Agronomic performance and quality of baby corn in response to the inoculation of seeds with Azospirillum brasilense and nitrogen fertilization in the summer harvest

Murilo Fuentes Pelloso; Pedro Soares Vidigal Filho; Carlos Alberto Scapim; Alex Henrique Tiene Ortiz; Alberto Yuji Numoto; Ivan Ramão Miranda Freitas

doi:10.1016/j.heliyon.2023.e14618

. 2023 Mar 18;9(4):e14618. doi: 10.1016/j.heliyon.2023.e14618

Agronomic performance and quality of baby corn in response to the inoculation of seeds with Azospirillum brasilense and nitrogen fertilization in the summer harvest^☆

Murilo Fuentes Pelloso ^a,^∗, Pedro Soares Vidigal Filho ^a,^b,^c, Carlos Alberto Scapim ^a,^b,^c, Alex Henrique Tiene Ortiz ^b, Alberto Yuji Numoto ^c, Ivan Ramão Miranda Freitas ^c

PMCID: PMC10073748 PMID: 37035362

Abstract

The association with Azospirillum brasilense promotes better growth and development in corn plants due to biological N fixation, the capacity to help in the synthesis of phytohormones and to improve the use of nutrients by crop plants. However, there aren't specific recommendations for the use of inoculation in baby corn crop. Thus, this study aimed to evaluate the effects of seed inoculation with A. brasilense, associated with nitrogen fertilization management, on the agronomic performance and chemical quality of baby corn grown in three summer growing seasons (2014/2015; 2015/2016 and 2016/2017). The evaluated treatments consisted of combination of five levels of seed inoculation (0.0, 50, 100, 150 and 200 mL 60,000 seeds⁻¹) based on Azospirillum brasilense, two levels of nitrogen fertilization at sowing time (0.0 and 30.0 kg of N ha⁻¹) and two levels of nitrogen in topdressing (0.0 and 110.0 kg of N ha⁻¹), applied at the V4 stage of the popcorn hybrid IAC 125. The characteristics evaluated were: leaf area index (LAI), leaf nitrogen content (LNC), total husked spikelets yield (HSY) and commercial spikelets yield (CSY), and the chemical characteristics of the commercial spikelets: crude protein content (CPC), starch content (STC) and total sugar content (TSC). The inoculation, when combined with nitrogen fertilization, provided positive responses for LAI and provided an average increment of 6 kg ha⁻¹ to CSY for every 10 mL 60,000 seeds⁻¹ of inoculant added to the seeds. The LNC, CPC, STC and TSC weren't affected by seed inoculation. Nitrogen fertilization provided increments for all characteristics evaluated, except for TSC, which was negatively affected by nitrogen topdressing. The baby corn crop responded positively to seed inoculation with Azospirillum brasilense, combined with Nitrogen fertilization.

Keywords: Diazotrophic bacteria, Spikelets, BNF, Inoculant, Zea mays L.

1. Introduction

Brazil, the third largest corn producer in the world [1], has favorable edaphoclimatic conditions to the production of baby corn, which is nothing more than the ear of corn harvested before being fertilized, at stage R1 [2], when the spikelet presents style-stigmas with length between two and three centimeters [3, 4]. After harvested, the baby corn spikelets can be consumed mainly fresh (in natura) or processed, as canned food [5].

Among the inputs used in the production of corn and, consequently, of baby corn, nitrogen fertilizers stand out as the main components of production costs, especially by the high responsiveness of the crop to N [6, 7] and the high potential for nutrient losses through volatilization, leaching and nitrification [8, 9]. Thus, the often irrational use of nitrogen fertilizers tends to raise production costs to levels that are not justifiable from the point of view of economic return, in addition to providing greater risks of environmental contamination [10]. This fact, highlights the importance of studies aimed at the more efficient use of N, in order to increase crop yields and reduce fertilizer costs.

In this context, the use of diazotrophic bacteria, which promotes plant growth, emerges as a sustainable alternative, since it can provide biological nitrogen fixation and, mainly, improve nutrient utilization by crops [9, 11, 12]. Among the diazotrophic bacteria capable of associating with the corn crop, stands out the species Azospirillum brasilense, which is the most studied for use in agricultural inoculants for non-legume crops [13, 14]. The association with Azospirillum brasilense promotes better growth and development in plants, through the biological fixation of N, the high capacity to help in the synthesis of phytohormones, such as auxins, gibberellins and cytokinins [12, 15, 16, 17, 18, 19, 20], in addition to having the ability to act in the physiological system of the plant, increasing, for example, the activity of the enzyme nitrate reductase [21, 22], improving the use of N in the soil.

According to Radwan et al. [23], the production of endolic substances by Azospirillum brasilense tends to be affected by conditions of high O₂ pressure, as well as salt stress. Additionally, nitrogenase components, a key enzyme in the symbiotic N fixation process [24], are highly sensitive to O₂, and its activity can be reduced when combined with both carbon monoxide (CO) and hydrogen (H₂) and with the N present in the soil [25, 26]. This fact highlights the importance of comparing the contribution of diazotrophic bacteria to crops when associated or not with the use of nitrogen fertilizers.

Therefore, it is assumed that the response of crops to Azospirillum brasilense can be affected by the management of nitrogen fertilization, or enable the reduction of the demand for chemical fertilizers. In addition, several studies have shown significant responses to plant growth and productivity of grass crops associated with inoculation with Azospirillum brasilense, such as for sugarcane [27], for rice [28, 29], for wheat [18, 30] and for different ways of using corn, such as corn in grains [31, 32, 33] and sweet corn [34], however, there are few studies that evaluate the effects of inoculation with A. brasilense on baby corn. So, this study aimed to evaluate the effects of increasing levels of seed inoculation with Azospirillum brasilense (strains AbV₅ and AbV₆) in association with nitrogen fertilization at sowing time and topdressing on the agronomic performance and chemical quality of baby corn spikelets cultivated in three summer growing season in Maringá, Northwestern Paraná, Brazil.

2. Material and methods

2.1. Characterization of the experimental area

The field experiments were conducted in three summer growing seasons (2014/2015, 2015/2016 and 2016/2017) at the Experimental Farm of Iguatemi, belonging to the State University of Maringá, and located at 23°20′48″ South and 52°04′17″ West, with an approximate altitude of 550 m, in the District of Iguatemi, municipality of Maringá, in the Northwest region of the State of Paraná, Brazil. The climate of the region is classified according to Köppen-Geiger as subtropical (Cfa) [35]. The climatological data of the experimental area during the period of the experiments were provided by SIMEPAR (Paraná Meteorological System) and are in Figure 1.

Rainfall (mm) and minimum (°C) and maximum (°C) average air temperatures occurred during the experiments in the summer growing seasons of the agricultural years 2014/2015 (1), 2015/2016 (2) and 2016/2017 (3), in Iguatemi, Maringá, Northwest Paraná, Brazil.

The soil in the experimental area was classified as a medium textured Dystroferric Red Nitosol [36], containing 570.0 g kg⁻¹ of sand, 95.0 g kg⁻¹ of silt and 330.0 g kg⁻¹ of clay. The chemical characteristics of the soil in the layers from 0.0 to 0.20 m, on the average of the chemical analyzes carried out before the implementation of each experiment were: pH = 5.07; C = 18.79 g kg⁻¹; P = 14.01 mg dm⁻³; H + Al⁺³ = 3.19 cmolc dm⁻³, K = 0.69 cmolc dm⁻³; Ca = 4.40 cmol dm⁻³ and Mg = 1.62 cmol dm⁻³.

2.2. Experimental design and treatments

The experimental design used was complete blocks, with randomized treatments, in a 5 × 2 × 2 crossover factorial scheme, with four replications. The treatments consisted of a combination of five seed inoculation levels (0.0, 50.0, 100.0, 150.0 and 200.0 mL 60,000 seeds⁻¹) based on Azospirillum brasilense, strains AbV₅ and AbV₆, with a minimum concentration of 2 × 10⁸ colony forming units (CFU) per mL, two levels of nitrogen fertilization performed at sowing time (0.0 and 30.0 kg N ha⁻¹) and two levels of nitrogen fertilization in topdressing (0.0 and 110.0 kg N ha⁻¹), applied at the V4 stage of the crop [2], using the triple top cross hybrid of popcorn IAC 125, whose seeds were industrially treated with the fungicide Vithavax-Thiram. The field experiments were conducted in the summer growing seasons of 2014/2015, 2015/2016 and 2016/2017.

Before sowing of each experiment, in all agricultural years, the experimental area was cultivated with black oat (Avena strigosa L.), which was dried with the herbicide glyphosate (480 g L⁻¹ of active ingredient) at a dose of 2.5 L ha⁻¹ when reaching full flowering, in order to produce straw for no-tillage seeding of baby corn. The experimental units consisted of five rows of plants with 6.0 m in length, spaced at 0.90 m, making a total area of 27 m². In the evaluations of the quantitative characteristics were considered as useful area of each plot the three central rows, excluding 0.50 m from the ends of each one of them, totaling 13.5 m². The experiments were carried out in a no-tillage system, with a population of 180 thousand plants ha⁻¹ (16.2 plants m⁻¹).

2.3. Seeds inoculation

Inoculation of popcorn seeds (IAC 125) used for baby corn production was performed using a commercial liquid inoculant, containing the AbV5 and AbV6 strains of Azospirillum brasilense, at the minimum concentration guaranteed by the manufacturer of 2 × 10⁸ viable cells for each mL of the commercial product. Just before sowing, the procedure was performed in plastic bags specifically identify for each pre-determined treatment in a shaded, dry area. After inoculation, the plastic bags were shaken so that the seeds were coated homogeneously, being transported to the field in styrofoam boxes and kept protected from the sun until sowing.

2.4. Harvest and crop characteristics evaluated

When at least 50% of the plants in each experimental unit reached the VT stage [2], the leaf area index (LAI) was evaluated in five random plants in each useful area, determined using the methodology proposed by Francis et al. [37], in which initially, leaf area (LF) was calculated using the expression LF = L × W × 0.74, where “L” represents the length and “W” the width of all leaves with at least 50% of green area. Next, the LAI was determined by the equation LAI = LF/(s1 × s2), where s1 and s2 represent, respectively, the space in meters between the sowing row and plant in the row.

When the plants reached the R1 stage of development [2], before the first spikelet harvest, the collect of the index leaf from 10 random plants of each experimental unit was performed. Next, the leaves were taken to the Production Physiology Laboratory, at Applied Agricultural Research Center (Nupagri), washed in distilled running water, stored in craft paper bags identified according to each treatment and dried at a constant temperature of 65 °C in a forced air circulation oven until they reach constant mass. Then, the dried leaves were ground in a Whiley-type mill and stored in clean, hermetically sealed jars. Afterwards, the samples were used to measure the leaf nitrogen content (LNC), using the Kjeldahl method [38].

The aforementioned method consisted of using 0.2 g of ground sample, which were transferred separately to digestion tubes, where 2 g of catalytic mixture (0.018 g of powdered selenium, 0.18 g of copper sulfate and 1.802 g of sodium sulfate), with 5 mL of concentrated sulfuric acid. The tubes were conditioned in a digester block and gradually heated to 350 °C. After the samples cooled, 20 mL of distilled water were added to each tube. In Erlenmeyers, 50 mL of boric acid at 4% concentration and three drops of indicator solution (0.132 g of methyl red, 70 mL of ethyl alcohol and 0.066 g of bromocresol green) were added. This solution was conditioned in a semiautomatic Kjeldahl distiller to receive all the ammonia removed from each sample, where 20 mL of sodium hydroxide (NaOH) at 50% concentration was added in the distiller. It was titrated with hydrochloric acid (HCl) at 0.1 N until the mixed indicator turned (from green to pink) and the amount used to perform the titration was noted for the calculation of the N content of the samples [39]. The N content present in each leaf sample was calculated according to the equation: LNC (g kg⁻¹) = V × 0.1 × 0.014 × 100 ÷ g; where LCN represents the nitrogen content present in the sample (g kg⁻¹); V is the amount of HCl used in the titration (mL) and g is the mass of sample used (0.2 g).

The first harvest of spikelets, in each agricultural year, was carried out about three days after the protrusion of the style-stigmas, when they were about two to three centimeters long [3, 4], that is, the spikelets were at stage R1 [2]. In total, six harvests were carried out for the growing seasons 2014/2015 and 2015/2016 and seven for the year 2016/2017, with intervals of two to three days between each harvest. The harvested spikelets were placed in properly identified plastic bags, packed in coolers [40] and taken to the Nupagri laboratory. The data referring to the total husked spikelets yield (HSY) and commercial spikelets yield (CSY) were obtained by weighing them in a digital scale, and the data were transformed into kg parcel⁻¹. HSY and CSY were obtained by adding, in both cases, the sum of data from each harvest, extrapolating the values obtained to Mg ha⁻¹. Commercial spikelets are characterized by not being fertilized and having a diameter between 0.8 and 1.8 cm, length between 4 and 12 cm, cylindrical shape and color ranging from pearly white to light cream, in addition to being whole and without damage caused by pests or diseases [4].

After evaluating the quantitative characteristics, 50 commercial spikelets were randomly collected from the useful area of each experimental unit, washed in distilled running water, to eliminate contaminants, placed in craft paper bags previously identified and dried in forced ventilation ovens at 55 °C, until constant mass. After drying, the spikelets were ground in a Willey-type mill to obtain a homogeneous dry flour. The material obtained was stored in clean, hermetically sealed jars and was used for chemical analysis of crude protein content (CPC), through the determination of total organic nitrogen from Kjeldahl method, previously described, and the value found for each sample was multiplied by the 6.25 factor to convert total N into CPC [41, 42, 43], and starch content (STC) and total sugars content (TSC), according to physicochemical methods for food analysis by Adolfo Lutz Institute [43], both by the Lane-Eynon method described below:

To evaluate the STC, initially, 5.0 g of each sample of dry baby corn flour were weighed, transferred to an Erlenmeyer flask, adding 100.0 mL of ethyl alcohol at 70% concentration. The solution was stirred and heated in a water bath for 1 h at a temperature of 83–87 °C, using a small funnel in the neck of the container to condense the vapors. After this period, with the samples already cooled, 50.0 mL of ethyl alcohol (70% concentration) were added. Then, the solution was filtered, and the residue was washed with ethyl alcohol (70%) and transferred with the aid of 150 mL of distilled water to an Erlenmeyer flask. five drops of 10% NaOH solution were added and the solution was heated for 1 h. After cooling the samples, 5.0 mL of hydrochloric acid were added, heating them again for another 30 min. After cooling, the solution had its pH corrected to 7.0, with sodium hydroxide at 40% concentration, with the aid of a bench pHmeter. A solution containing 10.0 mL of Fehling A, 10.0 mL of Fehling B and 40.0 mL of distilled water was prepared, then the solution was heated until it started to boil. Thus, the filtrate of the digested samples was titrated until Fehling's solution, initially blue, became transparent, with copper oxide residue (Cu₂O), red in color, deposited at the bottom of the container. Thus, the quantification of the starch present in each sample was performed according to the expression: STC = (100 × V × a × 0,9)/m × v; where: V: Volume of sample solution a: amount (g) of glucose present in 10.0 mL of Fehling's solutions; m: mass of the flour sample (g). v: volume of the sample solution used in the titration (mL).

In turn, for the TSC, a 5.0 g sample of dry baby corn flour was weighed, transferred to a 500 mL Erlenmeyer, to which 5.0 mL of hydrochloric acid was added, completing the volume to 250.0 mL with distilled water. Thus, the sample was placed on a heating plate at 300 °C for 3 h, counted from the beginning of boiling, for sample digestion. After natural cooling of the samples, they had their pH corrected to 7.0, with sodium hydroxide (40% concentration), with the aid of a bench pHmeter. Thus, the volume of the final solution was measured, which was then filtered into a 300.0 mL Erlenmeyer. The filtrate was transferred to a 50.0 mL burette in order to turn over the solution. After pH correction, Fehling's solution was prepared (10 mL of Fehling A + 10 mL of Fehling B + 40 mL of distilled water), which was heated and titrated with the final solution of the samples, as described for obtaining the content of starch. Thus, the quantification of total sugars in each sample was performed according to the expression: AT (%) = (V × 100 × a)/(v × m); where: AT: Proportion of total sugars present in the sample (%); V: volume of solution (pH7) added to the burette (mL); a: amount (g) of glucose present in 10.0 mL of Fehling's solutions; v: volume of filtrate used in the titration (mL); m: mass of the dry flour sample (g).

2.5. Statistical analysis

The experimental data from every growing season were separately submitted to the Shapiro-Wilk [44] and Levene [45] tests to verify the normality and homoscedasticity of the errors, respectively, both at a probability of 5% (p > 0.05). When meeting the assumptions, the data were individually submitted to analysis of variance (p < 0.05), in order to verify the magnitude of the mean squares of the residuals (MSR), observing the discrepancy between them in relation to the summer growing seasons (2014/2015, 2015/2016 and 2016/2017), taking as a limit the ratio of 7:1 between the highest and lowest MSR among the years (Hartley's maximum ratio test) [46]. Once observed the data were in the range of 7:1 for MSR, a joint analysis of the three growing seasons of evaluation was carried out.

In this context, the effects of seed inoculation, as well as their interactions, were analyzed using a polynomial regression test, based on the “F” test of the analysis of variance (p < 0.05), the significance of the regression coefficients (p < 0.05), the determination coefficients (R²) and the equations estimated by the tested polynomial models. In turn, the effects of nitrogen fertilization were studied using the “F” test (p < 0.05), since, for factors that have only two levels, this test is conclusive. The effects of growing years were evaluated using the “t” test (LSD) (p < 0.05). All factors (inoculation, nitrogen fertilization and growing seasons) were considered to have fixed effects and all statistical analysis were performed using the Sisvar software [47]. From the results with the polynomial regression test, graphs were formulated using the Graphpad prism software.

3. Results

All the characteristics, when analyzed individually in each summer growing seasons, presented normal distribution for the Shapiro-Wilk (SW) test [44] and error homogeneity by the Levene test (Lv) at a 5% probability level (p > 0.05) [45]. Furthermore, when evaluating the proportions between the highest and lowest MSR among the growing seasons, it was found a ratio of less than 7:1 for all characteristics evaluated [46], enabling the joint analysis of the data, including the growing seasons as a source of variation.

Table 1 presents the summary of the joint analysis of variance of the experiments conducted in the summer growing seasons 2014/2015, 2015/2016 and 2016/2017 for the characteristics: leaf area index (LAI), leaf nitrogen content (LNC), husked spikelet yield (HSY), commercial spikelet yield (CSY) and crude protein contents (CPC), starch (STC) and total sugar (TSC) contents in baby corn spikelet, based on dry mass.

Table 1.

Summary of the analysis of variance for leaf area index (LAI), leaf nitrogen content (LNC), husked spikelet yield (HSY), commercial spikelet yield (CSY) and contents of crude protein (CPC), of starch (STC) and total sugars (TSC) in commercial baby corn spikelets (IAC 125) as a function of seed inoculation with Azospirillum brasilense (IN) and nitrogen fertilization at sowing time (NS) and topdressing (NT). Joint analysis of data obtained in the summer growing seasons (GS) of 2014/15, 2015/2016 and 2016/2017. Maringá, Northwest Paraná, Brazil.

Source of variation	GL	Mean squares
Source of variation	GL	LAI (m² m⁻²)	LNC (g kg⁻¹)	HSY (Mg ha⁻¹)	CSY (Mg ha⁻¹)	CPC (%)	STC (%)	TSC (%)
Inoculant (IN)	4	1.939*	15.503^ns	0.244*	0.030*	0.009^ns	15.624^ns	0.004^ns
N at sowing (NS)	1	4.834*	50.821^ns	1.389*	1.933*	0.087*	489.147*	0.007^ns
N topdressing (NT)	1	28.690*	1805.443*	5.006*	8.096*	7.396*	1699.155*	0.406*
Growing Season (GS)	2	0.227*	78.342 *	0.630*	0.144*	0.067*	29.807^ns	0.006^ns
IN × NS	4	0.594*	6.744^ns	0.020*	0.040*	0.011^ns	3.590^ns	0.009^ns
IN × NT	4	0.603*	23.313^ns	0.066*	0.017^ns	0.007^ns	1.974^ns	0.013^ns
IN × GS	8	0.002^ns	19.650^ns	0.000^ns	0.025*	0.002^ns	4.036^ns	0.013^ns
NS × NT	1	0.272*	137.835*	0.008^ns	0.001^ns	0.010^ns	0.030^ns	0.014^ns
NS × GS	2	0.004^ns	11.598^ns	0.000^ns	0.062*	0.027^ns	27.883^ns	0.010^ns
NT × GS	2	0.003^ns	66.167*	0.001^ns	0.390*	0.021^ns	8.137^ns	0.024^ns
IN × NS × NT	4	0.731*	13.821^ns	0.071*	0.048*	0.008^ns	10.623^ns	0.010^ns
IN × NS × GS	8	0.007^ns	26.969^ns	0.000^ns	0.008^ns	0.004^ns	7.940^ns	0.017^ns
IN × NT × GS	8	0.003^ns	20.882^ns	0.000^ns	0.022*	0.004^ns	3.173^ns	0.008^ns
NS × NT × GS	2	0.003^ns	9.220^ns	0.000^ns	0.017^ns	0.006^ns	3.087^ns	0.008^ns
IN × NS × NT × GS	8	0.005^ns	29.682^ns	0.000^ns	0.009^ns	0.003^ns	1.237^ns	0.013^ns
BLOCOS/GS	9	2.334	147.284	0.070	0.060	0.135	133.117	0.054
Residue	171	0.049	8.677	0.003	0.011	0.009	10.188	0.010
CV (%)	–	5.89	13.04	5.34	10.03	5.35	5.58	6.03
Overall Average	–	3.76	30.31	1.46	1.04	1.79	57.17	1.65

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*significant (p < 0.05) by the F test; ns not significant (p > 0.05) by F test; DF: degrees of freedom and CV: coefficient of variation (%).

The Leaf area index (LAI) responded significantly to the second-order interaction among inoculation (IN), N at sowing (NS) and N topdressing (NT), in which a significant adjustment to the regression was found only for the combination of the absence of the NS (0.0 kg N ha⁻¹) with the presence of the NT (110.0 kg N ha⁻¹), which provided an increasing linear behavior, with an estimated addition of 0.032 m² m⁻² to the LAI for every 10.0 mL of inoculant added via seed treatment (Figure 2).

Leaf area index (m² m⁻²) of baby corn plants as a function of inoculation levels with *Azospirillum brasilense* unfolded within nitrogen levels at sowing time and topdressing, in the average of growing seasons 2014/2015, 2015/2016 and 2016/2017. Maringá, Northwest Paraná, Brazil.

By splitting the results obtained for the LAI as a function of the N applied at sowing time, within the combined levels of seed inoculation and nitrogen topdressing, it was possible to verify that in the treatment composed by the combination of the minimum volume of IN (0.0 mL 60,000 seeds⁻¹) and the absence of NT (0.0 kg N ha⁻¹), there was a decrease in the order of 0.32 m² m⁻² at the LAI (Table 2). However, in the treatment in which the absence of IN was combined with the maximum level of NT (110.0 kg N ha⁻¹), the N applied at sowing time (30.0 kg N ha⁻¹) provided an increase of 0.28 m² m⁻² in the LAI (Table 2). Analogously, all treatments composed of inoculation volumes greater than 100.0 mL 60,000 seeds⁻¹, in the absence of the NT, provided significant increases in the LAI (Table 2).

Table 2.

Leaf area index (m² m⁻²) in baby corn plants (IAC 125) as a function of N levels at sowing time and topdressing, unfolded among themselves and within the levels of inoculation of seeds with Azospirillum brasilense in the Summer growing seasons, in the average of the growing seasons of 2014/2015, 2015/2016 and 2016/2017. Maringá, Northwest Paraná, Brazil.

Inoculant (mL 60,000 seeds⁻¹)	N topdressing	N at sowing time
Inoculant (mL 60,000 seeds⁻¹)	N topdressing	Absence	Presence
0.0	Absence	3.44 Ab	3.12 Bb
0.0	Presence	3.62 Ba	3.90 Aa
50	Absence	3.51 Ab	3.61 Ab
50	Presence	3.87 Aa	4.11 Aa
100	Absence	2.85 Bb	3.49 Ab
100	Presence	4.02 Aa	4.07 Aa
150	Absence	3.35 Bb	3.87 Ab
150	Presence	4.26 Aa	4.43 Aa
200	Absence	3.08 Bb	3.88 Ab
200	Presence	4.23 Aa	4.58 Aa
M.S.D¹		0.1785

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Mean followed by different lowercase letters in the columns and uppercase letters in the rows differ from each other (p < 0.05), according to the F test. ¹Minimum significant difference.

In turn, the treatments composed by the IN of seeds with 50.0 mL 60,000 seeds⁻¹, regardless of the NT level, did not show a significant response to the N applied at sowing time (Table 2). Similar behavior (p > 0.05) was observed for all treatments with IN volumes above 100.0 mL 60,000 seeds⁻¹ combined with the application of NT (110.0 kg N ha⁻¹) (Table 2).

When proceeding with the breakdown of the LAI results as a function of the NT within the combined levels of IN and NS, there was a significant effect of the NT for all evaluated combinations, with higher values obtained from NT (110.0 kg N ha⁻¹), which provided LAI of 4.11 m² m⁻², representing an average increase of 20.18% compared to treatments that did not receive N (0.0 kg N ha⁻¹), whose average LAI was 3.42 m² m⁻² (Table 2).

By analyzing the LAI response according to the growing seasons, it was found that in 2014/2015 there was a higher mean value for this characteristic (3.81 m² m⁻²) compared to the 2015/2016 agricultural year (3.71 m² m⁻²). In turn, in the 2016/2017 agricultural year, the plants showed a mean value LAI value that did not differ statistically from the other periods (3.77 m² m⁻²).

When unfolding the NS × NT interaction for the leaf nitrogen content (LNC), it was possible to verify that the N significantly increased (p < 0.05) the LNC in detriment of treatments that did not receive the nutrient. However, the application of fertilization both at sowing time and in topdressing (30.0 and 110.0 kg N ha⁻¹) did not differ statistically (p > 0.05) in relation to the application performed alone in topdressing (110.0 kg N ha⁻¹) (Table 3). In turn, in the absence of the NT, the results obtained with fertilization with 30.0 kg N ha⁻¹ at sowing time had an increase of 9.22% of the LNC (Table 3).

Table 3.

Leaf nitrogen content (g kg⁻¹) in the index leaf in baby corn plants (IAC 125) as a function of nitrogen fertilization at sowing time and topdressing in the summer growing seasons, on average of seed inoculation levels and from growing seasons of 2014/2015, 2015/2016 and 2016/2017 at Maringá, Northwest Paraná, Brazil.

N at Sowing (kg ha⁻¹)		N topdressing		M.S.D.¹
N at Sowing (kg ha⁻¹)		Absence	Presence	M.S.D.¹
Absence Presence	26,35 bB 28,78 aB		33,35 aA 32,75 aA	1,4232

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Averages followed by different lowercase letters in the columns and uppercase letters in the rows differ from each other (p < 0.05), according to the F test. ¹Minimum significant difference.

The results of the unfolding of the interaction among nitrogen topdressing (NT) and growing seasons (GS) provided the verification that the maximum level of NT (110.0 kg N ha⁻¹) promoted significant increases (p < 0.05) to the LNC, regardless of the agricultural year evaluated, providing a LNC on average 19.91% higher when compared to the absence of N (0.0 kg N ha⁻¹) (Table 4). In turn, the growing seasons provided statistically different responses (p < 0.05) for the LNC only in absence situation of the NT, in which the 2014/2015 agricultural year showed inferior average, whereas the other two did not differ from each other (Table 4).

Table 4.

Leaf nitrogen content (g kg⁻¹) in the index leaf in baby corn plants (IAC 125) as a function of nitrogen topdressing and growing seasons, in the mean of seed inoculation and nitrogen levels at sowing. Maringá, Northwest Paraná, Brazil.

Growing Seasons		N topdressing	M.S.D.¹
		Absence	Presence
2014/2015	25,85 bB	32,48 aA	1,7431
2015/2016	27,71 aB	34,15 aA
2016/2017	29,13 aA	32,52 aA

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Means followed by different lowercase letters in the columns and by different uppercase letters in the rows differ from each other (p < 0.05) by the “t” (LSD) and F tests, respectively. ¹Minimum significant difference.

When unfolding the interaction IN x NS x NT observed for the husked spikelets yield (HSY), it was found that the IN of seeds in combination with the minimum levels of NS and NT (0.0 kg N ha⁻¹) showed quadratic adjustment to polynomial regression (Figure 3). The maximum HSY estimated by the derivation of the second degree equation was 1.19 Mg ha⁻¹, obtained from the IN of seeds with 100.0 mL 60,000 seeds⁻¹ (Figure 3). Analogously, with the realization of NS (30.0 kg N ha⁻¹) there was also a quadratic adjustment, whose maximum estimated HSY was 1.42 Mg ha⁻¹, provided by the inoculant volume of 120.0 mL 60,000 seeds⁻¹ (Figure 3). In turn, with regard to the combinations between NS (0.0 and 30.0 kg N ha⁻¹) with the maximum level of NT (110.0 kg N ha) there were no significant adjustments (p > 0.05) to the tested regression models (Figure 3).

Husked spikelets yield of baby corn (IAC 125) as a function of the inoculation of seeds with *Azospirillum brasilense* unfolded within the nitrogen levels at sowing and topdressing in the summer growing seasons, in the average of the growing seasons of 2014/2015, 2015/2016 and 2016/2017. Maringá, Northwest Paraná, Brazil.

When unfolding the HSY results as a function of NS, within the combined levels of IN of the seeds and NT, there was a significant increase (p < 0.05) provided by N for almost all evaluated combinations, except for the combination between the inoculant volume of 50.0 mL 60,000 seeds⁻¹ with the presence of NT (110.0 kg N ha⁻¹), where there was no significant response (p > 0.05) provided by the application of NS, and the combination of 200.0 mL 60,000 seeds⁻¹ with the presence of NT (110.0 kg N ha⁻¹), where it was possible to evidence a significant decrease (p < 0.05) of 50.0 kg ha⁻¹ of spikelets with the application of NS (Table 5).

Table 5.

Husked spikelets yield (Mg ha⁻¹) of baby corn (IAC 125) as a function of nitrogen levels at sowing in the average of inoculation levels of seeds with Azospirillum brasilense, of nitrogen topdressing and growing seasons 2014/2015, 2015/2016 and 2016/2017, in the summer growing season. Maringá, Northwest Paraná, Brazil.

N at sowing	HSY (Mg ha⁻¹)	M.S.D.¹
Absense Presence	1.38 b 1.54 a	0.0422

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Averages followed by different letters in the column differ from each other (p < 0.05) by the “t” test (LSD). ¹Minimum significant difference.

When unfolding the HSY results as a function of the NT within the combined levels of IN of the seeds and NS, there was a significant effect (p < 0.05) of the NT for all evaluated combinations, with higher values obtained from the level of 110.0 kg N ha⁻¹, which provided an average increase of 22.13% to the response variable in relation to treatments that did not receive the same amount of N (Table 6).

Table 6.

Husked spikelets yield (Mg ha⁻¹) of baby corn (IAC 125) as a function of nitrogen levels in topdressing in the mean of inoculation levels of seeds with Azospirillum brasilense, nitrogen at sowing and growing seasons 2014/2015, 2015/2016 and 2016/2017, in the summer growing season. Maringá, Northwest Paraná, Brazil.

N at sowing	HSY (Mg ha⁻¹)	M.S.D.¹
Absense Presence	1.32 b 1.61 a	0.0422

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Averages followed by different letters in the column differ from each other (p < 0.05) by the “t” test (LSD). ¹Minimum significant difference.

When unfolding the second order interaction IN x NS x NT observed for the commercial spikelets yield (CSY), it was found that only the combination of the IN of the seeds with the maximum levels of NS (30.0 kg N ha⁻¹) and NT (110.0 kg N ha⁻¹) significantly adjusted to the regression, showing an increasing linear behavior, with an increase estimated by the angular coefficient of 6.0 kg ha⁻¹to CSY for every 10.0 mL of inoculant added via treatment of seeds (Figure 4A). In turn, when analyzing the effects of the IN of the seeds split between the levels of NT and the growing seasons (IN x NT x GS) for the CSY, contacted a significant adjustment to the regression only for the foundations between the IN of seeds and minimum level of NT (0.0 kg N ha⁻¹) in the 2015/2016 agricultural year and maximum level of NT (110.0 kg N ha⁻¹) in the 2016/2017 agricultural year (Figure 4B), with linear increments of, respectively, 5.0 and 6.0 kg ha⁻¹ for each 10.0 mL of inoculant used.

Commercial baby corn spikelet yield (IAC 125) as a function of inoculation levels of seeds with *Azospirillum brasilense* unfolded within nitrogen levels at sowing and topdressing (A) and inoculation levels unfolded within nitrogen topdressing in growing seasons 2014/2015, 2015/2016 and 2016/2017 (B). Maringá, Northwest Paraná, Brazil.

Furthermore, when unfolding the results of CSY as a function of fertilization with NS, within the combined levels of IN and NT, there was a significant mean increase (p < 0.05) of 18.95% when the fertilizer was used (Table 7). Thus, as previously reported, the better vegetative development of the crop provided by NS (30.0 kg N ha⁻¹) has the potential to increase its productive yield. In turn, unfolding the CSY results as a function of topdressing N fertilization within the combined levels of IN and NS, the observed increment for the response variable was 42.82% from the completion of fertilization with 110.0 kg N ha⁻¹ (Table 7).

Table 7.

Commercial baby corn spikelet yield (IAC 125) as a function of growing seasons unfolded within the inoculation levels of seeds and nitrogen topdressing in the summer growing season, in the mean of the nitrogen levels at sowing. Maringá, Northwest Paraná, Brazil.

Inoculant (mL 60,000 seeds⁻¹)	N topdressing	Growing seasons
Inoculant (mL 60,000 seeds⁻¹)	N topdressing	2014/2015	2015/2016	2016/2017
0.0	Absense	1.02 a	0.75 b	0.72 b
0.0	Presense	1.14 b	1.25 a	1.17 ab
50	Absense	0.97 a	0.78 b	0.77 b
50	Presense	1.14 b	1.32 a	1.13 b
100	Absense	0.97 a	0.75 b	0.88 a
100	Presense	1.29 a	1.24 ab	1.17 b
150	Absense	0.97 a	0.89 ab	0.82 b
150	Presense	1.16 b	1.30 a	1.21 ab
200	Absense	0.94 a	0.78 b	0.83 b
200	Presense	1.22 b	1.33 a	1.28 ab
M.S.D.¹		0.1029

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Averages followed by different letters in the column differ from each other (p < 0.05) by the “t” test (LSD). ¹Minimum significant difference.

With regard to CSY as a function of the growing seasons factor deployed within the combination of IN and NT levels, it was found that, in general, for treatments in which NT was absent (0.0 kg N ha⁻¹), the 2014/2015 agricultural year showed a higher average than the others for the CSY (Table 7). However, when fertilization with nitrogen topdressing was carried out (110.0 kg N ha⁻¹), except for its combination with the inoculation volume of 100.0 mL 60,000 seeds⁻¹, the 2015/2016 agricultural year presented lower average CSY than the 2015/2016 agricultural year (Table 7). In general, the 2016/2017 agricultural year did not differ statistically from the others for the response variable in the combination of the IN of seeds with the level of 110.0 kg N ha⁻¹ (Table 7).

The results obtained for the commercial spikelets yield as a function of the growing seasons are correlated with those obtained for the leaf area index, in which the treatments where fertilization was not carried out with both NS and NT in the 2014/2015 agricultural year provided statistically lower values (p < 0.05) to the other periods. In this context, it is worth noting that the LAI is closely linked to the definition of the productive potential of plants, since it influences the interception of photosynthetically active radiation by plants [48].

Nitrogen fertilization performed at sowing time with 30.0 kg N ha⁻¹ provided an average crude protein (CPC) value of spikelets of 1.81%, representing an average increase of 2.26% compared to treatments that did not receive it, whose average value was 1.77%. The nitrogen fertilization performed in topdressing (110.0 kg N ha⁻¹) provided a CPC of 1.97%, which represents a significant increase (p < 0.05) of 21.60% in relation to the absence of fertilization (0.0 kg N ha⁻¹).

Regarding the CPC's response according to the growing seasons, a higher average value was found in 2014/2015 (1.83%) in relation to the periods of 2015/2016 and 2016/2017, which did not differ statistically from each other, with averages of 1.78 and 1.77%, respectively. The behavior that occurred for the CPC as a function of the growing seasons was inversely proportional to that visualized for the leaf nitrogen content (LNC) (Table 4). The most likely explanation for this relationship is that, at the time of collection of sheets for LNC analysis, the transfer of N to spikelets had already begun, reducing its concentration in the leaves. In turn, for the starch content (STC) present in commercial baby corn spikelets, NT (110.0 kg N ha⁻¹) increased the response variable by 9.76% in relation to the absence of NT (0.0 kg N ha⁻¹), with mean values of 59.83 and 54.51%, respectively.

The mean value obtained for the total sugar content (TSC) present in the commercial baby corn spikelets showed statistically lower (p < 0.05) for NT (110.0 kg N ha⁻¹), with a mean decrease of 4.73% compared to treatments that did not receive topdressing N fertilization (0.0 kg N ha⁻¹), from 1.69 to 1.61%.

4. Discussion

The answer observed for leaf area index (LAI) to the second-order interaction IN x NS x NT can be justified mainly by the action of phytohormones synthesized by diazotrophic bacteria on plants [12, 17, 19, 20, 49] and the optimized nutrient utilization by crop [9, 11, 12] including nitrogen [21, 22]. Analogously, Numoto et al. [34] evaluating the agronomic performance of sweet corn, Super Sweet group, as a function of the IN of the seeds with Azospirillum brasilense and nitrogen fertilization management, found a significant increase in the LAI as a function of seed inoculation. In turn, Santini et al. [50], evaluating the effects of levels and A. brasilense inoculation forms on plant nutrition and maize yield (hybrid DKB 350), in a greenhouse, did not observe significant effects of inoculation on plant height, stem diameter and leaf area.

The results presented in Table 2 for the interaction, make it possible to infer that N at sowing time (30.0 kg N ha⁻¹) may have contributed to a better root development of the plants in the initial stages, providing them with a greater water absorption capacity and nutrients present in the soil [51, 52] and, as a consequence, they present greater leaf development compared to treatments that did not receive N.

Several authors report the importance of an adequate supply of N for the foliar development of plants due to its functions related to participation in the synthesis of phytohormones [9, 49, 53] and in the division and cell expansion [9, 49]. Furthermore, the N is also characterized by participating directly in the composition of chlorophyll molecules [9, 49, 54]. In this context, plants with leaves that are well nourished by N show a greater capacity to assimilate CO₂ indispensable for the synthesis of carbohydrates in the photosynthetic process [55, 56, 57]. The leaves are determined between the V3 and V5 stages of the corn crop [2], which evidences even more the importance of good initial plant development on the leaf area index that it will present. It is worth noting that the leaves represent the main organ of photoassimilates production in corn plants and, when reaching the transition period between the vegetative and reproductive stages, with approximately 12 fully developed leaves (stage V12) [2], the plant tends to lose up to four older leaves, reaching between 85 and 95% of its total leaf area [58]. In this context, early leaf senescence is highly detrimental to crop development, negatively reflecting on its yield [58], a fact that can occur more drastically when N is insufficiently supplied to the crop [9, 57].

By the LAI response, according to the growing seasons, it is worth emphasizing that, as this is a species with C4 metabolism, the ideal period for corn plants to reach their maximum leaf area is the one coinciding with the longest days of the year, with high temperatures and better use of solar radiation, especially without water limitation [59, 60, 61]. Pinho et al. [58] emphasize that the genotype and environmental conditions are factors that determine the size and number of leaves per plant, which justifies the difference in LAI values observed between different growing seasons.

The response for NS × NT interaction for the leaf nitrogen content (LNC) probably due to the better initial development of the root system of the crop provided by N, which tends to maximize the absorption of other nutrients [51, 52]. The results obtained for the LNC corroborate with those presented by Machado et al. [62], who studying the effects of N and IN of seeds with diazotrophic bacteria on the biochemical characteristics of Nitroflint corn, obtained increments in the accumulation of N in the plants only with the use of N (100.0 kg N ha⁻¹), not observing significant effects of seed inoculation.

Furthermore, it was evident that the uptake and accumulation of N by plants vary according to the edaphoclimatic conditions of the environment or year of cultivation, especially when there is low availability of the nutrient in the soil. This variation, as well as the differences of absorption and accumulation of N by plants due to the characteristics of the soil, variety or hybrid used, were reported by several authors [63, 64, 65].

Raij et al. [66] define values between 27.5 and 32.5 g kg⁻¹ of N in the index leaf in corn plants as being adequate. That way, the results obtained under the conditions of this study were only inferior in cases of absence of NS and NT (Table 4), as well as in treatments where NT was not performed in the 2014/2015 agricultural year.

Lourente et al. [67], evaluating different sources and levels of NT in different crops in succession with common corn in no-tillage system, reported that the predecessor crop directly influences the foliar accumulation of N throughout the development of corn plants in combination with N. The authors also observed that the highest means of LNC obtained in their study occurred when the succession of the corn crop with fallow (29.6 g kg⁻¹) and black oat (27.4 g kg⁻¹) in combination with application of NT. In this context, it is possible to infer that there was an input of N by the mineralization of black oat straw cultivated in the off-season period in the present study.

The increments in husked spikelets yield (HSY) provided by the inoculation of seeds with A. brasilense can be justified by the contribution of N from the BNF, the greater synthesis of phytohormones provided by the bacteria [12, 68, 69] and the optimized nutrient utilization by crop [9, 11, 12, 22]. Furthermore, Müller et al. [70], evaluating the combination of seed inoculation methods with Azospirillum brasilense and NT, obtained results that indicated positive increments of seeds inoculation with A. brasilense on the total chlorophyll content in corn leaves. In this context, it is worth noting that the chlorophyll content in leaves is directly correlated with the N nutritional status of plants [49, 54, 71] and prolongs the photosynthetically active period of leaves [72, 73], tending to influence crop yield.

It is worth emphasizing that the results observed in Figure 3 show the unpredictability and inconsistency of the responses arising from the seed inoculation with Azospirillum brasilense [62,74,75], especially in the presence of the highest levels of nitrogen topdressing [26, 62], where even adjustments of the averages of HSY to the regression did not occur. Beyond the levels of N in the soil, several factors can influence bacterial activity, such as edaphoclimatic variations, temperature, humidity and pH of the soil, beyond its microbiological composition [76, 77]. In this context, it is worth noting that studies show negative effects of glyphosate use on the microbial activity on soil [78], as well as on the development of plants and the use of nutrients by them [[79], [80], [81]], fact that may have occurred in the present study due to the application of the herbicide aimed at desiccating the black oat (Avena strigosa L.), grown before maize as a cover crop.

In general, the action of microorganisms in the rhizosphere of plants is directly stimulated by nutritive and stimulant substances present in exudates released by the roots, such as sugars, amino acids and vitamins [82, 83]. The Bacteria of the genus Azospirillum also present positive chemotaxis in relation to root exudates, optimizing their use [[83], [84], [85]]. Therefore, the presence of a high number of bacteria from the use of the maximum seed inoculation volume (200 mL 60,000 seeds⁻¹) may have caused decompensation in the energy expenditure of the culture to supply the bacterial activity, reducing its yield.

Nitrogen fertilization at sowing tends to provide the best initial development of the corn crop, above all providing improvements in the development of the root system, optimizing the absorption of water and nutrients, which tends to be directed towards the rest of the vegetative cycle and performance production of plants [51, 52].

Comparatively to the aforementioned results, Thakur and Sharma [86], when evaluating the agronomic behavior of baby corn in two crops as a function of three levels of nitrogen fertilization (100.0, 150.0 and 200.0 kg N ha⁻¹) and splitting applications, obtained increases in total husked spikelets yield up to a dose of 150.0 kg N ha⁻¹.

Furthermore, the increases in HSY as a function of nitrogen fertilization in topdressing (110.0 kg N ha⁻¹) can be explained, above all by its effects on the developmental characters of plants previously observed in the present study and which have already been reported by several authors, such as Wolschick et al. [55] and Silva et al. [87], who found increases in shoot dry mass in common corn plants resulting from N fertilization in topdressing. Veloso et al. [64] and Numoto et al [34] obtained increases in the leaf area index in common corn and sweet corn, respectively, and Santos et al. [40], who reported positive responses for plant height and stem diameter in baby corn, as a function of split application of N.

It is worth noting that plants well supplied with N have a better ability to assimilate CO₂ and synthesize carbohydrates during the photosynthesis process [55, 56, 57, 88], which tends to influence directly on the yield of the crop. Bastiani et al. [89] also point out that nitrogen is the nutrient that most limits baby corn production.

Considering that the demand of the corn crop for N was supplied by nitrogen fertilization, it is estimated that the increase in yield resulted mainly from the synthesis of phytohormones [19, 20, 68, 69] and optimization of nutrients assimilation by the crop [9, 11, 12, 22] provided by diazotrophic bacteria, including effects on N uptake mechanisms at the molecular level [22]. It is important to emphasize that the association of bacteria with the corn crop provides effects from the beginning of plant growth and development [31, 90], which can directly influence spikelet yield, harvested at stage R1.

Skonieski et al. [91], when evaluating the effects of nitrogen topdressing and inoculation of seeds with Azospirillum brasilense on agronomic characteristics and hybrids grain yield of AS 1572 and AG 9030 of common corn, in Santa Maria, Rio Grande do Sul, Brazil, verified that the responses of culture to fertilization with N and to inoculation also depend on the genetic material used. The authors also concluded that field experiments are highly complex in relation to the interactions between the environment and diazotrophic bacteria.

Productive responses of baby corn to fertilization with N have already been reported by several authors, such as Bastiani et al. [89], who, evaluating increasing levels of N (0.0, 50.0, 100.0, 150.0 and 200.0 kg N ha⁻¹) in Campos dos Goytacazes, Rio de Janeiro, Brazil, obtained a linear increasing response for the commercial spikelets yield, showing that the highest level assessed by the authors may not have been enough to express the maximum response to fertilization. On the other hand, Santos et al. [40], evaluating four increasing doses of N (0.0, 50.0, 75.0 and 100.0 kg N ha⁻¹) in association with potassium (K) fertilization for baby corn (IAC 125) in the summer growing season in northwestern Paraná, Brazil, also verified positive effects of N on the commercial spikelets yield, whose amount of 64.35 kg N ha⁻¹ provided the highest CSY (1.034 Mg ha⁻¹).

The results observed for crude protein content (CPC) at sowing time with 30.0 kg N ha⁻¹, can be explained, above all, by the better development of the crop provided by the NS, increasing the capacity of plants to absorb water and nutrients [51, 52], especially the N, which participates directly in the composition of vegetable proteins [9, 49, 71]. Therefore, it is important to highlight that the supply of N is a fundamental factor for the formation of proteins in the final product [92], considering that it has approximately 16% of nitrogen in its molecules [41, 42].

The average values obtained for protein content in commercial baby corn spikelets in the present study are close to the values reported by Das et al. [93], who obtained CPC in spikelets of 1.99%, in a hybrid marketed specifically for baby corn production in India. Furthermore, the results obtained were superior to those reported by Pinho et al. [94], when evaluating hybrids of green corn (1.23%), sterile popcorn (0.83%) and silage corn (1.53%) for the production of spikelets.

With the results observed for the starch content, it is worth noting that the increase in starch concentration is inversely proportional to the protein concentration in grains of common corn [95, 96] and sweet corn [97], which suggest that the increase in starch concentration is inversely proportional to protein concentration. This fact was not observed for commercial baby corn spikelets in the present study, probably due to the early harvest compared to other cultivation purposes. Analogously to what was observed in the present study, Muthukumar et al. [98], evaluating the effects of growth regulators and N fertilization splitting strategies in the summer growing period in India, obtained results in which the splitting of nitrogen fertilization in baby corn provided an average increase of 9.61% to the STC.

The total sugar content (TSC) values obtained in the present study were below those observed by Raupp et al. [4], who, evaluating the production of baby corn spikelets from four early hybrids recommended for grain production (AG 6018, DKB 214, DKB 215 and P3021), obtained total sugar values between 1.90 and 2.20%. However, it is worth noting that, as reported by Pinho et al. [94], the sugar content present in spikelets varies according to the genetic material used in their production, as well as the climatic conditions of the cultivation's place. With regard to TSC, the authors also emphasize that sugars are of great importance in relation to the quality of baby corn spikelets, considering that they directly influence the flavor of the final product [94].

5. Conclusion

The popcorn corn hybrid IAC 125, cultivated for baby corn production, responded positively to seed inoculation with Azospirillum brasilense for the leaf area index and for commercial spikelets yield, showing a positive effect of inoculation in combination with nitrogen fertilizations at sowing time and in topdressing. In turn, the leaf N content and chemical characteristics of commercial spikelets (crude protein contents, total sugars and starch) were not affected by seed inoculation. Nitrogen fertilization provided significant increases for all characteristics evaluated, except for the content of total sugars in commercial spikelets, which was negatively affected by nitrogen topdressing.

Author contribution statement

LineNoBookmarkStart:ID:115 = = Name:Line_manuscript_102].

Murilo Fuentes Pelloso, Ph. D: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Pedro Soares Vidigal Filho, Ph. D: Conceived and designed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Carlos Alberto Scapim, Ph. D: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Alex Henrique Tiene Ortiz, Ph. D: Performed the experiments; Wrote the paper.

Alberto Yuji Numoto, Ph. D: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data.

Ivan Ramão Miranda Freitas, Ph. D: Performed the experiments.

Funding statement

This work was supported by Maringá State University and National Council for Scientific and Technological Development (CNPQ – Brasil) - 301861/2017.

Data availability statement

The authors are unable or have chosen not to specify which data has been used.

Additional information

LineNoBookmarkStart:ID:129 = = Name:Line_manuscript_115].

No additional information is available for this paper.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Footnotes

^☆

This article is a part of the "Genetic enhancement and advances in crop breeding".

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Agronomic performance and quality of baby corn in response to the inoculation of seeds with Azospirillum brasilense and nitrogen fertilization in the summer harvest☆

Murilo Fuentes Pelloso

Pedro Soares Vidigal Filho

Carlos Alberto Scapim

Alex Henrique Tiene Ortiz

Alberto Yuji Numoto

Ivan Ramão Miranda Freitas

Abstract

1. Introduction

2. Material and methods

2.1. Characterization of the experimental area

Figure 1.

2.2. Experimental design and treatments

2.3. Seeds inoculation

2.4. Harvest and crop characteristics evaluated

2.5. Statistical analysis

3. Results

Table 1.

Figure 2.

Table 2.

Table 3.

Table 4.

Figure 3.

Table 5.

Table 6.

Figure 4.

Table 7.

4. Discussion

5. Conclusion

Author contribution statement

Funding statement

Data availability statement

Additional information

Declaration of interests

Footnotes

References

Associated Data

Data Availability Statement

ACTIONS

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RESOURCES

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Agronomic performance and quality of baby corn in response to the inoculation of seeds with Azospirillum brasilense and nitrogen fertilization in the summer harvest^☆