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1.
Transformations of native soil organic materials, previously labelled with 14C, were investigated in soil planted with maize or perennial ryegrass and in fallow controls. There was more 14C in cold water extracts from planted soils than from fallow controls—an effect apparently caused by suppression of processes that remove labelled organic materials from this fraction of the soil organic matter. Decomposition of the labelled organic matter to 14CO2 was significantly less in the planted soils than in fallow controls. 相似文献
2.
Numerous studies have demonstrated that vegetation coverage is very important to control soil erosion by water. However, the combined impacts of plant roots and shoots on soil erosion by water and the relative contributions of the roots and shoots are not clearly understood. Four rainfall simulation experiments with the rainfall intensity at 1.5 mm min− 1 were conducted at an interval of 5 weeks to investigate the effects of ryegrass (Lolium perenne L.) shoots and roots on soil erosion and runoff reductions. Ten ryegrass planted pans and four fallow pans were prepared for the experiments. The first rainfall simulation experiment was conducted after ryegrass had been planted for 12 weeks. It showed that compared with the runoffs in the fallow pans, the runoff in the planted pans decreased 25% and 70% in the 12th week and the 27th week, respectively; and the sediment decrements amounted up to 95% in the 27th week. The results also indicated that the shoot effect on runoff reduction, accounting for over 50% except in the 27th week when the shoot affect also accounted for 44%, was relatively greater than the root effect. However, the roots contributed more to soil loss reduction than the shoots, and in particular accounted for 90% of soil loss reduction at the 27th week. Both the soil erosion rate and average infiltration rate were linearly correlated with root surface area density in cm2 root surface area per unit soil volume. Ryegrass planting could improve soil physical properties, especially soil aggregate stability, which increased from 33.1% in the 12th week to 38.5% in the 27th week. The study results are probably useful in evaluating the effects of plant shoots and roots on soil erosion control. 相似文献
3.
The effect of barley plants on the rate of decomposition of soil organic matter over a 6-week period was studied using soil that had been previously labelled by incubation with 14C-labelled ryegrass for 1 year. The plants reduced the loss of 14CO2, from soil by 70 per cent over 42 days. About half of the reduction was accounted for by the uptake of labelled C by the plant roots, very little 14C label being associated with the shoot. Chemical fractionation of the root showed that the 14C was chemically incorporated into cell wall materials such as cellulose and holocellulose. The reduction in organic matter decomposition in the presence of plants has been explained by earlier workers in terms ofa reduction in microbial activity as a result of a soil moisture deficit caused by plant transpiration. This explanation does not account for all the reduction in decomposition noted in the present experiments. Control soil (without a plant, but amended with glucose or yeast extract to simulate the effect of root exudates) showed a small positive priming effect, the release of 14CO2, being increased. Thus the mechanism by which plants conserve organic matter is complex and cannot be explained merely by analogy to an increased level of nutrients available for microbial metabolism. 相似文献
4.
J. F. Dormaar 《Biology and Fertility of Soils》1990,10(2):121-126
Summary The effect of one form of soil organic matter, such as living roots or root exudates on another form of soil organic matter, such as dead roots or incorporated litter and litter leachates, has been studied from various perspectives over the last 25 years. The effect seems to be either positive (priming) or negative (conserving). The present review concentrates on the conserving effect, measured as a decrease in 14CO2 released, in both field and greenhouse/growth chamber studies. The field experiments suggested that certain physical conditions in the soil, such as less available moisture or restricted aeration which led to lower microbial activity, explained the conserving effect of living roots on soil organic matter. Although more detailed greenhouse/growth chamber studies confirmed the conserving effect per se, it appears that biological rather than physical factors could better explain the reduction in the rate of decomposition of 14C-labelled plant residues in the presence of roots. However, a complex picture has emerged through a variety of postulates, all proposed in attempts to explain the conserving effect. Finally, the most recent studies have argued that the decrease in decomposition of labelled organic matter in planted soil is probably more apparent than real. A decrease in respired 14CO2 could be explained by an incorporation of 14C derived from old roots into the rhizosphere microbial populations of the living roots. To make any further progress on the fundamental question of how soil organic matter moves along its continuum from a living to a refractory state, the microenvironment needs to be examined at periodic intervals. New developments in improved histochemical and electron-probe microanalyses look promising.LRS Contribution no. 3878970 相似文献
5.
The effects of an intercrop catch crop (Italian ryegrass) on (i) the amounts and concentrations of nitrate leached during the autumn and winter intercrop period, and (ii) the following crop, were examined in a lysimeter experiment and compared with that from a bare fallow treatment. The catch crop was grown in a winter wheat/maize rotation, after harvest of the wheat, and incorporated into the soil before sowing the maize. A calcium and potassium nitrate fertilizer labelled with 15N (200 kg N ha?1; 9.35 atom per cent excess) was applied to the winter wheat in spring. Total N uptake by the winter wheat was 154 kg ha?1 and the recovery of fertilizer-derived N (labelled with 15N) was 60%. The catch crop (grown without further addition of N) yielded 3.8t ha?1 herbage dry matter, containing 43 kg N ha?1, of which 4.1 % was derived from the 15N-labelled fertilizer. Two-hundred kg unlabelled N ha?1 was applied to the maize crop. During the intercrop period the nitrate concentration in water draining from the bare fallow lysimeters reached 68 mg N1?1, with an average of 40 mg N1?1. With the catch crop, it declined rapidly, from 41 mg N I?1 to 0.25 mg N I?1, at the end of ryegrass growth. Over this period, 110 kg N ha?1 was leached under bare fallow, compared with 40 kg N ha?1 under the catch crop. 15N-labelled nitrate was detected in the first drainage water collected in autumn, 5 months after the spring application. The quantity of fertilizer-N that was leached during this winter period was greater under bare fallow (18.7% of applied N) than when a catch crop was grown (7.1 %). In both treatments, labelled fertilizer-N contributed about 34% of the total N lost during this period. With the ryegrass catch crop incorporated at the time of seedbed preparation in spring, the subsequent maize grain-yield was lowered by an average of 13%. Total N-uptake by the maize sown following bare fallow was 224 kg N ha?1, compared with 180 kg ha?1 with prior incorporation of ryegrass; the corresponding values for uptake of residual labelled N were 3% (bare fallow) and 2% (ryegrass) of the initial application. Following the maize harvest, where ryegrass was incorporated, 22.7% of the previous year's labelled fertilizer addition was present in an organic form on the top 30 cm of lysimeter soil. This compares with 15.7% for the bare fallow intercropping treatment. Tracer analyses showed overall recoveries of labelled N of 91.7% for the winter wheat/ ryegrass/maize rotation and 97% for the winter wheat/bare fallow/maize rotation. The study clearly demonstrated the ecological importance of a catch crop in reducing N-leaching as well as its efficient use of fertilizer in the plant-soil system from this particular rotation. However, the fate of the organic N in the ploughed-down catch crop is uncertain and problems were encountered in establishing the next crop of maize. 相似文献
6.
EFFECT OF LIVING ROOTS OF DIFFERENT PLANT SPECIES ON THE AGGREGATE STABILITY OF TWO ARABLE SOILS 总被引：3，自引：0，他引：3
The influence of root growth and activities on soil aggregate stability was investigated using five crop species and two soils. Single plants were grown in pots for 6 weeks or less to minimise any possibility of changes in aggregate stability caused by decomposition of dead roots. Planted soils were compared with fallow controls. Aggregate stability was estimated by a turbidimetric technique (used for fresh and air-dried samples) and by wet sieving (used for air-dried samples only). Root growth of perennial ryegrass and of lucerne for 42 days was generally associated with increases in aggregate stability whether the soil was tested in a fresh or an air-dried condition. These beneficial effects were associated with periodate-sensitive (probably polysaccharide) materials produced in the rhizosphere. Growth of maize, tomato and wheat roots for 25 days decreased the stability of fresh soil aggregates, although the effects of tomato and of wheat were not consistent. However, the deleterious effects of these three species on aggregate stability were not apparent after air-drying. The restabilization of maize soils (relative to fallow controls) on air-drying appeared to be caused by increased stabilization by periodate-sensitive materials. The results suggest that the growth and activities of living roots may be a major factor controlling the overall direction and magnitude of changes in aggregate stability under arable or ley crops. 相似文献
7.
The amounts of organic materials released into soil from roots during the first 4 weeks of growth were determined for 11 cultivars of wheat (Triticum aestivum L.). Carbon loss from roots was measured by supplying 14CO2 continuously to the shoots and measuring the 14C content of the roots, root-free soil, water-soluble material and CO2 flushed from the root chamber. Six cultivars were compared in each of two experiments, with the cultivar Condor common to both experiments. There were no significant differences between cultivars, relative to Condor, for 14C activity present in soil, roots, water-soluble material or rhizosphere CO2. There was a significant difference between cultivars in experiment 1, but not in experiment 2, for the variate log10 (14C lost from roots: 14C translocated to roots).There was evidence that a reduction in growth temperature, within the range 10–15°C, increased carbon loss from wheat roots into the rhizosphere. 相似文献
8.
The utilization of plant- and soil-C by the microbial biomass in the rhizosphere of maize plants was investigated as a function of root proximity. The plants were cultivated in pots with divided root chambers and their shoots supplied with 14CO2 for 23 days. Subsequently the individual soil zones were analyzed for organic C, 14C, biomass C and biomass 14C. Plant roots induced a 197% increase in microbial biomass and a 5.4% decrease in soil organic C compared with an 1.2% decrease in the unplanted control soil. The contributions of plant- and soil-C to this increased microbial growth amounted to 68% and 32% respectively. Biomass-14C corresponded to 1.6% of the total photosynthetically fixed 14C, to about 15% of the organic 14C-input into the rhizosphere and to 58% of the plant carbon remaining in soil after the removal of roots. 20% of this biomass-14C was found outside the immediate root zone. These results demonstrate that growing roots are a significant C-source for the microbial biomass and render an additional fraction of soil-C available to microbial utilization. The efficiency of C-utilization by the rhizosphere biomass is lower than values obtained with liquid cultures in laboratory experiments. The supply of plant-C to the microbial biomass outside the immediate root vicinity indicates that the overall volume of the maize rhizosphere is greater than what has been supposed so far. 相似文献
9.
以7年氮肥定位试验地玉米根茬为研究对象,通过把玉米根茬按2%比例与15 cm和45 cm土层深度的土壤混合后田间埋袋的方法,研究长期不同施氮量处理[分别为0 kg(N)?hm?2、120 kg(N)?hm?2和240 kg(N)?hm?2]的玉米根茬(分别用R0、R120、R240表示),在陕西省长武黑垆土中埋藏分解1 a后对土壤碳、氮组分的影响及根茬有机碳的分解特性。与未添加玉米根茬的对照土壤相比,玉米根茬加入能够显著增加各层土壤的微生物量碳、可溶性有机碳和矿质态氮含量,3种施氮量处理间差异不显著。随着分解时间延长,土壤可溶性有机物中结构相对复杂的芳香类化合物比例逐渐增加。分解1 a后,R0、R120和R240根茬的有机碳残留率在15 cm土层中分别为44.4%、35.3%和34.9%,在45 cm土层中分别为53.3%、44.3%和42.5%。R0根茬的碳残留率显著高于R120和R240;玉米根茬在15 cm土层的碳分解率和分解速率常数显著高于45 cm土层。采用一级动力学方程拟合玉米根茬碳残留率变化结果显示,R0、R120和R240根茬有机碳分解95%所需要的时间在45 cm土层比15cm土层分别长3.2 a、2.3 a和1.9 a。氮肥施用量影响玉米根茬在土壤中的分解特性,在评价农田氮肥施用与土壤固碳时,应考虑不同氮肥用量下残茬养分组成及其在土壤中分解的差异。 相似文献
10.
The inability of physical and chemical techniques to separate soil organic matter into fractions that have distinct turnover rates has hampered our understanding of carbon (C) and nutrient dynamics in soil. A series of soil organic matter fractionation techniques (chemical and physical) were evaluated for their ability to distinguish a potentially labile C pool, that is ‘recent’ root and root‐derived soil C. ‘Recent’ root and root‐derived C was operationally defined as root and soil C labelled by 14CO2 pulse labelling of rye grass–clover pasture growing on undisturbed cores of soil. Most (50–94%) of total soil + root 14C activity was recovered in roots. Sequential extraction of the soil + roots with resin, 0.1 m NaOH and 1 m NaOH allocated ‘recent’ soil + root 14C to all fractions including the alkali‐insoluble residual fraction. Approximately 50% was measured in the alkali‐insoluble residue but specific activity was greater in the resin and 1 m NaOH fractions. Hot 0.5 m H2SO4 hydrolysed 80% of the 14C in the alkali‐insoluble residue of soil + roots but this diminished specific activity by recovering much non‐14C organic matter. Pre‐alkali extraction treatment with 30% H2O2 and post‐alkali treatment extractions with hot 1 m HNO3 removed organic matter with a large 14C specific activity from the alkali‐insoluble residue. Density separation failed to isolate a significant pool of ‘recent’ root‐derived 14C. The density separation of 14C‐labelled roots, and roots remixed with non‐radioactive soil, showed that the adhesion of soil particles to young 14C‐labelled roots was the likely cause of the greater proportion of 14C in the heavy fraction. Simple chemical or density fractionations of C appear unsuitable for characterizing ‘recent’ root‐derived C into fractions that can be designated labile C (short turnover time). 相似文献
11.
Soil carbon dioxide emission from intensively cultivated black soil in Northeast China: nitrogen fertilization effect 总被引：1，自引：0，他引：1
Kang Ni Weixin Ding Zucong Cai Yufeng Wang Xilin Zhang Baoku Zhou 《Journal of Soils and Sediments》2012,12(7):1007-1018
Purpose
The aim of this study was to understand the effect of nitrogen fertilization on soil respiration and native soil organic carbon (SOC) decomposition and to identify the key factor affecting soil respiration in a cultivated black soil.Materials and methods
A field experiment was conducted at the Harbin State Key Agroecological Experimental Station, China. The study consisted of four treatments: unplanted and N-unfertilized soil (U0), unplanted soil treated with 225?kg?N?ha?1 (UN), maize planted and N-unfertilized soil (P0), and planted soil fertilized with 225?kg?N?ha?1 (PN). Soil CO2 and N2O fluxes were measured using the static closed chamber method.Results and discussion
Cumulative CO2 emissions during the maize growing season with the U0, UN, P0, and PN treatments were 1.29, 1.04, 2.30 and 2.27?Mg?C?ha?1, respectively, indicating that N fertilization significantly reduced the decomposition of native SOC. However, no marked effect on soil respiration in planted soil was observed because the increase of rhizosphere respiration caused by N addition was counteracted by the reduction of native SOC decomposition. Soil CO2 fluxes were significantly affected by soil temperature but not by soil moisture. The temperature sensitivity (Q 10) of soil respiration was 2.16?C2.47 for unplanted soil but increased to 3.16?C3.44 in planted soil. N addition reduced the Q 10 of native SOC decomposition possibly due to low labile organic C but increased the Q 10 of soil respiration due to the stimulation of maize growth. The estimated annual CO2 emission in N-fertilized soil was 1.28?Mg?C?ha?1 and was replenished by the residual stubble, roots, and exudates. In contrast, the lost C (1.53?Mg?C?ha?1) in N-unfertilized soil was not completely supplemented by maize residues, resulting in a reduction of SOC. Although N fertilization significantly increased N2O emissions, the global warming potential of N2O and CO2 emissions in N-fertilized soil was significantly lower than in N-unfertilized soil.Conclusions
The stimulatory or inhibitory effect of N fertilization on soil respiration and basal respiration may depend on labile organic C concentration in soil. The inhibitory effect of N fertilization on native SOC decomposition was mainly associated with low labile organic C in tested black soil. N application could reduce the global warming potential of CO2 and N2O emissions in black soil. 相似文献12.
Kees-Jan van Groenigen Antonie Gorissen Dave Harris Jan Willem van Groenigen 《Soil biology & biochemistry》2005,37(3):497-506
The net flux of soil C is determined by the balance between soil C input and microbial decomposition, both of which might be altered under prolonged elevated atmospheric CO2. In this study, we determined the effect of elevated CO2 on decomposition of grass root material (Lolium perenne L.). 14C-labeled root material, produced under ambient (35 Pa pCO2) or elevated CO2 (70 Pa pCO2) was incubated in soil for 64 days. The soils were taken from a pasture ecosystem which had been exposed to ambient (35 Pa pCO2) or elevated CO2 (60 Pa pCO2) under FACE-conditions for 10 years and two fertilizer N rates: 140 and 560 kg N ha−1 year−1. In soil exposed to elevated CO2, decomposition rates of root material grown at either ambient or elevated CO2 were always lower than in the control soil exposed to ambient CO2, demonstrating a change in microbial activity. In the soil that received the high rate of N fertilizer, decomposition of root material grown at elevated CO2 decreased by approximately 17% after incubation for 64 days compared to root material grown at ambient CO2. The amount of 14CO2 respired per amount of 14C incorporated in the microbial biomass (q14CO2) was significantly lower when roots were grown under high CO2 compared to roots grown under low CO2. We hypothesize that this decrease is the result of a shift in the microbial community, causing an increase in metabolic efficiency. Soils exposed to elevated CO2 tended to respire more native SOC, both with and without the addition of the root material, probably resulting from a higher C supply to the soil during the 10 years of treatment with elevated CO2. The results show the importance of using soils adapted to elevated CO2 in studies of decomposition of roots grown under elevated CO2. Our results further suggest that negative priming effects may obscure CO2 data in incubation experiments with unlabeled substrates. From the results obtained, we conclude that a slower turnover of root material grown in an ‘elevated-CO2 world’ may result in a limited net increase in C storage in ryegrass swards. 相似文献
13.
B. NICOLARDOT D. DENYS† B. LAGACHERIE D. CHENEBY M. MARIOTTI‡ 《European Journal of Soil Science》1995,46(1):115-123
The decomposition of 15N-labelled catch-crop materials (rape, radish and rye), obtained from field experiments, was studied in a chalky Champagne soil during a 60-week incubation at 28°C. Mineralized N was assumed to come from either labile or recalcitrant fractions of plant residues. The labile fraction represented about one-third of the catch-crop N; its mineralization rate constant varied from 0.06 to 0.12 d?1. The decomposition rate of the recalcitrant N fraction ranged from 0.03 × 10?2 to 0.06 × 10?2 d?1. Catch-crop species and rate of incorporation had no effect on N residue mineralized at the end of incubation. The decomposition of labelled rye was monitored in the same soil during a 5-month pot experiment to determine the N availability to an Italian ryegrass crop and the effect of plants on the decomposition processes. The 15N-rye decomposed rapidly both in the presence or absence of Italian ryegrass, but the amounts of N mineralized were influenced by the presence of living roots: 42% of the 15N in labelled rye was present as inorganic N in the pots without plants after 5 months, compared with only 32% in the ryegrass crop. Comparison of microbial-biomass dynamics in both treatments suggested that there had been preferential utilization by soil micro-organisms of materials released from the living roots than the labelled plant residues. 相似文献
14.
The flow of carbon from roots into the rhizosphere represents a significant C loss from plants. However, roots have the capacity to recapture low molecular weight C from soil although this is in direct competition with soil microorganisms. The aim of this study was to investigate the behaviour of glucose in rhizosphere and non-rhizosphere soil, the plant's potential to recapture sugars from soil and translocation and utilization of the recaptured sugars. In microcosms containing maize plants we injected 14C-glucose into the rhizosphere and followed its uptake into plants, upward and downward transport in the plant and soil, evolution as 14CO2 and incorporation into the soil microbial biomass. These fluxes were compared with non-rhizosphere soil. Glucose was rapidly mineralized in soil and the rate of turnover was significantly greater in the rhizosphere in comparison to non-rhizosphere soil. The amount of glucose captured by the maize plants was low (<10% of the total 14C-glucose added) in comparison to that captured by the soil microbial biomass. Only small amounts of the 14C-glucose were transported to the shoot (0.6% of the total). The degree of glucose capture by maize roots whilst in competition with soil microorganisms was similar to similar experiments performed for amino acids. We conclude that while plant roots can recapture low molecular weight C from the rhizosphere, intense competition from soil microorganisms may reduce the efficiency of this process. 相似文献
15.
《Communications in Soil Science and Plant Analysis》2012,43(10):1077-1087
Abstract A greenhouse experiment was conducted to investigate the effect of root growth and exudation of 3 crop species on soil aggregation. Two plant populations for each of 3 crops (corn, soybeans, and wheat) were grown in a Fincastle silt loam for 5 time periods (7, 14, 21, 28, and 41 days) and compared with fallow controls. Aggregate stability was estimated by the wet‐sieve method on both initially moist and air‐dry samples. Soil water content of initially moist soil samples varied widely among replicates, crops, and sampling dates. Wet‐sieving using initially moist soil showed that samples with higher initial soil water content had greater aggregate stability. Wet‐sieving performed on initially air‐dry soil samples was used for subsequent interpretation because the water content variable was removed. The presence of any crop and its roots in the planted soils versus the fallow controls was associated with increases in aggregate stability. No differences in aggregate stability were found among the different crops or over the established range of root length densities. Aggregate stability decreased from the original level during the first 14 to 21 days of the experiment, possibly due to daily watering. After 21 days, as root growth continued to increase, restabilization occurred until the original aggregate stability of the soil was exceeded for all crops. The observed increase in aggregate stability may be due in part to the physical entanglement of aggregates by roots and to the increased production of root exudates resulting from increased root growth. 相似文献
16.
Silke Vetter Oliver Fox Klemens Ekschmitt Volkmar Wolters 《Soil biology & biochemistry》2004,36(3):387-397
Soil animals are known to stimulate soil microbial activity and thereby to accelerate decomposition of soil organic matter. In this paper, we investigate potential limitations of soil animal effects on soil carbon flow by analysing how animal effects relate to the density of four major faunal groups. Specifically, we analyse the extent to which faunal effects are subject to biotic regulation or to mutual inhibition between groups under different levels of resource supply.In an extensive laboratory experiment, 96 microcosms established in three consecutive blocks were inoculated with nematodes, enchytraeids, microarthropods, and lumbricids. Each faunal group was inoculated in three densities, including combinations of groups. Introduced animal densities were within the natural range of densities in fallow soil. Bare agricultural soil and soil covered with maize litter were used as substrates. The microcosms were kept under constant conditions at 12 °C and 50% water holding capacity for 8 weeks. Soil CO2 evolution was measured daily by means of gas chromatography.Animal effects were on an average relatively stronger in bare soil (+95% CO2; R2=0.76) than in soil with litter (+14% CO2; R2=0.40), where organic matter decomposition was seven times more intense. Higher animal densities generally led to accelerated decomposition up to three times that of the controls. However, beyond a specific density, decomposition rates stopped increasing or even declined, depending on the faunal group. In addition, animal effects were limited by mutual inhibition between groups in bare soil where effects were strong, while stimulatory interactions were prominent in the litter treatments where effects were generally weak.We interpret the limitation of soil faunal effects on soil carbon flow in terms of incomplete habitat exploitation and biotic regulation. Under conditions of substrate homogeneity, such as in the bare soil treatments, animal effects were stronger, but they were limited by overexploitation. Under conditions of substrate heterogeneity, such as in the litter treatments, animal effects were limited by incomplete habitat utilisation. We assume that complementary habitat colonisation by different faunal groups in the litter treatments gave rise to positive diversity effects, but that these effects did not compensate for reduced overall habitat utilisation. We infer that a knowledge of faunal resource utilisation and of mutual inhibition of faunal groups can be exploited for ecological soil management towards stabilisation of soil organic matter. 相似文献
17.
Haiqing Chen Mingsheng Fan Norbert Billen Karl Stahr Yakov Kuzyakov 《European Journal of Soil Biology》2009,45(2):123-130
The effect of three land use types on decomposition of 14C-labelled maize (Zea mays L.) residues and soil organic matter were investigated under laboratory conditions. Samples of three Dystric Cambisols under plow tillage (PT), reduced tillage (RT) and grassland (GL) collected from the upper 5 cm of the soil profile were incubated for 159 days at 20 °C with or without 14C-labelled maize residue. After 7 days cumulative CO2 production was highest in GL and lowest in PT, reflecting differences in soil organic C (SOC) concentration among the three land use types and indicating that mineralized C is a sensitive indicator of the effects of land use regime on SOC. 14CO2 efflux from maize residue decomposition was higher in GL than in PT, possibly due to higher SOC and microbial biomass C (MBC) in GL than in PT. 14CO2 efflux dynamics from RT soil were different from those of PT and GL. RT had the lowest 14CO2 efflux from days 2 to 14 and the highest from days 28 to 159. The lowest MBC in RT explained the delayed decomposition of residues at the beginning. A double exponential model gave a good fit to the mineralization of SOC and residue-14C (R2 > 0.99) and allowed estimation of decomposition rates as dependent on land use. Land use affected the decomposition of labile fractions of SOC and of maize residue, but had no effect on the decomposition of recalcitrant fractions. We conclude that land use affected the decomposition dynamics within the first 1.5 months mainly because of differences in soil microbial biomass but had low effect on cumulative decomposition of maize residues within 5 months. 相似文献
18.
蚯蚓对红壤有机质分解的影响 总被引：5，自引：0，他引：5
The earthworms Pheretima carnosa, Drawida gisti and Eisenia foetida were studied to compare their contributions to the decomposition of various organic materials surface-applied on red soil in a 165-day greenhouse experiment. The native species Pheretima carnosa and Drawida gisti were equally effective in accelerating the decomposition of maize residue, according to fresh body weight, while commercial species Eisenia foetida had no significant influence on dry mass loss of maize residue. Liming with CaCO3 or CaO showed little effect on maize residue breakdown involved by Pheretima carnosa, but it inhibited this process involved by Drawida gisti. The capability of Pheretima carnosa to the decomposition of five kinds of organic materials was thoroughly examined. The dry mass losses in worm treatments were in the order of soybean residue ＞ maize residue ＞ pig manure ＞ semi-decayed maize ＞ ryegrass. However, the relative contributions of the earthworm to dry mass loss were in the order of pig manure (89.8%) ＞ semi-decayed maize residue (49.1%) ＞ maize residue (29.4%) ＞ soybean residue (20.9%) ＞ ryegrass residue (16.5%). Pheretima carnosa consumed 20～120 mg dry weight of organic material per gram fresh weight of biomass per day. 相似文献
19.
Influence of the rhizosphere on microbial biomass and recently formed organic matter 总被引：4，自引：0，他引：4
We have aimed to quantify the effect of roots on the size of the soil microbial biomass, and their influence on the turnover of soil organic matter and on the extent of the rhizosphere. We sampled a sandy clay loam topsoil from two subplots with different treatment histories. One had a normal arable fertilization record, the other had received only inorganic nitrogen fertilizer but no phosphorus and potassium for 30 years. Glucose labelled with 14C was added to both samples which were then incubated for 4 weeks before the soil was packed in cylinders and planted with ryegrass. In both soils, microbial biomass at the root surface doubled during the first 8 days. At day 15, the microbial biomass had further increased in the fertile soil, and the rhizosphere effect had extended 2.5 mm into the fertile soil, but to only 1 mm in the infertile soil. The microbial 14C increased threefold near the roots in the fertile soil as a result of assimilation of previously formed microbial residues, but in the infertile soil there was no increase. There was a close relation between the increase in microbial 14C and a decrease in 14C soluble in 2 m KCl, indicating that the microbial residues were more weakly adsorbed in the fertile soil. We conclude that the increased microbial population living near the root surfaces re‐assimilated part of the 14C‐labelled microbial residues in the fertile soil. In the infertile soil, microbial residues resisted decomposition because they were more strongly sorbed on to soil surfaces. 相似文献
20.
B. Vanlauwe K. Aihou S. Aman B. K. Tossah J. Diels O. Lyasse S. Hauser N. Sanginga R. Merckx 《Biology and Fertility of Soils》2000,30(5-6):440-449
The impact of land use (unfertilized continuous maize cropping, unfertilized and fertilized alley cropping with maize, Gliricidia sepium tree fallow, natural fallow) on the soil organic matter (SOM) status and general soil fertility characteristics were investigated
for a series of soils representative for the West African moist savanna zone. Three soils from the humid forest zone were
also included. In an associated pot experiment, relationships between maize N and P uptake and SOM and general soil characteristics
were developed. Soils under natural fallow contained the highest amount of organic C (1.72%), total N (0.158%), and had the
highest effective cation exchange capacity (ECEC) [8.9 mEq 100 g–1 dry soil], while the Olsen P content was highest in the fertilized alley cropping plots (13.7 mg kg–1) and lowest under natural fallow (6.3 mg kg–1). The N concentration of the particulate organic matter (POM) was highest in the unfertilized alley cropping plots (2.4%),
while the total POM N content was highest under natural fallow (370 mg N kg–1) and lowest in continuously cropped plots (107 mg N kg–1). After addition of all nutrients except N, a highly significant linear relationship (R
2=0.91) was observed between the total N uptake in the shoots and roots of 7-week-old maize and the POM N content for the savanna
soils. POM in the humid forest soils was presumably protected from decomposition due to its higher silt and clay content.
After addition of all nutrients except P, the total maize P uptake was linearly related to the Olsen P content. R
2 increased from 0.56 to 0.67 in a multiple linear regression analysis including the Olsen P content and clay content (which
explained 11% of the variation in P uptake). Both the SOM status and N availability were shown to be improved in land-use
systems with organic matter additions, while only the addition of P fertilizer could improve P availability.
Received: 9 April 1999 相似文献