Effects of Humic Substances on Plant Growth and Mineral Nutrients Uptake of Wheat (Triticum durum cv. Salihli) Under Conditions of Salinity
Baris Bulent Asik,
Murat Ali Turan,
Ali Vahap Katkat
The effects of foliar and soil application of humic substances on plant growth and some nutrient elements uptake of wheat (Triticum durum Salihli) grown on various salt concentrations were examined. Sodium chloride was added to soil to obtain 15 and 60 mM saline conditions. The solid humus was applied to the soil one month before planting and the liquid humic acid was sprayed twice on the leaves on day 20 and 35 after seedling emergence. The application doses of solid humus were 0, 1 and 2 g kg-1 and the liquid humic acids were 0, 0.1 and 0.2%. Salinity negatively affected the growth of wheat; also decreased the dry weight and the uptake of nutrient elements except for Na and Mn. Soil application of humus increased the N uptake of wheat and foliar application of humic acid increased the uptake of P, K, Mg, Na, Cu and Zn. Although the effect of interaction between salt and soil humus application was found statistically significant, the interaction effect between salt and foliar humic acid treatment was not found significant. Under salt stress, the first doses of both soil and foliar application of humic substances increased the uptake of nutrients.
to cite this article:
Baris Bulent Asik, Murat Ali Turan, Hakan Celik and Ali Vahap Katkat, 2009. Effects of Humic Substances on Plant Growth and Mineral Nutrients Uptake of Wheat (Triticum durum cv. Salihli) Under Conditions of Salinity. Asian Journal of Crop Science, 1: 87-95.
Arid and semi-arid lands constitute approximately one third of the worlds
land surface (Arcihold, 1995) and salinity is the most
important problem in these regions for agricultural production. About 9.5 billion
ha of the worlds soil are saline, except for large areas of secondarily
salinized soil in cultivated land (Li et al., 2005).
Salinity of soil is also becoming a major agricultural problem throughout some
cereal growing basins in Turkey.
Plant growth and yield are reduced in salt-affected soil because of the excess
uptake of potentially toxic ions (Grattan and Grieve, 1999).
Soil salinity is characterized by high amounts of Na+, Mg2+,
Ca2+, Cl¯, HCO3¯, SO42¯
and B ions which have negative effects on plant growth. Generally, NaCl forms
salt stress in nature. The general effect of soil salinity on plants is called
a physiological drought effect. The high salt content decreases the osmotic
potential of soil water and consequently, this reduces the availability of soil
water for plants. Briefly, the uptake of water by plant roots is limited by
increased amounts of Na and Cl. Eventually, high salt concentrations in the
soil reduce the absorption of nutrients of the plants. Thus, this affects the
fertility of the soil negatively.
It has known that fertility of soil is also related to soil organic matter
content. Humic matter is the major component of soil organic matter. As organic
materials in the soil decay, macromolecules of a mixed aliphatic and aromatic
nature are formed (Chen and Aviad, 1990). The humic substances
in the soil have multiple effects (Sangeetha et al.,
2006). It may have both direct and indirect effects on plant growth (Chen
and Aviad, 1990). Indirect effects involve improvements of soil properties
such as aggregation, aeration, permeability, water holding capacity, micronutrient
transport and availability (Tan, 2003). Direct effects
are those, which require uptake of humic substances into the plant tissue resulting
in various biochemical effects (Chen and Aviad, 1990).
Chen and Aviad (1990) and Varanini
and Pinton (1995) summarized the effects of humic substances on plant growth
and mineral nutrition, pointing out the positive effects on seed germination,
seedling growth, root initiation, root growth, shoot development and the uptake
of macro and microelements. Consequently, the use of humic substances has often
been proposed as a method to improve crop production (Adani
et al., 1998).
The agricultural areas affected by salt need amendments such as determination
of the most suitable salt tolerant plant species (Abrol et
al., 1988) or application of the different substances in order to reduce
the effects of salinity (Lynch and Lauchli, 1985).
Kulikova et al. (2005) and Xudan
(1986) also pointed out that humic substances might show anti-stress effects
under abiotic stress (unfavorable temperature, pH, salinity, etc.) conditions.
Humic substances may enhance the uptake of nutrients and reduce the uptake of
some toxic elements. Therefore, it could be said that the application of humic
substances could improve plant growth under the conditions of salinity. However,
there are very few researches about humic acid application and its effect on
the conditions of salinity (Masciandaro et al., 2002).
In this study, the effects of salinity, foliar and soil applications of humic substances on growth, mineral nutrients uptake of wheat and the comparisons of the soil and foliar applications of humic acid treatments at NaCl levels were investigated.
MATERIALS AND METHODS
The soil used in this study was collected from 0-20 cm depth of the field located
in the Agricultural Research and Application Center of Uludag University. The
soil was classified as Vertisol (Typic haploxerert) according to Soil
Taxonomy and in the unit of Eutric Vertisol according to FAO/Unesco classification
systems (Aksoy et al., 2001).
Some physical and chemical properties of the soil were analyzed; the texture
was determined with the hydrometer method (Tan, 2005).
pH and EC were measured in a 1:2.5 water extract, lime was determined according
to Richards (1954). Organic matter content was analyzed
according to the modified Walkley-Black method (Nelson and
Sommers, 1982). Total nitrogen was determined by Buchi K-437 / K-350 digestion/distillation
unit according to the Kjeldahl method (Bremmer, 1965). Available P was determined
by Shimadzu UV 1208 model spectrophotometer according to the Watanabe
and Olsen (1965). Exchangeable cations (Na, K, Ca and Mg) were extracted
with ammonium acetate at pH 7.0 (Jackson, 1958) and determined
by Eppendorf Elex 6361 model Flame photometer. Available Fe, Cu, Zn, Mn were
extracted with DTPA (0.005M DTPA+0.01M CaCl2+0.1M TEA pH 7.3) (Lindsay
and Norwell, 1978) and determined by Philips PU9200x model Atomic Absorption
Spectrophotometer. Some chemical and physical properties of the soil used in
the research are shown in Table 1. The soil used in the experiment
had sandy clay and neutral pH. It was low in terms of lime, salt and organic
matter contents. The soil was not adequate in terms of nitrogen, phosphorus
The experiment was conducted in a greenhouse in completely randomized factorial
design with three soil application doses of humus 0 (control) 1 and 2 g kg-1
three foliar application doses of humic acid (0, 0.1 and 0.2%) and three NaCl
doses 0 (control), 15 and 60 mM. Each application consists of three replications.
Soil applied humus was obtained from solid Deltahumus (65% w/w, pH 4.87, EC:
5.80 mS cm-1) and foliar applied humic acid was obtained from liquid
Deltahumat (humic acid: 12% w/v, pH 12.86, EC: 32.8 mS cm-1) derived
from leonardite which are the commercial products of Delta Chemicals Co.
Air-dried soil samples were passed through 4 mm sieve. For solid humus applications Deltahumus was put into a large bowl due to the application doses and the total weight of the soil was adjusted to 5 kg. The mixture was homogenized and put into polyethylene covered plastic pots. For foliar humic acid applications 5 kg of soil was put into polyethylene covered plastic pots. NaCl was added to the pots bought of soil and foliar treatments due to the application doses. The pots were exposed to 30 days of the incubation period. As a basal fertilizer, nitrogen (100 mg kg-1 as NH4NO3), phosphorus (80 mg kg-1), potassium (100 mg kg-1 as KH2PO4), zinc (0.5 mg kg-1 as ZnSO4) were applied to the pots before planting. Six durum wheat (Triticum durum) cultivar Salihli were grown in pots, which have 20 cm diameter and 18 cm depth. All pots was irrigated deionized water during with experiment. Deltahumat was sprayed twice in 5 L of deionized water, 20 and 35 days after seedling emergence as foliar treatment.
After two months vegetation period, plants were harvested, dried at 65°C,
dry weights were determined and plant samples were wet digested by using HNO3+HCIO4
(4:1) mixture. Nitrogen was determined by the Kjeldahl method (Bremmer,
1965) (Buchi K-437, K-350), P was determined by the Vanadomolybdophosphoric
method (Kacar and İnal, 2008) (Shimadzu UV 1208),
K, Na, Ca were determined by flame emission (Horneck and Hanson,
1998) (Ependorf Elex 6361) and Mg, Fe, Mn, Zn, Cu nutrients were determined
by atomic absorption spectrometry (Hanlon, 1998) (Philips
PU 9200x, Pye Unicam Ltd. GB).
All obtained data were subjected to statistical analysis. This analysis was
performed by using Tarist, a statistical software (Tarist,
1994) and mean values were grouped with LSD multiple range test (p<0.01
Effects of NaCl on Plant Growth and the Uptake of Plant Nutrients
According to the analysis results, application of 15 mM NaCl increased the
dry weight, N, P, K, Ca, Mg, Fe, Cu and Mn of the plants, but the amounts decreased
with the application of 60 mM NaCl (Table 2). Particularly
the effect of NaCl application at a dose of 60 mM had a negatively significant
effect (p<0.01) on dry weight and mineral elements uptake of wheat.
Effects of Soil Application of Humus on Plant Growth and the Uptake of Nutrients
Soil applications of humus had a significant effect on the uptake of N (p<0.05)
in wheat. When compared with the control treatment, the dry weight and mineral
nutrients uptake of wheat were found higher at both application doses of humus
|| Effect of NaCl to dry weight and plant nutrients uptake
|tdw: Total dry weight (g). **Significant at p<0.01. Values
with common letter(s) are not significantly different
The highest dry weight and the uptake of nutrients were obtained from 1 g
humus kg-1 treatment. Dry weight and the uptake of nutrients were
negatively affected from the application of 2 g humus kg-1.
Effects of Foliar Application of Humic Acid on Plant Growth and the Uptake
Foliar applications of humic acid had a significant effect on dry weight
and the uptake of mineral elements in wheat (Table 4). When
compared with the control treatment, the dry weight and the uptake of nutrients
were found higher in humic acid applications. Foliar application of humic acid
affected the uptake of P which was statistically significant in the uptake of
(p<0.01) Na, K, Cu and Zn (p<0.05) levels. However, its amounts were not
found statistically significant on other nutrients. The highest dry weight and
the uptake of nutrients were obtained from 0.1% dose of humic acid. Nevertheless,
dry weight and the uptake of nutrients were decreased in 0.2% dose of humic
acid, but the amounts except for Fe, Cu and Mn were found higher than control.
Interaction Effects Between Humic Substances and NaCl Treatment
Effects of foliar and soil application of humic substances on growth, the
uptake of mineral nutrients and their interactions between salt doses were represented
in Table 5. Interaction effect between soil humus and NaCl
treatment was found statistically significant in the Mn (p<0.01) Zn and Na
uptake (p<0.05) of wheat. The interactions in dry weight and the interaction
of the amount of N, P, K, Ca, Mg, Fe and Cu in wheat were found to be insignificant.
Although, the application of NaCl decreased the dry weight and the uptake of nutrients application of soil humus limited the decrease especially in 60 mM treatment of NaCl, it was examined that the effect of soil application of humus generally enhanced the uptake of plant nutrients especially in 60 mM NaCl treatment. This was seen when compared with the other applications (Table 5).
The interaction effect between the foliar application of humic acid and NaCl was not found statistically significant. Foliar application of humic acid treatment enhanced the dry weight and the uptake of mineral elements in NaCl treatments. However, the highest dry weight and the uptake of nutrients were obtained from 0.1% treatment of humic acid in NaCl treatments.
|| Effect of soil application of humic substance to dry weight
and plant nutrients uptake
|*p<0.05, tdw: Total dry weight (g ), ns: Not significant
|| Effect of foliar application of humic acid to dry weight
and plant nutrients uptake
|**p<0.01, *p<0.05, tdw: Total dry weight (g), ns: Not
|| Effect of soil and foliar application of humic substances
to plant nutrients uptake under NaCl salt conditions
|tdw: Total dry weight (g). Capital letter(s) for each row
and small letter(s) for each column for to compare the results
Little amounts of salt may cause a simulative effect on the growth and uptake
of nutrients, but it shows toxic effect when the concentration rises. Khan
et al. (2000) reported that the total dry weight accumulation of
plant was not inhibited at low salinities, but dry weight production was significantly
inhibited at high NaCl amounts. Kurban et al. (1999)
also pointed out that the optimum growth of plants increased at low salinity
but decreased at high salinity. The negative effect of salt on dry weight and
the uptake of mineral elements can be attributed to the lower osmotic potential
of the soil solution due to the increased concentration of NaCl. Many laboratory
and glasshouse studies have shown that salinity can reduce N accumulation in
plants (Alam, 1994), P concentrations (Navarro et al.,
2001) and the uptake of K in plants due to the competitive process by Na
(Lopez and Satti, 1996). High Na in soil solution also
has an antagonistic effect on the uptake of Ca and Mg (Bernstein,
1975). This is most likely caused by displacing Ca in membranes of root
cells (Yermiyahu et al., 1997). Furthermore,
the reduced the uptake of mineral has been observed in several species of plants
grown in saline conditions (Francois and Maas, 1999).
In saline soil, the solubility of micronutrient is particularly low and plants
grown in these soils often show deficiencies of this element (Page
et al., 1990).
Chen and Aviad (1990), Fagbenro and
Agboda (1993) and David et al. (1994) have
reported promoted growth and nutrient uptake of plant due to the addition of
humic substances. The plants take more mineral elements due to the better-developed
root systems. In addition, the stimulation of ion uptake in applications with
humic materials led many investigators to propose that these materials affect
membrane permeability (Zientara, 1983). It is related
to the surface activity of humic substances resulting from the presence of both
hydrophilic and hydrophobic sites (Chen and Schnitzer, 1978).
Therefore, the humic substances may interact with the phospholipids structures
of cell membranes and react as carriers of nutrients through them.
The features that were discussed were negatively affected with the application
of 2 g humus kg-1 level. This result might be related to levels of
application. On the other hand, the application of the very high dose of humic
acid is less effective (Lee and Bartlett, 1976). According
to several researches, results were changing due to the levels of treatment,
growing media and origin of humic substances (Chen and Aviad,
1990; Arancon et al., 2006).
There are a few researches on using humic substances as foliar application.
Cooper et al. (1998) applied creeping bent grass
in sand culture at rates of 100, 200 and 300 mg L-1 and they found
that the rate of application did not have any effect on plant growth. Fernandez
et al. (1996) pointed out that under field conditions, foliar application
of leonardite extracts stimulated shoot growth and promoted the accumulation
of K, B, Mg, Ca and Fe in leaves. However, when leaf N and leaf K values were
below the sufficiency range, the foliar application of humic substances was
ineffective to promote the accumulation of these nutrients in leaves. In a field
experiment Govindasmy and Chandrasekaran (1992) sprayed
humic acid extracted from lignite to sugarcane and they found that the addition
of humic acid improved sugar yield and nutrient concentration in leaf blades
and sheaths. Delfine et al. (2005) investigated
the effect of foliar application of N and humic acid on growth and yield of
durum wheat. Moreover, they specified that the foliar application of humic acid
caused a transitional production of plant dry mass with respect to unfertilized
control. In contrast to Delfine et al. (2005)
and Pavlikova et al. (1997) studied the effect
of potassium humate. Humic acid was applied by spray during the growth season
of cultivated crops at a dose of 20 mg mL-1. The yield of cultivated
crops was not affected significantly by the application of potassium humate
because of the high amounts of humic substances.
According to many researchers humic substances may enhance the uptake of some
nutrients, reduce the uptake of toxic elements and could improve plant response
to salinity. However, there are not many researches about humic acid application
and its effects on plant salinity tolerance. Liu (1998)
found out that the application of humic acid during salinity stress did not
increase the uptake of N, P, K and Ca. Also, in present study; foliar application
in 0.1% humic acid treatment increased the dry weight, N, P, K, Ca, Mg, Na,
Fe, Zn and Mn amounts in plants in 60 mM NaCl when compared with control and
0.2% humic acid treatments. Chavan and Karadge (1980)
also reported the increase of Mn contents in all the part of plant that have
been treated with salt.
Humic substances can ameliorate negative soil properties; improve the plant growth and uptake of nutrients. It may be used in case of the negative effect of salt that would inhibit the plant growth and the uptake of nutrient elements. Overall, we found out that the application doses are important for taking benefit from humic substances under salt conditions. Economical levels of application should be determinated and should not exceed 1 g humus kg-1 in soil and 0.1% in foliar.
This study was supported by the Research Fund of The University of Uludağ Project No. 2003/92 and The Scientific and Technical Research Council of Turkey (TOVAG 105 O 345). We also thank Mrs. Mine UZUN from English Language Studies, University of Wollongong, Australia, for her critical reading of the study.
1: Abrol, I.P., J.S.P. Yadav and F.I. Massuod, 1988. Salt affected soils and their management. Soil Resources, Management and Conservation Service, FAO Land and Water Development Division, FAO Soils Bulletin 39, Rome.
2: Adani, F., P. Genevini, P. Zaccheo and G. Zocchi, 1998. The effect of commercial humic acid on tomato plant growth and mineral nutrition. J. Plant Nutr., 21: 561-575.
CrossRef | Direct Link |
3: Aksoy, E., M.S. Dirim, Z. Tumsavas and G. Ozsoy, 2001. Formation of uludag university campus soils: Physical, chemical characteristics and classification. UU Research Projects Fond, Project No. 98/32, Bursa.
4: Alam, S.M., 1999. Nutrient by Plants Under Stress Conditions In: Handbook of Plant and Crop Stress, Pessarakli, M. (Ed.). CRC Press, USA., ISBN-10: 0824719484, pp: 285-313.
5: Arancon, N.Q., C.A. Edwards, S. Lee and R. Byrne, 2006. Effects of humic acids from vermicomposts on plant growth. Eur. J. Soil Biol., 42: S65-S69.
6: Arcihold, O.W., 1995. Ecology of World Vegetation. Chapman and Hall, London, ISBN: 0412443007, Pages: 510.
7: Bernstein, L., 1975. Effects of salinity and sodicity on plant growth. Ann. Rev. Phytopathol., 13: 295-312.
CrossRef | Direct Link |
8: Bremmer, J.M., 1982. Total Nitrogen. In: Methods of Soil Analysis, Part 2, Black, C.A. (Ed.). American Society Agriculture Inc., USA., pp: 1149-1178.
9: Chavan, P.D. and B.A. Karadge, 1980. Influence of salinity on mineral nutrition of peanut (Arachiz hypogea L.). Plant Soil, 54: 5-13.
10: Chen, Y. and M. Schnitzer, 1978. The surface tension of aqueous solutions of soil humic substances. Soil Sci., 125: 7-15.
Direct Link |
11: Chen, Y. and T. Aviad, 1990. Effect of Humic Substances on Plant Growth. In: Humic Substances in Soil and Crop Sciences: Selected Reading, MacCarthy, P., C.E. Clapp, R.L. Malcolm and P.R. Bloom (Eds). Soil Science Society America, Madison, WI., pp: 161-187.
12: Cooper, R.J., C. Liu and D.S. Fisher, 1998. Influence of humic substances on rooting and nutrient content of creeping bentgrass. Crop Sci., 38: 1639-1644.
Direct Link |
13: David, P.P., P.V. Nelson and D.C. Sanders, 1994. A humic acid improves growth of tomato seedling in solution culture. J. Plant Nutr., 17: 173-184.
CrossRef | Direct Link |
14: Delfine, S., R. Tognetti, E. Desiderio and A. Alvino, 2005. Effect of foliar application of N and humic acids on growth and yield of durum wheat. Agron. Sustainable Dev., 25: 183-191.
15: Fagbenro, J.A. and A.A. Agboola, 1993. Effect of different levels of humic acid on the growth and nutrient uptake of teak seedings. J. Plant Nutr., 16: 1465-1483.
16: Fernandez, R.E., M. Benlock, D. Barranco, A. Duenas and J.A.G. Ganan, 1996. Response of olive trees to foliar application of humic substances extracted from leonardite. Scientia Hortic., 66: 191-200.
17: Francois, L. and E.V. Maas, 1999. Crop response and Management of Salt-Affected Soils. In: Handbook of Plant and Crop Stress, Pessarakli, M. (Ed.). Marcel Dekker, USA., ISBN: 978-0-8247-1948-7, pp: 169-203.
18: Govindasmy, R. and S. Chandrasekaran, 1992. Effect of humic acids on the growth, yield and nutrient content of sugarcane. Sci. Total Environ., 117: 575-581.
19: Hanlon, E.A., 1998. Elemental Determination by Atomic Absorption Spectrophotometry. In: Handbook of Reference Methods for Plant Analysis, Karla, Y.P. (Ed). CRC Pres, USA., ISBN: 1-57444-124-8, pp: 157-164.
20: Horneck, D.A. and D. Hanson, 1998. Determination of Potassium and Sodium by Flame Emission Spectrophotometry. In: Handbook of Reference Methods for Plant Analysis, Karla, Y.P. (Ed.). CRC Press, USA., ISBN: 1-57444-124-8, pp: 157-164.
21: Jackson, M.L., 1958. Cation Exchange Capacity: Soil Chemical Analysis. Prentice-Hall, Inc., Englewood, pp: 59-67.
22: Kacar, B. and A. İnal, 2008. Plant Analysis. Nobel Publication, Ankara, ISBN: 978-605-395-036-3.
23: Khan, M.A., I.A. Ungar and A.M. Showalter, 2000. Effects of salinity on growth, water relations and ion accumulation of the subtropical perennial halophyte Atriplex griffthii var. Stocksii. Ann. Bot., 85: 225-232.
24: Kulikova, N.A., E.V. Stepanova and O.V. Koroleva, 2005. Mitigating Activity of Humic Substances: Direct Influence on Biota. In: Use of Humic Substances to Remediate Polluted Environments: From Theory to Practice, Perminova, I.V., K. Hatfield and N. Hertkorn (Eds.). Chapter 14, Springer, Netherlands, ISBN: 978-1-4020-3250-9, pp: 285-309.
25: Kurban, H., H. Saneoka, K. Nehira, R.Adilla, G.S. Premachandra and K. Fujita, 1999. Effect of salinity on growth, photosynthesis and mineral composition in leguminous plant Alhagi psedoalhagi (Bieb.). Soil Sci. Plant Nutr., 45: 851-862.
Direct Link |
26: Li, W., X. Liu, M.A. Khan and S. Yamaguchi, 2005. The effect of plant growth regulators, nitric oxide, nitrate, nitrite and light on the germination of dimorphic seeds of Suaeda salsa under saline conditions. J. Plant Res., 118: 207-214.
27: Lee, Y.S. and R.J. Bartlette, 1976. Stimulation of plant growth by humic substances. J. Am. Soil Sci. Soc., 40: 876-879.
Direct Link |
28: Lindsay, W.L. and W.A. Norvell, 1978. Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J., 42: 421-428.
CrossRef | Direct Link |
29: Liu, C., 1998. Effects of humic substances on creeping bentgrass growth and stress tolerance. Ph.D. Thesis, Philosophy Department of Crop Science, North Carolina State University.
30: Lopez, M.V. and S.M.E. Satti, 1996. Calcium and potassium-enhanced growth and yield of tomato under sodium chloride stress. Plant Sci., 114: 19-27.
CrossRef | Direct Link |
31: Lynch, J. and A. Lauchli, 1985. Salt stress disturbs the calcium nutrition of barley (Hordeum vulgare L.). New Phytol., 99: 345-354.
CrossRef | Direct Link |
32: Masciandaro, G., B. Ceccanti, V. Ronchi, S. Benedicto and L. Howard, 2002. Humic substances to reduce salt effect on plant germination and growth. Commun. Soil Sci. Plant Anal., 33: 365-378.
33: Navarro, J.M., M.A. Botella, A. Cerda and V. Martinez, 2001. Phosphorus uptake and translocation in salt-stressed melon plants. J. Plant Physiol., 158: 375-381.
34: Nelson, D.W. and L.E. Sommers, 1983. Total Carbon, Organic Carbon and Organic Matter. In: Methods of Soil Analysis, Part 2: Chemical and Microbiological Properties Page, A.L., R.H. Miller and D.R. Keeney (Eds.). 2nd Edn., ASA and SSSA, Madison, WI., USA., pp: 539-579.
35: Watanabe, F.S. and S.R. Olsen, 1965. Test of an ascorbic acid method for determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc. Am. J., 29: 677-678.
CrossRef | Direct Link |
36: Page, A.L., A.C. Chang and D.C. Adriano, 1990. Deficiencies and Toxicities of Trace Elements. In: Agricultural Salinity Assessment and Management, Tanji, K.K. (Ed.). ASCE, New York, ISBN: 0872627624, pp:138-160.
37: Pavlikova, D., P. Tlutos, J. Szakova and J. Balik, 1997. The effect of application of potassium humate on content of cadmium, zinc and arsenic in plants. Rostlinna Vyroba, 43: 481-486.
38: Richards, L.A., 1954. Diagnosis and improvement of saline and alkali soils. United State Department of Agriculture, Agriculture Handbook No. 60. United State Government Printing Office, Washington, DC., pp: 160.
39: Sangeetha, M., P. Singaram and R.D. Devi, 2006. Effect of lignite humic acid and fertilizers on the yield of onion and nutrient availability. Proceedings of 18th World Congress of Soil Science, July 9-15, Philadelphia, Pennsylvania, USA.
40: Tan, K.H., 2003. Humic Matter in Soil and Environment, Principles and Controversies. Marcel Dekker, Inc., Madison, New York, ISBN: 0-8247-4272-9.
41: Tan, K.H., 2005. Soil Sampling, Preparation and Analysis. 2nd Edn., Marcel Dekker Inc., New York, USA., ISBN-13: 9780849334993.
42: Tarist, 1994. General statistic, version 4.01. DOS, Serial No: A1001, Egean Forestry Research Inst.-Egean Uni. Agri. Faculty Field Crop Dept. Izmir.
43: Varanini, Z. and R. Pinton, 1995. Humic substances and plant nutrition. Prog. Bot., 56: 97-117.
44: Xudan, X., 1986. The effect of foliar application of fulvic acid on water use, nutrient uptake and wheat yield. Aust. J. Agric. Res., 37: 343-350.
45: Yermiyahu, U., S. Nir, G. Ben-Hayyim, U. Kafkafi and B. Kinraide, 1997. Root elongation in saline solution related to calcium binding to root cell plasma membranes. Plant Soil, 191: 67-76.
46: Zientara, M., 1983. Effect of sodium humate on membrane potential in internodal cells of Nitellopsis obtuse. Acta Societatis Botanicorum Poloniae, 52: 271-277.
47: Grattan, S.R. and C.M. Grieve, 1998. Salinity-mineral nutrient relations in horticultural crops. Scientia Horticulturae, 78: 127-157.
CrossRef | Direct Link |