**6.3 Manganese**

Plants vary considerably in their Mn requirements and levels only 20 ppm often being sufficient for normal plant growth. Levels of Mn in plants vary between species and soil properties more than those of other nutrients. Plants generally absorb Mn from the soil as Mn2 +. Mn is important in plant metabolism because of its redox properties and thus its ability to control oxidation, reduction and carboxilation reactions in the carbohydrate and protein metabolism.

Mn deficiency causes soybean plants to be stunted. The leaves are yellow to whitish but with green veins. Mn deficiency is most pronounced in cool weather on alkalic and slow alkalic soils rich in organic matter. Soil pH is the most important factor affecting Mn availability because it is extremely soluble at low pH and insoluble at high pH levels.

Foliar fertilization of young and moderately young crops with 8-15 kg MnSO4/ha as 1-2 % solution (2-3 applications) is recommendation for prevention of Mn deficiency on soils with a high pH value.

Manganese deficiencies in oats and soybeans were reported by Willis (1928), primarily in spots in the coastal plain of North Carolina. This problem was associated with very high soil pH, and thus this observation was likely the first evidence of "overliming." The soils in the coastal plain are inherently low in manganese, especially the more poorly drained ones, since manganese can be reduced and leached in the soil-forming process (Cox, 1965). Interveinal chlorosis is a clear symptom of manganese deficiency. Cox (1968) used both extractable manganese by the Mehlich-1 extract and soil pH and developed a yield response prediction and manganese soil test interpretation for soybeans. Extractable concentrations at the critical level, which varied from 3 to 9 with Mehlich-1 depending on pH, were sufficient to be measured readily. Critical levels of manganese in soybean leaves at various growth stages and effective rates of fertilization for correcting manganese deficiency in soybeans reported by Mascagni & Cox (1985a, 1985b).

## **6.4 Copper**

Copper (Cu) is seldom deficient in soil. Only on soils high in organic mater and under conditions pH above 6.0 would Cu likely be deficient. The color of legume and forage plants deficient in Cu tends to be grayish-green, blue-green or olive green. The internodes become shortened to produce a bushy type of plants (Sauchelli, 1969). Soybean has low requirements for Cu.

Williams (1930) noted that crops grown on muck soils in North Carolina often responded to copper application. This observation was researched in detail by Willis (1937), Willis & Piland (1936) and these researches centered on the aspect that copper may be a catalyst in oxidation-reduction processes in soils.

#### **6.5 Boron**

Total boron (B) contents in soils are into range of 20 to 200 mg/kg dry weight, most of which is unavailable for plants. The available, hot water soluble fraction in soils adequately supplied with B ranges from 0.5 to 2.0 mgB/L. Soluble B consists mainly of boric acid which under most soil pH conditions (ph 4-8) is undissociated. In soils of arid and semi arid regions, B may accumulate to toxic concentrations in the upper soil layer because lack of drainage and the reclamation of such soils requires about three times as much water as that of saline soils. Soil organic matter is closely associated with the accumulation and availability of B in soils (Mengel & Kirkby, 2001).

B deficiency leads to disturbance of growth and development of plants. B is known to influence carbohydrate metabolism, sugar transport, the nucleic acid and protein household, N metabolism, flower formation and pollen germination, water household, energetic processes of phosphorylation and dephosphorylation, etc. Conditions that favour B shortage are high pH (7.0-8.0), soils low in organic matter, drought, high concentrations of iron and aluminium hydroxide. Difference between adequate and toxic concentrations of B is very small. Soybean is very susceptible to B toxicity. Alfalfa and sugar beet have high requirements in B. Broadcasting and incorporation of 0.5 to 1.0 kg B/ha (for example, the most commonly used borax) is satisfied for needs of crops in rotation for a few years (Berrgmann, 1992; Mengel & Kirkby, 2001).

#### **6.6 Chlorine**

Chlorine (Cl) is in group of elements which can have a beneficial effects on plant growth. Plant tissues usually contain substantial amount of Cl often in range of 2 to 20 mg/kg dry weight. Soils considered low in Cl are below 2 mg water soluble Cl/kg soil which is rare. The effects of excess Cl in plants are more serious problem. Crops growing on salt affected soils often show symptoms of Cl toxicity. These include burning of leaf tips too margins, bronzing, premature yellowing and abscission of leaves. Plant species differ in their sensitivity to Cl. Some leguminous species are very prone to Cl toxicity and using of sulfate instead of chlorine fertilizers is recommend (Mengel and Kirkby, 2001).

#### **6.7 Molybdenum**

Molybdenum (Mo) is an essential plant nutrient. The concentrations of Mo may vary from less than 0.1 to more than 300 ppm. Roots contain a greater proportion of Mg than aboveground part or seed. Molybdenum is needed by the soybean and other leguminose plant itself and also by the nitrogen-fixing *Rhizobia* bacteria in the soil. In contrast to other micronutrients, Mo availability increases with soil pH. Seldom is there Mo deficiencies with soil pH above 6.0. Since the element is critical for nitrogen fixation, the pale green or yellow plants are identical to a nitrogen deficiency. In this case, leaves generally begin to yellow first on the lower leaves. Needless to say, symptoms usually do not occur on soils high enough in nitrogen to make up for lack of nodule fixation (Holshouser, 1997). Efficiency of symbiotic N2 fixation can be limited by micronutrient deficiencies, especially of molybdenum. Soybean generally responds positively to fertilization with Mo in soils of low fertility and in fertile soils depleted of Mo due to long-term cropping.

Sodium or ammonium molybdate are mainly used for correction of Mo deficiency either as a solid to the soil or by spraying on the foliage or by treating the seed. The first step, however, is always to establish the proper soil pH. The micronutrient can be supplied by seed treatment, however toxicity of Mo sources to *Bradyrhizobium* strains applied to seed as inoculant has been observed, resulting in bacterial death and reductions in nodulation, N2 fixation and grain yield. Therefore, use of seeds enriched in Mo could be a viable alternative to exterior seed treatment. Campo et al., (2009) demonstrated the feasibility of producing

supplied with B ranges from 0.5 to 2.0 mgB/L. Soluble B consists mainly of boric acid which under most soil pH conditions (ph 4-8) is undissociated. In soils of arid and semi arid regions, B may accumulate to toxic concentrations in the upper soil layer because lack of drainage and the reclamation of such soils requires about three times as much water as that of saline soils. Soil organic matter is closely associated with the accumulation and

B deficiency leads to disturbance of growth and development of plants. B is known to influence carbohydrate metabolism, sugar transport, the nucleic acid and protein household, N metabolism, flower formation and pollen germination, water household, energetic processes of phosphorylation and dephosphorylation, etc. Conditions that favour B shortage are high pH (7.0-8.0), soils low in organic matter, drought, high concentrations of iron and aluminium hydroxide. Difference between adequate and toxic concentrations of B is very small. Soybean is very susceptible to B toxicity. Alfalfa and sugar beet have high requirements in B. Broadcasting and incorporation of 0.5 to 1.0 kg B/ha (for example, the most commonly used borax) is satisfied for needs of crops in rotation for a few years

Chlorine (Cl) is in group of elements which can have a beneficial effects on plant growth. Plant tissues usually contain substantial amount of Cl often in range of 2 to 20 mg/kg dry weight. Soils considered low in Cl are below 2 mg water soluble Cl/kg soil which is rare. The effects of excess Cl in plants are more serious problem. Crops growing on salt affected soils often show symptoms of Cl toxicity. These include burning of leaf tips too margins, bronzing, premature yellowing and abscission of leaves. Plant species differ in their sensitivity to Cl. Some leguminous species are very prone to Cl toxicity and using of

Molybdenum (Mo) is an essential plant nutrient. The concentrations of Mo may vary from less than 0.1 to more than 300 ppm. Roots contain a greater proportion of Mg than aboveground part or seed. Molybdenum is needed by the soybean and other leguminose plant itself and also by the nitrogen-fixing *Rhizobia* bacteria in the soil. In contrast to other micronutrients, Mo availability increases with soil pH. Seldom is there Mo deficiencies with soil pH above 6.0. Since the element is critical for nitrogen fixation, the pale green or yellow plants are identical to a nitrogen deficiency. In this case, leaves generally begin to yellow first on the lower leaves. Needless to say, symptoms usually do not occur on soils high enough in nitrogen to make up for lack of nodule fixation (Holshouser, 1997). Efficiency of symbiotic N2 fixation can be limited by micronutrient deficiencies, especially of molybdenum. Soybean generally responds positively to fertilization with Mo in soils of low

Sodium or ammonium molybdate are mainly used for correction of Mo deficiency either as a solid to the soil or by spraying on the foliage or by treating the seed. The first step, however, is always to establish the proper soil pH. The micronutrient can be supplied by seed treatment, however toxicity of Mo sources to *Bradyrhizobium* strains applied to seed as inoculant has been observed, resulting in bacterial death and reductions in nodulation, N2 fixation and grain yield. Therefore, use of seeds enriched in Mo could be a viable alternative to exterior seed treatment. Campo et al., (2009) demonstrated the feasibility of producing

sulfate instead of chlorine fertilizers is recommend (Mengel and Kirkby, 2001).

fertility and in fertile soils depleted of Mo due to long-term cropping.

availability of B in soils (Mengel & Kirkby, 2001).

(Berrgmann, 1992; Mengel & Kirkby, 2001).

**6.6 Chlorine**

**6.7 Molybdenum** 

Mo-rich seeds of several soybean cultivars, by means of two foliar sprays of 400 g Mo/ha each, between the R3 and R5 stages, with a minimum interval of 10 days between sprays (Table 12). In most cases, Mo-rich soybean seeds did not require any further application of Mo-fertilizer (Campo et al., 2009).


Table 12. Impacts of foliar fertilization on Mo contents in soybean grain (Campo et al., 2009)
