Changes in the acidity and fertility of a red earth soil under wheat–annual pasture rotations

1997 ◽  
Vol 48 (5) ◽  
pp. 561 ◽  
Author(s):  
K. R. Helyar ◽  
B. R. Cullis ◽  
K. Furniss ◽  
G. D. Kohn ◽  
A. C. Taylor
Keyword(s):  
Wheat Crop ◽  
Soil N ◽  
Alkaline Ph ◽  
Waste Products ◽  
Organic C ◽  
Acid Ph ◽  
Rate Of Increase ◽  
Red Earth ◽  
Ph Increase ◽  
Ph Decrease

This paper reports the effects of 6 wheat–annual pasture rotations over 18 years on soil N, organic C, P, and pH in a red earth soil at Wagga Wagga (35° 03′ S, 147° 21′E), in southern NSW. There were 3 cropping intensities (33, 50, 67%) with pastures dominated by subterranean clover (Trifolium subterraneum L. cv. Bacchus Marsh) and annual ryegrass (Lolium rigidum Gaud. cv. Wimmera). Rotations were long (6-year) or short (2- or 3-year). Initial soil N and organic C concentrations (0–10 cm) were low, 1300–1400 kg N/ha and 0·7–0·9 g organic C/100 g. The rate of increase of total N in the top 20 cm was the same on short and long rotations, and increased with the proportion of pasture in the rotation from 2·0 to 12·1 to 20·7 kg N/ha · year for pasture to crop ratios of 0·33, 0·50, and 0·67. Estimates of the amounts of N fixed and the measured accumulation of N per pasture year varied within the narrow ranges of 95–113 and 45–64 kg N/ha · pasture year. Organic C increased faster as the proportion of pasture in the rotation increased and there was no evidence that steady-state concentrations were achieved by Year 18. Estimates of the average amount of N leached below 30 cm varied in the range 22–29 kg N/ha · year. Analysis of the individual crop and pasture effects on soil N in the surface 10 cm indicated that net nitrate leaching was greatest in the second pasture year or in the first crop year following 1 year of pasture. A significant amount of N leached during the first 2 or 3 pasture years in a rotation was recovered by the first wheat crop or by the third and fourth year pastures. Second to fourth cereal crops depleted soil N by an amount similar to that removed in the grain. Average grain N% for the rotation treatments was closely described (R2 = 0·96) as a function of the length of the pasture phase, the pasture to crop ratio, and the interaction pasture to crop ratio number of preceding wheat crops. In the top 30 cm the pH changed at a rate near –0·04 units/year on all treatments, equivalent to addition of 2·3–2·8 kmol H+/ha · year. The acid addition rate, and hence the long-term lime requirement (50 kg lime/kmol H+), did not vary with pasture to crop ratio or with the length of the rotation. The proportion of the acid added to the top 30 cm of soil that was contributed from the N cycle (nitrification followed by nitrate loss by leaching below 30 cm or by run-off) was 0·65 for rotations with 67% pasture and 0·80 for rotations with 33% pasture. Carbon cycle acids, produced during organic matter accumulation and the synthesis of products that were subsequently removed, accounted for the remainder. Individual crop and pasture effects on soil pH were near the overall mean of –0·04 units except in years preceding and following the transition from pasture to cereal phases of the rotations. In cereal-dominated rotations the last pasture year was strongly acid (pH decrease 0·13–0·17) and the following cereal year was alkaline (pH increase 0·05–0·08). In pasture-dominated rotations the effects were reversed, the last pasture being alkaline (pH increase 0·07–0·12) and the following cereal being acid (pH decrease 0·13–0·19). In the 50% rotations, effects were intermediate. Organic and inorganic forms of soil P in the surface 10 cm increased linearly with time, accounting for 38% of the applied fertiliser P. Of the applied P, 88% was accounted for by the sum of P accumulated in the surface 20 cm of soil and by removal in products and waste products. The remainder may have been lost by erosion or accumulated in forms resistant to extraction by 0·1 M H2SO4 after ignition at 550°C. There was a slightly greater rate of increase of organic P as the proportion of pasture in the rotation increased. The annual addition of 11·8 kg P/ha·year marginally exceeded the amount required to maintain the available P concentration.

Differential inactivation of three bacteriophages by acid and alkaline pH used in the membrane adsorption–elution method of virus recovery

1980 ◽  
Vol 26 (12) ◽  
pp. 1403-1407 ◽  
Author(s):  
Carolyn M. Sabatino ◽  
Siegfried Maier
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Differential Susceptibility ◽  
Alkaline Ph ◽  
Alkaline Elution ◽  
Adsorption Method ◽  
Acid Ph ◽  
Elution Method ◽  
Virus Recovery ◽  
General Method

The study was prompted by our inability to concentrate phages by a membrane adsorption method effective for polioviruses. Consequently two coliphages, WPK and T4, and F116 of Pseudomonas aeruginosa were tested for their resistance to acid (pH 5.2–3.2) and alkaline (pH 10–11.5) exposures. Only T4 proved acid resistant, allowing for acid adsorption, and only WPK was sufficiently alkaline resistant to allow for alkaline elution. Thus, the differential susceptibility of various phages precludes the use of the acid membrane adsorption–alkaline elution method as a general method for the concentration of phages from large volumes of water.

Quantifying N response and N use efficiency in rice–wheat (RW) cropping systems under different water management

2009 ◽  
Vol 147 (3) ◽  
pp. 303-312 ◽  
Author(s):  
Q. JING ◽  
H. VAN KEULEN ◽  
H. HENGSDIJK ◽  
W. CAO ◽  
P. S. BINDRABAN ◽  
...  
Keyword(s):  
Water Management ◽  
Management Practices ◽  
Cropping Systems ◽  
N Uptake ◽  
Production Costs ◽  
Wheat Crop ◽  
N Recovery ◽  
Soil Nitrate ◽  
Soil N ◽  
N Use

SUMMARYAbout 0·10 of the food supply in China is produced in rice–wheat (RW) cropping systems. In recent decades, nitrogen (N) input associated with intensification has increased much more rapidly than N use in these systems. The resulting nitrogen surplus increases the risk of environmental pollution as well as production costs. Limited information on N dynamics in RW systems in relation to water management hampers development of management practices leading to more efficient use of nitrogen and water. The present work studied the effects of N and water management on yields of rice and wheat, and nitrogen use efficiencies (NUEs) in RW systems. A RW field experiment with nitrogen rates from 0 to 300 kg N/ha with continuously flooded and intermittently irrigated rice crops was carried out at the Jiangpu experimental station of Nanjing Agricultural University of China from 2002 to 2004 to identify improved nitrogen management practices in terms of land productivity and NUE.Nitrogen uptake by rice and wheat increased with increasing N rates, while agronomic NUE (kg grain/kg N applied) declined at rates exceeding 150 kg N/ha. The highest combined grain yields of rice and wheat were obtained at 150 and 300 kg N/ha per season in rice and wheat, respectively. Carry-over of residual N from rice to the subsequent wheat crop was limited, consistent with low soil nitrate after rice harvest. Total soil N hardly changed during the experiment, while soil nitrate was much lower after wheat than after rice harvest. Water management did not affect yield and N uptake by rice, but apparent N recovery was higher under intermittent irrigation (II). In one season, II management in rice resulted in higher yield and N uptake in the subsequent wheat season. Uptake of indigenous soil N was much higher in rice than in wheat, while in rice it was much higher than values reported in the literature, which may have consequences for nitrogen fertilizer recommendations based on indigenous N supply.

scholarly journals Fate of Ascaris at various pH, temperature and moisture levels

2020 ◽  
Vol 18 (3) ◽  
pp. 375-382 ◽  
Author(s):  
Jenna Senecal ◽  
Annika Nordin ◽  
Björn Vinnerås
Keyword(s):  
Moisture Content ◽  
Treatment Temperature ◽  
Organic Wastes ◽  
Alkaline Ph ◽  
Egg Viability ◽  
High Ph ◽  
Soil Transmitted Helminths ◽  
Intestinal Worms ◽  
Ph Increase ◽  
Sanitation Systems

Abstract Soil-transmitted helminths (STH) are intestinal worms that infect 24% of the world's population. Stopping the spread of STH is difficult, as the eggs are resilient (can withstand high pH) and persistent (can remain viable in soils for several years). To ensure that new sanitation systems can inactivate STH, a better understanding of their resilience is required. This study assessed the inactivation of Ascaris eggs under various conditions, in terms of moisture content (MC) (<20 to >90%), temperature (20–50 °C) and pH (7–12.5). The results highlight that the exposure of Ascaris eggs to elevated pH (10.5–12.5) at temperatures ≤27.5 °C for >70 days had no effect on egg viability. Compounding effects of alkaline pH (≥10.5) or decreasing MC (<20%) was observed at 35 °C, with pH having more of an effect than decreasing MC. To accelerate the inactivation of STH, an increase in the treatment temperature is more effective than pH increase. Alkaline pH alone did not inactivate the eggs but can enhance the effect of ammonia, which is likely to be present in organic wastes.

Nitrogen benefits of lupins, field pea, and chickpea to wheat production in south-eastern Australia

1997 ◽  
Vol 48 (1) ◽  
pp. 39 ◽  
Author(s):  
E. L. Armstrong ◽  
D. P. Heenan ◽  
J. S. Pate ◽  
M. J. Unkovich
Keyword(s):  
N2 Fixation ◽  
Aboveground Biomass ◽  
Crop Residues ◽  
Field Pea ◽  
Superior Performance ◽  
Wheat Crop ◽  
Wagga Wagga ◽  
Soil N ◽  
Narrow Leaf ◽  
Eastern Australia

Nitrogen balances of narrow leaf lupin (Lupinus angustifolius L.), albus lupin (L. albus L.), field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.) sown over a range of dates were examined in 1992 in a rotation study at Wagga Wagga, NSW. Each N budget included assessment of dependence on fixed as opposed to soil N, peak aboveground biomass N, and N removed as grain or returned as unharvested aboveground crop residues. N balances of wheat sown across the plots in 1993 were assessed similarly in terms of biomass and grain yield. Yields, N2 fixation, and crop residue N balances of the legumes were markedly influenced by sowing time, and superior performance of lupins over other species was related to higher biomass production and proportional dependence on N2 fixation, together with a poorer harvest index. Residual N balances in aboveground biomass after harvest of the 1992 crops were significantly correlated with soil mineral N at 1993 sowing and with biomass and grain N yields of the resulting wheat crop. Best mean fixation and grain N yield came from albus lupin. Wheat grain N yields following the 2 lupins were some 20% greater than after fiield pea and chickpea and 3 times greater than after barley. Net soil N balance based solely on aboveground returns of N of legumes in 1992 through to harvest of wheat in 1993 was least for narrow leaf lupin-wheat ( –20 kg N/ha), followed by albus lupin-wheat ( –44), chickpea-wheat ( –74), and field pea-wheat ( –96). Corresponding combined grain N yields (legume+wheat) from the 4 rotations were 269, 361, 178, and 229 kg N/ha, respectively. The barley-wheat rotation yielded a similarly computed soil N deficit of 67 kg/ha. Data are discussed in relation to other studies on legume-based rotations.

Productivity and nitrogen use of three different wheat-based rotations in North West Syria

1998 ◽  
Vol 49 (3) ◽  
pp. 451 ◽  
Author(s):  
M. Wood ◽  
C. J. Pilbeam ◽  
H. C. Harris ◽  
J. Tuladhar
Keyword(s):  
Crop Residues ◽  
Wheat Crop ◽  
N Mineralisation ◽  
Soil N ◽  
N Budget ◽  
Mineral N ◽  
North West ◽  
System A ◽  
To Come ◽  
C 50

Productivity of 3 different 2-year crop rotations, namely continuous wheat, wheat-chickpea, and wheat-fallow, was measured over 4 consecutive seasons beginning in 1991-92 at the ICARDA station, Tel Hadya, Syria. Nitrogen (N) fertiliser (30 kg N/ha at sowing) was broadcast every other year in the continuous wheat only. 15N-labelled fertiliser was used to quantify the amount of nitrogen supplied to the crops through current and past applications of fertiliser and by N2 fixation. The remaining N in the crop was assumed to come from the soil. In any single season, wheat yields were unaffected by rotation or N level. However, 2-year biomass production was significantly greater (32%, on average) in the continuously cropped plots than in the wheat-fallow rotation. On average, <10% of the N in the wheat crop came from fertiliser in the season of application, and <1·2 kg N/ha of the residual fertiliser was recovered by a subsequent wheat crop. Chickpea fixed 16-48 kg N/ha, depending on the season, but a negative soil N budget was still likely because the amount of N removed in the grain was usually greater than the amount of atmospheric N2 fixed. Uptake of soil N was similar in the cereal phase of all 3 rotations (38 kg N/ha, on average), but over the whole rotation at least 33% more soil N was removed from continuously cropped plots than from the wheat-fallow rotation, suggesting that the latter is a more sustainable system. A laboratory study showed that although wheat and chickpea residues enhanced the gross rate of N mineralisation by c. 50%, net rates of N mineralisation were usually negative. Given the high C/N ratio of the residue, immobilisation, rather than loss processes, is the likely cause of the decline in the mineral N content of the soil. Consequently, decomposition of crop residues in the field may in the short term reduce rather than increase the availability of N for crop growth.

Three Novel α-Globin Variants: Hb Itapira [α30(B11) Glu→Val (α1)], Hb Bom Jesus Da Lapa [α30(B11) Glu→Ala (α1)] and Hb Boa Esperança [α16(A14) Lis→Thr (α2)].

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3739-3739
Author(s):  
Maria F. Sonati ◽  
Elza M. Kimura ◽  
Dulcineia M. Albuquerque ◽  
Denise M. Oliveira ◽  
Fernando F. Costa
Keyword(s):  
High Performance ◽  
Globin Gene ◽  
Southeastern Brazil ◽  
Base Substitution ◽  
Alkaline Ph ◽  
Globin Chain ◽  
Chinese Families ◽  
Acid Ph ◽  
Α Chain ◽  
Hematological Manifestations

Abstract Three new Hb variants were found in four blood donors, which we named Hb Itapira [α30(B11) Glu→Val)], Hb Bom Jesus da Lapa [α30(B11) Glu→Ala)] and Hb Boa Esperança [α16 (A14) Lis→Thr], according to their carriers’ origin. The first one was detected in a Caucasian man from Southeastern Brazil; electrophoresis at alkaline pH showed a low proportion Hb S-like band (5,5%), which was not distinguished from Hb A at acidic pH. High performance liquid chromatography-HPLC exhibited a short peak at D-Window. The abnormal α-globin was demonstrated by globin-chain electrophoresis at acid pH, with a slower migration than the normal α-chain. The α genes were sequenced (ABI PRISM-377-DNA automated sequencer, Applied Biosystems, CA, USA) and a base substitution found at the 30th codon of the α1-gene (GAG→GTG), in heterozygosis, causing Glu→Val replacement in the α-chain. Familial analysis revealed that the carrier’s mother and brother have the same alteration. All the affected members of this family are also heterozygous for the α-globin gene triplication (αααanti3.7), explaining the low percentage of the variant and suggesting an association of the mutation with the triplicate haplotype. Hb Bom Jesus da Lapa results of a mutation at the same gene and position: α1, 30th codon (GAG→GCG), causing Glu→Ala replacement. It was detected in an African descendant woman from the northeastern region of Brazil; the electrophoretic behaviour was similar to that of Hb Itapira, but it eluted with Hb A2 on HPLC, in a total of 24.8%, and the mutant did not separate from normal α-chain at the acidic globin electrophoresis. Two other variants with replacement of the α-chain 30th residue have been described [Hb O-Padova (Glu→Lys), found in Italian, Turkish and Spanish families, and Hb G-Chinese (or G-Honolulu, G-Hong Kong, G-Singapore) (Glu→Gln), encountered in Chinese families], none of them with clinical or hematological manifestations although this residue is involved in the αlβ1 contacts of the molecule. Hb Boa Esperança was detected in two apparently not-related individuals, one of them of African descent, both originate from the state of Minas Gerais, Southeast Brazil. This variant moved faster than Hb A at alkaline pH, was not distinguished at acid pH, and eluted as an additional peak at P3 on HPLC (25%); globin-chain electrophoresis showed a slower α-chain. Sequencing revealed a base substitution at the 16th codon of the α2-gene, in heterozygosis (AAG→ACG; Lys→Thr). Although the carriers have different surnames and do not know each other, β-cluster haplotypes are suggestive of a common ancestor. Three other mutations have already been described in this position [Hb I (Lys→Glu), Hb Beijing (Lys→Asn), in asymptomatic heterozigotes, and Hb Harbin (Lys→Met), slightly unstable, resulting in anemia to its carrier. All the three variants described here showed normal instability and solubility tests.

Management of sugarcane harvest residues: consequences for soil carbon and nitrogen

Soil Research ◽  
2007 ◽  
Vol 45 (1) ◽  
pp. 13 ◽  
Author(s):  
Fiona A. Robertson ◽  
Peter J. Thorburn
Keyword(s):  
Microbial Biomass ◽  
Soil Fertility ◽  
Microbial Activity ◽  
Soil N ◽  
Soil Organic C ◽  
Total N ◽  
Organic C ◽  
Soil Microbial ◽  
C And N

The Australian sugar industry is moving away from the practice of burning the crop before harvest to a system of green cane trash blanketing (GCTB). Since the residues that would have been lost in the fire are returned to the soil, nutrients and organic matter may be accumulating under trash blanketing. There is a need to know if this is the case, to better manage fertiliser inputs and maintain soil fertility. The objective of this work was to determine whether conversion from a burning to a GCTB trash management system is likely to affect soil fertility in terms of C and N. Indicators of short- and long-term soil C and N cycling were measured in 5 field experiments in contrasting climatic conditions. The effects of GCTB varied among experiments. Experiments that had been running for 1–2 years (Harwood) showed no significant trash management effects. In experiments that had been running for 3–6 years (Mackay and Tully), soil organic C and total N were up to 21% greater under trash blanketing than under burning, to 0.10 or 0.25 m depth (most of this effect being in the top 50 mm). Soil microbial activity (CO2 production) and soil microbial biomass also increased under GCTB, presumably as a consequence of the improved C availability. Most of the trash C was respired by the microbial biomass and lost from the system as CO2. The stimulation of microbial activity in these relatively short-term GCTB systems was not accompanied by increased net mineralisation of soil N, probably because of the greatly increased net immobilisation of N. It was calculated that, with standard fertiliser applications, the entire trash blanket could be decomposed without compromising the supply of N to the crop. Calculations of possible long-term effects of converting from a burnt to a GCTB production system suggested that, at the sites studied, soil organic C could increase by 8–15%, total soil N could increase by 9–24%, and inorganic soil N could increase by 37 kg/ha.year, and that it would take 20–30 years for the soils to approach this new equilibrium. The results suggest that fertiliser N application should not be reduced in the first 6 years after adoption of GCTB, but small reductions may be possible in the longer term (>15 years).

scholarly journals Chemical Attributes of Soil and Response of Wheat to Serpentinite in Direct Seeding System

2019 ◽  
Vol 11 (6) ◽  
pp. 460
Author(s):  
Alves A. Alovisi ◽  
Munir Mauad ◽  
Alessandra M. T. Alovisi ◽  
Luciene K. Tokura ◽  
Robervaldo S. Silva ◽  
...  
Keyword(s):  
Block Design ◽  
Residual Effect ◽  
Magnesium Silicate ◽  
Crop Productivity ◽  
Dry Mass ◽  
Exchange Capacity ◽  
Wheat Crop ◽  
Randomized Block Design ◽  
Chemical Attributes ◽  
Ph Decrease

The serpentinite is an alternative for the correction of soil acidity and is composed of calcium and magnesium silicate. The objective of this study was to evaluate the residual effect of the serpentinite application on soil chemical attributes and the effects on wheat crop productivity in a no-tillage system. The experimental design was a randomized block design, in a subdivided plot scheme, with four replications. The plots were constituted by serpentinite doses (0, 2, 4, 8 and 16 Mg ha-1) and in the subplots the soil collection layers (0.0-0.10 and 0.10-0.20 m). The chemical attributes of the soil evaluated at 41 months after the application of serpentinite, presented favorable results of the residual power of this corrective. The main results observed are related to the increase of pH, decrease of aluminum content and potential acidity, and increase of Ca, Mg and Si contents, cation exchange capacity (CTC) and base saturation. The residual of the serpentinite in the soil contributed with an improvement in the chemical attributes of the soil, which favored the increase of the dry mass, number of spikes and yield of the wheat crop.

scholarly journals Effect of elevated tropospheric ozone on soil carbon and nitrogen: A meta-analysis

2022 ◽  
Author(s):  
Enzhu Hu ◽  
Zhimin Ren ◽  
Xiaoke Wang ◽  
Hongxing Zhang ◽  
Weiwei Zhang
Keyword(s):  
Tropospheric Ozone ◽  
Terrestrial Ecosystem ◽  
Soil N ◽  
N Dynamics ◽  
Organic C ◽  
Soil C ◽  
Soil C And N ◽  
C And N ◽  
The Impact ◽  
C And N Dynamics

Abstract Elevated tropospheric ozone concentration ([O3]) may substantially influence the belowground processes of the terrestrial ecosystem. Nevertheless, a comprehensive and quantitative understanding of the responses of soil C and N dynamics to elevated [O3] remains elusive. In this study, the results of 41 peer-reviewed studies were synthesized using meta-analytic techniques, to quantify the impact of O3 on ten variables associated with soil C and N, i.e., total C (TC, including soil organic C), total N (TN), dissolved organic C (DOC), ammonia N (NH4 +), nitrate N (NO3 -), microbial biomass C (MBC) and N (MBN), rates of nitrification (NTF) and denitrification (DNF), as well as C/N ratio. The results depicted that all these variables showed significant changes (P < 0.05) with [O3] increased by 27.6 ± 18.7 nL/L (mean ± SD), including decreases in TC, DOC, TN, NH4 +, MBC, MBN and NTF, and increases in C/N, NO3 - and DNF. The effect sizes of TN, NTF, and DNF were significantly correlated with O3 fumigation level and experimental duration (P < 0.05). Soil pH and climate were essential in analyses of O3 impacts on soil C and N. However, the responses of most variables to elevated [O3] were generally independent of O3 fumigation method, terrestrial ecosystem type, and additional [CO2] exposure. The altered soil C and N dynamics under elevated [O3] may reduce its C sink capacity, and change soil N availability thus impact plant growth and enhance soil N losses.

A comparison of chickpeas and pasture legumes for sustaining yields and nitrogen status of subsequent wheat

1997 ◽  
Vol 48 (3) ◽  
pp. 305 ◽  
Author(s):  
I. C. R. Holford ◽  
G. J. Crocker
Keyword(s):  
Protein Content ◽  
Crop Residues ◽  
N Uptake ◽  
Yield Potential ◽  
Wheat Crop ◽  
N Fixation ◽  
Soil N ◽  
Red Clay ◽  
Mineral N ◽  
Positive Effects

Six treatments were compared for their effects on wheat yields, nitrogen (N) uptake, protein content, and fertiliser N requirements in a long-term rotation study on a black earth and a red clay in northern New South Wales. Three of the treatments were lucerne, subterranean clover, and snail medic, all grown simultaneously from 1988 to 1990 and all followed by 3 years of wheat. The other 3 treatments were biennial rotations of chickpea–wheat and long-fallow–wheat as well as a continuous wheat monoculture, all lasting 6 years. With the exception of the first wheat crop, which experienced very low growing-season rainfall, lucerne was more beneficial than other legumes to following wheat crops in terms of yield, protein content, and fertiliser N requirement. Clover closely followed lucerne in the magnitude of its positive effects, whereas medic and chickpea produced much smaller effects. Because of the amount of N removed in the chickpea grain, it appeared that the small positive effects of chickpea were due to soil N sparing or rapid mineralisation from crop residues rather than any net contribution of N fixation to soil N accretion. Average yields of the 3 wheat crops following lucerne and clover were much higher than average yields 20 years previously following lucerne, even though average yields of continuously grown wheat have declined over the past 20 years. However, lucerne eliminated the need for N fertiliser for no more than 2 following wheat crops, and clover for only the first wheat crop. It appears that the longer duration of lucerne benefits reported in earlier studies was due to the higher background soil N levels as well as the lower yield potential in the earlier years. Nevertheless, lucerne lowered the fertiliser requirement of the third wheat crop by more than 50%. In contrast to lucerne, annual legumes are probably most beneficial if grown in alternate years with wheat. The large benefits of long fallowing particularly on the black earth were apparently caused by its enhancement of soil moisture and mineral N accumulation. However, these N effects were surprisingly large considering the degree of depletion of organic matter in long-fallowed soils.

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