首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 656 毫秒
1.
 The influence of compaction on Diplocardia ornata (Smith) burrowing and casting activities, soil aggregation, and nutrient changes in a forest soil were investigated using pot microcosms. Treatments included two levels each of compaction, organic matter, and earthworms. Both burrowing and casting activities were more abundant in uncompacted soil than in compacted soil. Bulk density decreased in microcosms of compacted soil containing D. ornata from 1.76 g cm–3 to 1.49 g cm–3 over the study period. The overall percent of aggregates in the same size classes in compacted soil was less than the percent of aggregates in uncompacted soil. The mean percent of aggregates in earthworm casts for size classes 0.25–1.00 mm was higher for compacted soil than for uncompacted soil. The reverse was true for aggregates in class sizes 2.00–4.00 mm. Soil compaction also affected soil microbial biomass carbon and soil inorganic N concentrations. These results indicate that the burrowing and casting activities of earthworms in compacted forest soils, as in soils of agricultural and pastured lands, can help ameliorate disturbed soils by improving aggregation, reducing bulk density, and increasing nutrient availability. Received: 1 September 1999  相似文献   

2.
 The restoration of soil microbial activities is a basic step in the reclamation of burnt soils. For this reason, the ability of municipal solid waste compost to accelerate the re-establishment of bacterial and fungal populations, as well as to re-establish physical properties in a burnt soil, was evaluated in a field experiment. Four treatments were performed by adding different doses of compost (0, 0.5, 1 and 2 kg compost m–2 soil) to a burnt Calcic Rodoxeralf soil, and the changes in microbial populations, salt content, aggregate stability and bulk density were evaluated for 1 year. Initially, the addition of compost had a negative effect on soil microbial populations, but 3 months after compost addition, the number of viable fungal propagules increased in all the amended soils. This positive effect lasted until the end of the experiment. From 30 days onwards, all the amended soils showed a greater total number of bacterial cell forming units than the unamended burnt soil. Organic amendment increased the percentage of 2- to 4-mm aggregates, although the effect on the stability of the 0.2- to 2-mm aggregates and on bulk density was less noticeable. Received: 24 November 1999  相似文献   

3.
《Soil & Tillage Research》2007,92(1-2):109-119
Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m−3) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha−1) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH4+-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.  相似文献   

4.
The potential of Pontoscolex corethrurus to repair the physical degradation of a compacted Oxisol was studied. The Oxisol from Kingaroy, Queensland, Australia was uniformly packed to four treatments of different bulk densities (0.95, 1.15, 1.25, 1.35 Mg m–3) in pots of 0.24 m diameter and 0.22 m deep. Each pot was inoculated with 12 earthworms (equivalent to 300 m–2) and maintained close to field capacity water content for 3 months, after which selected soil physical (dry bulk density, penetration resistance, water infiltration), worm activity (cast production, worm weight) measurements and image analysis were carried out. Results showed that worm numbers were maintained at the initial levels in all the treatments except in the 1.35 Mg m–3 treatment, where there was a 33% decrease. The weight of surface casts per surviving worm was the greatest in the 1.35 Mg m–3 treatment compared to the lower density treatments. Final soil density was lessened in all treatments to a depth of 0.2 m. Surface cast production was positively correlated with the percentage reduction in bulk density. The greatest percentage reduction in bulk density was in the 1.35 Mg m–3 treatment and was equivalent to a doubling of soil aeration (to 18.4%). Penetration resistance to the 0.2-m layer was also reduced and values were less than 2 MPa. Slumping of the surface soil was evident in both the lowest and the highest bulk densities resulting in low rates of water infiltration. Image analysis supported the soil physical properties showing an abundance of both fine pores and worm channels in the three lowest bulk densities, and lesser activity (concentrated in the immediate soil surface) in the 1.35 Mg m–3 treatment. Received: 6 November 1996  相似文献   

5.
Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little information about which soil properties control carbon dioxide (CO2) emission from saline-sodic soils. In this study, eight field-collected saline–sodic soils, varying in electrical conductivity (ECe, a measure of salinity, ranging from 3 to 262 dS m−1) and sodium adsorption ratio (SARe, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration expressed per gram SOC increased in the following order: unamended soil<soil amended with wheat residues (C/N ratio 122)<soil with vetch residue (C/N ratio 18). Cumulative respiration was significantly (p < 0.05) negatively correlated with ECe but not with SARe. Our results show that the response to ECe and SARe of the microbial community activated by addition of organic C does not differ from that of the less active microbial community in unamended soils and that salinity is the main influential factor for C mineralization in saline–sodic soils.  相似文献   

6.
Effect of cropping systems on nitrogen mineralization in soils   总被引：3，自引：0，他引：3  
 Understanding the effect of cropping systems on N mineralization in soils is crucial for a better assessment of N fertilizer requirements of crops in order to minimize nitrate contamination of surface and groundwater resources. The effects of crop rotations and N fertilization on N mineralization were studied in soils from two long-term field experiments at the Northeast Research Center and the Clarion-Webster Research Center in Iowa that were initiated in 1979 and 1954, respectively. Surface soil samples were taken in 1996 from plots of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha–1 before corn and an annual application of 20 kg P and 56 kg K ha–1. N mineralization was studied in leaching columns under aerobic conditions at 30  °C for 24 weeks. The results showed that N mineralization was affected by cover crop at the time of sampling. Continuous soybean decreased, whereas inclusion of meadow increased, the amount of cumulative N mineralized. The mineralizable N pool (N o) varied considerably among the soil samples studied, ranging from 137 mg N kg–1 soil under continuous soybean to >500 mg N kg–1 soil under meadow-based rotations, sampled in meadow. The results suggest that the N o and/or organic N in soils under meadow-based cropping systems contained a higher proportion of active N fractions. Received: 10 February 1999  相似文献   

7.
 A routine soil testing procedure for soil N mineralization is needed that is rapid and precise. Not accounting for N mineralization can result in the over-application of N, especially in soils with a history of manure application. Our objectives were to compare results from a recently proposed rapid laboratory procedure with: (1) long-term N mineralization under standard laboratory conditions, and (2) actual forage N uptake from soil receiving dairy cattle (Bos taurus) manure in a 2-year field study. The rapid procedure is based on the quantity of CO2-C evolved during 24 h under optimum laboratory conditions following the rewetting of dried soil. Dairy cattle manure was surface applied beginning in 1992 at annual rates of 0, 112, 224, or 448 kg N ha–1 to field plots on a Windthorst fine sandy loam soil (fine, mixed, thermic Udic Paleustalf) near Stephenville, Texas (32°N, 98°W). Results of the one-day CO2 procedure were highly correlated with soil N mineralized from samples collected in March of 1995 (P=0.004) and 1996 (P<0.001) and with forage N uptake (P<0.001) both years of the study. Residual inorganic N in the same soil samples was poorly correlated with soil N mineralization and forage N uptake. Received: 23 February 2000  相似文献   

8.
 A study was conducted to determine mineralization rates in the field and in different soil layers under three grassland managements (viz. a reseeded sward, a permanent sward with a conventional N management, and a long-term grass sward with 0 N (0-N) input). Potential mineralization rates of soil particles (sand, silt and clay) and macro-organic matter fractions of different sizes (i.e. 0.2–0.5, 0.5–2.0 and >2 mm) were also determined in the laboratory. In the reseeded plots, net mineralization was unchanged down to 40 cm depth. In the undisturbed conventional-N swards, mineralization rates were substantially higher in the top layer (0–10 cm) than in the deeper layers. In plots which had received no fertilizer N, mineralization was consistently low in all the layers. There was more macro-organic matter (MOM) in the 0-N plots (equivalent to 23 g kg–1 soil for 0–40 cm) than in the two fertilized plots (i.e. conventional-N and reseeded) which contained similar amounts (ca. 15 g kg–1 soil). C and N contents of separated soil particles did not differ amongst the treatments, but there were large differences with depth. Potential mineralization in the bulk soil was greatest in the 0–10 cm layers and gradually decreased with depth in all the treatments. Separated sand particles had negligible rates of potential mineralization and the clay component had the highest rates in the subsurface layers (10–40 cm). MOMs had high potential rate of mineralization in the surface layer and decreased with soil depth, but there was no clear pattern in the differences between different size fractions. Received: 17 November 1997  相似文献   

9.
Soil compaction may affect N mineralization and the subsequent fate of N in agroecosystems. Laboratory incubation and field experiments were conducted to determine the effects of surface soil compaction on soil N mineralization in a claypan soil amended with poultry litter (i.e., Turkey excrement mixed with pine shavings as bedding). In a laboratory study, soil from the surface horizon of a Mexico silt loam soil was compacted to four bulk density levels (1.2, 1.4, 1.6 and 1.8 Mg m−3) with and without poultry litter and incubated at 25 °C for 42 days. A field trial planted to corn (Zea mays L.) was also conducted in 2002 on a Mexico silt loam claypan soil in North Central Missouri. Soil was amended with litter (0 and 19 Mg ha−1) and left uncompacted or uniformly compacted. Soil compaction decreased soil inorganic N by a maximum of 1.8 times in the laboratory study; this effect was also observed at all depths of the field trial. Compacted soil with a litter amendment accumulated NH4+-N up to 7.2 times higher than the noncompacted, litter-amended soil until Day 28 of the laboratory incubation and in the beginning of the growing season of the field study. Ammonium accumulation may have been due to decreased soil aeration under compacted conditions. Application of litter increased soil N mineralization throughout the growing season. In the laboratory study, soil inorganic N in unamended soil was negatively correlated with soil bulk density and the proportion of soil micropores, but was positively related with soil total porosity and the proportion of soil macropores. These results indicate that soil compaction, litter application and climate are interrelated in their influences on soil N mineralization in agroecosystems.  相似文献   

10.
 This study examines the effect of soil P status and N addition on the decomposition of 14C-labelled glucose to assess the consequences of reduced fertilizer inputs on the functioning of pastoral systems. A contrast in soil P fertility was obtained by selecting two hill pasture soils with different fertilizer history. At the two selected sites, representing low (LF) and high (HF) fertility status, total P concentrations were 640 and 820 mg kg–1 and annual pasture production was 4,868 and 14,120 kg DM ha–1 respectively. Soils were amended with 14C-labelled glucose (2,076 mg C kg–1 soil), with and without the addition of N (207 mg kg–1 soil), and incubated for 168 days. During incubation, the amounts of 14CO2 respired, microbial biomass C and 14C, microbial biomass P, extractable inorganic P (Pi) and net N mineralization were determined periodically. Carbon turnover was greatly influenced by nutrient P availability. The amount of glucose-derived 14CO2 production was high (72%) in the HF and low (67%) in the LF soil, as were microbial biomass C and P concentrations. The 14C that remained in the microbial biomass at the end of the 6-month incubation was higher in the LF soil (15%) than in the HF soil (11%). Fluctuations in Pi in the LF soil during incubation were small compared with those in HF soil, suggesting that P was cycling through microbial biomass. The concentrations of Pi were significantly greater in the HF samples throughout the incubation than in the LF samples. Net N mineralization and nitrification rates were also low in the LF soils, indicating a slow turnover of microorganisms under limited nutrient supply. Addition of N had little effect on biomass 14C and glucose utilization. This suggests that, at limiting P fertility, C turnover is retarded because microbial biomass becomes less efficient in the utilization of substrates. Received: 18 October 1999  相似文献   

11.
 An incubation experiment with composted sewage sludge (CSS) just added to the soil was conducted to determine its initial effects on C decomposition, N nitrification and the transformation of organic matter. CSS was mixed with a sandy loam soil from uncultivated ochric epipedon of a Typic Haploxeralf at rates of 0, 40 and 80 t ha–1 (dry weight). The data obtained showed that with regard to the unamended soil, both the 40 and the 80 t ha–1 treatments produced the same result in decreasing respiratory activity, but the addition of increasing amounts of CSS progressively delayed C decomposition. The nitrification index (NI), defined as the relation between nitrate-N and nitrate-N + ammonium-N, increased in correlation with the C mineralization coefficient. Total organic matter decreased after incubation whereas the humic substances increased in relation to the total C mineralized. Received: 28 October 1999  相似文献   

12.
 Nitrogen mineralization was measured in three permanent pastures – either fertilized or unfertilized grass, or a mixed grass-clover sward – which were further amended with either fertilizer or cattle dung over a summer growing season. Measurements were made at 4-weekly intervals from June to October. Rates of net mineralization were similar in each of the background treatments (overall mean 0.99±0.091 kg N ha–1 day–1) and did not change markedly during the experiment. From the second sampling (July) onwards, rates of mineralization in all the dung treatments were higher than in the control by a factor of up to 2. In the fertilizer-amended treatments, rates were also consistently (but not significantly) higher than in the control. However, the relatively small effect of fertilizer detected at each sampling had a significant cumulative effect by the end of the experiment. There was no interaction between the background and current treatments. Potential mineralization, measured by anaerobic incubation, increased in all the treatments over the period of the experiment, showing an accumulation of readily mineralizable residues. Total N mineralized and the N accumulated during the experiment were calculated and compared. This approach suggests that potential measurements could provide a good estimate of changes in soil N supply that would not be otherwise detectable in changes in soil total N in the short-term. Received: 12 June 2000  相似文献   

13.
A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha−1 of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid). A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha−1 cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH4 +–N kg−1 2 h−1. Values of the Michaelis constant (K m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V max (r = 0.919, P < 0.001) and K m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic reaction involved in N mineralization in soil.  相似文献   

14.
 Net mineralization was measured in free-draining and poorly drained pasture soils using three different field incubation methodologies. Two involved the use of enclosed incubation vessels (jar or box) containing C2H2 as a nitrification inhibitor. The third method confined soil cores in situ in an open tube in the ground, with an anion-exchange resin at the base to retain leached NO3 – (resin-core technique, RCT). Measurements were made on three occasions on three free-draining pastures of different ages and contrasting organic matter contents. In general, rates of net mineralization increased with pasture age and organic matter content (range: 0.5–1.5 kg N ha–1 day–1) and similar rates were obtained between the three techniques for a particular pasture. Coefficients of variation (CVs) were generally high (range: 10.4–98.5%), but the enclosed incubation methods were rather less variable than the RCT and were considered overall to be the more reliable. The RCT did not include C2H2 and, therefore, newly formed NO3 – may have been lost through denitrification. In a poorly drained pasture soil, there were discrepancies between the two enclosed methods, especially when the soil water content approached field capacity. The interpretation of the incubation measurements in relation to the flux of N through the soil inorganic N pool is discussed and the drawbacks of the various methodologies are evaluated. Received: 18 November 1999  相似文献   

15.
 Soil tillage was studied as a strategy to synchronize N mineralization with plant demand following ploughing of two types of grazed pastures [ryegrass/white clover (Lolium perenne/Trifolium repens) and pure ryegrass]. The swards were either rotovated and ploughed or ploughed only. Soil respiration, as determined by a dynamic chamber method, was related to net N mineralization and to plant N uptake in a subsequent spring barley crop (Hordeum vulgare). Diurnal variations in temperature were important for the CO2 flux and care must be taken that temperatures during measuring periods are representative of the daily mean. Soil tillage increased the CO2 flux considerably compared with untilled soil with total emissions of 2.6 and 1.4 t C ha–1, respectively, from start of April to end of June. Sward type or rotovation did not markedly influence accumulated emissions. Rotovation significantly increased the content of nitrate in the soil until 43 days after rotovation, showing that net N mineralization occurred rapidly during this period, in spite of low soil temperatures (5–10  °C). Rotovation increased barley grain yield by 10–12% and N-uptake by 14%. For both sward types, rotovation caused an extra N-uptake in harvested plant material of about 12 kg ha–1. The availability of soil inorganic N at the early stages of barley was important for the final yield and N-uptake. The results indicated that soil biological activity was not enhanced by rotovation and that the yield effect of rotovation was mainly caused by quicker availability and better synchrony between N mineralization and plant uptake due to earlier start of decomposition. Received: 3 May 2000  相似文献   

16.
Surfactants, such as non-ionic Surfynol 485 （ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol）, have been applied to accelerate removal of polycyclic aromatic hydrocarbons from soil. This study investigated the dissipation of anthracene, and carbon （C） and nitrogen （N） mineralization in soil amended with non-ionic Surfynol 485 at different rates. Soil samples of a Typic Fragiudept taken from Otumba, Mexico were spiked with anthracene at a final concentration of 520 mg kg^-1 dry soil using acetone as solvent, amended with 0.0, 24.9, 49.8 or 124.4 g kg^-1 soil of the surfactant and incubated in the laboratory. The soil not amended with anthracene, acetone and the surfactant was used as a control. Dynamics of C and N and the concentration of anthracene were monitored for 56 d. After 56 d of incubation, 38% of the anthracene was removed from the unamended soil, and 47%, 55% and 66% of the anthracene were removed when 24.9, 49.8 and 124.4 g kg^-1 of the surfactant were applied, respectively. Application of acetone, anthracene or surfactant increased the emission of CO2, but decreased the mineral N compared to the unamended control. Applying the surfactant to the acetone or anthracene-amended soil reduced emission of CO2, but increased the mineral N at the lower application rates of the surfactant. It was found that the application of the non-ionic surfactant increased the bioavailability of anthracene and thus its removal from soil, increased C mineralization, but decreased N miaeralization. Consequently, the application of non-ionic surfactant could be easily used to accelerate the removal of pollutants from hydrocarbon-contaminated soils, but mineral N in the soil would decrease, which might inhibit plant growth.  相似文献   

17.
Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An1, and An2) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g−1 dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days. The legume residues markedly enhanced the net cumulative CO2–C flux and its rate throughout the incubation period. The cumulative CO2–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO2–C. In one of the three soils (An1), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH4+–N and NO3−–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH4+–N and NO3−–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.  相似文献   

18.
A field experiment was conducted during 2003–2005 and 2004–2006 at the Indian Institute of Sugarcane Research, Lucknow, India to study the effect of Trichoderma viride inoculation in ratoon sugarcane with three trash management practices, i.e. trash mulching, trash burning and trash removal. Trichoderma inoculation with trash mulch increased soil organic carbon and phosphorus (P) content by 5.08 Mg ha−1 and 11.7 kg ha−1 over their initial contents of 15.75 Mg ha−1 and 12.5 kg ha−1, respectively. Soil compaction evaluated as bulk density in 0- to 15-cm soil layer, increased from 1.48 Mg m−3 at ratoon initiation (in April) to 1.53 Mg m−3 at harvest (in December) due to trash burning and from 1.42 Mg m−3 at ratoon initiation (in April) to 1.48 Mg m−3 at harvest (in December) due to trash mulching. The soil basal respiration was the highest during tillering phase and then decreased gradually, thereafter with the advancement of crop growth. On an average, at all the stages of crop growth, Trichoderma inoculation increased the soil basal respiration over no inoculation. Soil microbial biomass increased in all plots except in the plots of trash burning/removal without Trichoderma inoculation. The maximum increase (40 mg C kg−1 soil) in soil microbial biomass C, however, was observed in the plots of trash mulch with Trichoderma inoculation treatment which also recorded the highest uptake of nutrient and cane yield. On an average, Trichoderma inoculation with trash mulch increased N, P and K uptake by 15.9, 4.68 and 23.6 kg ha−1, respectively, over uninoculated condition. The cane yield was increased by 12.8 Mg ha−1 with trash mulch + Trichoderma over trash removal without Trichoderma. Upon degradation, trash mulch served as a source of energy for enhanced multiplication of soil bacteria and fungi and provided suitable niche for plant–microbe interaction.  相似文献   

19.
Simple methods for the measurement of nitrogen (N) availability are needed to assess the effect of low-input, organically based land management systems on the N supply of tropical soils. Our objectives were to determine the effect of contrasting land-use systems (LUS) on soil N availability and to identify measures of N availability that correlated with maize (Zea mays L.) grain yield. The LUS at the two sites in Kenya involved growth of a maize crop following 17 months of either: (1) Sesbania sesban (L.) Merr. tree growth (sesbania fallow), (2) natural regrowth of vegetation without cultivation (natural fallow), (3) three crops of unfertilized maize (maize monoculture), or (4) bare uncultivated soil (bare fallow). Soil was collected before the post-fallow maize crop was sown. The LUS had no effect on total soil N or amount of N in the heavy fraction soil organic matter (SOM) (>150 μm, >1.37 Mg m–3). Sesbania and natural fallows, as compared to maize monoculture, increased the N in light fraction SOM (>150 μm, <1.13Mgm–3), N in intermediate fraction SOM (>150 μm, 1.13 to 1.37 Mg m–3), ammonium-N and aerobic N mineralization at a depth of 0–15 cm. Maize yields were highest following the sesbania fallow. Nitrate-N, inorganic-N (ammonium plus nitrate) and anaerobic N mineralization correlated with maize grain yield at both sites. The relationship between maize yield and pre-season nitrate-N improved when the depth of soil sampling was increased to 1 m at one site (an Alfisol), but did not improve at the site with anion adsorption in the subsoil (an Oxisol). The sesbania fallow was more effective than the natural fallow in increasing available soil N. Maize yield was better related to pre-season nitrate than N in size-density fractions of SOM. Received: 5 May 1997  相似文献   

20.
 Microcosms were used to determine the influence of N additions on active bacterial and fungal biomass, atrazine and dichlorophenoxyacetic acid (2,4-D) mineralization at 5, 10 and 15 weeks in soils from blackwater and redwater wetland forest ecosystems in the northern Florida Panhandle. Active bacterial and fungal biomass was determined by staining techniques combined with direct microscopy. Atrazine and 2,4-D mineralization were measured radiometrically. Treatments were: soil type, (blackwater or redwater forested wetland soils) and N additions (soils amended with the equivalent of 0, 200 or 400 kg N ha–1 as NH4NO3). Redwater soils contained higher concentrations of C, total N, P, K, Ca, Mn, Fe, B and Zn than blackwater soils. After N addition and 15 weeks of incubation, active bacterial biomass in redwater soils was lower when N was added. Active bacterial biomass in blackwater soils was lower when 400 kg N ha–1, but not when 200 kg N ha–1, was added. Active fungal biomass in blackwater soils was higher when 400 kg N ha–1, but not when 200 kg N ha–1, was added. Active fungal biomass in redwater soils was lower when 200 kg N ha–1, but not when 400 kg N ha–1, was added. After 15 weeks of incubation 2,4-D degradation was higher in redwater wetland soils than in blackwater soils. After 10 and 15 weeks of incubation the addition of 200 or 400 kg N ha–1 decreased both atrazine and 2,4-D degradation in redwater soils. The addition of 400 kg N ha–1 decreased 2,4-D degradation but not atrazine degradation in blackwater soils after 10 and 15 weeks of incubation. High concentrations of N in surface runoff and groundwater resulting from agricultural operations may have resulted in the accumulation of N in many wetland soils. Large amounts of N accumulating in wetlands may decrease mineralization of toxic agricultural pesticides. Received: 26 June 1998  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号