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1.
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
2.
Anne Kjersti Bakken Tor Arvid Breland Trond K. Haraldsen Trygve S. Aamlid Tore E. Sveistrup 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(2):81-90
Abstract Temporal changes in the scores of selected soil fertility indices were studied over six years in three different cases of organic crop rotation located in southern, eastern and central Norway. The cropping history and the initial scores of fertility indices prior to conversion to organic cropping differed between the sites. Crop yields, regarded as an overall, integrating fertility indicator, were in all rotations highly variable with few consistent temporal trends following the first year after conversion. On the site in eastern Norway, where conversion followed several years of all-arable crop rotations, earthworm number and biomass and soil physical properties improved, whereas the system was apparently degrading with regard to P and K trade balances and contents in soil. On the other two sites, the picture was less clear. On the southern site, which had a relatively fertile soil before conversion, the contents of soil organic matter and K decreased during the six-year period, but the scores of other fertility indices showed no trends. On the site in central Norway, there were positive trends for earthworm-related indices such as worm biomass and tubular biopores, and negative trends for soil porosity. The results, especially those from the eastern site, illustrate the general difficulty in drawing conclusions about overall fertility or sustainability when partial indicators show divergent trends. Consequently, the study gave no unambiguous support to the initial working hypothesis that organic farming increases inherent overall soil fertility, but rather showed that the effect varied among indicators and depended on status of the cases at conversion. It is concluded that indicators are probably better used as tools to learn about and improve system components than as absolute measures of sustainability. 相似文献
3.
Inadequate nutrient and organic‐matter supply constitutes the principal cause for declining soil fertility and productivity in much of sub‐Saharan Africa (SSA). In a survey in Gare Arera, the central Ethiopian highland, farmyard manure (FYM) and compost enriched with ash were identified as underutilized organic nutrient sources. Mustard meal, a by‐product of mustard‐seed oil production, is also locally available. On‐farm experiments were carried out on two major soil types (Nitisol and Vertisol) to study effects of the organic fertilizers, synthetic fertilizer (urea + triple superphosphate) and an unfertilized control on the yield and yield components of tef [Eragrostis tef (Zucc) Trotter] and selected soil properties. Application of organic fertilizers at an N rate equivalent to that of urea produced grain yields of 82% and 99% of that produced with urea on Nitisol and Vertisol, respectively. The apparent N recovery from urea, mustard meal, FYM, and compost was, respectively, 31%, 25%, 16%, and 28% on Nitisol and 23%, 17%, 26%, and 21% on Vertisol. The mean agronomic efficiency for the organic and synthetic fertilizers on Nitisol was 20 and 24 kg grain (kg N)–1 applied, respectively, whereas on the Vertisol, it was 13 kg grain (kg N)–1 for both. On Vertisol, tef was most responsive to FYM and on Nitisol, it was most responsive to compost. Soil N and P contents increased due to organic‐fertilizer application. The results showed that compost enriched with ash is a good choice on Nitisol while FYM works well on Vertisol. Mustard meal can be applied on both soils. 相似文献
4.
Summary The effect of roots on microbial growth and N immobilization was investigated in a pot experiment with barley, Italian ryegrass, and white clover. We used a silty subsoil with a low soil organic matter content (0.16%C and 0.012%N), which allowed us to measure N immobilization as an increase in total soil organic N (planted versus unplanted). At sampling, the soil was easily removed from intact roots by gentle washing, with a negligible loss of root material. Plant growth and extra mineral N (in planted soil only) gave increased total counts (fluorescence microscopy) and viable counts (plate dilution) of bacteria, a higher proportion of larger cells, and increased viable counts as a percentage of total counts. Under monocots, 12–17% of the added fertilizer N was recovered as soil organic N. Although this N immobilization was attributed to microbial assimilation, less than 1/4 was actually recovered as microbial biomass N, as measured with the chloroform fumigation/N-extraction method or calculated from total bacterial counts. The white clover accumulated substantial amounts of N due to N2 fixation. However, microbial N immobilization represented only 3% of the total N accumulation, showing that the microorganisms obtained a smaller share of biologically fixed N2 than of the N applied as fertilizer. Extra additions of mineral N (monocots) enhanced microbial N assimilation, partly due to increased plant growth. The results also strongly indicated, however, that the microbial growth under monocots was N-limited in the latter part of the experiment and that fertilizer N had a direct effect on microbial growth. In the early phase of plant growth, N immobilization ranged from 33 to 58 mg N g-1 root C. This level of immobilization required a release of organic C into the soil representing a minimum of 60–100% of that found in intact roots. 相似文献
5.
Tor Arvid Breland 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2013,63(3):178-185
Abstract In three field trials in southern Norway, Italian ryegrass (Lolium multiflorum Lam.), white clover (Trifolium repens L.) or subterranean clover (T. subterraneuni L.) was undersown in spring grain at three N fertilizer rates and ploughed under in late October as a green manure for a succeeding spring grain crop. The content of topsoil (0-20 cm) mineral nitrogen was determined during the growth of the grain crop, after grain harvest and after ploughing. In addition, mineralization of nitrogen and carbon was measured in green-manured soil incubated at 15°C and controlled moisture conditions. During grain crop growth, ryegrass tended to reduce soil mineral N compared with the other treatments. After grain harvest, in a small-plot experiment where extra nitrate was added, ryegrass reduced soil nitrate N (0-18 cm) from 4.2 to 0.4 g m?2 within 13 days, while the clovers had negligible effect compared with bare soil. Up to 9.4 g N m?2 was present in above-plus below-ground ryegrass biomass at ploughing. In incubated ryegrass soil, there was a temporary net N immobilization of up to 0.9 g N m?2 as compared with unamended soil. In clover-amended soil, mineral N exceeded that in unamended soil by up to 5 g N m?2. 相似文献
6.
Breland HM 《Science (New York, N.Y.)》1974,184(4133):114
7.
In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage
(FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring
grain plots and incubated for 449 days at controlled temperature (15 °C) and moisture content (50% water-holding capacity).
There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of
microbial biomass C and N, microbial quotient (Cmic/Corg), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were
similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient
(qCO2) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not
differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a
decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE
of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil
aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized
that the lower qCO2 values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms
within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations,
but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced
tillage intensity in the ECO-ARABLE rotation.
Received: 28 October 1998 相似文献
8.
On the central portion of the west Florida continental shelf, radionuclide activities show unusually wide variations: radium-226 activities up to 350 disintegrations per minute per 100 liters, radon-222 activities up to 1300 disintegrations per minute per 100 liters, and deficiencies of radon-222 as low as -10 disintegrations per minute per 100 liters. Florida's phosphate-rich strata seerm to be the principal source of the radionuclides, with the transfer occurring directly from sediments or indirectly in streams, ground-water flow, and geothermal springs. Winter storm fronts may enhance radon degassing in the shelf waters. 相似文献
9.
Zhenkang Xu Jennifer Wyrzykowski Acacia Alcivar-Warren Shaun M. Moss Brad J. Argue Steve M. Arce Monica Traub Fernanda R. O. Calderon Jeffrey Lotz Verlee Breland 《Journal of the World Aquaculture Society》2003,34(3):332-343
Allelic frequency differences at the highly polymorphic MI microsatellite of B20 locus were examined in Taura Syndrome Virus (TSV)-susceptible (Kona) and TSV-resistant (Select) lines of Pacific white shrimp Litopenaeus vannamei . DNA was screened from 1,009 cultured L. vannamei , 166 from the Kona line and 843 (97 broodstock and 746 offspring) from the Select line. A total of 34 different MI alleles were found, 41.2% of which were shared by the two lines, and 58.2% were unique to either line. Only seven (20.6%) of the 34 alleles had similar frequencies in the two lines. The most frequent (22.4%) allele in the Select line (218 bp) was absent from the Kona line. The most frequent (9.6%) allele in the Kona line (236 bp) was not observed in the Select line. Significant genetic differentiation between the two lines was shown using contingency table analysis (X2 = 891.20, df = 33, P < 0.0001), the exact test ( P < 0.00001), and Fst , analysis (0.06). Comparison of MI allele frequencies between the TSVresistant Select and TSV-susceptible Kona lines and between the top 12.5% (Top Select) and the bottom 12.5% (Bottom Select) surviving families to TSV challenge in the Select line suggested associations of MI alleles with TSV resistance. These observations suggest testable hypotheses in future experiments aimed at finding genetic markers associated with resistance to TSV and markers that could be used for marker-assisted selection of broodstock. 相似文献
10.
T.A. Breland 《Soil Use and Management》1995,11(4):163-167
Abstract. The objective of the present study was to investigate the potential of undersown catch crops to counteract soil degradation after autumn ploughing. Italian ryegrass (Lolium multiflorum Lam.) and white clover (Trifolium repens L.) were undersown in spring wheat on a loam soil in southern Norway, allowed to grow as cover crops after grain harvest and ploughed in to 20 cm depth as green manure in late October. Ryegrass prevented a collapse of the ridged plough furrow profile during winter, which occurred on grain monoculture and white-clover plots. Also, it tended to improve the water stability of aggregates, aggregate size distribution, bulk density, and pore volume in soil sampled in May. The preservation of the plough furrow profile was mainly attributed to enmeshment by an extensive system of fine roots and less to rhizosphere and microbial effects on aggregate stability. The results showed that ryegrass catch crops may give rapid structure improvements that are likely to contribute appreciably to easier seedbed preparation and less soil degradation in arable farming systems, even if the soil is ploughed in autumn. 相似文献