**6. Micronutrients (Zn, Mn, Fe, Cu, B, Cl, Mo)**

#### **6.1 Zinc**

Soybean, maize and flax are the most susceptible field crops to Zn deficiency. It is often found on sandy soils low in organic matter, on high soil pH and calcaric soils, as well as on soils rich in available P. Cold and wet weather promoting Zn deficiency. N improving, while Fe and especially P, decreasing Zn uptake by plants. The first symptom of Zn deficiency in soybean is usually light green color developing between the veins on the older leaves. New young leaves will be abnormally small. Bronzing of the older leaves may occur. When the deficiency is severe, leaves may develop necrotic spots. Shortened internodes will give plants a stunted, rosetted appearance (Dahnke et al., 1992).

Zinc is essential element in metabolism of protein, carbohydrate and lipids. Zinc is compound of some enzymes (carboanhydrase, glutamat and malat-hydrogenase, alcalic phosphatase, proteinase, peptidase, etc.). Zinc has influences on auxine synthesis, intensity of respiration and uptake of Cu, Mn and especially P. Also Zn contributing to increase resistance to viruses diseases, drought and low temperature stress. Soil and leaf testing use in diagnosis of Zn status in plants. Also, important is P/Zn ratio.

Incorporation of anorganic Zn in form of ZnSO4.7H2O (2-22 kg Zn/ha) or organic Zn in chelate form (03-6.0 kg Zn/ha), as well as foliar fertilization (0.5% solution of zinc sulfate) could be use for corrections of Zn deficiencies.

Nutritional disorders were found in soybeans grown on Osijek calcareous eutrical cambisol. Growth retardation and chlorosis were accompanied with the alkaline or a neutral soil reaction. By the foliar diagnosis zinc deficiency was found. Zinc deficiency was promoted by the excess of phosphorus or iron/aluminum in plants while K deficiency was accompanied with the excess of magnesium uptake. For example, chlorotic soybean contained in means only 16 ppm Z in dry matter (into normal soybean 27 ppm Zn). At the same time, the P:Zn ratio was 239 (the normal levels are under 180), while Fe:Zn ratio was 34 (the normal levels are under 15). The analogous values for the normal soybeans were 150 and 7, respectively (Kovacevic et al., 1991). The higher soil pH and oversupplies of plant available P are factors promoting Zn deficiency in soybean (Table 9).


Table 9. Plant and soil status (eutric cambisol of Agricultural Institute Osijek): symptoms of Zn deficiency in soybean (Kovacevic et al., 1991)

interaction were not significant. The highest biological yield and most of the yield atributes

Soybean, maize and flax are the most susceptible field crops to Zn deficiency. It is often found on sandy soils low in organic matter, on high soil pH and calcaric soils, as well as on soils rich in available P. Cold and wet weather promoting Zn deficiency. N improving, while Fe and especially P, decreasing Zn uptake by plants. The first symptom of Zn deficiency in soybean is usually light green color developing between the veins on the older leaves. New young leaves will be abnormally small. Bronzing of the older leaves may occur. When the deficiency is severe, leaves may develop necrotic spots. Shortened internodes will

Zinc is essential element in metabolism of protein, carbohydrate and lipids. Zinc is compound of some enzymes (carboanhydrase, glutamat and malat-hydrogenase, alcalic phosphatase, proteinase, peptidase, etc.). Zinc has influences on auxine synthesis, intensity of respiration and uptake of Cu, Mn and especially P. Also Zn contributing to increase resistance to viruses diseases, drought and low temperature stress. Soil and leaf testing use

Incorporation of anorganic Zn in form of ZnSO4.7H2O (2-22 kg Zn/ha) or organic Zn in chelate form (03-6.0 kg Zn/ha), as well as foliar fertilization (0.5% solution of zinc sulfate)

Nutritional disorders were found in soybeans grown on Osijek calcareous eutrical cambisol. Growth retardation and chlorosis were accompanied with the alkaline or a neutral soil reaction. By the foliar diagnosis zinc deficiency was found. Zinc deficiency was promoted by the excess of phosphorus or iron/aluminum in plants while K deficiency was accompanied with the excess of magnesium uptake. For example, chlorotic soybean contained in means only 16 ppm Z in dry matter (into normal soybean 27 ppm Zn). At the same time, the P:Zn ratio was 239 (the normal levels are under 180), while Fe:Zn ratio was 34 (the normal levels are under 15). The analogous values for the normal soybeans were 150 and 7, respectively (Kovacevic et al., 1991). The higher soil pH and oversupplies of plant available P are factors promoting Zn deficiency in soybean

Percent in dry matter mg/kg in dry matter pH mg/100 g P K Ca Mg Zn Mn Fe Al H2O KCl P2O5 K2O

0.39 2.36 2.51 0.88 16.3 124 547 301 7.47 6.60 62.6 45.3

0.37 2.52 1.93 0.68 26.8 86 195 147 6.70 5.90 42.5 54.5 Table 9. Plant and soil status (eutric cambisol of Agricultural Institute Osijek): symptoms of

Soil (0-30 cm of depth); mg/100 g = AL-method

were obtained for the treatment combination of 30 kg S/ha and 1.0 kg B/ha.

**6. Micronutrients (Zn, Mn, Fe, Cu, B, Cl, Mo)**

give plants a stunted, rosetted appearance (Dahnke et al., 1992).

in diagnosis of Zn status in plants. Also, important is P/Zn ratio.

could be use for corrections of Zn deficiencies.

Soybean: The uppermost full-developed trifoliate leaf

Zn deficiency in soybean (Kovacevic et al., 1991)

Chlorotic and growth-retarded soybean (means of three samples)

Normal soybean (oasis at the same plot: means of five samples)

**6.1 Zinc**

(Table 9).

(June 6, 1990)


Response of soybean to fertilization: pods/plant (P/P), grain/pod (G/P) ,

Table 10. Effect of N, P; K and Zn application on yield attributes and grain yield of soybean (Singh et al., 2001)

Rose et al. (1981) were studied response of four soybean varieties (*Lee*, *Forrest*, *Bragg* and *Dodds*) to foliar zinc fertilization (ZnSO4.7H2O before flowering) at three sites in central and north-west New South Wales. At Narrabri one spray of 4 kg/ha gave a yield increase of 13 %. At Trangie and Breeza, two spray each of 4 kg/ha increased yield by 57 % and 208 %, respectively. Lee was the least responsive variety at each site and Dodds and Forrest the most responsive to applied zinc. Zinc fertilizer increased plant height, leaf-Zn, oil contents (at two sites) but decreased leaf-P. Leaf-P in untreated plots was indicative of varietal sensitivity to zinc deficiency both within and between sites.

Singh et al., (2001) tested twelve nutrient combinations comprising of three levels each of nitrogen ( 30, 60 and 90 kg N/ha), phosphorus (40, 60 and 80 kg P2O5/ha) two levels of potassium ( 30 and 60 kg K2O/ha) and a single level of zinc (25 kg Zn/ha) along with control. Zinc fertilization in combination with N, P and K significantly increased the growth attributes and grain yield of soybean, The highest number of pods per plant and grain yield were obtained with the joint application of N, P, K and Zn at the rates of 90, 80, 60, and 25 kg/ha, respectively (Table 10).

#### **6.2 Iron**

Leguminose plants have higher needs for Fe in comparison to cereals. Fe participating in numerous metabolic processes including protein synthesis. Under F deficiency conditions were found high levels of low-molecular N substances, especially amino acid arginine. Soybean is susceptible to Fe deficiency. Fe deficiency is a common yield limiting factor for soybean grown on high-pH, calcareous soils, as well as on some seasonally poorly drained soils. Cool and wet periods are promoting Fe deficiency. Iron may be unavailable for root absorption, not transported after absorption, or may not be utilized by the plant.

In Iowa and Minnesota, over ten million dollars in potential soybean production were lost annually due to iron chlorosis (Fleming et al., 1984). With the potential increase in alkalinity of Texas soils due to irrigation, reduced soybean production may become a problem. The problem could result from decreased yield per acre or from acreage with decreased productivity due to increased alkalinity. Iron deficiency is not easy or inexpensive to correct in the field. According to Gray et al. (1982) it would take five tons of sulfuric acid per acre to neutralize one per cent calcium carbonate in a 16.5 cm layer of soil.

Fe deficiency results in a characteristic interveinal chlorosis in new leaves and can cause substantial yield loss in soybean. In some years, developed during early growth stages and disappears as the plants mature. In more severe cases, chlorosis can persist throughout the entire season. There is wide variation in susceptibility to Fe deficiencies among soybean varieties.

Soybean in chlorotic areas had lower leaf chlorophyll concentrations, stunted growth, and poor nodule development relative to nonchlorotic plants. Also, compared to nonchlorotic areas, soil in chlorotic areas had greater soil moisture contents and concentrations of soluble salts and carbonates (Hansen et al., 2003).

Correcting Fe chlorosis often requires a combination of management practices including variety selection, application of Fe fertilizers with the seed (for example iron chelate Fe-EDDHA) or foliar treatment with 1 % solution of ferrous sulfate.

Franzen and Richardson (2000) tested soil factors affecting iron chlorosis of soybean. Total 12 sites of Red River valley of North Dakota and Minnesota were studied in the 1996-1998 period. Calcium carbonate equivalence and soluble salts were most often correlated with chlorosis symptoms.

Plant response to iron chlorosis varies between cultivars and environmental conditions (Coulombe et al., 1984; Gray et al., 1982). The reduction of iron at the root surface from Fe to Fe is an adaptive mechanism which iron efficient plants use to overcome iron deficiency. Soybean cultivars like Hawkeye have been shown to be rather effective in facilitating iron uptake by this method (Brown & Jones, 1976). Iron uptake is (1) as iron in association with chelate molecules and (2) as ionic iron after chelate splitting. Iron efficient plants have a much increased rate of iron uptake after chelate splitting during iron deficiency chlorosis (IDC)-induced stress; iron inefficient plants do not (Romheld & Marschner, 1981). Iron efficient and iron inefficient plants reportedly are distinguishable in terms of extent of iron uptake as a function of phosphorus content in the soil. Chaney & Coulombe (1982) reported that increased phosphorus inhibited the increase in iron uptake of inefficient types and slightly reduced iron uptake of efficient types.

Goos & Johnson (2003) found considerable differences of resistance of soybean varieties to iron clorosis. (Table 11) Growing of more tolerant varieties is solution for alleviation of nutritional problems induced by iron deficiency.


Table 11. Chlorosis scores of soybean varieties in Minnesota 2003 (Goos & Johnson, 2003): score 1.0 = no chlorosis, 5 = most severe chlorosis (choice 20 extremely of 104 tested genotypes)

Fe deficiency results in a characteristic interveinal chlorosis in new leaves and can cause substantial yield loss in soybean. In some years, developed during early growth stages and disappears as the plants mature. In more severe cases, chlorosis can persist throughout the entire season. There is wide variation in susceptibility to Fe deficiencies among soybean

Soybean in chlorotic areas had lower leaf chlorophyll concentrations, stunted growth, and poor nodule development relative to nonchlorotic plants. Also, compared to nonchlorotic areas, soil in chlorotic areas had greater soil moisture contents and concentrations of soluble

Correcting Fe chlorosis often requires a combination of management practices including variety selection, application of Fe fertilizers with the seed (for example iron chelate Fe-

Franzen and Richardson (2000) tested soil factors affecting iron chlorosis of soybean. Total 12 sites of Red River valley of North Dakota and Minnesota were studied in the 1996-1998 period. Calcium carbonate equivalence and soluble salts were most often correlated with

Plant response to iron chlorosis varies between cultivars and environmental conditions (Coulombe et al., 1984; Gray et al., 1982). The reduction of iron at the root surface from Fe to Fe is an adaptive mechanism which iron efficient plants use to overcome iron deficiency. Soybean cultivars like Hawkeye have been shown to be rather effective in facilitating iron uptake by this method (Brown & Jones, 1976). Iron uptake is (1) as iron in association with chelate molecules and (2) as ionic iron after chelate splitting. Iron efficient plants have a much increased rate of iron uptake after chelate splitting during iron deficiency chlorosis (IDC)-induced stress; iron inefficient plants do not (Romheld & Marschner, 1981). Iron efficient and iron inefficient plants reportedly are distinguishable in terms of extent of iron uptake as a function of phosphorus content in the soil. Chaney & Coulombe (1982) reported that increased phosphorus inhibited the increase in iron uptake of inefficient types and

Goos & Johnson (2003) found considerable differences of resistance of soybean varieties to iron clorosis. (Table 11) Growing of more tolerant varieties is solution for alleviation of

Variety Originator CS Variety Originator CS Trail N.D. AES 1.7 IA 2042 Iowa AES 3.7 Danatto N.D. AES 2.0 IA 2041 Iowa AES 3.7 MN 0201 Minn. AES 2.0 MN 1103SP Minn. AES 3.7 92 M10 Pioneer 2.0 MN 101SP Minn. AES 3.7 IA 1005 Iowa AES 2.0 Minnatto Minn. AES 3.5 Jim N.D. AES 2.2 IA 2050 Iowa AES 3.3 MN 0203 SP Minn. AES 2.2 IA 2033 Iowa AES 3.3 Mn 0302 Minn. AES 2.2 MN 2101SP Minn. AES 3.3 Nornatto N.D. AES 2.2 IA 2050 Iowa AES 3.3 MK 0649 Richland Organics 2.2 Parker Minn. AES 3.3

Table 11. Chlorosis scores of soybean varieties in Minnesota 2003 (Goos & Johnson, 2003): score 1.0 = no chlorosis, 5 = most severe chlorosis (choice 20 extremely of 104 tested genotypes)

Soybean varieties characterizing

high score (CS >3.2)

varieties.

chlorosis symptoms.

salts and carbonates (Hansen et al., 2003).

slightly reduced iron uptake of efficient types.

nutritional problems induced by iron deficiency.

Soybean varieties characterizing low chlorosis score ( CS <2.3)

CV = 31.7; LSD 5% = 1.0

EDDHA) or foliar treatment with 1 % solution of ferrous sulfate.

Silman and Motto (1990) tested under greenhouse conditions in nutrient solutions influences zinc on the growth and composition of an Fe-efficient (*Hawkeye*) and Feinefficient (*PI-54619-5-1*) soybean genotypes in various levels of Fe. In general, increased Zn levels resulted in growth reduction in both genotypes with the Fe-inefficeint plants being more sensitive to Zn level. The Fe-efficient genotype had a higher Fe content than the Feinefficient at corresponding treatment levels.
