Effect of organic and mineral fertilizers on soil respiration and enzyme activities of two Mediterranean horticultural soils

The effects of municipal food waste compost addition and mineral fertilization on selected soil microbiological activities were investigated during 3 years of reiterated treatments on two Mediterranean agricultural soils with different organic carbon content. Compost at 15, 30 and 45 t ha⁻¹ (dry matter), mineral (NPK) fertilizers and combined fertilizers with 15 t ha⁻¹ of compost plus two reduced doses of mineral N were applied to both soils. At both sites, organic amendment increased soil respiration, fluorescein diacetate hydrolysis, phosphatase and arylsulphatase activities. The differences in soil microbial activities among treatments, found after 3 years of repeated treatments, were attributable to the variations of soil organic C content and to the impact of soil tillage. Our results show that, in Mediterranean intensively cultivated agroecosystems, annual organic amendments improve the microbial activity of soil and produce cumulative effects, suggesting the usefulness of repeated high-rate compost applications.     

Community level functional diversity and enzyme activities in paddy soils under different long-term fertilizer management practices

Soil microbial community structure and function are commonly used as indicators for soil quality and fertility. The present study deals with the effect of different long-term fertilizer management practices on community-level physiological profiles (CLPP) and soil enzyme activities of paddy soils. Since 1954, chemical fertilizers have been applied in the fields as N–P₂O₅–K₂O, and compost has been added as rice straw at 0, 7.5, 22.5, and 30.0 Mg ha⁻¹ in NPK, NPKC750, NPKC2250, and NPKC3000 treatments, respectively. Community-level functional diversity was significantly enhanced in the plots treated with both chemical fertilizer and compost as compared to only chemical fertilizer and untreated control plots. Average well color development (AWCD) obtained by the Biolog Eco plate indicates that there were few differences among soil samples. Shannon diversity and evenness indices were the highest in NPKC750-treated soil and the lowest in chemically fertilized soil. Dehydrogenase, cellulose, β-glucosidase, and acid and alkaline phosphomonoesterase activities were significantly increased depending on the amount of added compost with inorganic fertilizers; the alkaline phosphomonoesterase activity was the most sensitive to treatments. Our results demonstrated that enzyme activities can be used as sensitive and liable indicators in long-term managed rice-paddy ecosystems.     

Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions

 Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg^–1 soil in unfertilized soil to 423 mg kg^–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by use of organic amendments along with inorganic fertilizers. Received: 6 May 1998     

Changes in Biological Properties in Soil Amended with Rock Phosphate and Waste Mica Enriched Compost using Biological Amendments and Chemical Fertilizers Under Wheat-Soybean Rotation

The main aim of this research work is to prepare an enriched compost using rice straw mixed with rock phosphate, waste mica and Aspergillus awamori and to study their effect on changes in microbial properties in soils with and without chemical fertilizers under wheat-soybean rotation. Data revealed that significant increase in microbial biomass carbon (MBC), dehydrogenase activity, phosphatase activities, and microbial biomass phosphorus (MBP) in soil were maintained in enriched compost than ordinary compost after both the crops. Significant increase in MBC, dehydrogenase activity, phosphatase activities, and MBP were found in surface soil. The maximum microbial activities were observed in the treatment receiving 50% recommended dose of fertilizer (RDF) + enriched compost at 5 t ha^?1 indicating that integrated use of chemical fertilizers and enriched compost significantly improved the biological properties of soil under wheat–soybean rotation thereby enhanced soil fertility and crop production.     

Aerobic short-term microbial utilization and degradation of humic acids extracted from soils of long-term field experiments

A humic acid (HA) fraction of the soil organic matter (SOM) was extracted with alkali from soil samples originated in non-fertilized and fertilized (NPK + organic manure) plots of long-term (45 years) field experiments. The HA preparations served as supplemental sources of nutrients or as sole source of either C or N for soil micro-organisms indigenous to the same soils. Under aerobic conditions (shake cultures) between 15% and 45% of HA were degraded in 21 days. The degradation was minimum if HAs were added supplementary, although the biomass formation was strongly enhanced. Preparations of HA from long-term fertilized soils appeared somewhat less susceptible to microbial degradation but they were capable of supporting microbial growth. Under copious nutritional conditions some novel HA-like substances were formed. The HA preparations re-isolated from individual cultures exhibited differences in elemental and structural characteristics. The FTIR spectra indicated an increasing proportion of aromatic structures that appeared as associated with mineral moieties. Conclusively, HAs from long-term fertilized and manured soils could be considered as more resistant to microbial activities than those from control soil, but under limited nutrient conditions their aliphatic constituents appear utilizable by micro-organisms.     

Growth and Heavy-Metal Uptake by Lettuce Grown in Soils Applied with Sewage Sludge Compost

A pot experiment was conducted to investigate the effect of sewage sludge compost (SSC) alone and applied with chemical fertilizer on growth and heavy-metal accumulations in lettuce grown on two soils, a Xanthi-Udic Ferralosol and a Typic Purpli-Udic Cambosol. The treatments included control; nitrogen–phosphorus–potassium (NPK) fertilizer; sewage sludge compost applied at the rates of 27.54 (SSC), 82.62 (3SSC), 165.24 (6SSC) t hm^–2; and coapplication treatment (1/2 SSC + 1/2 NPK), where the N, P, and K inputs from NPK fertilizer, SSC, and coapplication treatments were normalized to the local recommend rates. The SSC application increased the biomass; copper, zinc, and lead contents in lettuce; and soil total and diethylenetriaminepentaacetic acid (DTPA)–extractable metals. However, SSC alone at the recommended rate caused less plant biomass than NPK fertilizer alone. Coapplication treatment obtained greater or similar biomass to NPK fertilizer alone and did not increase heavy-metal accumulation in soils and plants. The results demonstrated that SSC should be applied to soils with chemical fertilizers.     

肥料重金属含量状况及施肥对土壤和作物重金属富集的影响

本文对肥料中重金属的含量状况以及施肥对土壤和农作物重金属累积影响的研究进展进行了系统分析和总结。过磷酸钙中锌（Zn）、 铜（Cu）、 镉（Cd）、 铅（Pb）含量高于氮肥、 钾肥和三元复合肥,有机-无机复混肥料中的Pb含量高于其他化肥。有机肥如畜禽粪便、 污泥及其堆肥中的重金属含量高于化肥,猪粪中的Cu、 Zn、 砷（As）、 Cd含量明显高于其他有机废弃物,鸡粪中铬（Cr）含量高;污泥和垃圾堆肥中Pb或汞（Hg）含量高。商品有机肥Zn、 Pb和镍（Ni）含量高于堆肥,Hg含量高于畜禽粪便。多数研究表明,氮磷钾配施与不施肥相比土壤Cd和Pb含量增加,施用有机肥比不施肥提高土壤Cu、 Zn、 Pb、 Cd含量。施用化肥对农作物重金属富集的影响不明确,而施用有机肥可提高作物可食部位Cu、 Zn、 Cd、 Pb 的含量,影响大小与有机肥种类、 用量、 土壤类型和pH以及作物种类等有很大关系。在今后的研究中应着重以下几个方面, 1）典型种植体系下土壤重金属的投入/产出平衡; 2）不同种植体系下长期不同施肥措施对土壤重金属含量、 有效性影响的动态趋势; 3）典型种植体系和施肥措施下土壤对重金属的最高承载年限; 4）现有施肥措施下肥料中重金属的最高限量标准。     

Agriculturally relevant microbial community structure in long-term fertilized paddy soils as revealed by phospholipid fatty acid (PLFA) and pyrosequencing analyses

Evidence linking the direct impact of fertilization on diversity, function and phylogeny of N-fixing and P-solubilizing bacteria in rice ecosystem is lacking. This study using phospholipid fatty acid (PLFA) and 454 pyrosequencing analyses was conducted in long-term fertilized (NP, NK, PK, NPK, compost, NPK + compost) paddy field soil, the objective being to examine the community structure of the functionally important beneficial soil microbial communities. Maximum total PLFAs were observed in organic fertilizer treatments, viz. compost (881.5 ± 11.1 nmol g^?1) and NPK + compost (866.5 ± 10.8 nmol g^?1). Pyrosequencing revealed that the overall bacterial and eukaryal compositions at phyla level were not significant for all treatments, while the distribution of each phyla differed. Specifically, the major classified bacterial phyla for all treatments were Proteobacteria, Actinobacteria, Cyanobacteria and Firmicutes. Supported by the high throughput sequencing approach we hereby propose that the mechanism of N and P cycling under long-term balanced fertilization in a rice ecosystem is largely governed by microbes, notably by the free living N-fixing and/or P solubilizing heterocystous and/or non-heterocystous cyanobacteria, autotrophic bacteria and heterotrophic bacteria. The current study thus proposes that balanced fertilizers may be used without detrimental effects on rice soils in the long-term.     

Carbon uptake by a microbial community during 30-day treatment with 13C-glucose of a sandy loam soil fertilized for 20 years with NPK or compost as determined by a GC–C–IRMS analysis of phospholipid fatty acids

To investigate the uptake by the microbial community of easily decomposable exogenous organic C and the proportion of this organic C remaining in soils under long-term fertilization schemes, ¹³C-glucose was supplied to arable soils (aquic inceptisol) following a 20-year (1989–2009) application of compost (CM) or inorganic NPK (NPK), along with a control (no fertilizer). Phospholipid fatty acids (PLFAs) were used as biomarkers for actinobacteria, bacteria and fungi. Gas chromatography–combustion–stable isotope ratio mass spectrometry (GC–C–IRMS) was used to determine the incorporation of ¹³C into individual PLFAs. The concentrations of soil microbial PLFAs significantly (P < 0.05) increased in all three soils after the addition of ¹³C-glucose. Over a 30-day incubation period, the highest PLFA concentrations were on day 7 (control) or day 15 (NPK and CM) for bacteria, and on day 30 for both fungi and actinobacteria. The added ¹³C-glucose was incorporated into bacterial PLFAs first, whilst an increase of ¹³C in fungal and actinobacterial PLFAs was measured on day 7 and 15, respectively. The mean amounts of ¹³C in bacterial, actinobacterial and fungal PLFAs in CM-treated soil during the 30-day incubation period were 0.589, 0.030 and 0.056 μg g⁻¹ soil, respectively, which were significantly (P < 0.05) higher than levels measured in the NPK and control soils. Among the bacterial groups, the amount of ¹³C in Gram-positive (G⁺) bacteria over the entire incubation ranged from 0.326 to 0.440 μg g⁻¹ soil in the CM scheme, which was significantly (P < 0.05) higher than levels detected in the NPK and control regimes. In contrast, ¹³C concentrations in monounsaturated PLFAs (aerobic microorganisms) in the CM-treated soil were 0.030–0.045 μg g⁻¹ soil, which was significantly (P < 0.05) lower than in the NPK schemes. The proportion of glucose-derived ¹³C remaining in soils was ranked as follows: CM (53%) > NPK (41%) > control (28%) after 30 days of incubation. Easily decomposable exogenous organic C was thus more effectively maintained under the CM regime, primarily because, after 20 years, CM had altered the microbial community by reducing the ratio of aerobic to anaerobic microorganisms whilst increasing levels of G⁺ bacteria in soil compared to the control and NPK soils. This study aids our understanding of the transformation and maintenance of easily decomposable organic C in soil over long-term fertilization regimes.     

Rapid microbial phosphorus immobilization dominates gross phosphorus fluxes in a grassland soil with low inorganic phosphorus availability

Gross phosphorus (P) fluxes measured in isotopic dilution studies with ³³P labeled soils include the biological processes of microbial P immobilization, remineralization of immobilized P and mineralization of non-microbial soil organic P. In this approach, isotopic dilution due to physicochemical processes is taken into account. Our objectives were to assess the effect of inorganic P availability on gross P mineralization and immobilization in soil under permanent grassland, and to relate these fluxes to soil respiration, phosphatase activity and substrate availability as assessed by an enzyme addition method. We used soils from an 18-year-old grassland fertilization experiment near Zurich, Switzerland, that were collected in two treatments which differed only in the amount of mineral P applied (0 and 17 kg P ha⁻¹ yr⁻¹ in NK and NPK, respectively). Water-extractable phosphate was low (0.1 and 0.4 mg P kg⁻¹ soil in NK and NPK, while hexanol-labile (microbial) P was high (36 and 54 mg P kg⁻¹ soil in NK and NPK). Extremely fast microbial P uptake under P-limited conditions in NK necessitated the use of a microbial inhibitor when determining isotopic dilution due to physicochemical processes. At the higher inorganic P availability in NPK, however, isotopic exchange parameters were similar in the presence and absence of a microbial inhibitor. Phosphatase activity was higher in NK than in NPK, while soil respiration, water-extractable organic P and its enzyme-labile fraction were not affected by P status. Together, the results showed that inorganic P availability primarily affected microbial P immobilization which was the main component of gross P fluxes in both treatments. Gross P mineralization rates (8.2 and 3.1 mg P kg⁻¹ d⁻¹ for NK and NPK) during the first week were higher than reported in other studies on arable and forest soils and at least equal to isotopically exchangeable P due to physicochemical processes, confirming the importance of microbial processes in grassland soils.     

Incorporation of natural hydrocarbons from plant residues into an hydromorphic humic podzol following afforestation and fertilization

The content and composition of natural hydrocarbons from plant residues (Pinus maritima sp.) of a hydromorphic humic podzol were investigated following the addition of NPK and P fertilizers. L and F layers and the A, horizon from non-fertilized and fertilized soil were analysed for total lipids and hydrocarbons, and non-linear and linear hydrocarbons. The decrease in non-linear hydrocarbons extracted following the addition of fertilizers was attributed to the incorporation of non-linear hydrocarbons into humus, rather than to their biodegradation by soil micro-organisms. Short- and medium-chain linear hydrocarbons from plant residues or of microbial origin were rapidly biodegraded or fixed by soil micro-organisms, resulting in a very low concentration in the A, horizon. In contrast, long-chain linear hydrocarbons of plant origin accumulated in the non-fertilized soil, while the addition of P fertilizer slightly stimulated their biodegradation. oration is needed before firm conclusions can be drawn.     

Denitrification with and without maize plants (Zea mays L.) under irrigated field conditions

The study was conducted under irrigated field conditions to examine the effect of maize plants on denitrification. Both planted and unplanted field plots received 150kgNha^–1 as urea. In a third treatment, which was also planted and received urea at 150kgNha^–1, the soil nitrate N content was brought up to equal to that in the unplanted plots by applying additional doses of N as calcium nitrate. Soil cores were collected 24 and 72h after irrigation and the denitrification rate was measured by the acetylene inhibition method. Nitrate-N content, aerobically mineralizable C, microbial biomass carrying capacity and denitrification potential were also studied on field-moist soil. Maize plants grown under field conditions always had the potential to increase denitrification in conditions of both high and low water-filled porosity. When nitrate-N content of the planted soil decreased due to plant uptake, denitrification was reduced in the planted soils. However, when nitrate-N uptake by plants was compensated through additional doses of nitrate fertilizer, denitrification was always higher in planted than unplanted soil. The stimulatory effect of plants on denitrification was observed at both high and low soil nitrate-N concentrations, though it was more pronounced at high nitrate-N levels. The effect of plants on denitrification and related parameters was confined to the root zone. Received: 15 April 1996     

适宜水分和养分提高土壤中磺酸二甲嘧啶降解率

医疗和养殖过程中抗生素的广泛使用导致了土壤环境中抗生素的污染。为了解进入农田土壤中抗生素的降解规律,该文以养殖业广泛使用的磺胺二甲嘧啶和2种不同养分水平的土壤为试验材料,采用盆栽方法研究了肥料种类(有机肥、NPK肥、N肥、PK肥等)、耕作强度(翻耕、免耕)、水分条件(长期干燥、长期湿润、干湿交替、长期潮湿)及种植作物(种植蔬菜、不种蔬菜)对土壤中磺胺二甲嘧啶降解的影响。结果表明,与不施肥处理比较,施用有机肥、NPK肥、N肥可促进土壤中磺胺二甲嘧啶在土壤中的降解,并以施用有机肥的效果最为明显;但施用PK肥对土壤中磺胺二甲嘧啶的降解影响不明显。翻耕可促进土壤中磺胺二甲嘧啶的降解,干湿交替、长期湿润比长期干燥和长期潮湿土壤环境下更有利于磺胺二甲嘧啶的降解。种植蔬菜比不种蔬菜土壤的磺胺二甲嘧啶的降解率高,根际土壤中磺胺二甲嘧啶的降解高于总体土壤。高养分土壤中磺胺二甲嘧啶的降解一般高于低养分土壤。分析认为,施肥、土壤养分水平、种植蔬菜对土壤中磺胺二甲嘧啶的降解的影响可能主要与这些因素改变了土壤微生物活性有关;翻耕可促进土壤中抗生素的光降解强度。研究认为,施肥、耕作和水分管理可以在一定程度上加速土壤中磺胺二甲嘧啶的降解。     

Microbial activities in a histosol: Effects of wood ash and NPK fertilizers

Mineralization of organic matter and microbial activities in an intensively cultivated acid, N-rich peat soil planted with Salix sp. cv. aquatica were examined for 3 yr. The soil was amended with wood ash or NPK fertilizers providing N as ammonium nitrate or urea. The wood ash amendment (10 tons ha^?1) increased soil pH from 4.6 to 5.5 and increased markedly all microbial activities measured, resulting in increased mineralization and N availability, and in loss of 9% total soil N during the first year. The addition of ammonium nitrate caused a corresponding though less pronounced increase in N mineralization. Cellulose decomposition increased in all amended soils, reaching rates 53–86% higher than in non-amended soil. Potential N₂ fixation (C₂H₂ reduction) by free-living organisms was increased by the ash-amendment. Potential denitrification rates were positively correlated (r = 0.98) with the presence of water-soluble organic-C, which was more abundant in ash-amended and non-amended soils than in the soils fertilized with N.     

Stable carbon isotope ratios of water-extractable organic carbon affected by application of rice straw and rice straw compost during a long-term rice experiment in Yamagata,Japan

ABSTRACT

Hot-water- and water-extractable organic matter were obtained from soil samples collected from a rice paddy 31 years after the start of a long-term rice experiment in Yamagata, Japan. Specifically, hot-water-extractable organic carbon and nitrogen (HWEOC and HWEON) were obtained by extraction at 80°C for 16 h, and water-extractable organic carbon and nitrogen (WEOC and WEON) were obtained by extraction at room temperature. The soil samples were collected from surface (0–15 cm) and subsurface (15–25 cm) layers of five plots that had been treated with inorganic fertilizers alone or with inorganic fertilizers plus organic matter, as follows: PK, NPK, NPK plus rice straw (RS), NPK plus rice straw compost (CM1), and NPK plus a high dose of rice straw compost (CM3). The soil/water ratio was 1:10 for both extraction temperatures. We found that the organic carbon and total nitrogen contents of the bulk soils were highly correlated with the extractable organic carbon and nitrogen contents regardless of extraction temperature, and the extractable organic carbon and nitrogen contents were higher in the plots that were treated with inorganic fertilizers plus organic matter than in the PK and NPK plots. The HWEOC and WEOC δ¹³C values ranged from ?28.2% to ?26.4% and were similar to the values for the applied rice straw and rice straw compost. There were no correlations between the HWEOC or WEOC δ¹³C values and the amounts of HWEOC or WEOC. The δ¹³C values of the bulk soils ranged from ?25.7% to ?23.2% and were lower for the RS and CM plots than for the PK and NPK plots. These results indicate that HWEOC and WEOC originated mainly from rice plants and the applied organic matter rather than from the indigenous soil organic matter. The significant positive correlations between the amounts of HWEOC and HWEON and the amount of available nitrogen (P < 0.001) imply that extractable organic matter can be used as an index for soil fertility in this long-term experiment. We concluded that the applied organic matter decomposed more rapidly than the indigenous soil organic matter and affected WEOC δ¹³C values and amounts.     

Soil aggregation and distribution of carbon and nitrogen in different fractions under long-term application of compost in rice–wheat system

Soil organic matter improves the physical, chemical and biological properties of soil, and crop residue recycling is an important factor influencing soil organic matter levels. We studied the impact of continuous application of rice straw compost either alone or in conjunction with inorganic fertilizers on aggregate stability and distribution of carbon (C) and nitrogen (N) in different aggregate fractions after 10 cycles of rice–wheat cropping on a sandy loam soil at Punjab Agricultural University research farm, Ludhiana, India. Changes in water stable aggregates (WSA), mean weight diameter (MWD), aggregate-associated C and N, total soil C and N, relative to control and inorganically fertilized soil were measured. Total WSA were significantly (p = 0.05) higher for soils when rice straw compost either alone or in combination with inorganic fertilizers was applied as compared to control. The application of rice straw compost either alone or in combination with inorganic fertilizers increased the macroaggregate size fractions except for 0.25–0.50 mm fraction. The MWD was significantly (p = 0.05) higher in plots receiving rice straw compost either alone at 8 tonnes ha⁻¹ (0.51 mm at wheat harvest and 0.41 mm at rice harvest) or at 2 tonnes ha⁻¹ in combination with inorganic fertilizers (0.43 and 0.38 mm) as compared to control (0.34 and 0.33 mm) or inorganically fertilized plots (0.33 and 0.31 mm). The macroaggregates had higher C and N density compared to microaggregates. Application of rice straw compost at 2 tonnes ha⁻¹ along with inorganic fertilizers (IN + 2RSC) increased C and N concentration significantly over control. The C and N concentration increased further when rice straw compost at 8 tonnes ha⁻¹ (8RSC) was added. It is concluded that soils can be rehabilitated and can sustain the soil C and N levels with the continuous application of rice straw compost either alone or in combination with inorganic fertilizers. This will also help in controlling the rising levels of atmospheric carbon dioxide.     

Impact of Long-Term Application of Organics,Biological, and Inorganic Fertilizers on Microbial Activities in Rice-Based Cropping System

Organics, biological, and inorganic fertilizers play a crucial role for improving crop yield and soil properties. Accordingly, we assessed their impact on yield, microbial activities, and transformations of carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in soils under a 12-year-old intensively cultivated rice (Oriza sativa L.), mustard (Brassica juncea L.), sesame (Sesamum indicum L.) system with sole inorganic (NPK); NPK + farmyard manure (NPKF); NPK + green manure (NPKG) (Sesbania sesban L.), and NPK + green manure + bio-fertilizer (NPKGB) (Azotobacter chroococcum+ pseudomonas putida) treatments in sub-tropical India. The system yield was much higher with NPKF (23%) and NPKGB (18%) than that with NPK. Organic supplementation had a favorable influence on soil microbial biomass C (C_mic), N (N_mic), and activities of extracellular enzymes. Results of principal component and multiple regression analyses showed significant influence of C_mic on system yield (R² = 91, p = 0.001) and S availability (R² = 62, p = 0.001). Similarly, mineralizable N and acid phosphatase could predict significantly soil available N (R² = 85, p = 0.001) and P (R² = 51; p = 0.001), respectively. Results thus indicated that integrated nutrient management (NPKF/G) improved system yield, nutrient accumulation, and microbial activities in soils.     

Effect of 46 years' application of fertilizers,FYM and lime on physical,chemical and biological properties of soil under maize–wheat system in an acid Alfisol of northwest Himalayas

Imbalanced fertilizer use with intensive cropping has threatened the sustainability of agroecosystems, especially on acid soils. An understanding of the long-term effects of fertilizers and amendments on soil health is essential for sustaining high crop yields. The effects of application of fertilizers, and amendments for 46 years on soil properties and maize yield in an acid Alfisol were investigated in this study. Ten fertilizer treatments comprising different amounts of NPK fertilizers, farmyard manure (FYM) and lime, and one control, were replicated three times in a randomized block design. At 0–15 cm soil depth, bulk density was least (1.20 t/m³), porosity (49.8%) and water holding capacity (61.7%) were greatest in 100% NPK + FYM, corresponding to the largest organic carbon content (13.93 g/kg). Microbial biomass C and dehydrogenase activity in 100% NPK + FYM were 42% and 13.7% greater than 100% NPK, respectively. Available nutrients were significantly more with 100% NPK + FYM and 100% NPK + lime than control and other fertilizer treatments. At 15–30 cm depth, the effect of various treatments was comparable to the surface layer. Grain yield declined by 55% and 53% in 100% NPK(-S) and 100% NP, respectively, compared with 100% NPK, whereas 100% N as urea alone eventually led to crop failure. Soil porosity recorded the greatest positive correlation (r = .933**), whereas bulk density recorded a negative significant correlation (r = −.942**) with grain yield. The results suggest that integrated use of FYM/lime with chemical fertilizers is a sustainable practice in terms of crop yield and soil health, whereas continuous application of urea alone is detrimental to the soil health.     

Effect of long-term fertilizers and manure application on microbial biomass and microbial activity of a tropical agricultural soil

We investigated some aspects of soil quality and community-level physiological profiles (CLPP) of bacteria in soil under a long-term (37 years) trial with either exclusive inorganic fertilizers or fertilizers combined with farmyard manure cultivated with jute–rice–wheat system. The treatments consisted of 100% recommended dose (RD) of NPK, 150% RD of NPK, 100% RD of N, 100% RD of NPK + FYM (10 t ha⁻¹ year⁻¹), and untreated control. Long-term application of 150% RD of NPK lowered the soil pH considerably while the soils in the other treatments remained near neutral. The 100% RD of NPK + FYM treated plot showed significantly highest accumulation of organic carbon, total nitrogen, microbial biomass carbon, basal soil respiration, and fluorescein diacetate hydrolyzing activity among the treatments. CLPP analysis in Biolog Ecoplates revealed that utilization of carbohydrates was enhanced in all input treated regimes, while the same for polymers, carboxylic acids, amino acids, and amines/amides were similar or less than the untreated control. However, within these groups of carbon sources, heterogeneity of individual substrate utilization between treatments was also noted. Taken together, addition of organic supplements showed significantly increased microbial biomass carbon and microbial activity, but input of nutrient supplements, both inorganic and organic, only marginally affected the overall substrate utilization pattern of soil microorganisms.     

有机无机肥配施对酸性菜地土壤硝化作用的影响

通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理（NPK）相比,鲜猪粪配施无机肥（FPM+NPK）和猪粪堆肥配施无机肥（CPM+NPK）均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。