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1.
Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH4 +–N+NO3 ?–N)], NH4 +–N, and accumulation of NO3 ?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg?1 soil day?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO3 ?–N was 13.2, 10.6, and 14.6 mg kg?1 soil relative to 7.4 mg NO3 ?–N kg?1 in the control soil, indicating that manures accumulated NO3 ?–N almost double than the control. The proportion of total mineral N to NO3 ?–N revealed that a total of 44–61% of mineral N is converted into NO3 ?–N, indicating that nitrifiers were unable to completely oxidize the available NH4 +. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.  相似文献   

2.
This study provided an insight on improving soil-plant micronutrients availability in response to poultry manure (PM), wheat milling residues (WMR) and urea N (UN) and their integration in wheat–soybean cropping system. The treatments were: control; poultry manure full, PM100; wheat milling residues full, WMR100; urea N full, UN100; PM half and WMR half, PM50+WMR50; UN50+PM50; UN50+WMR50; UN50+PM25+WMR25. All amendments were added at the rate or equivalent to 100 kg total N ha–1. Results indicated that the integrated treatments increased Cu, Fe, Mn and Zn uptake of wheat by 35.7–103%, 48.4–111.1%, 85.2–267.0% and 33.8–128.2%, respectively over control. In soybean the corresponding increase in micronutrient uptake (Cu, Fe, Mn and Zn) was 18.3–60.3%, 27.5–87.4%, 14.1–54.6% and 13.2–58.0% in integrated treatments. The post-harvest soil analysis indicated 2 to 3-fold increase in micronutrient content with highest values in PM100 i.e., 2.66 mg kg?1 for Cu, 14.41 mg kg?1 for Fe, 18.58 mg kg?1 for Mn and 2.44 mg kg?1 for Zn, respectively. The results showed that the PM either alone or in integrated with WMR and UN can be an effective management strategy for improving micronutrient content of soil–plant.  相似文献   

3.
Inhibition of nitrification as a mitigation tool to abate nitrogen (N) losses and improve N use efficiency (NUE) is a promising technology. Nitrification inhibitor (dicyandiamide, DCD) was evaluated in two consecutive wheat-maize rotations (2015–2017), with two different N fertilizer levels applied in wheat (160, 220 kg N ha?1) and maize (180, 280 kg N ha?1). More NH4+-N contents (101% and 102% in wheat and 74% and 73% in maize) and less NO3–-N contents (37% and 43% in wheat and 46% and 57% in maize) were observed at both N levels treated with DCD compared to without DCD. Higher pH, lower EC and reduced NO3–-N accumulation were the other benefits of DCD. The NO3–-N accumulation within the 0–200 cm soil profile was significantly less at both N levels with DCD (66 mg kg?1 and 121 mg kg?1) compared to without DCD (96 mg kg?1 and 169 mg kg?1). Application of DCD also improved the growth and yield in both crops. Increase in NUE from 38% to 49% in wheat and 27% to 33% in maize with DCD at higher N level was also observed. Overall, the effectiveness of DCD in retarding the nitrification process was higher in wheat than maize.  相似文献   

4.
Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO3-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L?1 K2SO4 extractable N (extractable N), NO3-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha?1 containing 158 kg N ha?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO3-N leaching were monitored in soil treated with SDC (20 Mg ha?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha?1 containing 0, 15, 29, 44 and 59 kg N ha?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH4)2SO4 at rates of 220 kg N ha?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO3-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO3-N leaching in the CF treatment was 146 kg N ha?1, which was equal to half of the applied N, but only 53 kg N ha?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO3-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO3-N leaching without impacting negatively on N uptake by plants.  相似文献   

5.
Abstract

A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH4-N concentrations varied from 50 – 280 mg kg?1 in the CM amended soil with negligible amounts of NO3-N. Subsequently, the concentration of NH4-N decreased while that of NO3-N increased rapidly. In soil amended with SS at 20 – 80 g kg?1 rates, the NO3-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg?1 SS rate, there were three distinct phases of NO3-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH4-N and NO3-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively.  相似文献   

6.
Pot experiments were conducted in the greenhouse on a calcareous soil to study effect of nitrogen (N) on the alleviation of boron (B) toxicity in rice. The treatments consisted of factorial combination of six levels of B (0, 2.5, 5, 10, 20, and 40 mg kg?1 as boric acid), and four levels of N (0, 75, 150, and 300 mg kg?1 as urea) in a completely randomized design with three replicates. Boron addition (higher than 2.5 mg kg?1) significantly reduced the seeds yield. Nitrogen addition alleviated the growth suppression effects caused by B supplements. Yield was increased by application of 2.5 mg B kg?1 at all N levels, but at higher levels, B significantly decreased the yield of rice. Boron concentration declined with increasing N levels. Boron application increased the concentrations of B, potassium, phosphorous (P), and zinc. Nitrogen application decreased the concentration of Zn and increased the concentration of N and P.  相似文献   

7.
Phospho-compost (PC) and poultry manure (PM) were evaluated in field experiments to diversify integrated nutrient management (INM) for rain-fed cotton. Seed cotton yield in the PC (2501–2579 kg ha?1) was similar to the recommended INM (2673 kg ha?1) treatment and was significantly better than nitrogen, phosphorus and potassium (100% NPK) (2130 kg ha?1) and farmers practice (FP) (1886 kg ha?1). Yield was lower in the PM (2476–2617 kg ha?1) than in the PC. Nutrient uptake was higher in all INM intervention plots due to an improvement in soil nutrient status compared with those receiving 100% NPK. Soil labile carbon values were higher in the INM treatments (333–452 mg kg?1), with a greater magnitude in the PC-amended plots (402–452 mg kg?1). Carbon management index (CMI) values were higher for the INM than treatments NPK and FP. Among INM interventions, PC plots had higher values than the PM.  相似文献   

8.
This study evaluated the petiole uptake of nitrogen, phosphorus, potassium, and sulfur (N, P, K, and S) by the potato from two seed meals, mint compost, and five commercially available organic fertilizers under an irrigated certified organic production system. Available soil nitrate (NO3-N) and ammonium (NH4-N) from each amendment averaged 115 kg N ha?1 at application and 25 kg N ha?1 30 d after planting through harvest, with minor differences between fertilizers. Petiole N declined from an average of 25,000 mg N kg?1, 4 wk after emergence to 3,000 mg N kg?1 prior to harvest. Petiole P and K concentrations were maintained above 4,000 mg P kg?1, 10,000 mg K kg?1, and 2,000 mg S kg?1 tissue, respectively, throughout the growing season in all treatments. Tuber yields were not different between fertilized treatments averaging 53 Mg ha?1. This study provides organic potato growers baseline information on the performance of a diverse array of organic fertilizers and amendments.  相似文献   

9.
Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH4+)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z0: (100 kg (N) ha?1) as urea, two levels of raw zeolite; Z1:(0.5 g kg?1 + 100 kg ha?1) and Z2: (1 g kg?1 + 100 kg ha?1), and two levels of NH4+-enriched zeolite; Z3: (0.5 g kg?1 + 80 kg ha?1) and Z4: (1 g kg?1 + 60 kg ha?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO3?) and NH4+ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH4+ and NO3? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH4+-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH4+-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH4+-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.  相似文献   

10.
Microbial mineralization of urea and uric acid in poultry litter can lead to loss of nitrogen (N) content and its value as a fertilizer. To minimize the loss of N in the composting processes, controlling the water content in litters is a key to reduce the mineralization processes of N compounds. The N content of litter may be influenced by diets, hen age and the type of poultry houses used. The objectives of the present study were i) to determine the relationship between the water content and the decomposition rate of uric acid in poultry litter and ii) to investigate the effect of hen age and crude protein (CP) percentages in diets on the N content of poultry litter. A layer feeding trial was conducted in two poultry farms with windowless and open-floor houses. An incubation study of poultry litter was performed under different levels of water content. Our study found that the diet CP percentage (16.5–18%) and the growth stage of laying hens did not have a significant effect on the amount of total N (52–56?g?kg?1) and uric acid-N (26–31g?kg?1) in fresh litters. At the 7th day of litter incubation study, the concentration of uric acid-N was 22 g kg?1 in litters with a water content of 35%, whereas it further decreased to less than 1.3 g kg?1 in litters with a water content of 55% and higher levels. The decomposition rate of uric acid-N in litter was 0.3–3.1g?kg?1?day?1 in the windowless house and 3.1–7.1g?kg?1?day?1 in the open-floor house. Decomposition of uric acid in litters was positively correlated to the litter moisture content that is controlled to be lower in windowless houses (40–50%) than in open-floor houses (55–80%) during the composting period. Our study suggests that the use of windowless houses for layer chicken production is effective for producing poultry manure with a high N content.  相似文献   

11.

Purpose

Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH.

Materials and methods

Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg?1 (w/w), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH4+) and nitrate plus nitrite (NO3??+?NO2?).

Results and discussion

All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg?1 in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol(+) kg?1 compared to 2.82 and 4.19 cmol(+) kg?1 by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol(+) kg?1 per pH unit increase for both straws compared to 6.25 cmol(+) kg?1 per pH unit from the manure. The NO3??+?NO2? concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase.

Conclusions

While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.
  相似文献   

12.
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 B0.44 S13.4 treatment combination. The combined applications of sulfur and boron yielded highest oil content with B0.44S13.4 (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 B0.44 S13.4 treatment level for sulfur and boron uptake in straw and grains.  相似文献   

13.
A laboratory incubation experiment was conducted to evaluate the effect of magnesium chloride–induced salinity on carbon dioxide (CO2) evolution and nitrogen (N) mineralization in a silty loam nonsaline alkaline soil. Magnesium chloride (MgCl2) salinity was induced at 0, 4, 8, 12, 16, 20, 30, and 40.0 dS m?1 and measured CO2 evolution and N mineralization during 30 days of incubation. Both CO2 evolution and N mineralization decreased significantly with increasing salinity. The cumulative CO2 evolution decreased from 235 mg kg?1 soil at electrical conductivity (EC) 0.65 dS m?1 to 11.9 mg kg?1 soil at 40 dS m?1 during 30 days of incubation. Similarly, N mineralization decreased from 185.4 mg kg?1 at EC 0.65 dS m?1 to 34.45 mg kg?1 at EC 40.0 dS m?1 during the same period. These results suggested that increasing magnesium chloride salinity from 4 dS m?1 adversely affect microbial activity in terms of carbon dioxide evolution and N mineralization.  相似文献   

14.
The combination of inorganic fertilizers and compost is a technique aimed at improving crop growth and maintaining soil health. Understanding the rate of nutrient release from enriched compost is important for effective nutrient management. A laboratory incubation study was conducted for 112 days to study the nutrient mineralization pattern of poultry manure compost enriched with inorganic nitrogen (N) and phosphorus (P) fertilizer nutrients in an Ultisol. Compost applied at the rate of either 5 or 10 g kg?1 was blended with N (50 kg N ha?1) and P (30 kg P ha?1). Carbon dioxide evolution and N and P mineralization were measured fortnightly. The bacterial and fungal populations were determined at the mid and end of the experiment. The combination of compost and inorganic N and P increased carbon (C) and P mineralization by 4?8% and 56?289%, respectively, over the application of either compost or inorganic N and P. However, P addition influenced the amount of C mineralized. Inorganic N and P, on the other hand, were better at increasing N mineralization than compost blended with inorganic N and P over a short time. The addition of compost stimulated bacterial and actinomycete populations, while fungal populations were unaffected. Actinomycetes and bacteria had similar and higher relationship trend with C (R2 = 0.24) and P (R2 = 0.47) mineralization and were key determinants in nutrient mineralization from compost in this Ultisol. Integrating compost with inorganic fertilizers improves nutrient availability through the growth and activities of beneficial microorganisms.  相似文献   

15.
A field experiment was conducted on an Alfisol (kandic paleustalf) in Abeokuta, Southwestern Nigeria, for two seasons to assess the influence of inorganic and organic fertilizers on nitrogen (N), phosphorus (P), potassium (K), nutrient uptake and maize yield. The treatments consisted of three rates of organic fertilizer 0, 5 and 10 t ha?1 in the form of poultry manure and NPK fertilizer (20:10:10) applied at 0 and 120 kg ha?1. Maize (Zea mays) was used as the test crop. The results showed that the combined application of 10 t ha?1 poultry manure and 120 kg ha?1 NPK fertilizer enhanced the uptake of N, P and K better than other treatment combinations. Application of 10 t ha?1 poultry manure alone gave the highest grain yield, which was 67.02% higher than the control in the first season. Complementary application of 5 t ha?1 poultry manure with 120 kg ha?1 NPK 20–10-10 was recommended for grain yield.  相似文献   

16.
Ammonia-oxidizing archaea (AOA) and bacteria (AOB), which convert NH3 to NO2? in soils, are important for agricultural production. It is well known that N addition can strongly affect soil ammonia oxidizers, but little is known about P addition. Based on microcosm experiments, this study assessed the responses of ammonia oxidizers to chemical P addition in a typically high P agricultural soil with or without N supply. Six treatments examined were neither N nor P, P alone (0.15, 0.45, and 0.75 g P2O5 kg?1 soil, respectively), N alone (0.25 g N kg?1 soil), and N plus P (0.25 g N and 0.15 g P2O5 kg?1 soil). Quantitative real-time PCR for the abundance and high-throughput sequencing for community structure were applied. The results revealed that P addition did not affect the abundances and community structures of AOA and AOB, but N addition significantly increased AOB abundance and alter its community structure. Without N supply, continuously increasing soil P availability did not affect these two groups of ammonia oxidizers. This study highlights the relationship between soil P availability and ammonia oxidizers and suggests that soil P availability could be as a potential indicator for predicting N-related ecosystem functions in agricultural production.  相似文献   

17.
Abstract

To optimize the efficient use of nutrients in pig slurry by crops and to reduce the pollution risks to surface and groundwater, a full knowledge of the fate of nitrogen (N) in amended soils is needed. A 120 day laboratory incubation experiment was conducted to study the effects of pig slurry application on soil N transformations. Pig slurry was added at the rates of 50 and 100 g kg?1. A nonamended soil was used as a control treatment. Soil samples were taken after 0, 7, 14, 30, 45, 60, and 120 days of incubation and analyzed for NH4 +‐N and NO3 ?‐N. Initially, the application of pig slurry produced significant increases in NH4 +‐N, especially at the highest application rate, whereas NO3 ?‐N content was not affected. Nitrification processes were active during the entire incubation time in the three treatments. In the control soil, the net N mineralization rate was highest during the 1st week (5.7 mg kg?1 d?1), followed by a low‐steady phase. Initially, net N mineralization rate was slower in soil with the lowest slurry rate (2.7 mg kg?1 d?1), whereas in the treatment with the highest slurry rate, a net N immobilization was observed during the 1st week (4.8 mg kg?1 d?1). Mineral‐N concentrations after 120 days were 180, 310, and 475 mg kg?1 in soils amended with 0, 50, and 100 g kg?1 of pig slurry, respectively. However, when results were expressed as net mineralized N, the opposite trend was observed: 74, 65, and 44 mg kg?1. Of the six kinetic models tested to describe the mineralization process, a two‐component, first exponential model (double model) offered the best results for all treatments.  相似文献   

18.
The study was carried out between 2008 and 2010 on 8-year-old pomegranate (Punica granatum L.) trees cultivar ‘Kandhari Kabuli.’ The potential efficiency of bio-organics used along with chemical fertilizers on cropping behavior, quality attributes, nutrient availability, physico-chemical, and biological properties of soil were investigated. Bioorganic nutrient sources, namely, vermicompost (VC), biofertilizers (BF), farm yard manure (FYM), and green manure (GM), along with chemical fertilizers was evaluated in 13 different treatment combinations. Conjoint treatment application of VC at 20 kg tree?1, BF at 80 g tree?1, FYM at 20 kg tree?1, GM as sun hemp (Crotalaria juncea L.) along with 75% of the recommended dose of nitrogen–phosphorus–potassium (N–P–K) chemical fertilizers significantly resulted in maximum fruit set (52.03%) and fruit yield (34.02 kg tree?1). All of the fruit quality characteristics were also improved significantly when compared to nitrogen–phosphorus–potassium (N–P–K) chemical fertilizers. This superior combination also enhanced physical-chemical and biological properties of the rhizosphere soil. Microbial biomass of in terms of Pseudomonas, total culturable soil fungi, Azotobacter chroococcum, actinobacteria, and arbuscular mycorrhizal (AM) fungi improved 385.57, 60.26, 134.19, 168.02, and 39.87%, respectively, over control. This combination also resulted in considerable greater concentration of leaf macro-and micronutrients: N (2.63%), P (0.25%), K (1.57%), iron (Fe; 197.87 mg kg?1), copper (Cu; 14.65 mg kg?1), zinc (Zn; 59.36 mg kg?1), and manganese (Mn; 200.45 mg kg?1).  相似文献   

19.
The potential of Nostoc 9v for improving the nitrogen (N)2–fixing capacity and nutrient status of semi‐arid soils from Tanzania, Zimbabwe, and South Africa was studied in a laboratory experiment. Nostoc 9v was inoculated on nonsterilized and sterilized soils. Inoculum rates were 2.5 mg dry biomass g?1 soil and 5 mg dry biomass g?1 soil. The soils were incubated for 3 months at 27 °C under 22 W m2 illumination with a photoperiod of 16 h light and 8 h dark. The moisture was maintained at 60% of field capacity. In all soils, Nostoc 9v proliferated and colonized the soil surfaces very quickly and was tolerant to acidity and low nutrient availability. Cyanobacteria promoted soil N2 fixation and had a pronounced effect on total soil organic carbon (SOC), which increased by 30–100%. Total N also increased, but the enrichment was, in most soils, comparatively lower than for carbon (C). Nitrate and ammonium concentrations, in contrast, decreased in all the soils studied. Increases in the concentration of available macronutrients were produced in most soils and treatments, ranging from 3 to 20 mg phosphorus (P) kg?1 soil, from 5 to 58 mg potassium (K) kg?1 soil, from 4 to 285 mg calcium (Ca) kg?1, and from 12 to 90 mg magnesium (Mg) kg?1 soil. Positive effects on the levels of available manganese (Mn) and zinc (Zn) were also observed.  相似文献   

20.
To date, occurrence and stimulation of different nitrification pathways in acidic soils remains unclear. Laboratory incubation experiments, using the acetylene inhibition and 15N tracing methods, were conducted to study the relative importance of heterotrophic and autotrophic nitrification in two acid soils (arable (AR) and coniferous forest) in subtropical China, and to verify the reliability of the 15N tracing model. The gross rate of autotrophic nitrification was 2.28 mg?kg?1?day?1, while that of the heterotrophic nitrification (0.01 mg?kg?1?day?1) was negligible in the AR soil. On the contrary, the gross rate of autotrophic nitrification was very low (0.05 mg?kg?1?day?1) and the heterotrophic nitrification (0.98 mg?kg?1?day?1) was the predominant NO3 ? production pathway accounting for more than 95 % of the total nitrification in the coniferous forest soil. Our results showed that the 15N tracing model was reliable when used to study soil N transformation in acid subtropical soils.  相似文献   

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