不同磷源对设施菜田土壤速效磷及其淋溶阈值的影响

土壤中磷的移动性不仅取决于磷的数量且与磷肥形态有关。了解不同磷源（有机肥和化肥）对设施菜田土壤磷素的影响对于指导科学施肥和面源污染防治至关重要。本文选取河北省饶阳县3种不同磷含量的农田土壤（未种植过蔬菜的土壤、种植蔬菜30年的塑料大棚土壤和种植蔬菜4年的日光温室土壤）为研究对象,采用室内培养试验和数学模型模拟方法研究有机无机磷源对设施菜田土壤磷素的影响,确定无机肥和有机肥源土壤磷素淋溶的环境阈值。结果表明添加有机肥和无机磷肥都会显著增加3种不同种植年限设施菜田土壤速效磷（Olsen-P）和氯化钙磷（CaCl₂-P）含量,但增加速度不同。对于未种植过蔬菜的低磷对照土壤,磷投入量高于50 mg·kg^-1（干土）后,无机肥比有机肥显著提高了土壤Olsen-P含量。对于已种植蔬菜30年的塑料大棚土壤,高磷投入时[300 mg·kg^-1（干土）和600 mg·kg^-1（干土）],无机肥比有机肥显著提高了土壤Olsen-P含量,低于此磷投入量时有机肥和无机肥处理之间没有显著差异。3种不同农田土壤CaCl₂-P的含量所有处理均表现出无机肥显著高于有机肥处理,尤其是在高磷量[>300 mg·kg^-1（干土）]投入时表现更加明显。两段式线性模拟结果表明,设施菜田土壤有机肥源磷素和无机肥源磷素淋溶阈值分别为87.8 mg·kg^-1和198.7 mg·kg^-1。随着土壤Olsen-P的增加,添加无机肥源磷对设施菜田土壤CaCl₂-P含量的增加速率是有机肥源磷的两倍。因此,建议在河北省高磷设施菜田应减少无机磷肥的投入,特别是土壤速效磷高于198.7 mg·kg^-1的设施菜田应禁止使用化学磷肥和有机肥,在土壤速效磷低于198.7 mg·kg^-1的设施菜田应加大有机肥适度替代无机肥技术的推广。     

Kinetics of nutrient release from different organic residues using a laboratory system

Organic residues play a vital role in maintaining soil fertility in arid and semi-arid regions. Knowledge of the nutrient release from organic residues will help in optimizing nutrient efficiency in agricultural crop production systems. This study was conducted to assess the continuous release of phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) from eight different organic residues (sheep manure, beet, waste material, rape, poultry manure, sunflower, potato and garlic) using successive extractions with distilled water. The residues were shaken for 1 h and equilibrated for longer intervals (1, 3.5, 18, 42, 72, 192, 768, 1248, 1608, 1968 and 2328 h) with successive extractions. Cumulative nutrient release curves by different organic residues versus time showed an initial rapid phase followed by a slow phase. The average percentage of nutrients released and the average release rate of nutrients found using a power model was different and were in the order K > P > Ca > Mg and Ca > Mg > P > K, respectively. According to MINTEQ software, the partitioning of total P between HPO₄ ^2? and H₂PO₄ ^? is sensitive to the type of organic residue. On average (pooled over all extractions), between 13% (rape) to 40% (poultry) and 27% (poultry manure) to 79% (beet) of total P in aqueous solutions present as HPO₄ ^2? and H₂PO₄ ^?, respectively. Among the various organic residues and in the first stage of release, sunflower residue, beet residue, poultry manure and garlic residue had the highest rate constant for Ca, Mg, P and K, respectively, indicating the high potential availability of these nutrients in the early stage of application to soils.     

有机肥在侵蚀退化土壤生产力恢复中的作用研究

风蚀土壤施用不同有机肥和化肥的作物反应以及土壤生产力恢复效果的试验在温室条件下进行,旨在探讨经济高效恢复风蚀退化土壤的生产力的有机肥种类。结果表明,猪粪、鸡粪、腐熟牛粪对表土完全损失的土壤生产力恢复效果最好;新鲜牛粪的作物产量较低,宜腐熟后施用;苜蓿、兵豆、燕麦青体和麦秸有效磷低,短期内恢复土壤生产力的效果差;磷肥容易被高钙底土固定,效果低于有机肥。鸡粪中磷的有效性高,猪粪供磷多,腐热牛粪供磷稳,而麦秸含有效磷最少。有机肥除了提供丰富的磷素,还有保护其磷素免被土壤固定,促进作物吸收利用的作用。有机肥中的Olsen-P和树脂磷与生物产量相关性极显著,Olsen-P作为有机肥培育土壤的有效磷指标比树脂磷更适用。     

长期不同施肥红壤磷素特征和流失风险研究

为探索长期施肥对红壤磷素吸附固持的影响,分析不同施肥土壤磷流失风险及影响因素。在南方丘陵区红壤上开展了持续25年的长期定位试验,处理包括:不施肥(CK)、施氮肥(N)、施磷肥(P)、施钾肥(K)、施氮磷钾肥(NPK1)、施2倍量氮磷钾肥(NPK2)、单施有机肥(OM)和氮磷钾配施有机肥(MNPK)。研究了不同施肥下土壤全磷、Olsen-P、Mehlich1-P、CaCl2-P含量及磷吸持指数(PSI)、磷饱和度(DPS)的变化,探讨不同施肥处理土壤对磷的吸附和解吸特征,并分析了土壤磷指标与土壤有机碳、pH、CEC之间的关系。结果表明:长期施用化学磷肥有利于补充土壤磷素,特别是土壤全磷,并使Olesn-P和Mehlich 1-P有增加趋势,而对CaCl2-P影响不显著;施用化肥对DPS影响不显著,单施磷会降低PSI,低量氮磷钾提高了PSI,高量氮磷钾处理与对照差异不显著;长期施用有机肥(猪粪)土壤全磷增加,而Olsen-P、Mehlich 1-P和CaCl2-P则大幅累积, PSI显著降低, DPS显著增加。长期施用化肥处理土壤对新添加磷的吸附较强,长期施用有机肥降低了土壤对新添加磷的吸附;土壤全磷、Olsen-P、Mehlich1-P、CaCl2-P、PSI、DPS及最大吸附容量(Qm)与土壤pH、CEC、土壤总有机碳(TSOC)、土壤水溶性有机碳[冷水提取水溶性有机碳(CWSOC)和热水提取水溶性有机碳(HWSOC)]间相关性较高;土壤磷指标和土壤有机碳、pH、CEC指标之间存在典型相关关系,第1对和第2对典型变量的典型相关系数分别为0.997和0.951,达显著水平。研究表明,施用有机肥是调节土壤磷的供给和保持的重要措施,土壤水溶性有机碳和pH可能是反映红壤磷素供应和流失的关键指标。     

磷肥和有机肥对不同磷水平土壤磷渗漏影响研究

采用土柱培养的模拟试验方法研究了在不同磷水平土壤上大量施用磷肥和有机肥对土壤测试磷、土壤磷渗漏的影响及影响机理。结果表明,不同磷水平土壤施用磷肥或有机肥土壤CaCl2-P、Olsen—P和土壤渗漏液中可溶性磷均显著增加;单位量磷肥或有机肥所增加土壤各形态磷量随土壤磷水平的增加而增大;随着磷肥或有机肥用量的增加,单位量磷肥或有机肥所增加各形态磷量也逐渐增大,差异均达到显著和极显著水平。在施用磷肥的基础上增施有机肥可以提高土壤CaCl2-P、Olsen—P含量和土壤渗漏液中可溶性磷的增长幅度。土壤磷的渗漏量与土壤测试磷呈显著正相关;单位量磷肥或有机肥所增加的土壤渗漏磷量随着磷肥或有机肥用量以及土壤磷水平的增加而增加。Olsen—P含量与土壤磷吸持指数（PSI）呈显著负相关关系,与土壤磷的吸附饱和度（DPS）呈显著正相关关系。     

Effect of organic manures,crop residues and green manure (Sesbania aculeata) on nitrogen and phosphorus transformations in a sandy loam at field capacity and under waterlogged conditions

Summary The influence of the water regime on mineralization and immobilization of N and P was investigated in a calcareous sandy loam incubated with cattle, poultry and green manure (Sesbania aculeata), and wheat and rice straw in a pot experiment. At field capacity, N released from poultry and green manure during the first 4 weeks of incubation was 45% and 59%, respectively. During the next 12 weeks, only around 40% more organic N was mineralized from both sources. In contrast, addition of cattle manure resulted in a period of net N immobilization lasting up to 4 weeks. By the end of 16 weeks of incubation only about 19010 of the added N was mineralized. High rates of N immobilization were observed during the first 4 weeks of incubation of rice or wheat straw with C/N ratios of 78 and 85, respectively. The N mineralization kinetics of poultry and green manure and of untreated soil showed an initial fast reaction followed by a slow release of inorganic N and could be described by two simultaneous first-order reactions. Under waterlogged conditions mineralized N was lost simultaneously in significant amounts possibly through nitrification — denitrification reactions. At field capacity, the largest amount of Olsen P was accumulated in the soil amended with poultry manure, followed by cattle manure. Results from other treatments did not differ much from those of the untreated soil. About 15% of P from poultry manure was mineralized during the 1st week of incubation. In contrast to the field-capacity moisture regime, marked increases in Olsen P in the soils amended with green manure and crop residues were observed under water-logged conditions.     

施加粪肥对潮土有机磷形态转化的影响

施加粪肥是提高土壤肥力的重要措施,为了解粪肥磷在潮土中的化学行为,通过室内培养试验,采用NaOH-EDTA 浸提和 31P 核磁共振技术分析比较了鸡粪、牛粪及施肥后土壤中的磷形态及含量,并研究了施肥对潮土有效磷的影响。结果表明,粪肥磷主要以无机态形式存在,2 种粪肥的有机磷形态及含量有明显不同,肌醇六磷酸在鸡粪中的含量明显高于牛粪。粪肥施加到潮土后丰富了土壤有机磷的形态。随时间延长,潮土中各形态磷发生相互转化,以肌醇六磷酸为主的正磷酸单酯含量明显降低,核酸等正磷酸双酯显著升高。鸡粪处理的土壤有效磷含量逐渐升高,牛粪处理则表现出相反的趋势。施加粪肥后,土壤有效磷呈现不同的变化规律可能是无机磷在土壤中固定或沉淀,有机磷矿化和无机磷被微生物固持这三方面综合作用的结果。     

Changes in mineral nitrogen, phosphorus availability and salt-extractable aluminium following the application of green manure residues in two weathered soils of South Vietnam

Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha⁻¹ to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg⁻¹ in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha⁻¹, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.     

Fertilizer value of phosphorus in different residues

The phosphorus (P) fertilizer effect of a range of commonly available manure, waste treatment and by‐product residues was tested in pot, field and incubation experiments. The effect of the residues on P offtake was compared with that of commercial mineral P (super phosphate) to calculate the mineral fertilizer equivalent (MFE). Possible relationships between MFE and P extractable from residues using different agents (ammonium lactate, citrate, water) were examined. Dry matter yield and P concentration were measured in ryegrass grown in pots amended with 14 different residues. The effect on the first cut (after 5 weeks) was significantly higher for residues with a low organic matter content, for example ash and biogas residues (MFE = 74–85%), than for many other products with higher organic matter content, for example meat meal (MFE = 44%), cattle slurry (MFE = 57%) and sewage sludge (MFE = 0–37%). However, the effect on two combined cuts (after 11 weeks) was more similar between residues (MFE = 40–60% for most residues). Ammonium lactate‐extractable P (P‐AL) in residues correlated better with MFE (r² = 0.48) than water‐extractable or citrate‐extractable P. Grain yield and P concentration were measured in a field experiment with spring wheat fertilized with four different residues. Pelleted meat meal had a similar effect on yield and P offtake as mineral fertilizer P, whereas two different sewage sludge and chicken manure had approximately 50% of the mineral fertilizer effect. The effect of residues on soil P‐AL (the Swedish measure of easily available soil P) in the incubation experiment showed no correlation with MFE from the pot experiments.     

Kinetics of native and added carbon mineralization on incubating at different soil and moisture conditions in Typic Ustochrepts and Typic Halustalf

The carbon dynamics in soils is of great importance due to its links to the global carbon cycle. The prediction of the behavior of native soil organic carbon (SOC) and organic amendments via incubation studies and mathematical modeling may bridge the knowledge gap in understanding complex soil ecosystems. Three alkaline Typic Ustochrepts and one Typic Halustalf with sandy, loamy sand, and clay loam texture, varying in percent SOC of 0.2; S₁, 0.42; S₂, 0.67; S₃ and 0.82; S₄ soils, were amended with wheat straw (WS), WS + P, sesbania green manure (GM), and poultry manure (PM) on 0.5% C rate at field capacity (FC) and ponding (P) moisture levels and incubated at 35 °C for 1, 15, 30 and 45 d. Carbon mineralization was determined via the alkali titration method after 1, 5, 7 14, 21, and 28 d. The SOC and inorganic carbon contents were determined from dried up (50 °C) soil samples after 1, 15, 30, and 45 d of incubation. Carbon from residue mineralization was determined by subtracting the amount of CO₂-C evolved from control soils. The kinetic models; monocomponent first order, two-component first order, and modified Gompertz equations were fitted to the carbon mineralization data from native and added carbon. The SOC decomposition was dependent upon soil properties, and moisture, however, added C was relatively independent. The carbon from PM was immobilized in S₄. All the models fitted to the data predicted carbon mineralization in a similar range with few exceptions. The residues lead to the OC build-up in fine-textured soils having relatively high OC and cation exchange capacities. Whereas, fast degradation of applied OC in coarse-textured soils leads to faster mineralization and lower build-up from residues. The decline in CaCO₃ after incubation was higher at FC than in the P moisture regime.     

Effect of mixing soil saprophytic fungi with organic residues on the response of Solanum lycopersicum to arbuscular mycorrhizal fungi

The effect of the dual inoculation with arbuscular mycorrhizal (AM) and saprophytic fungi and a combination of wheat straw and sewage sludge residues were studied by determining their effect on dry weight of tomato and on chemical and biochemical properties of soil. Incubation of organic residue (sewage sludge combined with wheat straw) with saprophytic fungi and plant inoculation with mycorrhizal fungi was essential to study plant growth promotion. Soil application of organic residues increased the dry weight of tomato inoculated with Rhizophagus irregularis. The greatest shoot dry mass was obtained when the organic residues were incubated with Trichoderma harzianum and applied to AM plants. However, the greatest percentage of root length colonized with AM in the presence of the organic residues was obtained with inoculation with Coriolopsis rigida. The relative chlorophyll was greatest in mycorrhizal plants regardless of the presence of either saprophytic fungus. The presence of the saprophytic fungi increased soil pH as the incubation time increased. Soil nitrogen and phosphorus contents and acid phosphatase were stimulated by the addition of organic residues, and contents of N and P. Total N and P content in soil increased when the organic residue was incubated with saprobe fungi, but this effect decreased as the incubation period of the residue with saprobe fungi increased. The same trend was observed for soil β‐glucosidase and fluorescein diacetate activities. The application of organic residues in the presence of AM and saprophytic fungi seems to be an interesting option as a biofertilizer to improve plant growth and biochemical parameters of soils.     

Detectability of degradable organic matter in agricultural soils by thermogravimetry

Sustainable agricultural land use requires an assessment of degradable soil organic matter (SOM) because of its key function for soil fertility and plant nutrition. Such an assessment for practical land use should consider transformation processes of SOM and its sources of different origin. In this study, we combined a 120‐day incubation experiment with thermal decay dynamics of agricultural soils altered by added organic amendments. The aim was to determine the abilities and limits of thermal analysis as a rapid approach revealing differences in the degradability of SOM. The carried out experiments based on two independent sampling sets. The first sample set consisted of soil samples taken from non‐fertilized plots of three German long‐term agricultural field experiments (LTAEs), then artificially mixed with straw, farmyard manure, sheep faeces, and charcoal equal to 60 Mg ha^?1 under laboratory conditions. The second sample set based on soil samples of different treatments (e.g., crop type, fertilization, cultivation) in LTAEs at Bad Lauchstädt and Müncheberg, Germany. Before and after the incubation experiment, thermal mass losses (TML) at selected temperatures were determined by thermogravimetry indicating the degradability of organic amendments mixed in soils. The results confirmed different microbial degradability of organic amendments and SOM under laboratory conditions. Thermal decay dynamics revealed incubation‐induced changes in the artificial soil mixtures primarily at TML around 300°C in the case of applied straw and sheep faeces, whereas farmyard manure showed mainly changes in TML around 450°C. Charcoal did not show significant degradation during incubation, which was confirmed by TML. Detailed analyses of the artificial soil mixtures revealed close correlations between CO₂‐C evolution during incubation and changes in TML at 300°C with R² > 0.96. Results of the soils from LTAEs showed similar incubation‐induced changes in thermal decay dynamics for fresh plant residues and farmyard manure. We conclude that the practical assessment of SOM could be facilitated by thermal decay dynamics if modified sample preparation and evaluation algorithms are used beyond traditional peak analysis.     

The Effect of Vermicompost on Transformation Rate of Available P Applied as Chemical Fertilizer in a Calcareous Clay Soil

The effects of vermicompost (VC) (0% and 1% w/w) on treated calcareous clay soil with 0 and 50 mg phosphorus (P) kg^?1 as calcium phosphate [Ca(H₂PO₄)₂.H₂O] was investigated. The soil samples were incubated for 7, 30, 60, 120, and 150 d at 25 ± 1°C and Olsen-P was measured after each incubation time. Results showed that Olsen-P increased 36% and 38% after VC addition in treated soil with 0 and 50 mg P kg^?1, respectively. Recovery of Olsen-P in treated soils with VC, combined fertilizer VC + P, and fertilizer P was 42%, 42%, and 17%, respectively. The rate coefficient in treated soils with fertilizer, VC, and combined fertilizer VC + P was 0.033, 0.026, and 0.023 mg kg^?1 d^?1/2, respectively. It seems that the process that leads to the decrease in available P in amended soils, is controlled by P diffusion into sorption sites in micropores of aggregates.     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Rice-residue biochar influences phosphorus availability in soil with contrasting P status

ABSTRACT

Thermo-chemical conversion of crop residues to produce biochar is an emerging strategy in the context of sustainable phosphorous (P) use and residue management. An incubation study for 90 d was conducted to investigate the effects of rice-residue biochar (0, 10, 20 and 40 g kg^?1) in combination with inorganic-P (KH₂PO₄) (0, 25 and 50 mg kg^?1) on phosphorous availability in medium- and high-P status soils. Increasing biochar addition rates alone or in combination with inorganic-P resulted in a significant increase in P pools, i.e. plant available P or Olsen-P (from 8 to 132 mg kg^?1 in medium-P and 15 to 160 mg kg^?1 in high-P soils), microbial biomass P and various mineral-bound inorganic-P fractions in the order (Ca-P > organic-P > Al-P > loosely held/soluble-P > Fe-P > reductant soluble-P). Further, lower phosphatase activity (19–50%) with increasing rates of biochar addition in both soils elucidates the ability of biochar to act as a long-term source of available P in the experimental soils. The results demonstrate that rice-residue biochar can directly or indirectly enhance the status of available P in soils and hence can be used as a beneficial amendment to meet the crop P demand.     

长期施肥对塿土磷素状况的影响

利用塿土12年长期肥料定位试验,研究了不同施肥方式对耕层土壤全磷(TP)、有机磷(OP)与有效磷（Olsen-P）的影响。结果表明,施用化学磷肥提高了耕层土壤TP、Olsen-P含量,但并未提高OP含量;对照与磷钾处理的OP含量有降低趋势。当基于含氮量施有机肥时,土壤TP和Olsen-P含量大幅度提高,也提高了OP含量,但OP/TP比率在降低到一定程度后维持在一个较为稳定的水平;即使施用有机肥的处理,磷素也主要以无机形态累积。土壤Olsen-P与TP或两者的增加量都呈显著的线性相关,塿土TP每提高100 mg/kg,Olsen-P增加量约为20.8 mg/kg,且单位土壤全磷增加带来的Olsen-P增加有随施肥时间降低的趋势。在土壤Olsen-P含量达到一定水平时应考虑减少磷肥用量。基于有机肥中磷素含量来推荐有机肥施用或延长其施用的时间间隔,将有助于减少由于有机肥施用带来的磷素大量快速累积。     

Using Wood Ash to Ameliorate Acidity and Improve Phosphorus Availability in Soils Amended with Partially Decomposed Cattle or Chicken Manure

The application of partially decomposed animal manure can acidify the soil by nitrification and may cause problems with phosphorus (P) availability. This study investigated the influence of applying wood ash to two soils amended with partially decomposed cattle or chicken manure on pH and P. The treatments consisted of two soils, a clay loam and sandy loam, each amended with partially decomposed chicken or cattle manure applied at 0, 5, or 15 t ha^?1, and wood ash was applied to each manure treatment at rates of 0 or 2 t ha^?1. The addition of wood ash significantly increased pH, thereby making more P available in soil and maize (Zea mays L.) tissues for both soils after being amended by manure. Both chicken and cattle manure significantly increased all the measured variables compared to the unamended soils. These results suggest that wood ash is an important amendment that could be used to amend partially decomposed manure, thereby not jeopardizing P availability to crops.     

Effect of organic manure on organic phosphorus fractions in two paddy soils

We investigated the transformation of the organic P fractions from organic manure in two paddy soils (Ultisol, Entisol) and the influence of organic manure or cellulose on organic P under anaerobic conditions. The results obtained from the P fractionation experiment indicated that during the incubation labile and moderately labile organic P fractions increased in the Ultisol and decreased in the Entisol, which might be related to the difference in the organic matter content of both soils. Immediately after the application of organic manure, a large part of labile and moderately labile organic P supplied with the manure was transformed into moderately resistant organic P, possibly Ca- or Mg-inositol P were transformed into Fe-inositol P. During anaerobic incubation, the labile forms of organic P in the soils treated with organic manure were increased along with the incubation period in the first 4 weeks. The change in the moderately labile fraction was dramatic. It increased sharply in the first 2 weeks, then decreased, which was more pronounced in the soils treated with pig faeces. The moderately resistant fraction decreased during the whole incubation period. This indicated that under anaerobic conditions, the moderately resistant fraction can be transformed into labile and moderately labile organic P fractions, perhaps as Fe³⁺-inositol P is reduced to Fe⁺²-inositol P. Cellulose as an organic substrate had an increasing effect on organic P, especially when it was combined with inorganic P. Therefore, it is suggested that the application of inorganic P fertilizer combined with organic manure may be an effective way of protecting inorganic P against intensive sorption in soils.     

Sulfur mineralization in two soils amended with organic manures,crop residues,and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field‐moist soils amended with 10 g kg^—1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl₂ to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO₄‐S. The amount of S mineralized in control and in manure‐amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil)^—1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil)^—1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S_o) and first‐order rate constant (k) varied considerably among the different types of organic materials added and soil. The S_o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.     

Phosphorus Availability and Some Biological Properties in the Bean (Phaseolus vulgaris) Rhizosphere

The objectives of this research were to evaluate the rhizospheric effects of bean (Phaseolus vulgaris) on phosphorus (P) availability and dissolved organic carbon (DOC), microbial biomass carbon (MBC), microbial biomass phosphorus (MBP), alkaline phosphatase (ALP) and P in the particulate fraction (PF-P) in some calcareous soils under rhizobox conditions. The results showed that DOC, MBC, MBP and ALP strongly increased in the rhizosphere soils compared with the bulk soils (p < 0.05). Also, the amounts of PF-P and P extracted with different tests in the rhizosphere were lower compared to the bulk soils (p < 0.05). The correlation studies showed that plant indices (dry yield and P uptake) had a positive relationship with Olsen-P, MBP, DOC, ALP and PF-P in both the rhizosphere and the bulk soil. Therefore, bean rhizosphere caused increases of DOC, MBC, MBP and ALP and decreases of available P and PF-P in the studied soils. In addition, the results of this research showed that the Olsen-P method and MBP and PF-P could be used to estimate bean-available P in the studied calcareous soils.