Effect of Soil and Foliar‐applied Manganese on the Micronutrient Content and Yield of Soybeans¹

Abstract

Manganese deficiency of soybeans (Glycine max (L.) Merr.) will undoubtedly become more prevalent as soybean acreage increases along with strong emphasis on yield maximization. Thus, field experiments were conducted on two soils (Argiaquoll and a Hapludoll) in southern Wisconsin to evaluate sources, rates, and methods of application of Mn fertilizers on soybeans. Two sources, MnSO4 and Mn‐ethylenediaminetetraacetic acid (MnEDTA), were broadcast, row or foliar‐applied at various rates to Mn‐deficient soils and/or soybeans. Micronutrient concentrations, Mn uptake, and various production parameters were measured. All rates and application methods of MnSO4 and foliar applications of Mn‐EDTA were effective in supplying Mn to the plant. Row applications of MnSO4 were somewhat more efficient than broadcast applications. Manganese applied at rates ranging from 5 to 22 kg Mn/ha as MnSO4 with the starter fertilizer in the row at planting time appeared to be most efficient soil treatments in increasing seed yields. The MnEDTA applied in the row reduced plant weight, leaf Mn, and soybean yields slightly. When Zn was not included in the starter fertilizer, leaf Zn and Cu were increased by the soil‐applied MnEDTA treatments. Leaf Fe was not affected by any of the Mn treatments. Foliar applications of Mn were most effective when applied at the early blossom or early pod set stages or in multiple applications at these stages. Single applications of 2.24 and 4.48 kg Mn/ha as MnSO4 or 0.51 kg Mn/ha as MnEDTA caused some burning of the foliage. Combined row and foliar methods of application also appeared to relieve Mn deficiency effectively. Small amounts of MnSO4 applied in the row corrected the Mn deficiency early in the season, whereas foliar applications adequately supplied Mn to the plant later in the growing season. This combination resulted in higher yields than with either row or foliar treatments applied alone.

Effects of chelating agents on protein, oil, fatty acids, and minerals in soybean seed

“…However, we cannot explain the high level of manganese in leaves during the flowering stages [32]. In spite of the importance of macro-and micro-elements [13][14][15][16][17][18][19][20][21] for soybean growth and development, further research is needed to understand the mechanisms controlling the relationships between chelating agents and nutrient uptake by plants and the relationships between chelating agents and nutrient deposition in the seed. Altering the composition of soybean seed with applications of CA, SA, *Means given within a column with the same letter are not significantly different at p ≤ 0.05.…”

“…A strong metal ions-EDTA complex is made, and this is due to the EDTA-binding constant, 10 [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] , which varies depending on the type of metal ions. Citric (10 2.8-11.85 ) and salicylic acids (10 2.7-16.35 ) weakly bind with the metal ions.…”

“…Although using synthetic chelating agents helped to understand plant nutrition, the micronutrient carrier from soil to plants [12] and the uptake of iron-chelating agents by plants are still not fully understood. Application of micronutrients is important for soybean yield and seed quality, especially in nutrient-deficient soil [13][14][15][16][17][18][19][20][21]. Iron is critical for chlorophyll formation, photosynthesis, respiration [21].…”

“…Our hypothesis was that the plants may absorb the naturally occurring low binding (10 3-16 ) citric and Salicylic acids as chelating agents for metal ions over EDTA, which have higher binding constants (10 [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] ) to different metal ions [23] for transporting iron and other micro-and macro-nutrients into the plants. Our hypothesis was based on the fact that metal ions (M) bind differently to different chelating agents (called also ligand, L), and form metal-ligand complexes (ML).…”

Physiological Functions of Manganese in Plants

“…Although oats is a species known to be very sensitive to Mn nutrition and can be used as an indicator plant for Mn deficiency, the yield of legumes is likewise relatively quickly depressed by Mn deficiency or toxicity (43,49,80,133). In soybeans, the decrease in yield at both deficiency and toxicity levels is largely due to fewer fertile nodes (and pods) on a plant (39, 49) and lighter seeds (15,39,49,110). However fertility of a node or a pod is not affected.…”