Leaf and Seed Micronutrient Accumulation in Soybean Cultivars in Response to Integrated Organic and Chemical Fertilizers Application
Mohammad Ali Bahmanyar
Plant nutrients can be influenced by organic
materials of soils. An experiment was conducted to evaluate the effect
of organic amendments on elements uptake by soybean cultivars in a silty
loam soil in Mazandaran province, Iran. The experiment was carried out
in split plot based on randomized complete block design with three replications
in 2006. Main plots were included 8 fertilizer treatments consisted of
20 and 40 Mg ha-1 Municipal Solid Waste Compost
(MSW), Vermicompost (VC) and Sewage Sludge (SS) which enriched with 50%
chemical fertilizers needed by soil, only chemical fertilizer treatment
and control. Sub plots consisted of three genotypes of soybean (032, 033
and JK). Grain yield was determined and soybean leaves and seeds were
digested and analyzed for Mn, Cu, Zn and Fe. Results showed that yield
and elements content in soybean leaves and seeds (Mn, Cu, Zn and Fe) were
influenced by all treatments. The 40 Mg ha-1 of sewage sludge
enriched with chemical fertilizers produced maximum grain yield. Different
soybean cultivars had also significant differences in terms of leaf and
seed micronutrients accumulation. Maximum grain yield was observed in
JK and 033. Mean comparisons showed that interaction effects of fertilizer
and cultivar had significant differences on Mn, Cu and Fe content in soybean
leaves, so that the maximum Cu content was observed in 032 cultivars with
40 Mg ha-1 enriched sewage sludge and municipal waste compost.
Also the highest amount of Fe was obtained for JK cultivar when the 40
Mg ha-1 of municipal compost was used. Among different mentioned
traits, Fe and Cu content in leaf and seed and Zn content in leaf had
a positive and significant correlation with grain yield.
Soil organic matter (SOM) is universally recognized to be essential
for a healthy and productive soil. Among the several agronomic and environmental
functions exerted by SOM, nutrient cycling, water retention and drainage,
soil susceptibility to contamination and erosion and crop resistance to
pests and diseases are those especially dependent on SOM quality and quantity
(Rees et al., 2001; Magdoff and Weil, 2004). Amount of organic
wastes produced by farms, food industries and municipalities including
animal manure, municipal Sewage Sludge (SS) and urban solid waste, has
also increased (Brebbia et al., 2004). Furthermore large volumes
of organic waste is generated by the textile industry and released into
the environment (Kaushik and Garg, 2003). Concerns about environmental
quality have led to the introduction of alternative disposal methods such
as the use as nutrient source for plants and as soil conditioners. Municipal
Waste Compost (MWC) provides an input of readily available plant nutrients,
stimulates microbial activity and contributes to maintaining of nutrient
and organic matter pools. The fertilizer value of MWC can be significant
but varies considerably depending on origin and processing prior to application
(Peterson et al., 2003). Sewage sludge composting is being increasingly
considered by many municipalities throughout the world because it has
several advantages over other disposal strategies. Additionally, the application
of composts to agricultural soils has many advantages which include providing
a whole array of nutrients to the soil (Gonzalez et al., 1992;
Sikora and Enkiri, 1999; He et al., 2000; Chodak et al.,
2001; Tejada et al., 2001).
The primary plant nutrient associated with sewage sludge is nitrogen
(N), however, sludges also contribute significant amounts of other macro
and micronutrients (Shober et al., 2003; Sims, 1990; Warman, 1986;
Zebarth et al., 2000). Boron, Fe, Mn, Cu, Zn, Mo and Cl are plant
essential micronutrients that are present in sewage sludge and sewage
sludge compost, yet some of these elements can also be toxic to plants
and animals when applied in excessive amounts (Warman and Termeer, 2005).
Many researchers have studied the effects of applied sewage sludge on
the levels of Cu and/or Zn in corn (Cajuste et al., 2000; Cripps
et al., 1992; Reddy et al., 1989). Along with Cu and Zn,
other workers have also evaluated Mn (Kiemnec et al., 1990; Lutrick
et al., 1982; Ramachandran and De Souza, 1998) and Mn and Fe (Hernandez
et al., 1991; Juste and Solda, 1985). Soon et al. (1980),
Warman (1986) and McBride and Evans (2002) also reported on Mn and Tiffany
et al. (2000) and Zebarth et al. (2000) also evaluated Fe
and Mn. Investigations of plant Cu and Zn following sludge compost applications
are relatively recent (Sims, 1990; Pichtel and Anderson, 1997; Warman
and Termeer, 1996; Wen et al., 1999), with fewer studies involving
corn (Cajuste et al., 2000) or forage compared to other crops.
The application of sewage sludge to agricultural land usually increases
the Cu and Zn concentrations of amended plants (Warman and Termeer, 2005).
The National Research Council (1980) has set the domestic animal mineral
tolerance level for Cu at 100 mg Cu kg-1 feed (except for sheep,
which is set at 25 mg Cu kg-1 feed) and for Zn at 300 mg Zn
kg-1 feed (except for Japanese quail, which is set at 125 mg
Zn kg-1 feed). Based on a review of the literature, Chang et
al. (1992) described a methodology for establishing phytotoxicity
criteria for Cr, Cu, Ni and Zn from agricultural land application of municipal
sewage sludges; they found that the Cu concentration in corn did not rise
above the 25 mg Cu kg-1 feed quality limit even when 1500 kg
Cu ha-1 was applied. However, the Zn content in corn leaf tissue
can exceed the 300 Mg kg-1 limit if high amounts of Zn are
applied by sewage sludge (Hinesly et al., 1984; Lutrick et al.,
1982). Chang et al. (1992) recommended that up to 3500 kg Zn could
be applied per hectare without adverse effects on plant growth; however,
there has been strong criticism of these recommendations by Schmidt (1997)
and others. Several researchers have shown that the Cu and Zn applied
in sewage sludge remained in the plow layer of the soil and does not leach
downward (Cripps et al., 1992). Kanal and Kuldkepp (1993) compared
eight organic treatments including three composts, with and without additional
NPK. Their study revealed that some organic amendments were better than
others and that additional NPK from chemical fertilizer improved overall
potato production. In another experiment, application of sludge amendment
(80, 130 and 160 Mg ha-1) increased the average dry weight
of sunflower plants (Helianthus annus L.) compared to unamended
soil (Morera et al., 2002). Yield of maize and barley also enhanced
as a result of sludge application (Hernandez et al., 1991). Use
of sewage sludge resulted in more robust plants of Linium usitatissimum
with faster development and greater biomass production (Tsakou et al.,
2002). In contrast, Moreno et al. (1997) reported negative effects
of sludge amendment on yield of Lactuca sativa.
The objectives of this study was to evaluate the effect of organic fertilizers
enriched with chemical fertilizer on grain yield of soybean and Mn, Cu,
Zn and Fe accumulation in soybean seed and leaves.
MATERIALS AND METHODS
General description: The experimental site was
located in the North of Iran, in the country of Sari. Soil and organic
amendments characteristics at the beginning of the experiment are shown
in Table 1 and 2. These soils originated
from silty and clay mineral parent material. The soils were sampled on
10 June 2006 between soybean rows, from the 0 to 30 cm layer. According
to Table 2, the highest K, Cu and Zn content were observed
in MSW compost.
Experimental design and procedures: The experiment was
carried out as split plot based on randomized complete block design with
two factors and three replications. Main plots were included 8 fertilizer
treatments consisted of one rate of chemical fertilizer (potassium sulphate
and triple super phosphate (75 kg ha-1) based on soil test
recommendations and two rates (20 and 40 Mg ha-1) of MSW compost,
SS and VC enriched with half chemical
||Chemical properties of the soil used in the study (g
kg-1 dry soil)
|aData refer to dry matter (105 ºC) of surface soil
(0–30 cm) sieved at < 2 mm.
||Chemical properties of the municipal solid waste (MSW)
compost, vermicompost (VC), sewage sludge (SS) used in the study
fertilizer needed by soybean based on soil test recommendation.
Sub plots consisted of three genotypes of soybean (032, 033 promising
lines and JK cultivar). All of the MSW compost, SS, VC and chemical fertilizer
were broadcast by hand and immediately mixed into the soil using a rototiller
a day before planting. Plot sizes for crop were 3.0X4.0 m with 5 rows
of crops per plot. Space between row and within row was 50 and 6 cm (providing
250 plants per plot), respectively. Sowing in 10 May was done by hand
after tilling with a rototiller several times to a depth of about 30 cm.
Weeds were controlled by hand weeding using a hoe whenever necessary.
Plant sampling and laboratory analysis: Soybean grain
yield was determined by combining a swath in 1X2 m spacing in the center
of each split plot. Grain samples were then oven dried (60°C for 48
h) to calculate yield on a dry-matter basis. At flowering initiation,
leaf samples were prepared from eight whole plants from each plot. Vegetative
samples then were transported in a cool box to the laboratory the same
day of sampling washed with distilled water, put in paper bags and oven
dried at 65°C for at least 2 days. Once dry, the plant parts were
weighed to determine total dry matter. Also grains were hand- harvested
in harvest date and dried at 65°C for at least 48 h. Metal contents
were determined by Atomic Absorption Spectrometry after calcinations of
the sample (0.5 g) at 550°C and solution of the ashes in concentrated
HCl (38%) and further dilution to 50 cm3. Tissue N was determined
by digestion in H2SO4-H2O2.
Digests were distilled with 10 M NaOH into boric acid and quantitatively
titrated with HCl. The digested samples were analyzed micro element (Mn,
Cu, Zn, Fe) and Atomic absorption (Spectra aa-Australia).
Statistical analysis: All data were subjected to Analysis
of Variance (ANOVA) using the PROC GLM function of SAS statistical program
(SAS, 1997). When there was a significant (p<0.05) treatment effect
means were compared using Duncan`s Multiple Range Test (DMRT).
RESULTS AND DISCUSSION
Grain yield: Results showed that 40 Mg ha-1
of sewage sludge enriched with chemical fertilizers (T6) produced
significantly higher (p<0.05) grain yield than the other treatments
also (averaged 3.8 t ha-1), the 20 Mg ha-1 of sewage
sludge enriched with chemical fertilizers treatment produced higher crop
yield compared to the chemical fertilizers treatment, while no significant
differences were detected among both the levels of vermicompost treatment
enriched with chemical fertilizers and chemical fertilizers alone (data
not shown). Several studies revealed that an increase in soybean yield
in three years with compost could be attribute to more favorable plant
N status from N mineralization because several studies have presented
inconsistent soybean yield responses from in-season N application (Wesley
et al., 1998; Freeborn et al., 2001). While Warman and Havard
(1996) reported that in two out of 3 years, conventionally grown (NPK
fertilized) potatoes yielded higher than organically grown (compost fertilized)
potatoes. With regard to different soybean cultivars, the JK and 033 cultivars
produced significantly higher grain yields compared to 032 (Table
||Mean comparison of study traits in different fertilizer
amounts and cultivars
|*Means with similar letter(s) are not significantly
different at 5% level of probability (DMRT),T1: 20 Mg ha-1
municipal compost+50% chemical fertilizer, T2: 20
Mg ha-1 vermicompost+50% chemical fertilizer, T3:
20 Mg ha-1 sewage sludge+50% chemical fertilizer, T4:
40 Mg ha-1 municipal compost+50% chemical fertilizer, T5:
40 Mg ha-1 vermicompost+50% chemical fertilizer, T6:
40 Mg ha-1 sewage sludge+50% chemical fertilizer, T7:
Chemical fertilizer (Potassium sulphate, Triple superphosphate (75
kg ha-1) and T8: Control (without chemical or
organic fertilizer), ns: not significant
||Interaction effects means comparison of fertilizer and
cultivar on study traits
|Means with similar letter(s) are not significantly different
at 5% level of probability (DMRT), T: Different fertilizer treatments
V1: JK, V2: 032 and V3: 033
Seed Mn: All of organic fertilizers enriched with chemical
fertilizer except 20 Mg ha-1 municipal solid waste treatment
increased the Mn content of the soybean seeds. Among genotypes Mn concentrations
in seeds were highest in the 033 cultivar (Table 3).
The application of AES to the corn plots resulted in higher tissue Mn
compared to synthetic fertilizer or compost applications. Since Mn availability
is strongly affected by the soil oxidation-reduction potential, the response
may be the combined effect of high Mn content in the Aerobically-digested
Sludge (AES) and low oxygen conditions in the sewage sludge clods which
lowered the soil redox potential, causing an increase in stover Mn (Warman
and Termeer, 2005).
Leaf Mn: Application of T4 (40 Mg ha-1
MWS+50% fertilizer) and T6 (40 Mg ha-1 SS+50%
fertilizer) to the soybean plots increased the leaf Mn concentration compared
to chemical fertilizer and other organic fertilizers plots. Mn concentrations
in soybean leaves were highest in 033 and 032 cultivars (Table
3). The Mn content of the soybean leaves was highest in 032 cultivar
when the 40 Mg ha-1 sewage sludge enriched with 50% chemical
fertilizer were applied (Table 4). Warman and Havard
(1998) revealed that Phosphorus, Mg and Na were higher in the tubers of
organically grown potatoes and B and Fe were higher in the leaves; tuber
Mn and leaf N and Mg were higher in conventionally grown potato leaves.
As indicated above, tuber Mn and leaf Fe were the only micronutrients
statistically influenced by treatments; however, leaf Mn and Cu were always
higher in the conventionally grown potatoes although the treatments had
no effect on soil Mn and soil Cu was higher in the compost-amended soil.
Mn concentrations in shoots and roots of plants, however, were lower when
grown in sewage sludge amended soil as compared to those grown in un amended
ones (Singh and Agrawal, 2007).
Seed Cu: Results in Table 3 showed
that in all of organic fertilizers treatments enriched with chemical fertilizer
and control the Cu content of the soybean seeds was highest than chemical
fertilizer. Cu concentrations in soybean seeds was highest in 033 cultivar
compared to other genotypes (Table 3). The Anaerobic
septic sludge (ANS) used had a copper content of 848 mg Cu kg-1,
which was the highest copper content, all the amendments Septic sludge
applications provided 13.7 kg Cu ha-1 for the two years, well
below the NSDEL guideline of 150 kg ha-1; however, this application
still increased the grass forage Cu concentration. The sludge compost
applied had copper content of 238 mg Cu kg-1, but the applications
did not increase the Cu concentrations in either the grass forage or corn
tissue. The Cu content of the AES amended corn stover was significantly
greater than the compost and fertilizer amended corn in 1994, but was
not significantly different possibly due to high replicate variability
(Warman and Termeer, 2005).
Leaf Cu: The highest leaf Cu content were observed in
the 20, 40 Mg ha-1 SS and the 40 Mg ha-1 MWS in
combination with 50% chemical fertilizer treatments (Table
3). Soon et al. (1980) reported small increases in the Cu content
of bromegrass and corn grain following five years of sewage sludge applications
of as high as 31 kg Cu ha-1, while Kiemnec et al. (1990)
recorded only modest increases in sweet corn leaf and grain Cu content
after seven years of sewage sludge applications of as high as 62 kg Cu
ha-1 to a silt loam soil. Cu concentrations in soybean leaves
were highest in 033 line (Table 3). Also, the Cu content
of the soybean leaves was highest in 032 cultivar when the 40 Mg ha-1
municipal solid waste compost and sewage sludge enriched with 50% chemical
fertilizer were applied (Table 4).
Seed Zn: All of organic fertilizers enriched with chemical
fertilizer except 20 Mg ha-1 VC applications produced higher
seed Zn content compared to the chemical fertilizer and Control at three
the soybean cultivars. Among cultivars, the seed Zn concentrations were
highest in 033 line (Table 3). Applications of both
ANS and compost increased zinc concentrations in the grass forage tissue,
but the increase was greater from the ANS, which is related to its total
Zn content (Warman and Termeer, 2005).
Leaf Zn: The Zn content of the soybean leaves was highest
in the 40 Mg ha-1 municipal solid waste compost and sewage
sludge enriched with chemical fertilizer plots (averaged 62.6 and 67.6
mg kg-1 dry weight, respectively). Although the long term studies
of Soon et al. (1980) and Kiemnec et al. (1990) indicated
relatively small increases in corn Zn content, very high Zn applications
in sewage sludge can increase tissue Zn above 300 mg Zn kg-1
feed (Warman and Termeer, 2005). Zn concentrations in soybean leaves were
highest in 033 line (Table 3). Heavy metal (Zn, Ni,
Cd and Cu) accumulation in plant tissues was reported in plants grown
on sludge-amended soil (Moreno et al., 1997). Zn, Pb, Cd, Ni, Cr
and Cu concentrations in shoots and roots of plants grown in
sewage sludge-amended soils were significantly higher as compared to
those in unamended soil. Ni, Cd, Pb and Cr concentrations in shoot were
higher at 40% than 20% Sewage Sludge Amendment (SSA), whereas Cu and Zn
showed a reverse trend of higher concentration at 20% SSA. Cd, Ni, Zn,
Cr and Cu concentrations in roots were significantly higher in plants
grown at 40% as compared to 20% SSA, however, Pb concentration was higher
at 20% then 40% SSA (Singh and Agrawal, 2007). Normally the Zn content
increases more substantially than the Cu content. The factors that affect
the bioavailability of an element include soil pH, plant species and their
cultivars, growth stage, biosolid source, soil conditions and the chemistry
of the element (Warman and Termeer, 2005).
Seed Fe: The Fe content of the soybean seeds was higher in organic
treatment plots compared to control. The highest Fe content in seed of
soybean cultivars belonged to 033 line (Table 3). Although
AES and the compost made from it have a high concentration of iron and
considerable amounts of Fe were applied by the organic amendments to the
forage and corn plots, only the ANS had much of an effect on tissue Fe
concentrations (Warman and Termeer, 2005).
Leaf Fe: The 40 Mg ha-1 MSW enriched with chemical
fertilizer caused the highest concentrations of Fe in the plant leaves
compared to other treatments. The highest Fe content in seed of soybean
cultivars was observed in JK cultivar (Table 3). The
result of ANOVA showed that interaction effects of fertilizer and cultivar
had significant differences on Fe content in soybean leaves so that the
highest amount of iron was obtained when the 40 Mg ha-1 municipal
compost enriched with chemical fertilizer for JK cultivar was used. Higher
amounts of Fe, Cu and Zn were absorbed in maize and barley grown on sludge-amended
soil than those grown on the unamended ones (Hernandez et al.,
1991). There was a significant correlation between grain yield
soybean and Cu (r = 0.25*), seed Fe (r = 0.28*), Cu (r = 0.36**), Zn (r
= 0.44**) and leaf Fe (r = 0.27*) (Table 5).
In conclusion, we observed that a mixture of 40 Mg ha-1
sewage sludge and inorganic fertilizers produce higher yields than other
fertilizer treatments. The 40 Mg ha-1 of sewage sludge enriched
with half chemical fertilizer increased the grain yield and all of seed
micronutrients concentration compared to other fertilizer treatments.
Also the 40 of municipal waste compost enriched with half chemical fertilizer
increased the all of leaf micronutrients concentration compared to other
fertilizers. Therefore, based on the results of the current experiment,
organic fertilizers which enriched with chemical fertilizer can be used
in place of inorganic fertilizer alone to supply Mn, Cu, Fe and Zn of
soybean grown. This can help recycle plant nutrients and thus reduce environmental
degradation associated with the disposal of MSW, SS and VC to landfills.
The result of mean comparisons showed that interaction effects of fertilizer
and cultivar had significant differences on Mn, Cu and Fe content in soybean
leaves so that most Cu amounts were observed in 032 line and in 40 Mg
ha-1 enriched SS and MSW compost enriched with half chemical
fertilizer. Also the highest leaf Fe was obtained when the 40 Mg ha-1
MSW compost enriched with half chemical fertilizer for JK cultivar was
used. The highest leaf Mn was obtained when the 40 Mg ha-1
SS enriched with half chemical fertilizer for 032 line was used. Fe and
Cu content in leaf and seed and Zn content in leaf had a positive and
significant correlation with grain yield.
The authors would like to thank the University of Mazandaran for
a research grant in support of this project.
1: Brebbia, C.A., S. Kungolos, V. Popov and H. Itoh, 2004. Waste Management and the Environment II. WIT Press, Southampton, Boston, pp: 696.
2: Cajuste, L.J., J. Cruz-Diaz and C. Garcia-Osorio, 2000. Extraction of heavy metals from contaminated soils: Sequential extraction in surface soils and their relationships to DTPA extractable metals and metal plant uptake. J. Environ. Sci. Health, 35: 1141-1152.
Direct Link |
3: Chang, A.C., T.C. Granato and A.L. Page, 1992. A methodology for establishing phyto-toxicity criteria for Cr, Cu, Ni and Zn in agricultural land application of municipal sewage sludges. J. Environ. Qual., 21: 521-536.
4: Chodak, M., W. Borken, B. Ludwig and F. Beese, 2001. Effect of temperature on the mineralization of C and N of fresh and mature compost in sandy material. J. Soil Sci. Plant Nutr., 164: 289-294.
Direct Link |
5: Cripps, R.W., S.K. Winfree and J.L. Reagan, 1992. Effects of sewage sludge application method on corn production. Commun. Soil Sci. Plant Anal., 23: 1705-1715.
CrossRef | Direct Link |
6: Freeborn, J.R., D.L. Holshouser, M.M. Alley, N.L. Powell and D.M. Orcutt, 2001. Soybean yield response to reproductive stage soil-applied nitrogen and foliar-applied boron. Agron. J., 93: 1200-1209.
Direct Link |
7: Gonzalez, J.L., I.C. Benitez, M.I. Perez and M. Medina, 1992. Pig slurry compost as wheat fertilizers. Bioresour. Technol., 40: 125-130.
8: He, Z.L., A.K. Alva, P. Yan, Y.C. Li, D.V. Calvert, P.J. Stoffella and D.J. Banks, 2000. Nitrogen mineralization and transformation from composts and biosolids during field incubation in a sandy soil. Soil Sci., 165: 161-169.
Direct Link |
9: Hernandez, T., J.I. Moreno and F. Costa, 1991. Influence of sewage sludge application on crop yields and heavy metal availability. J. Soil Sci. Plant Nutr., 37: 201-210.
Direct Link |
10: Hinesly, T.D., K.E. Redborg, R.I. Pitz and E.L. Ziegler, 1984. Cadmium and zinc uptake by corn (Zea mays L.) with repeated applications of sewage sludge. J. Agric. Food Chem., 32: 155-163.
11: Juste, C. and P. Solda, 1985. Heavy Metal Availability in Long Term Experiments. In: Factors Influencing Sludge Utilization Practices in Europe, Davis, R.D., H. Haeni and P.L. Hermite (Eds.). Elsevier Applied Science Publishers, London, pp: 12-23.
12: Kanal, A. and P. Kuldkepp, 1993. Direct and residual effect of different organic fertilizers on potato and cereals. J. Agron. Crop Sci., 171: 185-195.
13: Kaushik, P. and V.K. Garg, 2003. Vermicomposting of mixed solid textile mill sludge and cow dung with the epigeic earthworm Eisenia foetida. Bioresour. Technol., 90: 311-316.
Direct Link |
14: Kiemnec, G.L., D.D. Jr. Hemphill, M. Hickey, T.L. Jackson and V.V. Volk, 1990. Sweet corn yield and tissue metal concentration after seven years of sewage sludge applications. J. Agric. Prod., 3: 232-237.
15: Lutrick, M.C., W.K. Robertson and J.A. Cornell, 1982. Heavy applications of liquid-digested sludge on three Utisols: II. Effect on mineral uptake and crop yield. J. Environ. Qual., 11: 283-287.
16: Magdoff, F. and R.R. Weil, 2004. Soil Organic Matter in Sustainable Agriculture. CRC Press, Boca Raton, pp: 398.
17: McBride, M.B. and L.J. Evans, 2002. Trace metal extractability in soils and uptake by bromegrass 20 years after sewage sludge application. Can. J. Soil Sci., 82: 323-333.
Direct Link |
18: Moreno, J.L., C. Garcia, T. Hernandez and M. Ayuso, 1997. Application of composted sewage sludges contaminated with heavy metals to an agricultural soil: Effect on lettuce growth. J. Soil Sci. Plant Nutr., 4: 565-573.
19: Morera, M.T., J. Echeverria and J. Garrido, 2002. Bioavailability of heavy metals in soils amended with sewage sludge. Can. J. Soil Sci., 82: 433-438.
Direct Link |
20: NRC., 1980. Mineral Tolerance of Domestic Animals. National Academy of Sciences, Washington, DC., USA., Pages: 557.
21: Peterson, S.O., K. Henriksen, G.K. Mortensen, P.H. Krogh and K.K. Brandt et al., 2003. Recycling of sewage sludge and household compost to arable land: Fate and effects of organic contaminants and impact on soil fertility. Soil Tillage Res., 72: 139-152.
Direct Link |
22: Pichtel, J. and M. Anderson, 1997. Trace metal bioavailability in municipal solid waste and sewage sludge composts. Bioresour. Technol., 60: 223-229.
23: Ramachandran, V. and T.J. De Souza, 1998. Plant uptake of cadmium, zinc and manganese in soils amended with sewage sludge and city compost. Bull. Environ. Contam. Toxicol., 61: 347-354.
24: Reddy, M.R., D. Lameck and M.E. Rezania, 1989. Uptake and distribution of copper and zinc by soybean and corn from soil treated with sewage sludge. Plant Soil, 113: 271-274.
25: Rees, R.M., B.C. Ball, C.A. Watson and C.D. Campbell, 2001. Sustainable Management of Soil Organic Matter. CAB International, Oxfordshire, UK., pp: 464.
26: SAS Institute. 1995. SAS User's Guide: Statistics. Version 7, SAS Institute, Cary, NC.
27: Schmidt, J.P., 1997. Understanding phytotoxicity thresholds for trace elements in land-applied sewage sludge. J. Environ. Qual., 26: 4-10.
CrossRef | Direct Link |
28: Shober, A.L., R.C. Stehouwer and K.E. Macneal, 2003. On-farm assessment of biosolids effects on soil and crop tissue quality. J. Environ. Qual., 32: 1873-1880.
PubMed | Direct Link |
29: Sikora, L.J. and N.K. Enkiri, 1999. Growth of tall fescue in compost/fertilizer blends. Soil Sci., 56: 125-137.
30: Sims, J.T., 1990. Nitrogen mineralization and elemental availability in soils amended with composted sewage sludge. J. Environ. Qual., 19: 669-675.
31: Singh, R.P. and M. Agrawal, 2007. Effects of sewage sludge amendment on heavy metal accumulation and consequent responses of Beta vulgaris plants. Chemosphere, 67: 2229-2240.
CrossRef | Direct Link |
32: Soon, Y.K., T.E. Bates and J.R. Moyer, 1980. Land application of chemically treated sewage sludge. III. Effects on soil and plant heavy metal content. J. Environ. Qual., 9: 497-504.
33: Tejada, M., M.M. Dobao, C. Benitez and J.L. Gonzalez, 2001. Study of composting of cotton residues. Bioresour. Technol., 79: 199-202.
Direct Link |
34: Tiffany, M.E., L.R. McDowell, G.A. O’Connor, H. Nguyen, F.G. Martin, N.S. Wilkinson and E.C. Cardoso, 2000. Effects of pasture applied sewage sludge on forage and soil concentrations over a grazing season in North Florida. II. Microminerals. Commun. Soil Sci. Plant Anal., 31: 215-227.
35: Tsakou, A., M. Roulia and N.S. Christodoulakis, 2002. Growth of flax plants (Linum usitatissimum) as affected by water and sludge from a sewage treatment plant. Bull. Environ. Contam. Toxicol., 68: 56-63.
Direct Link |
36: Warman, P.R., 1986. Effects of fertilizer, pig manure and sewage sludge on timothy and soils. J. Environ. Qual., 15: 95-100.
37: Warman, P.R. and K.A. Havard, 1996. Yield, vitamin and mineral content of four vegetables grown with either composted manure or conventional fertilizer. J. Vegetable Crop Prod., 2: 13-25.
38: Warman, P.R. and W.C. Termeer, 1996. Composting and evaluation of racetrack manure, grass clippings and sewage sludge. Bioresour. Technol., 55: 95-101.
39: Warman, P.R. and K.A. Havard, 1998. Yield, vitamin and mineral contents of organically and conventionally grown potatoes and sweet corn. Agric. Ecosyst. Environ., 68: 207-216.
40: Warman, P.R. and W.C. Termeer, 2005. Evaluation of sewage sludge, septic waste and sludge compost applications to corn and forage: Ca, Mg, S, Fe, Mn, Cu, Zn and B content of crops and soils. Bioresour. Technol., 96: 1029-1038.
Direct Link |
41: Wen, G., T.E. Bates, R.P. Voroney, J.P. Winter and M.P. Schellenberg, 1999. Influence of application of sewage sludges and sludge and manure composts on plant Ca and Mg concentration and soil extractability in field experiments. Nutr. Cycl. Agroecosyst., 55: 51-61.
42: Wesley, T.L., R.E. Lamond, V.L. Martin and S.R. Duncan, 1998. Effects of late-season nitrogen fertilizer on irrigated soybean yield and composition. J. Agric. Prod., 11: 331-336.
43: Zebarth, B.J., R. Mc Dougall, G. Neilsen and D. Neilsen, 2000. Availability of nitrogen from municipal biosolids for dryland forage grass. Can. J. Plant Sci., 80: 575-582.
Direct Link |