Effect of Different Fertilizer Types on the Availability of Manganese in Soil Cultivated with Maize (Zea mays L.) During Different Growth Periods

The research aimed to determine the availability of manganese in the rhizosphere of maize plants at various growth and development stages. The treatments of the field trial were: nitrogen fertilizer, urea type, 400 and 200 kg hectare-1, humic acid 500 and 250 cm liter-1 per dunum, and organic fertilization (sheep manure) were applied at rates of 8 and 4 ton hectare-1 reflecting the recommended doses and half of the recommendation in addition to the control treatment. In the summer of 2022, a field experiment was conducted. Three replications were used according to the Randomized Complete Block design (R.C.B.D.). The local maize variety was seeded in 9 m2 (3m x 3m) in plots. After 70 and 100 days of planting, the concentration of manganese in the rhizosphere and bulk soil were examined. For the two cultivation periods (70 and 100 days), the levels of accessible manganese to plant were greatest with the O1 treatment and lowest with the M2 treatment in the rhizosphere soil and bulk soils. The data also revealed a drop in the accessible manganese concentration in the soil and outside the rhizosphere as the growth time (100 days) increased, indicating increased plant absorption.


Introduction
Manganese is the most abundant element in soil and the twelfth element overall [1].There are more than five valence states, Mn +2 is the most prevalent, followed by Mn +3 , Mn +4 , Mn +5 , Mn +6 , and Mn +7 [2].The soil contains three types of manganese: manganese is dissolved in the soil solution, but its concentration is negligible compared to the overall concentration of manganese, which is the bivalent Mn +2 .This state is accessible for plant absorption, is regarded as one of the most significant manganese states, and is in equilibrium with other.Manganese is adsorbed by organic matter and free oxides, where it is slow to readiness and has low solubility, which is the trivalent Mn +3 .The mineral manganese is included in the composition of the minerals that make up the manganese compounds spread in the soil, and this case is considered not available, and it is Quartervalent Mn +4 [3].Manganese is an essential element for many living organisms as it is a catalyst for many enzymes, such as Superoxide, dismutase, Glutamine synthetase, and Arginase, as well as a role in vital oxidation-reduction reactions [4].Plants only need manganese in small amounts, but it is as essential for growth as other nutrients [5].The availability of manganese is high in acidic soils, and this is due to the high solubility of manganese compounds under conditions where the soil pH is low.In addition, 2 the activity of microorganisms affecting manganese oxidation also depends on the degree of soil reactivity and the optimum degree of activity at pH 7 [6].Therefore, the high degree of soil reaction is higher than 8, accompanied by the dominance of oxidation conditions, as the availability of manganese decreases, and the form of manganese Mn +4 is dominant.While at the degree of soil reaction equal to 7, the form of manganese Mn +3 prevails, and at the degree of acidic reaction, the form of manganese Mn +2 prevails.This means that manganese availability is high in acidic soils due to the dissolution of manganese-bearing compounds in such conditions [7].Root zone pH changes depend on soil storage capacity, pH, and other factors [8].Both root and microbial cells produce low molecular weight substances that either supply manganese in the rhizosphere or facilitate transport across the root cell plasma membrane [9].Manganese uptake by some Mn-hyperaccumulators, such as Phytolacca species, depends on radical solid acidification [10].Radical carboxylate production also increases manganese availability, which chelates Mn and reduces Mn +4 to Mn +2 [11].In addition, soil microorganisms may supply manganese by reducing manganese oxides (MnOx) favored by H + secreted by the root.On the other hand, manganese-oxidizing bacteria can reduce the availability of manganese in (under oxidation conditions) aerobic, calcareous, and calcareous soils or poorly ventilated or submerged soils.Organic matter is negatively charged and has a large adsorption capacity, forming Mn compounds that reduce the amount of replaceable Mn.However, Mn adsorbed by O.M. can be replaced by H + released from radicals [12].By altering the soil's pH, urea affects the availability of nutrients in the soil solution.By reducing the pH, using urea increases the manganese concentration in the soil.In contrast, a low soil pH reduces the C.E.C. and, thus, the soil's capacity to hold cations such as Mn and Ca [13].As for the application of humic acid to the soil, it contributed to increasing soil fertility and improving its structure, despite the low ratio of organic matter to soil weight, by increasing the readiness of the soil's microelements and their influence on the soil's chemical, biological, and physical properties [14].In addition to enhancing soil's chemical characteristics, organic matter (sheep manure) is a vital, safe source of nutrients for plants and people.Applying organic leftovers to soil has a significant role in supplying nutrients to the soil, enhancing its fertility, and improving the soil's physical and chemical features, such as its water storage capacity, ion exchange capacity, and the release of amino acids acidderived catalysts [15].The degree of soil interaction (pH) and the soil's organic content influence the availability of microelements.Depending on the nature of the organic matter and the kind of element, the aqueous extracts of various degraded organic wastes include most of the elements required by the plant.Therefore, providing the plant with a portion of the nutrients is feasible [16].This study aimed to determine the influence of fertilization and growth phases on manganese availability in maizecultivated soil.

Materials and Methods
The field experiment was conducted in one of the fields belonging to the Directorate of Al-Shamiya Municipality, about 34 kilometers west of the district center of Al-Diwaniyah.During the summer of 2022, the field soil (silty clay loam) was cultivated.The field's soil has been prepared by plowing, smoothing, and leveling, and three significant watercourses and minor watercourses for each slab have been opened along the field.The field was divided into three sectors, between each sector and the last, a distance of 1 m.Each sector was divided into 7 panels (experimental unit) with an area of (3m x 3m) for the experimental unit, representing an area of 9m 2 .A distance of 1-2m was left between each experimental unit and another, so the total number of experimental units became 21 plots.A factorial experiment was conducted using a randomized complete block design (R.C.B.D) with three replications.The 7 treatments were distributed randomly to the experimental units in each sector, and the experiment included the following treatments:  Urea (M) fertilizer with two treatments of 400 kg ha -1 (M1) and 200 kg ha -1 (M2) to represent the recommendation and half of the recommendation doses, respectively.Half of the recommended treatment dose was applied after 15 days of cultivation and the other half after 30 days of the first batch.

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 Organic matter, sheep waste, (O) in two treatments of 8 tons ha -1 (O1) and 4 tons ha -1 (O2), where the organic fertilizer was mixed with the surface layer of the soil before planting for each experimental unit to represent the recommendation and half of the recommended doses, respectively. Humic acid (H) with two treatments, 500 ml 3 liters -1 per dunum (H1) and 250 ml 3 liters -1 per dunum (H2) and was applied with irrigation when planting to represent the recommendation and half of the recommended doses, respectively.Seeds of yellow maize (Zea mays L.), Bohuth (local) variety, were planted on 7/20/2022 on lines.The distance between one line and another was 75 cm, and between one Jorah and the other, 25 cm, with four lines on the board.Three seeds were planted in each hole, and after 10 days, the plants were thinned to one plant in each, and the number of plants per plate was 48 plants.DAB fertilizer 46% P2O5 with a treatment of 200 kg P2O5 ha -1 was applied to the field before cultivation and for all experimental units.The maize stem borer (Sesamia cailica L.) was controlled using diazinon granular 10% effective substance, inoculated on the growing tops of the plants twice, the first after 25 days of germination, and the second after 10 days of the first control.The hoeing and weeding process was also carried out manually whenever needed to get rid of the bush plants growing with the crop.As for the irrigation, the experimental units were irrigated by tourists with approximately equal amounts of irrigation water regularly and according to the plant's needs.

Soil Chemical and Physical Analyzes
Before planting, at 0-30 cm field soil depth, samples were collected randomly and thoroughly mixed for homogenization.Then, a composite sample was extracted, air-dried, crushed with a plastic hammer, and sieved with a 2-mm-diameter sieve to undertake the chemical and physical analyses of the field soil listed in Table 1.Soil samples were also collected outside the root zone and inside the root zone of each plot at 70 and 100 days of cultivation, representing the flowering and physiological maturity stages, to measure the available manganese concentration.

Size Distribution of Soil Particles
Soil compositions were estimated using the hydrometer method, according to what was reported in [17].

Bulk Density
The bulk density was estimated using the core sample method, as reported in [17].

Degree of Reaction (pH)
The degree of soil reactivity was measured using a P.H. meter in a soil: water extract (1:1) according to the method presented in [18].

Electrical Conductivity (E.C.)
The electrical conductivity of the soil was measured using an E.C. meter in a soil extract: (1:1) according to the method presented in [18].

The Exchange Capacity of Positive Ions (C.E.C.)
The cation exchange capacity of the positive ions was measured using ammonium acetate and sodium acetate, as [17] reported.

Organic Matter (O.M)
The organic matter was determined by wet digestion using N1 of K2Cr2O7 according to the method of Walkly, and Black mentioned in [17].

Soluble Cations and Anions
 Calcium (Ca +2 ): Calcium was estimated by titration with fernsite (Na - 2 EDTA) using Ammonium Parpurate reagent according to the method of Lanyon and Heald reported in [18]. Magnesium (Mg +2 ): It was estimated by estimating calcium and magnesium together by trituration with fernsite (Na 2 -EDTA) using Erichrome Black T reagent, then subtracting calcium from the total calcium and magnesium according to the method of Lanyon and Heald reported in [18]. Sodium (Na + ): Determine sodium using a flame photometer, as [18] reported. Potassium (K + ): Dissolved potassium was estimated using a flame photometer according to the method proposed by Knudsen et al. reported in [18]. Sulfates (SO 4 = ): Sulfates were determined by precipitation in the form of barium sulfate, according to what was reported in [17]. Carbonates and Bicarbonates (HCO3 -): Bicarbonates were estimated by denaturation with (sulfuric acid) (H 2 SO 4 ) at a concentration of (0.01N) in the presence of (indicator) methyl (orange) according to the method mentioned in [18]. Chloride (Cl -): Chlorine was determined by leaching with silver nitrate (AgNO 3 ) at a concentration of 0.01N in the presence of potassium chromate, according to the method of [18]. Available manganese: The ion of this element was estimated in the soil by the method described by [19] by adding 20 ml of the extraction solution DTPA (0.005 N) with reactivity of (7.3) to 10 g of soil and shaking for two hours with an electric shaker, after filtering it.The element was estimated using an atomic absorption spectrophotometer (AA-7000).Soil Texture Silty clay loam

Available Manganese Concentration in the Soil After 70 Days of Planting
The results of Table (2) illustrate the impact of the treatments of applying nitrogen fertilizer (urea), humic acid, and sheep manure on the manganese concentration available to the soil after 70 days of sowing.The Table results showed that applying nitrogen fertilizer to soil M1 (recommended dose) increased the manganese concentration available to the rhizosphere and bulk soil.The values obtained under this treatment increased significantly compared with the control, and the available manganese concentration for the rhizosphere and bulk soils were 13.28, and 15.04 mg kg -1 soil, with an increased rate of 25.16 and 17.96%, respectively, compared to the control treatment, which resulted in the lowest concentration of available manganese for the rhizosphere and bulk soils 10.16 and 12.75 mg kg -1 soil, respectively.
As for the application of nitrogen fertilizer, the M2 treatment (half of the fertilizer recommendation dose) was significantly superior compared to the control treatment for rhizosphere and bulk soils, and the available manganese concentration values were 12.34, 14.05 mg kg -1 soil, with an increase of 16.30 and 10.19%, respectively.The reason is attributed to the effect of urea in changing the chemistry of the roots significantly and increasing their growth by reducing the degree of soil interaction and releasing necessary secretions in increasing the absorption of micronutrients, including manganese, and thus reducing the concentration of manganese in it [20].These results are consistent with the findings of [21] when applying different levels of urea fertilizer (0 and 50 h/N kg), and he obtained significant differences in the available manganese concentration, with an increase of 31% compared to the control treatment.The impact of applying humic acid H1 (recommended dose) to the soil on the available manganese concentration in the rhizosphere and bulk soils is depicted in Table (2).The values of available manganese increased significantly with this treatment compared with the control treatment, and the available manganese concentration was 16.06 and 14.60 mg kg -1 soil, with an increased rate of 37.60 and 25.96%, respectively.As for treatment H2 (half of the recommended dose), this treatment was significantly superior to the control treatment, and the concentration of manganese available for rhizosphere and outside soil was 13.61 and 15.51 mg kg -1 soil, with an increase of 38.22 and 41.46%, respectively.The reason for the increase is that humic acids increase the ability of cation exchange and chelation of micronutrients, improve the photosynthesis process of the plant, increase the plant's absorption of water and nutrients, and increase the availability of manganese in the soil, and its role in increasing the activity of the root system of the plant and thus the ease of its absorption from the roots [22].These results are consistent with what [23] reached when applying humic acid to the treatment of (10 kg ha -1 ), as he obtained significant differences in the concentration of available manganese in the soil, and the percentage of increase was 27% in a growth period of 70 days.The results present that applying organic matter O1 (recommended dose) to the soil affected the manganese concentration availability for the rhizosphere and bulk soils.The concentration of available manganese increased significantly with this treatment compared with the control treatment of 18.67 and 20.15 mg kg -1 soil, with an increased rate of 44.29 and 33.41%, respectively.As for applying the organic matter O2 (half of the recommended dose), they affected the available manganese concentration.This treatment was significantly superior to the control treatment, and the concentration of manganese available for rhizosphere and bulk soils was 15.31 and 17.01 mg kg -1 , with an increase of 44.29 and 33.41%, respectively.The increase is attributed to the effect of organic matter on the biosoil characteristics by increasing the activity of microorganisms, their numbers, strains activity, and multiplicity of forms, as well as their role in equipping microorganisms with energy and growth sources.This was confirmed by [24] when applying organic matter to the soil led to an increase in 1259 (2023) 012009 IOP Publishing doi:10.1088/1755-1315/1259/1/0120096 manganese availability in the soil due to the activity of microorganisms and the activity of the root system.The results of Table (2) also present that the values of available manganese in the treatments that represent the recommendation for all fertilizer treatments were superior in increasing the concentration of available manganese in the rhizosphere and bulk soils.This may be because applying the fertilizer recommendation increased plant growth and caused significant changes in the roots, which helped reduce the degree of soil reaction compared to half of the recommendation and increased the manganese concentration.Based on the above, the order of the studied parameters in the rhizosphere soil, from lowest to highest, was as follows: The presence of organic residues and humic acid provides manganese in a greater quantity than in mineral fertilizer.This may be due to the effect of organic matter on vital soil properties by increasing the activity of microorganisms in the soil and containing manganese concentrations.

Available Manganese Concentration in the Soil After 100 Days of Planting
Table (3) results illustrate the effect of applying nitrogen fertilizer, humic acid, and sheep manure on the available manganese concentration in the soil after 100 days of planting.In addition, the Table results present the impact of applying urea at the M1 to the soil on the manganese concentration available for the rhizosphere and bulk soil.The available manganese concentration increased significantly for the rhizosphere and bulk soils 10.12 and 12.31 mg kg -1 soil with an increase of 27.29 and 30.95% compared to the control treatment that resulted in the lowest concentration of available manganese for the rhizosphere and bulk soils 7.95 and 9.40 mg kg -1 soil, respectively.As for the effect of applying urea at the M2 to the soil on the available manganese concentration in the soil, the available manganese concentration values increased significantly with this treatment compared to the control treatment 9.40 and 11.39 mg kg -1 soil, with an increased rate of 18.23 and 21.17%, respectively.The reason is attributed to the effect of urea in increasing plant growth and the density of micro-roots, which helped to increase the uptake of manganese by expanding the surface uptake of the root and enhancing the uptake of micronutrients [25].This was confirmed by [26], who confirmed that the application of urea leads to increased plant growth and stimulates the elongation and branching of roots, thus reducing the concentration of micronutrients in the soil solution as a result of increased absorption by plant roots.The results of Table (3) present the impact of applying humic acid, H1, to the soil, on the manganese concentration availability for the plant, as this treatment was significantly superior to the control treatment.The results of the Table also showed the effect of adding humic acid, H2, on the manganese concentration available for the plant, to the superiority of this treatment significantly over the control treatment.The reason is attributed to the fact that humic acids are a means of transporting nutrients from the soil to the plant due to their ability to hold ionized nutrients, which prevents or reduces loss or leaching, thus increasing the readiness of manganese, and humic acids are attracted to the plant rhizosphere and when they reach the rhizosphere they provide what the plant needs in terms of water and nutrients.Furthermore, the roots more easily absorb positive ions because the root has a negative charge, as humic acids contain cations (positive ions).In a certain way, it can be absorbed by the roots of plants more efficiently, which improves the transfer of micronutrients and increases their absorption by the roots of the plant, as the acids take positive ions and are attracted to the root zone and into the plant through the roots [27].These results are consistent with what [23] reached when applying humic acid to the treatment (10 kg ha -1 ) obtained a significant increase in the available manganese concentration in the soil, as the percentage of increase reached 70.7% after 100 days of cultivation.(3) results present the impact of applying organic matter to the soil on manganese availability.The treatment O1 significantly increased the values of available manganese concentration for soil and outside the rhizosphere, compared with the control treatment 16.77 and 19.37 mg kg -1 soil, with an increased rate of 110.94 and 116.06%, respectively.On the other hand, applying the organic matter with O2 treatment on the ready manganese concentration in the soil showed a significant superiority over the control treatment.The reason for the increase is attributed to mineralization and manganese release.This was mentioned by [28] who noticed an increase in manganese availability in the soil with the application of organic residues, as well as the effect of organic residues in the processing of micronutrients through the formation of chelated forms and the formation of an adequate root system capable of absorbing nutrients Minor.In this period (100 days), it was repeated with the period (70 days), the recommendation coefficients (M1, H1, and O1) exceeded half of the fertilizer recommendation in the rhizosphere and bulk soils, and this may be due to the same reason mentioned above (increased plant growth and its root system and reduced soil reaction) and about the life stage of the plant.The order of the studied parameters in the rhizosphere soil, from lowest to highest, was as follows: This sequence was similar to that of after 70 days, confirming the role of organic residues and humic acid in increasing manganese supply to the rhizosphere and bulk soils.Figure (1) presents the impact of fertilizer application on the available manganese concentration in the soil during plant growth periods 70 and 100 days.As we find that the available manganese concentration during the plant growth periods decreased for the rhizosphere soil and outside it with the increase in the period of plant growth, this is due to the increase in plant growth and thus the increased depletion of manganese from the soil.The continued decrease in the available manganese concentration in 100 days indicates a continued increase in plant requirements for this element, and this situation occurred in the soil of the rhizosphere and outside it.This indicates the ease of absorption of this element by plant roots from outside the rhizosphere to the rhizosphere (activity zone) and compensates for the decrease in the concentration of the element within the vital activity zone.These results are consistent with the findings of [29], who found the highest increase in sulfur concentration in the root system 40 days after planting, which decreased with increasing plant growth.Treatment O1 resulted in the highest concentration of available manganese during the plant growth period of all periods, and the lowest concentration of available manganese was in the control treatment of rhizosphere soil.The reason is attributed to the effect of organic fertilizer on reducing the degree of soil interaction and as a result of the increase in the activity of microorganisms in the rhizosphere and its role in the availability of micronutrients through the formation of claw shapes and the development of an adequate root system as well as its content of this element.The available manganese concentration for all treatments at 100 days was less than 70 days for the rhizosphere and bulk soils.

Figure 1 .
Figure 1.The effect of the growth periods of 70 and 100 days on the available Manganese concentration in the soil (mg kg -1 soil).

Table 1 .
Some chemical and physical properties before cultivation.

Table 2 .
The effect of fertilizer type on the available Manganese concentration (mg kg -1 soil) of the soil after 70 days of planting.

Table 3 .
The effect of fertilizer type on the available Manganese concentration (mg.kg -1 soil) of the soil after 100 days of planting.