共查询到20条相似文献,搜索用时 109 毫秒
1.
Summary Inoculation of water fernAzolla pinnata R. Brown (Bangkok isolate) at the rate of 500kg fresh weight ha−1 in rice fields at weekly intervals after planting in addition to 30 kg N ha−1 as urea showed a decrease in its growth and N2-fixation with delay in application. Use of Azolla up to 3 weeks after planting (WAP) during wet and 4 WAP during dry season
produced significantly more grain yield than 30 kg N ha−1, whereas its application upto one WAP produced more grain yield than 60 kg N ha−1. Grain yield with Azolla applied at the time of planting was similar to that of 60 kg N treatment during the wet season.
Higher grain yields in zero and one WAP Azolla treatments resulted due to increase in both number of panicles m−2 and number of grains/panicle while the subsequent Azolla inoculations increased grain yield mainly by producing more number
of grains/panicle.
Dry matter and total N yields at maturity of rice crop were more with Azolla application upto 3 WAP during wet and 2 WAP during
dry season while the reduction in sterility (%) was observed upto one WAP over 30 kg N ha−1 during both seasons. Number of tillers m−2 and dry matter production at maximum tillering and flowering were more than 30 kg N ha−1 with the use of Azolla upto one WAP. Increased grain N yield was observed with the use of Azolla upto 4 WAP during two seasons
whereas straw N yield increased upto one WAP during wet and 2 WAP during dry season. 相似文献
2.
A field experiment conducted at Central Rice Research Institute, Cuttack, during three successive seasons showed that with
the 120-day-duration variety Ratna two dual crops ofAzolla pinnata R. Brown (Bangkok isolate) could be achieved 25 and 50 days after transplanting (DAT) by inoculating 2.0 t ha−1 of fresh Azolla 10 and 30 DAT respectively. One basal crop of Azolla could also be grown using the same inoculum 20 days
before transplanting (DBT) in fallow rice fields. The three crops of Azolla grown—once before transplanting and twice after
transplanting—gave an average total biomass of 38–63 and 43–64 t ha−1 fresh Azolla containing 64–90 and 76–94 kg N ha−1 respectively in the square and rectangular spacings. Two crops of Azolla grown only as a dual crop, on the other hand, gave
26–39 and 29–41 t ha−1 fresh Azolla which contained 44–61 and 43–59 kg N ha−1 respectively.
Growth and yield of rice were significantly higher in Azolla basal plus Azolla dual twice incorporated treatments than in
the Azolla dual twice incorporation, Azolla basal plus 30 kg N ha−1 urea and 60 kg N ha−1 urea treatments. Azolla basal plus 30 kg N ha−1 urea and 60 kg N ha−1 urea showed similar yields but Azolla dual twice incorporation was significantly lower than those. The different spacing
with same plant populations did not affect growth and yield significantly, whereas Azolla growth during dual cropping was
8.3 and 64% more in the rectangular spacing than in the square spacing in Azolla basal plus Azolla dual twice incorporation
and Azolla dual twice incorporation treatments. 相似文献
3.
Plant and microbial nitrogen use and turnover: Rapid conversion of nitrate to ammonium in soil with roots 总被引:2,自引:0,他引:2
Immobilization of ammonium (NH
4
+
) by plants and microbes, a controlling factor of ecosystem nitrogen (N) retention, has usually been measured based on uptake
of15NH
4
+
solutions injected into soil. To study the influence of roots on N dynamics without stimulating consumption of NH
4
+
, we estimated gross nitrification in the presence or absence of live roots in an agricultural soil. Tomato (Lycopersicon esculentum var. Peto76) plants were grown in microcosms containing root exclosures. When the plants were 7 weeks old,15N enriched nitrate (NO
3
−
) was applied in the 0–150 mm soil layer. After 24 h, > 30 times more15NH
4
+
was found in the soil with roots than in the soil of the root exclosures. At least 18% of the NH
4
+
-N present at this time in the soil with roots had been converted from NO
3
−
. We estimated rates of conversion of NO
3
−
to NH
4
+
, and rates ofNH
4
+
immobilization by plants and microbes, by simulating N-flow of14+15N and15N in three models representing mechanisms that may be underlying the experimental data: Dissimilatory NO
3
−
reduction to NH
4
+
(DNRA), plant N efflux, and microbial biomass nitrogen (MBN) turnover. Compared to NO
3
−
uptake, plant NH
4
+
uptake was modest. Ammonium immobilization by plants and microbes was equal to at least 35% of nitrification rates. The rapid
recycling of NO
3
−
to NH
4
+
via plants and/or microbes contributes to ecosystem N retention and may enable plants growing in agricultural soils to capture
more NH
4
+
than generally assumed. 相似文献
4.
A field study was conducted on a clay soil (Andaqueptic Haplaquoll) in the Philippines to directly measure the evolution of
(N2+N2O)−15N from 98 atom %15N-labeled urea broadcast at 29 kg N ha−1 into 0.05-m-deep floodwater at 15 days after transplanting (DT) rice. The flux of (N2+N2O)−15N during the 19 days following urea application never exceeded 28 g N ha−1 day−1. The total recovery of (N2+N2O)−15N evolved from the field was only 0.51% of the applied N, whereas total gaseous15N loss estimated from unrecovered15N in the15N balance was 41% of the applied N. Floodwater (nitrate+nitrite)−N in the 5 days following urea application never exceeded
0.14 g N m−3 or 0.3% of the applied N. Prior cropping of cowpea [Vigna unguiculata (L.) Walp.] to flowering with subsequent incorporation of the green manure (dry matter=2.5 Mg ha−1, C/N=15) at 15 days before rice transplanting had no effect on fate of urea applied to rice at 15 DT. The recovery of (N2+N2O)−15N and total15N loss during the 19 days following urea application were 0.46 and 40%, respectively. Direct recovery of evolved (N2+N2O)−15N and total15N loss from 27 kg applied nitrate-N ha−1 were 20% and 53% during the same 19-day period. The failure of directly-recovered (N2+N2O)−15N to match total15N loss from added nitrate-15N might be due to entrapment of denitrification end products in soil or transport of gaseous end products to the atmosphere
through rice plants. The rapid conversion of added nitrate-N to (N2+N2O)−N, the apparently sufficient water soluble soil organic C for denitrification (101 μg C g−1 in the top 0.15-m soil layer), and the low floodwater nitrate following urea application suggested that denitrification loss
from urea was controlled by supply of nitrate rather than by availability of organic C. 相似文献
5.
Effects of N-fertilizers,straw, and dry fallow on the nitrogen balance of a flooded soil planted with rice 总被引:1,自引:0,他引:1
Teresita Santiago-Ventura Marjorie Bravo C. Daez V. Ventura I. Watanabe A. A. App 《Plant and Soil》1986,93(3):405-411
Summary Nitrogen balance studies were made on rice (Oryza sativa) grown in flooded soil in pots. A low rate of fertilizer (5.64 mg N. kg−1 soil) did not depress the N gain, but a high rate (99.72 mg N. kg−1 soil) elminated the N gain. Soil N loss was negligible since15N applied as ammonium sulfate and thoroughly mixed with the soil was recovered from the soil-plant system after 3 crops. The
observed N gain, therefore, was caused by N2-fixation, not by a reduction of soil N loss.
Straw enhanced N gain at the rate of 2–4 mg per g straw. However, this gain was not observed when soil N availability was
high. Dry fallow between rice crops decreased the N gain. 相似文献
6.
We used the natural abundance of 15N in soils in forests, pastures and cultivated lands in the Menagesha and Wendo-Genet areas of Ethiopia to make inferences
about the N cycles in these ecosystems. Since we have described the history of these sites based on variations in 13C natural abundance, patterns of δ15N and δ13C values were compared to determine if shifts of 15N correlate with shifts of vegetation. At Menagesha, a > 500-yr-old planted forest, we found δ15N values from −8.8 to +3.5‰ in litter, from −3.5 to +4.5‰ in 0–10 cm soil layer, and from −1.5 to +6.8‰ at >20 cm soil depth.
The low δ15N in litter and surface mineral soils suggests that a closed N cycle has operated for a long time. At this site, the low δ13C of the surface horizon and the high δ13C of the lower soil horizons is clear evidence of a long phase of C4 grass dominance or cultivation of C4 crops before the establishment of the forest >500 years ago. In contrast, at Wendo-Genet, high δ13C of soils reveals that most of the land has been uncovered by forests until recently. Soil δ15N was high throughout (3.4–9.8‰), and there were no major differences between forested, cultivated and pasture soils in δ15N values of surface mineral soils. The high δ15N values suggest that open N cycles operate in the Wendo-Genet area. From the points of view of soil fertility management,
it is interesting that tall forest ecosystems with relatively closed N cycling could be established on the fairly steep slopes
at Menagesha after a long period of grass vegetation cover or cultivation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
T. Rütting D. Huygens C. Müller O. Van Cleemput R. Godoy P. Boeckx 《Biogeochemistry》2008,90(3):243-258
Nitrite (NO2
−) is an intermediate in a variety of soil N cycling processes. However, NO2
− dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics
were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3
−, NH4
+ and NO2
−. Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of
functional links between (1) NH4
+ oxidation, the main process for NO2
− production (nitritation), and NO2
− reduction, and (2) oxidation of soil organic N, the dominant NO3
− production process in this soil, and dissimilatory NO3
− reduction to NH4
+ (DNRA). The production of NH4
+ via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the
rate of DNRA was several magnitudes higher than the rate of other NO3
− reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process
in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic
conditions of this Nothofagus ecosystem. 相似文献
8.
The chemical composition of rainwater is altered upon its passage through tree canopies. In order to investigate how rainwater
chemistry is affected by canopy-dependent processes in characteristic forest types of Northwest German sandy lowland regions
– oak–birch-forests, Betula pubescens Ehrh. swamp forests, and stands of Pinus sylvestris L. – comparative studies on the chemical composition of throughfall were carried out at seven forest sites, situated in close
proximity within a nature reserve. Additionally, rainwater was sampled at three heathland sites for analysis of open-field
precipitation and at three sites along an oak–birch-forest edge. Throughfall concentrations of most of the parameters analysed
were significantly higher than open-field concentrations, especially with regard to electric conductivity, NH4-N, K+, and KMnO4-index. Ion concentrations in throughfall were the lowest in a 10-year-old stand of Betula pendula Roth. and Pinus sylvestris and in a Betula pubescens swamp forest and were highest beneath a stand of Pinus sylvestris. Except for Na+, Cl−, and NO3−, ion concentrations in both throughfall and open-field precipitation increased during the growing season (May–October). In
throughfall, Ca2+, Mg2+, K+, and Mn2+ were strongly correlated. Enrichment ratios between throughfall and open-field deposition varied among sites and elements
and were the highest for K‰+, Mg2‰+, and Mn2‰+. Estimates of canopy leaching indicated high leaching rates of K‰+ and Mn2‰+ and moderate leaching of Mg2‰+. The contribution of foliar leaching to throughfall deposition was higher at the deciduous than at the coniferous stands. 相似文献
9.
Availability and utilization of fertilizer nitrogen by rice under alternate flooding 总被引:1,自引:0,他引:1
Summary A greenhouse pot experiment with three N sources—15N-depleted ammonium sulfate, urea and sulfur-coated urea (SCU), three N levels—0, 50 and 200 ppm, and three irrigation treatments
was conducted with rice in an Alamo clay soil. The irrigation treatments consisted of continuous flooding, alternating flooded-saturated
and alternating flooded-drained conditions. The kinetics of NH
4
+
and NH
4
+
+NO
3
−
(available N) in soil was investigated under rice culture.
Alternating flooded-drained conditions maintained a significantly lower level of available N in the soil than the other irrigation
treatments. Among the N sources evaluated, urea and A/S had similar effects but SCU maintained significantly lower levels
of available N in the soil during the growth of rice. Appreciable quantities of NO
3
−
accumulated during the draining periods of alternating flooded-drained treatments were apparently lost from the soil system
upon reflooding. 相似文献
10.
A field experiment was conducted at the Bangladesh Rice Research Institute, Joydebpur, Dhaka during the late wet season. Basal
application of P at both 5 and 10 kg ha−1 significantly increased total biomass production and nitrogen fixation byAzolla pinnata R. Brown (local strain). Addition of both 5 and 10 kg P ha−1 in equal splits at inoculation and at six day intervals thereafter during growth periods of 12, 24 and 36 days increased
biomass production and nitrogen fixation by Azolla over that attained with the basal application. Biomass and nitrogen fixation
using a split application of 5 kg P ha−1 exceeded that attained with basal application of 10 kg P ha−1 and split application of 10 kg P ha−1 resulted in 0.58, 11.2, and 18.3 t ha−1 more biomass, and 0.47, 18.9, and 18.3 more kg fixed N ha−1 at 12, 24 and 36 days, respectively, than the same amount applied as a basal application. Analyses indicated that the critical
level of dry weight P in Azolla for sustained growth was in the range of 0.15–0.17%. Compared with the control, where no P
was added, and additional 30 and 36 kg N ha−1 were fixed after 24 and 36 days, respectively, when P was provided at 10 kg ha−1 using a split application. A separate field study showed that flooded rice plants received P from incorporated Azolla with
about 28% of the P present in the supplied Azolla being incorporated into the rice plants. 相似文献
11.
Methane emissions associated with a green manure amendment to flooded rice in California 总被引:3,自引:0,他引:3
The goals of sustainable food production and mitigation of greenhouse gas emissions may be in conflict when green manures
are used in flooded rice systems. A field study was initiated in early spring 1992 near Sacramento, California to quantify
the potential for enhanced methane emissions following a green manure amendment to rice. Replicate flux measurements were
made twice a day every 3–4 days throughout the growing season in four treatment plots: burned rice straw, spring incorporated
rice straw, burned straw plus purple vetch and spring incorporated straw plus vetch. Seasonal methane emissions ranged from
66–136 g CH4 m−2 and were 1.5 to 1.8 times higher from the straw plus vetch treatments relative to the straw only treatments. No significant
differences in emissions were found between the two straw only treatments or the straw plus vetch treatments. Methane fluxes
were exponentially related to soil temperature, but no effect of redox potential or floodwater depth were observed. The potential
impact of these results on the global methane budget is discussed. 相似文献
12.
15N labelled (NH4)2SO4 was applied to barley at 5 g N m−2 (50 kg N ha−1) in microplots at sowing to study the timing of the N losses and the contribution of soil and fertilizer N to the plant.
Water treatments included rainfed and irrigation at 45–50 mm deficit beginning in the spring.
Recovery of15N in the plant increased to a maximum of about 20% within 91 days after sowing (DAS 91) and then remained constant. Approximately
16% (0.8 g N m−2) of the fertilizer was in the stem and leaves at DAS 91 and this N was subsequently redistributed to the head. At maturity,
approximately 75% of the15N assimilated by the tops was recovered in the grain. Soil N contributed 3.6 g N m−2 to the head; 2.2 g N m−2 was remobilized from the stem and leaves, and the balance, approximately 1.4 g N m−2, was taken up from the soil between DAS 69 to 91. Effects of irrigation treatments on N accumulation were not significant.
Residual15N fertilizer in the soil decreased with time from sowing, and at maturity 40% of the applied N was recovered in the surface
0.15 m.15N movement to depth was limited and less than 5% of the fertilizer was recovered below 0.15 m. Irrigation had no effect on
the15N recovery at depth.
Total recovery of the15N varied between 60 and 67% and implies that 33–40% was lost from the soil-plant system. The total recovery in the soil and
plant was not affected by time or irrigation in the interval DAS 39 to 134. Losses occurred before DAS 39 when crop uptake
of N was small and soil mineral N content was high. There was an apparent loss of 1.9 g fertilizer N m−2 (i.e. 38% of that applied) between DAS 1 and 15. This loss occurred before crop emergence when rainfall provided conditions suitable
for denitrification. 相似文献
13.
E. Wada R. Imaizumi Y. Kabaya T. Yasuda T. Kanamori G. Saito A. Nishimune 《Plant and Soil》1986,93(2):269-286
Summary Plants from agricultural and natural upland ecosystem were investigated for15N content to evaluate the role of symbiotic N2-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ15N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N2 fixation. A fairly large discrepancy was found between estimations by δ15N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ15N when fertilizer δ15N was varied near15N natural abundance level. Clearcut linear relationships between δ15N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental
field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N2 fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in
Alluvial soil, respectively. These values for N2 fixation coincided with each corresponding estimation by N yield method.
Other results include: 1)15N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics,
and 2) nitrogen isotopic discrimination during fertilizer uptake (δ15N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species.
The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans
growing in agricultural settings. 相似文献
14.
Site-dependent N uptake from N-form mixtures by arctic plants,soil microbes and ectomycorrhizal fungi 总被引:1,自引:0,他引:1
Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability
is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific
N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and
microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+–N and NO3−–N, with one N form labelled with 15N at a time, and in the case of glycine, also labelled with 13C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath
tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and NO3−–15N, respectively, recovered in the plant–soil system, and the major part of 15N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover
transferred about half of the immobilized 15N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention
in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution
of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated
against NO3−. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake
patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study
furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well
as for soil microorganisms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
15.
Summary The importance of initial exchangeable soil NH
4
+
in nitrogen nutrition and grain yield of rice was studied in a number of representative lowland rice soils in the Philippines. The initial exchangeable soil NH
4
+
+fertilizer N plotted against nitrogen uptake by the crop resulted in a highly significant linear relationship (R2=0.91), suggesting that the presence of exchangeable NH
4
+
in the soil at transplanting behaved like fertilizer nitrogen. The correlation between N fertilizer rate and N uptake by the rice crop was relatively poor (R2=0.73). On the other hand, relative grain yield was more closely correlated with the initial exchangeable soil NH
4
+
+fertilizer N than with fertilizer nitrogen applied alone. These results indicate that the initial exchangeable NH
4
+
in the soil contributed substantially to the nitrogen uptake of the crop.Critical nitrogen levels in the soil defined as the initial exchangeable soil NH
4
+
+fertilizer N at which the optimum grain yield (95% of the maximum yield) is obtained, varied from 60 to 100 kg N/ha in the wet season and from 100 to 120 kg N/ha in the dry season for the different fertilizer treatments. The results further suggest that the initial exchangeable soil NH
4
+
should serve as a guide in selecting an optimum nitrogen fertilizer rate for high grain yields. 相似文献
16.
免耕稻田氮肥运筹对土壤NH3挥发及氮肥利用率的影响 总被引:2,自引:0,他引:2
通过大田试验,设置5种不同的施肥比例(基肥:分蘖肥:拔节肥:穗肥-2:2:3:3(R1)、3:2:2:3(R2)、4:2:2:2(R3)、4:3:1:2(R4)与0:0:0:0(CK)),研究氮肥运筹对稻田NH3挥发和氮肥利用率的影响。结果表明,(1)相对于不施肥,施肥显著提高了稻田NH3挥发量。氮肥施用后,NH3挥发损失量占施氮量的6.2%-8.5%,其中,以分蘖期NH3挥发损失量最大,齐穗期次之,苗期和拔节期最小。施肥处理间,处理R1稻田累积NH3挥发量最小,显著低于其它施肥处理,比处理R2、R3和R4分别低9.1%(P<0.05)、10.9%(P<0.05)和17.7%(P<0.05)。(2)相关分析表明,田面水NH4+、pH值和土壤NH4+和pH值均与稻田土壤NH3挥发通量呈显著或者极显著相关;(3)处理R1水稻氮肥利用率相对于处理R2、R3和R4增加了28.4%(P<0.05)、55.4%(P<0.05)和74.9%(P<0.05)。研究表明,氮肥后移能有效降低免耕稻田NH3挥发,提高水稻的氮肥利用率。 相似文献
17.
Laboratory incubations were used to investigate the influence of soil mixing intensity and waterlogged conditions on nutrient
mobilisation from models of cultivated heathland soil. Fragmentation of the peaty surface horizon after different soil cultivation
intensities was simulated using four different surface areas of peat organic matter. In well aerated conditions, increased
mobilisation of C, NH
4
+
−N, PO
4
3−
, K+, Ca2+ and Mg2+ was observed with increased mixing intensity and increased surface area of peat. For all nutrients apart from calcium, intensively
mixed treatments showed higher mobilisation rates under waterlogging than under well aerated conditions. This was particularly
clear for NH
4
−
−N and PO
4
3−
mobilisation. Simple linear regression analysis showed that, under aerated conditions, for four mixing intensities, rates
of mobilisation of NH
4
+
−N, PO
4
3−
, K+, Ca2+ and Mg2+ were approximately constant per unit of peat surface area exposed during soil mixing. Waterlogging was more important than
soil mixing intensity in determining nitrogen mobilisation rates in saturated soil. 相似文献
18.
Phosphorus cycling in rainfed lowland rice ecosystems is poorly understood. Soil drying and grazing of rice straw during the
long dry season, the growth of volunteer pastures during the early wet season, and intermittent loss of soil-water saturation
while the rice crop is growing are important distinguishing characteristics of the rainfed lowlands in relation to P cycling.
We studied P cycling in an acid sandy rainfed lowland soil that covers about 30% of the rice growing area of Cambodia. Soils
with similar properties in comparable rainfed sub- ecosystems occur in Laos and northeast Thailand. We developed a general
schema of P pools and fluxes in the crop and soil for rice-based cropping systems in the rainfed lowlands of Cambodia. The
schema was derived from a number of field experiments carried out over five consecutive cropping seasons to quantify the residual
value of P fertiliser, P mass balances, soil P fractions, the effect on subsequent rice crops of crop residues and volunteer
pastures incorporated into the soils, and the dynamics of P turnover in the soil. With a single rice crop yielding 2.5–3 t
ha−1, application of 8–10 kg P ha−1 maintained yields and a small positive P balance in the soil. However, the soil P balance was sensitive to the proportion
of rice straw returned to the soil. Volunteer pastures growing during the early wet season accumulated significant amounts
of P, and increased their P uptake when soils were previously fertilised with P. These pastures recycled 3–10 kg P ha−1 for the succeeding rice crops. While inorganic soil P pools extractable with ion exchange resins and 0.1 M NaOH appeared
to be the main source of P absorbed by rice, microbial and organically-bound P pools responded dynamically to variation in
soil water regimes of the main wet, dry and early wet seasons. The schema needs to be developed further to incorporate site-specific
conditions and management factors that directly or indirectly affect P cycling, especially loss of soil-water saturation during
the rice cropping cycle. The paper discusses the application of results for acid sandy soils to other significant rice soils
in the rainfed lowlands of southeast Asia. 相似文献
19.
20.
Soluble Organic Nitrogen Pools in Forest soils of Subtropical Australia 总被引:15,自引:0,他引:15
Soil soluble organic N (SON) plays an important role in N biogeochemical cycling. In this study, 22 surface forest soils (0–10 cm)
were collected from southeast Queensland, Australia, to investigate the size of SON pools extracted by water and salt solutions.
Approximately 5–45 mg SON kg−1, 2–42 mg SON kg−1 and 1–24 SON mg kg−1 were extracted by 2 M KCl, 0.5 M K2SO4 and water, on average, corresponding to about 21.1, 13.5 and 7.0 kg SON ha−1 at the 0–10 cm forest soils, respectively. These SON pools, on average, accounted for 39% (KCl extracts), 42% (K2SO4 extracts) and 43% (water extracts) of total soluble N (TSN), and 2.3% (KCl extracts), 1.3% (K2SO4 extracts) and 0.7% (water extracts) of soil total N, respectively. Large variation in SON pools observed across the sites
in the present study may be attributed to a combination of factors including soil types, tree species, management practices
and environmental conditions. Significant relationships were observed among the SON pools extracted by water, KCl and K2SO4 and microbial biomass N (MBN). In general, KCl and K2SO4 extracted more SON than water from the forest soils, while KCl extracted more SON than K2SO4. The SON and soluble organic C (SOC) in KCl, K2SO4 and water extracts were all positively related to soil organic C, total N and clay contents. This indicates that clay and
soil organic matter play a key role in the retention of SON in soil. 相似文献