils used in the greenhouse study, maize yield, vegetative P concentration, and total P uptake by maize were predicted by PHW‐extractable P (R²=0.72, 0.75, and 0.90, respectively). In the field experiment, grain yield was not improved by P or K application, but P concentration of maize leaf tissue did relate significantly with PHW‐extracted P (R²=0.40). Mehlich I did not. There were no yield responses to K application in any experiment, but relationships defined between extractable K for all five K‐extraction procedures and soil‐applied K were similarly significant. In comparison, PHW was as good as or better than Olsen whereas Bray 1 and Mehlich III were less consistent. Mehlich I was overall the poorest P extractant. Mehlich I extraction of P should be replaced by one of the four alternatives tested. PHW is the least expensive and, therefore, most viable for use in Guatemala soils.     

Urea Hydrolysis of Tea Soils as Influenced by Incubation Period,Soil pH,and Nitrification Inhibitor

Abstract

Laboratory incubation studies were conducted with south Indian tea soils to investigate the influence of soil pH, incubation period, and nitrification inhibitor on urea hydrolysis. The soils used in this experiment were sampled from six different regions of south India. The physicochemical properties, urea hydrolysis as influenced by soil pH, incubation period, and nitrification inhibitor were determined. There was a strong positive correlation between urease activity and organic‐matter content of tea soils, whereas physicochemical properties failed to show any relationship with urease activity. The urease activity was highest in Munnar soils. At 25°C, the activity reached maximum within 15 days after fertilizer application, and it was considerably high up to 36 days in the soils of Anamallais, 18 days in Munnar, and 27 days in other zones studied, which revealed the minimum interval between two successive urea fertilizer applications. Soils of different zones showed a different pattern of urease activity when the soil pH was changed artificially between 4 and 5.5. Addition of nitrification inhibitor [dicyandiamide, DCD] to urea prevented nitrate ion formation, resulting in the accumulation of desirable ammonium ions.