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921.
By influencing belowground processes, streamside vegetation affects soil processes important to surface water quality. We
conducted this study to compare root distributions and dynamics, and total soil respiration among six sites comprising an
agricultural buffer system: poplar (Populus × euroamericana‘ Eugenei), switchgrass, cool-season pasture grasses, corn (Zea
mays L.), and soybean (Glycine max (L.) Merr.). The dynamics of fine (0--2 mm) and small roots (2--5 mm) were assessed by
sequentially collecting 35 cm deep, 5.4 cm diameter cores from April through November. Coarse roots were described by excavating
1 × 1 × 2 m pits and collecting all roots in 20 cm depth increments. Root distributions within the soil profile were determined
by counting roots that intersected the walls of the excavated pits. Soil respiration was measured monthly from July to October
using the soda-lime technique. Over the sampling period, live fine-root biomass in the top 35 cm of soil averaged over 6 Mg
ha-1 for the cool-season grass, poplar, and switchgrass sites while root biomass in the crop fields was < 2.3 Mg ha-1 at its maximum. Roots of trees, cool-season grasses, and switchgrass extended to more than 1.5 m in depth, with switchgrass
roots being more widely distributed in deeper horizons. Root density was significantly greater under switchgrass and cool-season
grasses than under corn or soybean. Soil respiration rates, which ranged from 1.4--7.2 g C m-2 day-1, were up to twice as high under the poplar, switchgrass and cool-season grasses as in the cropped fields. Abundant fine roots,
deep rooting depths, and high soil respiration rates in the multispecies riparian buffer zones suggest that these buffer systems
added more organic matter to the soil profile, and therefore provided better conditions for nutrient sequestration within
the riparian buffers.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
922.
The effects of two pruning regimes on the above-ground biomass allocation and nodulation of Gliricidia sepium (Jacq.) Walp.
(Leguminosae: Robinieae) were studied in a cut-and-carry forage production system under humid tropical conditions in Guadeloupe,
French Antilles. The grass layer composed of a mixture dominated by Paspalum notatum Flügge (80%) and Digitaria decumbens
Stent. The pruning regimes were partial pruning (ca. 50%) every two months and complete pruning every six months. The complete
pruning caused an almost complete turnover of N2 fixing nodules. The nodule biomass decreased after the partial pruning, but
the turnover was not complete. The nodule to foliage biomass ratio followed the same pattern under both treatments, and the
values of the ratio converged towards the end of the experimental period. The maxima of standing nodule biomass were 7.2 and
13.0 kg ha−1 in the partially and completely pruned trees, respectively. The cumulative leaf fodder harvest was higher under
partial pruning management, due to smaller litter loss. The branch biomass production was higher under complete pruning management.
Grass production was not affected by the pruning pattern of G. sepium. It was concluded that the partial pruning management
produces more fodder in the studied association, and the nodulation probably adjusts to the canopy N requirements. The potential
N release to soil in the turnover of nodules of G. sepium (max. 0.82 kg ha−1) is negligible compared to the N export in tree
and grass fodder harvest, 190 and 215 kg ha−1 in partially and completely pruned plots, respectively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
923.
Efforts to overcome declining soil fertility on small holder farms in western Kenya must be consistent with the reality of
low utilization of inorganic fertilizers. Likewise organic inputs alone cannot supply adequate nutrients. The use of two organic
resources, Tithonia diversifolia (tithonia) and Senna spectabilis (senna) leaves, and their combination with inorganic P for
improving soil fertility and maize yields was investigated on a P limiting soil in Western Kenya. Treatments included: 1)
control, no inputs; 2) 5 t ha−1 (dry matter) tithonia leaves; 3) 5 t ha−1 senna leaves; 4) 5 t ha−1 tithonia leaves + 25 kg P ha−1 as triple superphosphate (TSP); 5) 5 t ha−1 senna leaves + 25 kg P ha−1 (as TSP); and 6) 25 kg P ha−1 of TSP. Maize was used as a test crop. Decomposition and P and N release of tithonia and senna leaves were determined in
a litterbag study. Tithonia + TSP applications tripled maize yields compared to the control, senna + TSP and tithonia sole
application doubled yields, while senna sole applications did not increase yields substantially. A large residual yield was
produced in the tithonia treatments in a subsequent crop. These yield results were consistent with the higher quality and
faster release of N and P from the tithonia leaves compared to senna. The tithonia biomass transfer system can improve yields
in the short term but has limitations because of the large amount of biomass and the associated labor requirements.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
924.
925.
黄山松人工林生物产量及生产力的研究 总被引:4,自引:0,他引:4
以湖南省测阳市大围山实验林场的10年生黄山松人工林为对象,对林分的生物量进行了测定分析,结果表明,密度为1530株/hm2的林分,生产力为1.675t/(hm2·a).黄山松在该场生长良好,经济系数较高,保持水土的能力较强,可在海拔1000~1600m范围内适当发展. 相似文献
926.
Quality of agricultural soils is largely a function of soil organic matter. Tillage and crop management impact soil organic matter dynamics by modification of the soil environment and quantity and quality of C input. We investigated changes in pools and fluxes of soil organic C (SOC) during the ninth and tenth year of cropping with various intensities under conventional disk-and-bed tillage (CT) and no tillage (NT). Soil organic C to a depth of 0.2 m increased with cropping intensity as a result of greater C input and was 10% to 30% greater under NT than under CT. Sequestration of crop-derived C input into SOC was 22±2% under NT and 9±4% under CT (mean of cropping intensities ± standard deviation of cropping systems). Greater sequestration of SOC under NT was due to a lower rate of in situ soil CO2 evolution than under CT (0.22±0.03 vs. 0.27±0.06 g CO2–C g−1 SOC yr−1). Despite a similar labile pool of SOC under NT than under CT (1.1±0.1 vs. 1.0±0.1 g mineralizable C kg−1 SOC d−1), the ratio of in situ to potential CO2 evolution was less under NT (0.56±0.03) than under CT (0.73±0.08), suggesting strong environmental controls on SOC turnover, such as temperature, moisture, and residue placement. Both increased C sequestration and a greater labile SOC pool were achieved in this low-SOC soil using NT and high-intensity cropping. 相似文献
927.
We compared the dynamics of net mineralization of nitrogen (N) derived from white clover material (Ndfc) as measured by the
difference and the 15N methods in a pot experiment with a sandy loam (15°C and pF 2.4) planted with Italian ryegrass. On day 22, mineralized Ndfc
(soil mineral N plus plant N uptake) was 5.8% and 1.3% of added N for the 15N and the difference methods, respectively. The discrepancy was reduced on day 43. On day 64, the relationship was reversed,
and on day 98 the values given by the two methods were 22.8% and 29.5%, respectively. The results obtained by the two methods
were linearly correlated (r = 0.987) and, on average, did not differ significantly. Nevertheless, the different temporal patterns led to appreciably
different parameter values as estimated by fitting of a reparameterized Richards model. On day 22, clover amendment reduced
mineralized N derived from soil (Ndfs) by 3.4 mg N pot–1. The reason for this was that the clover amendment led to a reduction in plant growth and uptake of Ndfs, most likely because
of allelopathy, while mineral Ndfs did not increase correspondingly. Clover-induced Ndfs in the microbial biomass of 5.1 mg
N pot–1 suggested that the mineral Ndfs not taken up by plants had been reimmobilized. Towards the end of the experiment, clover-induced
Ndfs in the biomass declined to 1.5 mg N pot–1, while mineralized Ndfs due to clover amendment increased to 5.1 mg N pot–1. The results strongly suggested that this increase was caused by a real stimulation of humus N mineralization by clover amendment
rather than by isotope displacement or pool substitution.
Received: 5 May 1997 相似文献
928.
The present work aims at evaluating the effect of cycloheximide at concentrations of between 0.5 and 5mgg–1 on N2O and NO3
– production in two slightly alkaline soils, sampled from deciduous woodland and arable cultivation. In the first experiment,
peptone was used as the “inducing substrate” for heterotrophic activity, and soil was incubated with cycloheximide (at different
concentrations) and/or acetylene (1mll–1) to block induced eukaryotic protein synthesis and ammonia monooxygenase activity, respectively. Peptone addition stimulated
N2O and NO3
– production significantly in woodland soil, whereas arable soil showed no significant N2O emissions and low NO3
– production. Low cycloheximide concentrations drastically reduced N2O emissions in woodland soil, suggesting a potential role of fungi in N2O emissions. However, acetylene was equally effective in blocking N2O emissions and part of NO3
– production, so that a possible role of ammonia monooxygenase in an organic-inorganic pathway of N nitrification in fungal
metabolism can be hypothesized. A second experiment was carried out on the woodland soil to check if low cycloheximide concentrations
had non-target biocidal effects on soil microorganisms. Attention was focused on the range of concentrations which had reduced
N2O emission in the woodland soil. The results suggested that at concentrations of cycloheximide between 0.5 and 2mgg–1 any biocidal effect on microbial biomass was negligible in the first 48h; therefore only selective inhibition of protein
synthesis could be expected. The whole nitrifier population seemed to be particularly sensitive to cycloheximide concentrations
higher than 2.5mgg–1.
Received: 4 July 1997 相似文献
929.
Soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system 总被引:14,自引:0,他引:14
The effects of growing trees in combination with field crops on soil organic matter, microbial biomass C, basal respiration
and dehydrogenase and alkaline phosphatase activities were studied in soils under a 12-year-old Dalbergia sissoo (a N2-fixing tree) plantation intercropped with a wheat (Triticum aestivum) – cowpea (Vigna sinensis) cropping sequence. The inputs of organic matter through D. sissoo leaf litter increased and crop roots decreased with the increase in tree density. Higher organic C and total N, microbial
biomass C, basal soil respiration and activities of dehydrogenase and alkaline phosphatase were observed in treatments with
tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activities
increased with the decrease in the spacing of the D. sissoo plantation. The results indicate that adoption of the agroforestry practices led to an improved organic matter status of
the soil, which is also reflected in the increased nutrient pool and microbial activities necessary for long-term productivity
of the soil. However, tree spacing should be properly maintained to minimize the effects of shading on the intercrops.
Received: 21 February 1997 相似文献
930.
Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management 总被引:5,自引:0,他引:5
C. Witt Kenneth G. Cassman Johannes C. G. Ottow Ulrich Biker 《Biology and Fertility of Soils》1998,28(1):71-80
Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives
of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (CBIO) and microbial biomass N (NBIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping
system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and
WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following
DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time
of residue incorporation had a large effect on NO3
–-N accumulation during the fallow period and also on extractable NH4
+-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence
on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake
or yield. In both cropping systems, CBIO and NBIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue
C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after
mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic
N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration
as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant
effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics.
Received: 31 October 1997 相似文献