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1.
Ecosystem Restoration of Jhum Fallows in Northeast India: Microbial C and N Along Altitudinal and Successional Gradients 总被引:9,自引:0,他引:9
Abstract To characterize the altitudinal and successional trends in microbial biomass and to understand their role in soil nutrient dynamics during the aggradation phase (vegetation recovery) of abandoned shifting cultivation systems, we determined the soil properties and microbial C and N in jhum (slash‐and‐burn) cultivation systems at different altitudes and 1‐, 7‐, and 16‐year‐old fallow agricultural lands at lower and higher altitudes in the northeastern Indian hills. Density of ground vegetation was lower in the undisturbed forest than in the jhum fallows. In general, 1‐year jhum fallow had greater herbaceous vegetation both at lower and higher altitudes. Although woody plants were observed in 7‐ and 16‐year‐old jhum fallows, their density was highest in the forest. Soil moisture, organic C, and total N also increased gradually with increasing altitude and progressive secondary succession. Soil pH showed a negative correlation with altitude (as also confounded by soil type) and fallow age. Both microbial C and N had a close correlation with altitude and fallow age. Contribution of microbial C to soil organic C was 2.0–2.6% and microbial N to total N 1.4–2.2% in jhum fields, 2.4–4.3% and 1.2–2.1%, respectively, in jhum fallows, and 2.5–2.9% and 1.6–1.9% in the forests. Microbial C and N showed a negative correlation with herbaceous plant density. Microbial biomass in the jhum fallows and forest stands had a positive relationship with woody vegetation. Along an altitudinal and/or successional gradient, microbial C and N were positively correlated with water‐holding capacity, soil moisture, organic C, and total N and negatively correlated with soil pH. Microbial C and N were positively correlated with each other. Therefore, the study suggests that the altitudinal and successional dynamics of microbial C and N are linked to, among other properties, soil organic matter and total nitrogen contents in the soil during community development after land abandonment from shifting cultivation. 相似文献
2.
Changes in soil fertility were evaluated on young (6 year) and old (20 year) jhum fields in Mizoram, north-eastern India in
response to various operations involved injhum such as slashing and burning of vegetation, cropping period, and intervening
fallow period between first and second year cropping. The results demonstrate that the soil is richer in nutrients in old
than young field prior to the start of jhum cultivation. Slash burning depletes soil acidity, carbon and nitrogen but elevates
phosphorus and cations. Soil fertility declined during first cropping phase, and further declined during second cropping phase.
After two cropping years, soil fertility of old field was almost at par with that of young field, signifying that the loss
of soil fertility was more in old than young field. A short intervening fallow period between first and second year of cropping
did not show any pronounced improvement in soil fertility, though it provided some biomass for second burning. Tilling caused
maximum loss to soil fertility. The fertilizer treatments ended with comparable or better soil fertility in comparison to
no-treatment plot. There seems to be none of the fertilizer treatments superior over others from the standpoint of ending
soil fertility. The unifying conclusions of this series of investigations support the hypothesis that the second year cropping
holds promise to reduce the demand for forested land for jhum, and lengthen the jhum cycle substantially. 相似文献
3.
Summary The nitrogen budge of rotational bush fallow agriculture (jhum) was investigated at higher elevations of Meghalaya in north-eastern India under 15, 10 and 5 year fallow cycles (the intervening fallow period between one or two croppings on the same site). Nitrogen depletion was affected by initial stocks in the soil and vegetation compartment at the time of slash and burn as well as the rate at which this was lost during the subsequent land use. While nitrogen losses due to the burn was more severe under longer cycles compared to the 5 year cycle the losses through sediment and water was more under a 15 year cycle compared to 10 and 5 year cycles. Transfer of nitrogen from soil to the weed biomass increased with shortening of the fallow cycle. The positive role of weeds in conservation of nitrogen in their biomass and subsequent release through organic manure into the agriculture system has been highlighed. Under a short fallow cycle of 5 years, considered on a time scale of 15 years, the soil nitrogen was depleted to a very low level compared to a 15 year cycle, suggesting that a 5 year cycle as prevalent today is not viable from the point of view of nitrogen economy. 相似文献
4.
The role of secondary vegetation in restoring soil fertility during shifting cultivation in the tropics is well known. Yet
the effect of secondary succession on the spatial patterns of soil properties has received little attention. To determine
whether changes in the plant community as a result of shifting cultivation affect the scale of spatial dependence for biologically
important soil nutrients, we sampled three dry tropical forest stands in Campeche, Mexico. These stands represented a gradient
of cultivation history: one mature forest stand, a forest fallow that had undergone one cultivation-fallow cycle, and a forest
fallow that had undergone two cultivation-fallow cycles. We used an analysis of semivariance to quantify the scale and magnitude
of spatial dependence for organic matter content (OM), phosphorus (P), potassium (K), and aluminum (Al) in each stand. The
scale of spatial dependence varied with cultivation history, but the degree of spatial dependence did not differ among stands.
In the mature forest P and K were autocorrelated over distances >7.5 m. In the forest fallows 48–88% of the variation in soil
P and K was autocorrelated over distances up to 1.1–5.1 m. In contrast, the range of autocorrelation for Al (∼2.5 m) did not
differ among stands. We conclude that shifting cultivation changes the range of autocorrelation for biologically important
soil nutrients at a scale that may influence plant growth. The finer scaled pattern of soil nutrients in forest fallows is
likely to persist with continued shifting cultivation, since fallows are cleared every 3–15 years. 相似文献
5.
Cropping on jhum fallows in north-eartern India is predominantly done for one year in a jhum cycle. If second year cropping
is done, expanse of the forest land required for slashing and burning could be reduced significantly. We tested this hypothesis
in a young (6 yr) and an old (20 yr) jhum fallow. We also evaluated if the productivity during second year cropping could
be alleviated by auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or
both in combination). The results demonstrate that the ecosystem productivity (total dry matter production) and economic yield
(rice grain production) decline with shortening of jhum cycle. Second year cropping causes a further decline in ecosystem
productivity in old jhum field, but not in young jhum field. Economic yield from second year cropping in its traditional form
(without any fertilizer treatment) is not much lower than that in the first year, and can be improved further by manuring
the soil. Tilling of soil improves neither ecosystem productivity nor economic yield. Different fertilization treatments respond
differently; while inorganic manuring enhances ecosystem productivity, a combination of inorganic and organic manuring improves
economic yield 相似文献
6.
Plant lifeform composition and levels of nutrients accumulated by fallows aged 1, 2 and 3 years under shifting (milpa) cultivation in Belize were measured. Levels of N, P and K allocated to leaves rapidly reached a plateau in 1 year old fallows with little increase in 2 and 3 year old sites. In stem material, K was accumulated rapidly, with little increase after the first year of fallow growth, while N and P accumulation proceeded at steady rates during three years of fallow development. Total biomass in 3 year old fallows averaged 2070 g m–2 with 10.3 g m–2 N, 0.73 g m–2P and 13.2 g m–2K. Nutrient concentrations in early successional species were higher than in species of later successional status, suggesting different strategies for nutrient utilization.Woody lifeforms dominated the fallow vegetation, accounting for 80% of total biomass in first year fallows and eliminating herbaceous species after 2 and 3 years of fallow growth. The importance of rapid recovery of woody species is discussed as it relates to fallow management and weed control. 相似文献
7.
Managed fallows which recover nutrients more rapidly than natural secondary vegetation may improve the performance of shifting
agriculture systems operating under inadequately long fallow cycles. Our objective was to construct nutrient balances for
the soil, vegetation, and litter compartments of six planted leguminous fallows and natural secondary vegetation during 53
months. The fallows were planted on a previously cultivated Ultisol (Acrisol) in the Peruvian Amazon and included:Centrosema macrocarpum (Centrosema),Pueraria phaseoloides (Pueraria),Stylosanthes guianensis (Stylosanthes),Desmodium ovalifolium (Desmodium),Cajanus cajan (Cajanus), andInga edulis (Inga). In addition, in the natural fallow treatment secondary vegetation was allowed to establish and grow naturally. Quantities
of extractable P, K, Ca, and Mg, total N, and organic C in soil to a 45 cm depth, and macrouttrients in aboveground biomass,
roots, and litter were estimated at fallow planting, at 8, 17, and 29 months afterward, and at fallow clearing (53 months).
Total N stocks increased by 10% in the Stylosanthes, Desmodium, Pueraria, and Inga treatments, but changed little in the Cajanus,
Centrosema and natural fallows. This difference was largely due to greater net increases in both soil and vegetation compartments
in the former group of treatments. In the Inga, Desmodium, and natural fallows, total stocks of P and K at 53 months were
about 40% to 80% greater and 12% greater, respectively, than initial values, but Ca and Mg stocks were reduced by 25% to 40%.
In the other treatments, there was generally little change in P stocks, but large (30% to 60%) reductions in K, Ca, and Mg
during the course of the fallow. Although there were net decreases of stocks of P, K, Ca, and Mg in soil in all treatments
during the fallow, storage of P and K in vegetation and litter in the Inga, Desmodium, and natural fallows offset losses of
these nutrients from soil. These treatments also tended to accumulate more Ca and Mg in biomass and litter than the other
treatments. These results suggest that leguminous fallow vegetation that accumulates large amounts of biomass may increase
N, P, and K stocks, but that incomplete recuperation of Ca and Mg may limit the sustainability of short-rotation fallow-based
systems on acidic, infertile soils. ei]Section editor: G R Stewart 相似文献
8.
Increasing population density and food needs in the Sahel are major drivers behind the conversion of land under natural vegetation to arable land. Intensification of agriculture is a necessity for farmers to produce enough food. As manure is scarce and fertilizers expensive, this study looks into the potential role of cowpea (Vigna unguiculata L.) and short duration fallow in maintaining soil fertility and productivity and in reducing the major weed problem Striga hermonthica (Del.) Benth. The research was carried out ‘on-farm’ in a traditional millet (Pennisetum glaucum (L.) R.Br.) growing area in the Malian Sahel, near Bankass. The four year experiment combined 0, 2, 5, and 7 years of preceding fallow with (i) 4 years of millet, (ii) 1 year of cowpea + 3 years of millet, and (iii) 1 year of cowpea + 3 years of millet/cowpea inter-cropping. Total millet production (4 years) was 1440 kg ha−1 for all systems with 2, 5 or 7 years of preceding fallow against 1180 kg ha−1 for systems without fallow. Cowpea grain production showed no significant differences between fallow treatments. Over 4 years, all cropping systems produced similar total amounts of millet grain, implying that the millet ‘lost’ during the year with a pure cowpea crop in treatments (ii) and (iii) was compensated within three years, while the cowpea grain production was an additional benefit. Such compensation was however not observed for increasing number of preceding fallow years, showing that there is no additional production benefit in 5–7 years of fallow as compared to 2 years.The soil organic carbon content decreased more slowly in treatments with a cowpea pure crop in 1998 than in the millet pure crop, while overall higher contents were observed after preceding fallow also after four years of cropping. Striga hermonthica infestation decreased linearly with duration of preceding fallow, but also after seven years of fallow and one year of cowpea the hemi-parasitic weed still re-appeared. Overall the intensification through a cowpea pure crop and cowpea intercrop in these millet-based systems improved production and a number of other characteristics of the system, making it more viable.Treatments used in the experiments reported here are indicated by the following abbreviations, for further details see text below. 相似文献
9.
半干旱黄土区苜蓿草地轮作农田土壤氮、磷和有机质变化 总被引:28,自引:0,他引:28
大田试验研究了多年生苜蓿草地轮作农田2年内的耕层土壤氮、磷养分和有机质变化.结果表明,与苜蓿连作相比,苜蓿草地轮作成农田后,土壤N和有机质消耗增加,2年中耕层土壤全氮含量平均分别下降了5.4%和19.5%、有机质下降了46.8%和28.2%,土壤全磷无显著变化;轮作提高了土壤氮、磷养分有效性及其活化率,土壤硝态氮含量2年分别提高了15.5%和159.1%、速效磷含量提高了44.5%和48.0%,差异显著.不同轮作方式对土壤养分变化有显著影响.苜蓿草地轮作后第2年,种植春小麦与种植玉米相比差异显著,种植马铃薯和休闲处理土壤养分变化幅度处于二者之间.种植春小麦能够维持农田土壤肥力生长季平衡,种植玉米增加了对土壤全氮、有机质和速效磷的消耗,土壤养分含量出现季节性下降,C/N和C/P降低.在半干旱地区多年生苜蓿草地向农田转变过程中,以轮作春小麦为宜,应避免种植玉米作物,以维持农田肥力平衡. 相似文献
10.
Rotational fallows as overwintering habitat for grassland arthropods: the case of spiders in fen meadows 总被引:1,自引:0,他引:1
Martin H. Schmidt Sabine Rocker Jamal Hanafi Andreas Gigon 《Biodiversity and Conservation》2008,17(12):3003-3012
Regular mowing of grassland is often necessary for plant conservation, but uncut vegetation is needed by many arthropods for
overwintering. This may lead to conflicting management strategies for plant and arthropod conservation. Rotational fallows
are a possible solution. They provide a spatio-temporal mosaic of mown and unmown areas that may combine benefits to both
plants and arthropods. We tested if rotational fallows enhance spider overwintering in fen meadows. Rotational fallows consisted
of three adjoining strips 10 m wide and 35–50 m long. Each year, one of these strips was left unmown (fallow) in an alternating
manner so that each strip was mown two out of three years. Spiders were sampled during spring with emergence traps in nine
pairs of currently unmown fallow strips and completely mown reference plots. Fallows significantly enhanced orb-weavers (Araneidae),
sac spiders (Clubionidae) and ground spiders (Gnaphosidae). However, only 4.7% of the total variation in community composition
was attributable to fallows. Community variation was larger between landscapes (34.5%) and sites (38.2%). Also β diversity
was much higher between landscapes (45 species) and sites (22 species) than between fallows and mown reference plots (10 species).
We conclude that the first priority for spider conservation is to preserve as many fen meadows in different landscapes as
possible. Locally, rotational fallows enhance overwintering of the above-mentioned spider families, which are sensitive to
mowing in other grassland types as well. Thus, rotational fallows would probably foster spider conservation in a wide range
of situations. However, stronger effects can be expected from larger and/or older fallow areas. 相似文献
11.
Changes in microbial nutrient status during secondary succession and its modification by earthworms 总被引:3,自引:0,他引:3
S. Scheu 《Oecologia》1990,84(3):351-358
Summary Microbial biomass, nutrient (N and P) status, and carbon and nutrient limitation of the microflora were investigated in soils from five different sites (field, 5-, 12-, and about 50-year-old fallow, beechwood), which represent different stages of a secondary succession from a wheat field to the climax ecosystem of a beechwood on limestone. In addition, the effect of faeces production by the substrate feeding earthworm species Octolasion lacteum (Örley) on the nutrient status of the soil microflora of these sites was studied. Humus had accumulated in the soil of the third fallow site, with an enhanced biomass of microflora. However, in the beechwood soil, which had the highest humus content, microbial biomass was lower than in the soil of the third fallow site and similar to that of the field and the two younger fallow sites. In general, soil microbial biomass was little affected by the passage of soil through the gut of O. lacteum. The soil microflora of the field, the 5-, 12-, and about 50-year-old fallow was limited by carbon, whereas in the beechwood soil phosphorus limited microbial growth. NItrogen availability to the soil microflora was low in the two younger fallow sites and high in the field and the third fallow. In the beechwood soil nitrogen supply did not affect microbial carbon utilization. Application of phosphorus stimulated glucose mineralization in the soil of the field, the third fallow, and the beechwood, but not in the two younger fallow sites. Therefor, the nutrient status of the soil microflora seems to have changed during secondary succession: presumably, during the first phase the availability of nitrogen decreased, whereas during the second phase microbial phosphorus supply became more important, which resulted in phosphorus limitation of the soil microflora in the climax ecosystem. The passage of soil through the gut of O. lacteum caused an alteration in the microbial nutrient status. Generally, microbial growth in earthworm casts was limited by carbon. The relative effect of the gut passage of the soils on microbial carbon utilization seems to increase during succession. Therefore, the effect of decomposer invertebrates on microbial nutrient supply seems to increase during secondary succession. In general, nitrogen did not limit microbial carbon utilization in earthworm casts. Phosphorus requirements of the soil microflora were lowered by the gut passage of the soil of the third fallow site and the beechwood, which indicates an increased phosphorus supply in earthworm casts. Howerver, this additional supply was not sufficient to enable optimal carbon utilization by the soil microflora. The results indicate that the effect of decomposer invertebrates on the soil microflora depends on the nutrient status of the ecosystem. 相似文献
12.
黄土丘陵区小流域土地利用和植被恢复对土壤质量的影响 总被引:69,自引:11,他引:58
土壤质量的维护和提高是全球生物圈可持续发展的重要因素之一.对黄土丘陵小流域持续利用25年后的荒草地、山杏林地、农地、油松林地、灌木林地和撂荒地土壤性状的研究结果表明,不同土地利用方式和植被恢复类型对土壤质量有很大影响;植被恢复重建和农地撂荒将增加土壤有机质含量,提高土壤质量;粗放的农业耕作措施将降低土壤质量并引起土壤退化;灌丛有明显的肥力岛屿作用;撂荒在一定程度上可以培肥土壤。随着“西部大开发”、“退耕还林还草”和生态重建工程的开展,在半干旱黄土丘陵沟壑区,建植灌木、种植牧草、农地撂荒和自然恢复是较好的生态重建和植被恢复方式。 相似文献
13.
Laki-laki (Dennstaedtia glauca,polypodiaceae): A green manure used in traditional andean agriculture
Dennstaedia glauca is used as a green manure in specific agricultural contexts in Puno, Perü. It is applied in conjunction with animal manure and prior to potato cultivation in the first year after a period of fallow. Fronds ofD. glauca, while containing average or low amounts of micronutrients, are high in nitrogen, phosphorus, and potassium in comparison with other fern species and plant material in general. We suggest this fern contributes to fertility of soil used for tuber crops. The plant grows in abundance along watercourses and may play an important role as a recycler of nutrients leached from terraced fields. 相似文献
14.
黑土长期施肥及养分循环再利用的作物产量及土壤肥力质量变化Ⅲ.土壤养分收支 总被引:8,自引:1,他引:7
许了1985-1999年试验期间各模拟施肥模型的作物移出养分量和施肥输入养分量,结果表明,施用N肥可加剧土壤P收支赤字,而施用N,P肥则加剧土壤K收支赤字,实验展示了我国在20世纪70年代大面积贫P土壤和80年代大面积缺K土壤出现的原因,保持养分循环再利用可缓解土壤养分收支赤字,但不能满足丰产作物的养分需求,在保持养分循环利用基础上根据土壤肥力适当施用化肥,可满足丰产作物的养分需求和平衡土壤养分收支,不致发生大量过剩N进入环境。 相似文献
15.
Alexandru Milcu Angela Heim Richard J. Ellis Stefan Scheu Pete Manning 《Ecosystems》2011,14(5):710-719
Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks. However, general rules regarding
the operation of these factors across a range of soil nutrient availabilities and substrate qualities are unidentified. “Priming”
(stimulated decomposition by labile C inputs) and ‘preferential substrate utilization’ (retarded decomposition due to shifts
in community composition towards microbes that do not mineralize SOC) are two hypotheses to explain effects of labile C additions
on SOC dynamics. For effects of nutrient additions (nitrogen and phosphorus) on SOC dynamics, the stoichiometric (faster decomposition
of materials of low carbon-to-nutrient ratios) and ‘microbial mining’ (that is, reduced breakdown of recalcitrant C forms
for nutrients under fertile conditions) hypotheses have been proposed. Using the natural gradient of soil nutrient availability
and substrate quality of a chronosequence, combined with labile C and nutrient amendments, we explored the support for these
contrasting hypotheses. Additions of labile C, nitrogen (N), phosphorus (P), and combinations of C and N and C and P were
applied to three sites: 2-year fallow grassland, mature grassland and forest, and the effects of site and nutrient additions
on litter decomposition and soil C dynamics were assessed. The response to C addition supported the preferential substrate
hypothesis for easily degradable litter C and the priming hypothesis for SOC, but only in nitrogen-enriched soils of the forest
site. Responses to N addition supported the microbial mining hypothesis irrespective of C substrate (litter or SOC), but only
in the forest site. Further, P addition effects on SOC support the stoichiometric hypothesis; P availability appeared key
to soil C release (priming) in the forest site if labile C and N is available. These results clearly link previously contrasting
hypotheses of the factors controlling SOC with the natural gradient in litter quality and nutrient availability that exists
in ecosystems at different successional stages. A holistic theory that incorporates this variability of responses, due to
different mechanisms, depending on nutrient availability and substrate quality is essential for devising management strategies
to safeguard soil C stocks. 相似文献
16.
通过样方调查和采样 ,对云南省西盟县新厂乡阿莫村自然条件相似、经历了相同休闲年限的桤木休闲地和自然休闲地的地上部分植被生物量和养分蓄积量进行了比较研究 ,结果表明 ,休闲 3a后 ,桤木休闲地的休闲效果显著高于自然休闲地。表现在桤木休闲地的地上部分生物量高于自然休闲地 ,休闲 6 a后 ,桤木林的地上部分生物量干重达到 6 9,6 4 0 kg/hm2 ,是自然休闲地的 4倍 ;桤木休闲地 N、P、K三大营养元素的地上部分蓄积量 ,经过 2~ 3a超过自然休闲地 ,并在休闲 3a后显著高于自然休闲地 ,休闲 6 a后 ,N蓄积量达到 5 5 7kg/hm2 ,是自然休闲地的 3倍 ,P、K的蓄积量分别达到 4 1kg/hm2 、2 6 5 kg/hm2 ,是自然休闲地的 2倍。目前研究说明桤木种植有改进轮歇农业的明显作用 ,具有在类似地区推广应用的价值。 相似文献
17.
The rapid decline of soil fertility of cultivated lands in the sub-Saharan savannas of West Africa is considered to be the
main cause of the increasingly severe constraints of food production. The soils in this tropical area are highly fragile,
and crop yields are limited by characteristically low levels of available phosphorus. Under such preconditions, the multiple
benefits of the arbuscular mycorrhizal (AM) symbiosis are likely to play a pivotal role for maintaining natural soil fertility
by enhancing plant nutrient use efficiency, plant health, and stabilization of a favorable soil structure. Thus, it is important
to explore the impact of the commonly applied farming practices on the native AM fungal community. In the present study, we
determined the AM fungal species composition in three ecological zones differing by an increasingly prolonged dry season from
South to North, from the Southern Guinea Savanna (SG), to the Northern Guinea Savanna (NG), to the Sudan Savanna (SU). In
each zone, four “natural” and four “cultivated” sites were selected. “Natural” sites were three natural forest savannas (at
least 25–30 years old) and a long-term fallow (6–7 years old). “Cultivated” sites comprised a field with yam (Dioscorea spp.) established during the first year after forest clearance, a field under mixed cropping with maize (Zea mays) and peanut (Arachis hypogaea), a field under peanut, and a field under cotton (Gossypium hirsutum) which was the most intensively managed crop. Soil samples were collected towards the end of the wet season in each zone.
AM fungal spores were extracted and morphologically identified. Soil subsamples were used to inoculate AM fungal trap cultures
using Stylosanthes guianensis and Brachiaria humidicola as host plants to monitor AM root colonization and spore formation over 10 and 24 months, respectively. A total of 60 AM
fungal species were detected, with only seven species sporulating in the trap cultures. Spore density and species richness
were generally higher in the natural savannas and under yam than at the other cultivated sites and lowest under the intensively
managed cotton. In the fallows, species richness was intermediate, indicating that the high richness of the natural savannas
was not restored. Surprisingly, higher species richness was observed in the SU than in the SG and NG, mainly due to a high
proportion of species in the Gigasporaceae, Acaulosporaceae, and Glomeraceae. We conclude that the West African savannas contain
a high natural AM fungal species richness, but that this natural richness is significantly affected by the common agricultural
land use practices and appears not to be quickly restored by fallow. 相似文献
18.
The aim of this study was to analyze indicators of soil restoration during secondary succession in a heterogeneous valley in the high tropical Andes. A combination of chronosequence and permanent plot methods was used to detect changes in this heterogeneous matrix. Thirty-six plots with different fallow times (1–9 years) and four noncultivated plots with natural vegetation (páramo) were sampled twice in a 3-year interval (1996 and 1999). The following soil properties were determined: total C and N, pH, exchangeable bases, cation exchange capacity, and microbial biomass N (MB-N). Using the chronosequence approach, successional increases in soil pH and Mg were detected, pointing to these variables as indicators of soil restoration during the fallow period. Comparing the noncultivated páramo with the fallow plots, a significant decrease in MB-N was found, suggesting that this is a sensitive agricultural disturbance indicator. The permanent plot analysis failed to detect successional trends in any of the study variables, probably as a result of a lack of sensitivity of the indicators used within the 3-year interval. Nevertheless, a strong acidification was detected by the permanent plot method when fallow plots were cultivated. We conclude that the size of important soil components such as total soil organic matter or microbial biomass is not a sensitive soil restoration indicator in these heterogeneous mountain systems but that other integrative variables such as pH could be more sensitive to successional changes in key soil processes (e.g., nitrification or nutrient losses). 相似文献
19.
Non-cultivated N2-fixing indigenous legumes can be harnessed to enhance soil fertility replenishment of smallholder farms. Understanding N release patterns of biomass generated by such legumes is key in managing N availability to crops. Nitrogen and C mineralization patterns of indigenous legume species, mainly ofTephrosia andCrotalaria genera, and of soils sampled at termination of 1- and 2-year indigenous legume fallows (indifallows)were investigated in leaching tube incubations under laboratory conditions. With the exception ofTephrosia longipes Meisn (2.4%) andCrotalaria cylindrostachys Welw.ex Baker (1.8%), all indigenous legumes had >2.5% N. Total polyphenols and lignin were <4% and 15%, respectively, for all species.Crotalaria pallida (L.) andEriosema ellipticum Welw.ex Baker mineralized >50% of the added N in the first 30 days of incubation. Similar to mixed plant biomass from natural weed fallow,C. Cylindrostachys immobilized N during the 155-day incubation period. Indifallow fallow biomass reached peak N mineralization 55 days after most legumes had leveled off. Carbon release by legume species closely followedN release patterns,with mostCrotalaria species releasing >500 mg CO2-C kg?1 soil. Soils sampled at termination of fallows reached peak N mineralization in the first 21 days of incubation, with indifallows mineralizing significantly (P<0.05) more N than natural fallows. Application of mineral P fertilizer to indifallows and natural fallows increased C and N mineralization relative to control treatments. It was concluded that (i) indigenous legumes generate biomass of high quality within a single growing season, (ii) the slow N release of biomass generated under indifallow systems suggests that such fallows can potentially be manipulated to enhance N availability to crops, and (iii) N and C mineralization of organic materials in sandy soils is likely controlled by availability of P to the soil microbial pool. 相似文献
20.
桂西北喀斯特峰丛洼地表层土壤养分时空分异特征 总被引:16,自引:8,他引:16
本文运用传统统计方法研究了典型喀斯特峰丛洼地4个植被演替阶段(草地、灌木林、次生林、原生林)表层(0—15 cm)土壤养分的空间分异特征,并分析其成因。结果表明:(1)不同植被演替阶段土壤养分(有机碳、全氮、碳氮比、全磷、全钾、碱解氮、速效磷、速效钾)及pH值有明显差异(P<0.05);除全钾外,其他养分含量均随植被正向演替而增加。(2)地貌部位对养分含量的影响不尽一致:各植被演替阶段的磷、钾及原生林的碳氮均符合养分的“洼积效应”,只有受人为干扰较强的草地、灌木林、次生林的碳氮养分存在随坡位升高而增加的现象。通过本研究得知,植被演替对养分积累具有积极作用;磷素(速效磷3.55—11.41 mg/kg)、钾素(速效钾64.05—105.75 mg/kg)是该区域的养分限制性因子;该区域养分的“倒置现象”并不普遍存在。 相似文献