Means and Tukey’s test concerning nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, cooper, iron, manganese, and zinc grain and straw concentrations of wheat affected by nitrogen rates, with or without inoculation by
The management of nitrogen fertilization is performed in order to ensure adequate productivity, and depending on the N dynamics in the soil, large amount of N is added to the soil, raising production cost for the farmers. Considering the benefits attributed by seed inoculation with Azospirillum brasilense (diazotrophic bacteria), with emphasis on biological nitrogen fixation (BNF), greater development of the root system, and, consequently, greater absorption of water and nutrients, it infers that inoculation can improve crop performance allowing greater efficiency of nitrogen fertilization. Thus, the research that evaluates nutritional status and wheat yield, in terms of nitrogen rates in association with inoculation with A. brasilense is important. We found that increment of N rates in association with A. brasilense inoculation increases the wheat yield up to 139 kg ha−1 N, whereas without this inoculation linear increase occurred with lower maximum yield of wheat. That is, the inoculation afforded higher grain yield applying less nitrogen fertilizer in topdressing. This research demonstrated that inoculation with A. brasilense associated with nitrogen fertilization in topdressing is beneficial to nutrition and wheat yield. Therefore, inoculation is a low-cost technique, easy to apply and use, and nonpolluting, which fall within the desired sustainable context in actuality.
- diazotrophic bacteria
- nutrient concentrations
- bacterial promoters of plant growth
- agronomic efficiency
The final crop yield is defined according to the cultivar used, the amount of agricultural supplies, and management techniques employed. The increasing use of high-yield potential wheat has implicated in more frequent use of agricultural supplies, among which nitrogen fertilization shown to be important in defining the grain yield . Therefore, there is a need to study wheat cultivars verifying their response to the uptake and utilization of nutrients in the soil and their performance and cultural practices in different environments .
Nitrogen fertilization is one of the highest costs of the production process of nonleguminous crops . Wheat, corn, and rice crops utilize approximately 60% of the N fertilizer produced in the world . The use of N fertilizer must be carefully controlled to ensure good yield and manage N in the soil; N fertilizer increases production costs for farmers .
Several authors reported a positive response of nitrogen fertilization on grain yield of wheat [3, 7–11]. Due to the high cost of fertilizers and awareness in support of sustainable agriculture and less polluting, in which the research is growing, one possibility would be to use inoculants containing bacteria that promote growth and increase the productivity of plants. Studies on biological nitrogen fixation (BNF) by
Although the plant genotype performs an essential role in the colonization of bacteria, cultivars with high and low potential of association exist . Several studies have been published confirming that
In addition, the increase in root development caused by inoculation with
Considering the benefits attributed to several crops by inoculation with
2. Materials and methods
The wheat experiment was conducted in 2014, in an experimental area that belongs to the UNESP Engineering Faculty, located in Selvíria—MS/Brazil—with the following geographical coordinates 20°22′S and 51°22′W and an altitude of 335 m. Soil in this experimental area was classified as Distroferric Red Oxisol with clay texture (with values of particle size of 420, 50 kg−1, and 530 g of sand, silt, and clay, respectively), according to Embrapa , which has been cultivated with annual cultures over 27 years and the last 11 years with no-tillage system. The area was under corn cultivation before sowing wheat. The annual average temperature was 23.5°C, annual average pluvial precipitation was 1370 mm, and annual average relative air humidity was between 70 and 80%.
Glyphosate [1800 g ha−1 of active ingredient (a.i.) and 2,4-D (670 g ha−1 of a.i.)] herbicides were used for desiccation and applied in 2 weeks prior to sowing wheat. Chemical attributes of the soil in the tillable layer were determined before the wheat experiment began. The methods proposed by van Raij et al.  showed the following results: 13 mg dm−3 of P (resin), 6 mg dm−3 of S═SO4, 23 g dm−3 of organic matter (OM), pH (CaCl2) of 4.8, 2.6 mmolc dm−3 of K+, 13.0 mmolc dm−3 of Ca2+, 8.0 mmolc dm−3 of Mg2+, 42.0 mmolc dm−3 of H + Al, 5.9 mg dm−3 of Cu, 30.0 mg dm−3 of Fe, 93.9 mg dm−3 of Mn, 1.0 mg dm−3 of Zn (DTPA), 0.24 mg dm−3 of B (hot water), and 36% base saturation. After soil chemical analysis, 2.5 t ha−1 of dolomitic limestone (with 88% relative total neutralizing power) was directly applied as topdressing 80 days before the wheat was sown in 2014 in order to elevate base saturation to 70%, as recommended by Cantarella et al. .
The experimental design was a randomized block with four replications, in a factorial scheme 5 × 2, with five N rates (0, 50, 100, 150, and 200 kg ha−1, as urea) applied as topdressing at the growth stage 3.2 on Zadok’s scale , with and without seed inoculation with
Were applied 350 kg ha−1 of the 08-28-16 formulation in the forms of urea, triple superphosphate, and potassium chloride, respectively, at wheat sowing was applied. The experiments were conducted in a no-tillage system. The area in both crops was irrigated by a central pivot sprinkler system. The water coverage was 14 mm over a period of around 72 h. The cultivar used was the CD 116, and sowing was done with an experimental machine on 05/16/14, with 80 seeds being sown per meter. Metsulfuron-methyl (3.0 g a.i. ha−1), a postemergence herbicide, was applied 20 days after emergence (DAE) to control weeds, like
Concentrations of N, P, K, Ca, Mg, S, Cu, Fe, Mn, and Zn were measured in the grain and straw (above the soil) of wheat at harvest occasion (the end of the crop cycle), in 10 plants per useful area of plot. The determination of nutrients was carried out as described by Malavolta et al. . The wheat was harvested from the plants in the useful area of each plot, and grain yield was calculated after mechanical threshing. Data were transformed into kg ha−1 and corrected for 13% moisture (wet basis). The agronomic efficiency of the treatments was determined:
The results were subjected to analysis of variance and Tukey’s test at 5% probability to compare the averages of plants that had been inoculated with
3. Results and discussion
The increase in nitrogen rates isolated did not influence the nutrients concentrations in irrigated wheat grains, inclusive of N ( Table 1 ). However, it is worth noting that the nutrients N, P, and S concentrations presented in the diagnosis leaf (data not shown) were higher than average recommended by Cantarella et al. , whose ranges for these nutrients are 20–34, 1.5–3, and 2.1–3.3 g kg−1, respectively. For average of Ca and Mg, leaf concentrations are within the recommendation by Cantarella et al.  as appropriate, whose ranges for such nutrients are 2.5–10.0 and 1.5–4.0 g kg−1. The K leaf concentration was slightly below 15 (13.5 g kg−1), being the critical level considered as appropriate. However, the average of leaf concentrations of Cu, Fe, Mn, and Zn were suitable, whose ranges for these nutrients are 5–25; 10–300, 25–150, and 20–70 mg kg−1 , respectively.
|N rates (kg ha −1 )||N (g kg −1 )||P (g kg −1 )||K (g kg −1 )||Ca (g kg −1 )||Mg (g kg −1 )|
|With ||26.92 a||5.23 a||5.23 a||0.35 b||7.08 a||22.09 a||0.56 a||1.30 a||1.65 a||0.70 a|
|Without ||26.29 a||4.70 b||4.72 b||0.88 a||6.76 a||22.42a||0.43 b||1.40 a||1.30 b||0.67 a|
|N rates (kg ha −1 )||S (g kg −1 )||Cu (mg kg −1 )||Fe (mg kg −1 )||Mn (mg kg −1 )||Zn (mg kg −1 )|
|With ||2.57 a||1.92 a||6.87 a||7.87 a||46.33 a||270.30 a||76.30 a||82.47 a||44.53 a||9.40 a|
|Without ||2.64 a||1.49 b||7.63 a||9.23 a||42.53 a||260.73 a||62.53 b||82.43 a||37.93 b||8.70 a|
With regard to inoculation with
The interaction between nitrogen rates and inoculation with
|Inoculation||N rates (kg ha−1)|
|With ||1.77 a||1.65 a||1.68 a||1.47 a||1.62 a|
|Without ||1.18 b||1.22 b||1.23 b||1.43 a||1.43 a|
The increase in nitrogen rates did not influence the concentration of macronutrients and Cu, Mn, and Zn in wheat straw ( Table 1 ). Only the Fe straw concentration was influenced by N rates, adjusting the increasing linear function ( Figure 2 ).
The interaction between nitrogen rates and inoculation was significant for the N concentration in the straw. The treatments that were inoculated by seed with the bacteria
|Inoculation||Doses de N (kg ha−1)|
|With ||5.23 a||4.62 a||5.32 a||5.88 a||5.08 a|
|Without ||5.40 a||4.97 a||4.20 b||4.67 b||4.25 a|
For treatments not inoculated, the Pearson correlation was significant between the concentration of N in the grains and K concentration in straw (0.5131*), Cu in straw (−0.5584*), and Zn in grains (0.4573*). For the treatments inoculated with
The Pearson correlation was significant between the concentration of N in straw and concentrations in grains of N (1.0000**), of K (0.4547*), of Ca (0.4994*), and of Mg (0.5087*) in the treatments inoculated with
For the agronomic efficiency of wheat, there was no significant difference between with or without inoculation by
|N rates (kg ha−1)||Grains yield (kg ha−1)||Agronomic efficiency (kg grain kg−1 N)|
|With ||2996||9.40 a|
|Without ||2937||7.61 a|
|Inoculation||N rates (kg ha−1)|
|With ||2196 a||2916 a||3205 a||3544 a||3119 a|
|Without ||2342 a||3092 a||3060 a||2989 b||3203 a|
Regarding grain yield, several authors also reported a positive response to nitrogen fertilization on wheat [2, 3, 7–10]. In similar climatic conditions for the cultivation of wheat as a winter crop in the Cerrado region with low altitude, Cazetta et al.  and Teixeira Filho et al. [3, 8, 9] suggested maximum grain yield with N doses ranging from 78 kg ha−1 , 90 kg ha−1 [3, 8] to 120 kg ha−1 . These differences in rates of N that provide maximum productivity of wheat are due to different requirements of N from the cultivars, as well as the variation in climate and soil conditions.
Lemos et al.  studied five wheat cultivars (CD 104, CD 108, CD 119, CD 120, and CD 150), with and without inoculation and, associated with nitrogen rates, found that response to inoculation with
Tarumoto et al. , analyzing inoculation with
Agronomic efficiency was negatively affected by the increase of N rates ( Table 4 ), with adjustment to decreasing linear function due to higher losses of N in the soil ( Figure 5 ), as we know, the higher the dose, the greater will be the loss. Increases in the efficiency of nitrogen fertilization associated with inoculation with
The straw concentration of N decreased linearly with the increase of N doses, only without inoculation with
The increase in N rates in association with
This research demonstrated that inoculation with
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