THE STABILITY OF DICALCIUM PHOSPHATE DIHYDRATE IN SOIL

The rate of dissolution of dicalcium phosphate dihydrate (DCP) when incorporated in moist soil was investigated using ³²P. The moisture content of the DCP-soil mixture, the surface area of the DCP particles and the temperature of incubation of the system are all directly related to the rate of dissolution of the DCP. These results may be explained using a diffusion model in which phosphate ions diffuse from a water film adjacent to the DCP towards a sink provided by the soil.     

THE SOLUBILITY OF PHOSPHATE IN A CALCAREOUS SOIL

The concept of chemical potentials was used to study the solubility of phosphate in a calcareous soil when equilibrium was approached by precipitation. By comparison with results obtained by dissolution of soil phosphate it was demonstrated that precipitation resulted in a considerably greater solubility than did dissolution. The relationship between the monocalcium phosphate potential and lime potential could be reconciled with the presence of hydroxyapatite in the soil. Ion activity products near to those of pure hydroxyapatite in the presence of calcium carbonate were also obtained.     

涂层尿素在石灰性土壤上的行为

本项试验主要探索涂层尿素在石灰性土壤上的变化规律。试验结果表明，在三种不同水分含量条件下（10％、15％、20％），涂层尿素施入土壤后氨挥发速率均比普遍尿素低;涂层尿素施入土壤随即浇水，有良好的随水移动性能，肥料氮在土体中的移动深度和肥料氮的回收率随浇水量的不同表现出明显的差异;涂层尿素肥料氮的回收率比普通尿素高2.28个百分点。涂层尿素做底肥时，在小麦上的利用率比普通尿素高3.4个百分点，在玉米上高5.18个百分点;底、追结合施用涂层尿素在小麦上的利用率比普通尿素高5.6个百分点，在玉米上高9.5个百分点。涂层尿素在小麦和玉米上施用，其氮素的损失率比普通尿素低5.4～11.4个百分点。在种植小麦条件下涂层尿素施入土壤后，肥料矿化和供氮特征表现为小麦生长前期0～40Cm土层中速效氮含量低于普通尿素，小麦起身拔节以后，速效氮含量则高于普通尿素。     

石灰性土壤与磷酸盐的反应及吸持态磷的同位素交换性

本文研究了种石灰性土壤（Ｌｏｕ土）与磷酸盐的反应动态过程，短期反应的等温吸附研究表明，在低磷浓度下，以吸附反应机制为主，吸持态磷的同位素交换性随着吸持量的增加而增加；在高磷浓度下，以形成磷酸盐的沉淀反应机制为主，吸持态磷的同位素交换性随着反应时间的延长和吸持量磷数量的增加而了降低。认为在低施磷水平下，土壤中铁，铝氧化物对磷的吸持起重要作用。本文还探讨了在长期（２６０天）恒温恒湿培养过程中，土壤可溶     

RESPONSE OF SOYBEAN TO SOIL APPLIED SULFUR AND BORON IN A CALCAREOUS SOIL

A greenhouse experiment with soybean grown on sulfur (S) and boron (B) deficient calcareous soil was conducted for two years in northwest India to study the influence of increasing sulfur and boron levels on yield and its attributing characters at different growth stages (55 days, maturity). The treatments included four levels each of soil applied sulfur viz. 0, 6.5, 13.4, 20.1 mg S kg^?1 and boron viz. 0, 0.22, 0.44, 0.88 mg B kg^?1 at the time of sowing. The highest dry matter yield at 55 days after sowing, DAS (19.3 g pot^?1) and maturity (straw yield ?25.2 g pot^?1 and grain yield ?7.3 g pot^?1) was recorded with B_0.44 S_13.4 treatment combination. The combined applications of sulfur and boron yielded highest oil content with B_0.44S_13.4 (21.7%) treatment level. Chlorophyll ‘a’ and ‘b’ increased significantly with successive levels of sulfur and boron addition at 55 DAS. The mean sulfur and boron uptake in straw and grains increased significantly with increasing levels of sulfur and boron up to 13.4 mg kg^?1 and 0.44 mg kg^?1 and decreased non-significantly thereafter. At both the growth stages, a synergistic interactive effect of combined application of sulfur and boron was observed with B_0.44 S_13.4 treatment level for sulfur and boron uptake in straw and grains.     

RATE-CONTROLLING PROCESSES IN THE RELEASE OF SOIL PHOSPHATE

The isotopic exchange of phosphate ions in a deep river gravel soil, maintained at different pHs from 3.5 to 6.7 in a field experiment, established by the N.A.A.S. at Shardlow, was governed initially (<20 h) by simultaneous ‘first-order’ and ‘bulk diffusion’ kinetics, but later by ‘bulk-diffusion’ kinetics only. The ‘bulk-’ or ‘intracrumb-’ diffusion coefficient was independent of phosphate manuring, was least at pH 5.5 and increased on either side of this critical pH. The rate constant for the phosphate component exchanging initially with ‘first-order’ kinetics increased significantly with phosphate manuring at pH 3.5, 4.4, and 5.5, although the constants for unmanured and manured soils did not change with soil pH. But at pH 6.7, the rate constants for the unmanured and phosphate-treated soils were greater than those in the more acid soils, although the constant for the manured soil was just significantly greater than that of the unmanured soil. Residual phosphate (i.e. the difference between manured and unmanured soils) adsorbed on the soil was greatest in the more acid soils but water-soluble residual phosphate increased with soil pH to a maximum at pH 5.5. Residual phosphate, exchanging initially, decreased to nothing above pH 6.5.     

从土壤肥力变化预测中国未来磷肥需求

近年来,我国磷肥用量持续增长,土壤有效磷含量也增加很快,这些变化对磷肥生产和施用将产生什么影响？这是一个关乎我国粮食安全和环境安全的重要问题,值得进行深入地探讨。本研究通过对我国8种典型农业土壤上磷收支平衡和有效磷消长关系的分析,获得预测我国主要农田土壤中有效磷变化模型的参数,即每100kg hm^-2磷盈余平均可使我国土壤有效磷水平提高约3.1mg kg^-1。结果表明,从1980年到2003年我国除经济作物外的主要农田土壤上累积磷盈余约为392kg hm^-2,由此推出目前我国农田土壤有效磷水平约为19mg kg^-1左右。从农业需求和环境保护角度确定的土壤有效磷最适范围应在30～50mg kg^-1之间。而要在未来的30a内使我国土壤有效磷水平提高并维持在40mg kg^-1左右,磷肥的消费将在30a间经历一个先升后降的过程,磷肥需求将在2020年左右达到最高峰1250万t,到2035年降至1050万t,此后应一直维持这一水平。     

石灰性土壤小麦根际pH及磷动态变化的研究

本文采用网隔栽培室种植小麦,置于人工气候室内生长,对不同温度条件下土小麦根际及距根不同距离土体中ｐＨ,Ｏｌｓｅｎ-Ｐ及无机磷组分动态变化进行了研究。主要结果有:（１）根际及０～３ｍｍ土体ｐＨ较低,而３～８ｍｍ和８～５０ｍｍ土体ｐＨ较高;（２）Ｏｌｓｅｎ-Ｐ含量为根际＜０～３ｍｍ土体＜３～８ｍｍ和８～５０ｍｍ土体,温度升高,各土层Ｏｌｓｅｎ-Ｐ含量呈降低趋势;（３）距小麦根系越近,Ca2-P、Ａｌ Ｐ、Ｆｅ-Ｐ和Ca8-P含量越低,Ｏ-Ｐ和Ca10-P变化不明显;随时间延长和温度升高,Ca10-P含量有所增加,Ca2-P、Ａｌ-Ｐ、Ｆｅ-Ｐ和Ca8-P含量有所降低,Ｏ-Ｐ含量变化不大     

石灰性土壤Ca-P分布及转化特征的研究

在石灰性土壤无机磷中约有70%～80%是以Ca-P形态存在［1～3］。水溶性磷肥施入土壤后短期内以磷酸二钙形式存在，随着时间的推移逐步向磷酸八钙转化［4］。研究表明正常施磷情况下，一个生长季节在水溶性磷肥转化的各级无机磷中Ca-P约占80%［5］。     

石灰性土壤难溶态磷的微生物转化和利用

目前农业生产中大多通过施用可溶性磷肥为植物提供有效磷。磷酸根化学性质活泼,施入土壤后能很快与土壤中的其它成分发生反应,使植物对其利用的有效度随时间延长而降低,最终以难溶性磷酸盐或吸附态形式滞留于土壤中,难以被植物直接吸收。据估计,在石灰性土壤中约有80% 的磷肥以难溶性磷酸盐存在。为此人们采用了许多方法提高磷肥的利用率,其中利用植物根际与磷循环相关的生物学系统来调节植物根际磷的有效性是重要的途径之一。这个生物学系统包括植物本身对土壤难溶态磷的吸收与利用以及土壤中某些微生物参与的难溶态磷的释放与利用。本文论述了微生物( 细菌和真菌) 转化和利用石灰性土壤中难溶态磷的研究进展。     

深浅施肥的肥料氮在碳酸盐土壤中的转化

利用15_N示踪技术,采用不同追施方法研究碳铵、硫铵、尿素在碳酸盐土壤中的转化表明:在种植作物条件下,肥料氮施入土壤后所发生的矿物固定与生物固定具有负相关关系.由于施用方法不同,肥料氮的矿物固定和损失不同,深施氮素矿物固定与损失呈显著负相关(r=—0.8359)。肥料氮在土壤中转化固定有助于减弱氮素的损失。后茬作物对残留氮的利用与生物固定态氮的多少关系不大。但与矿物固定和无机氮总量之和有密切关系。     

THE CALCAREOUS SOILS OF AZERBAIJAN II. PHOSPHATE STATUS

The phosphate status, before and after P treatment in the laboratory, of surface soils from thirteen profiles of an Iranian catena, described in Part I, was investigated by determining the distribution of labile phosphate in solution and external and internal surfaces, and by examining their calcium phosphate solubility relationships. The labile P distribution of added P suggests generally that soils with most carbonate in the silt fraction (Part I) hold added P mostly on external surfaces, and those with increasing carbonate in the clay fraction, less so. Recovery of 200 and 400 mg/kg soil of added P in the labile phosphate was related to soil phosphate status directly and to the total carbonate area of the soil inversely. Solubility relationships indicated saturation with CaCO₃ and a compound approaching octacalcium phosphate in composition. The two saline-alkaline end-members of the catena from the Low Land area differed somewhat in having more of their P content in soluble and labile forms, and in storing added P uniformly on external and internal surfaces.     

三种施肥模式对石灰性土壤培肥的影响

试验在中国科学院封丘农业生态实验站的石灰性潮土上进行 ,在氮、磷、钾固定用量和比例的基础上 ,选定全施有机肥、全施化肥、有机肥和无机肥配合施用三种处理。结果表明 ,这三种施肥模式都显著地提高了土壤全氮和速效氮、土壤全磷和有效磷、土壤全钾和速效钾含量。有机肥在提高土壤全氮和速效氮含量方面效果明显优于无机肥 ,对土壤速效磷含量的影响也高于无机肥 ,但是对土壤全磷含量的增加效应上不如无机肥大。无论是有机肥中的钾还是无机肥中的钾 ,对土壤全钾的贡献没有明显的差别 ;但是在土壤速效钾方面 ,无机肥中的钾对其影响大于有机肥中的钾。有机肥和无机肥的配合施用是提高石灰性潮土土壤肥力更好的方法。     

长期施肥对石灰性潮土氮素形态的影响

采用Bremner1 965年提出的土壤氮素分级方法 ,对 1 6年肥料长期定位试验中的耕层以及剖面各层次土壤的氮素形态进行了分级。结果表明 ,施用化肥不能提高耕层土壤各形态氮的含量 ,对土壤氮素的组成也无明显的影响 ;有机肥和化肥配合施用 ,耕层土壤各形态氮的含量都有不同程度的提高 ,其中氨基酸态氮的增加最为明显。有机无机肥配合施用 ,可提高土壤氮素的储量和质量 ,不仅对耕层土壤氮素的含量和组成有影响 ,而且对耕层以下土壤各形态氮的含量也有一定的影响。一般随着有机肥用量的增加 ,下层土壤各形态氮含量的增加幅度也越大 ,而且影响深度也更深。在本试验条件下 ,施肥对氮素形态的最大影响深度为 30cm左右。     

THE HIGH- AND LOW-ENERGY PHOSPHATE ADSORBING SURFACES IN CALCAREOUS SOILS

The two-surface Langmuir equation was used to study P adsorption by 24 calcareous soils (pH 7.2-7.6; 0.8-24.2 per cent CaCO₃) from the Sherborne soil series, which are derived from Jurassic limestone. High-energy P adsorption capacities (x″_m) ranged from 140–345 μg P/g and were most closely correlated with dithionite-soluble Fe. Hydrous oxides therefore appear to provide the principal sites, even in calcareous soils, on which P is strongly adsorbed (x″_m 6–51 ml/μg P). The low-energy adsorption capacities (x″_m) ranged from 400–663 μg P/g and were correlated with organic matter contents and the total surface areas of CaCO₃ but not with per cent CaCO₃, pH, or dithionite-soluble Fe. Total surface areas of CaCO₃ in the soils ranged from 4.0 to 8.5 m²/g soil. Low-energy P adsorption capacities agree reasonably with values (100 pg P/m²) for the sorption of phosphate on Jurassic limestones but phosphate was bonded much less strongly by soil carbonates (k″= 0.08–0.45 ml/μg P) than by limestones (k～10.0 ml/μg P). Low-energy P adsorption in these soils is tentatively ascribed to adsorption on sites already occupied by organic anions (and probably also by bicarbonate and silicate ions) which lessen the bonding energy of co-adsorbed P.     

VA菌根真菌对石灰性土壤不同形态磷酸盐有效性的影响

用32P示踪法研究了VA菌根真菌对石灰性土壤不同形态磷酸盐有效性的影响。结果表明，VA菌很真菌显著增加了玉米吸收肥料和土壤的磷量。菌根植物和非菌根植物都可不同程度地吸收利用土壤中的Ca2-P、Ca8-P、Fe-P和Al-P，VA菌根真菌增加了玉米对它们的吸收。试验结果还表明，施Ca10-P时接种VA菌很真菌对玉米生长的促进作用比施用其它磷酸盐明显，但Ca10-P不能直接被玉米植株所利用。说明VA菌根真菌能提高土壤中的有效性磷（Ca2-P和Al-P）和缓效性磷（Ca8-P和Fe-P）的有效性。