The Effect of Tillage Systems and Weed Control Methods on Grain Yield and Gluten Protein Compositional and Content-Related Changes in Hybrid Bread Wheat

Abstract

The use of simplified tillage systems and weed control methods using reduced herbicide doses in wheat production technology is one of the basic requirements of sustainable agriculture in terms of obtaining high-quality grain of this species. The aim of three-year field studies was to determine the yield and quality characteristics of hybrid wheat grain depending on two tillage systems (CT and RT) and four weed control methods: mechanical (M) and mechanical–chemical, using recommended herbicide doses (MH100) and doses reduced by 25 and 50% (MH75, MH50). A comparable grain yield, number of grains per spike, weight of one thousand wheat grains, and amount of gluten and ω gliadin subunits (GLI) were obtained in the RT and CT systems. The CT system increased protein content (by 15.2 g kg⁻¹) and the increase in the sum of gluten protein fractions was higher for glutenins (GLU) and their LMW and HMW subunits (from 20.9 to 29.8%). The application of the method with the recommended herbicide dose (MH100), compared to M and MH50, resulted in an increase in grain yield by 0.89 and 1.04 t ha⁻¹, respectively, as well as in the sum of GLI (by 8.4 and 12.3%) and GLU (by 13.7 and 25.3%). The application of the herbicide dose reduced by 25% (MH75) compared to the recommended dose (MH100), especially in the RT system, did not cause a significant decrease in protein content and the amount of GLI and GLU, while reducing grain yield (by 0.26 t ha⁻¹) and the amount of gluten (by 3.1%).

1. Introduction

Among crop plants edible for humans, common wheat (Triticum aestivum L.) plays a pivotal role. This is associated with the great nutritional significance of wheat proteins [1]. The wheat grain is mostly used in the milling and baking industries. Therefore, it ought to feature adequate milling and baking values, which correspond to the quantity and quality of the protein [2]. Gliadins (GLI) and glutenins (GLU) are the main groups of gluten proteins, making up 60–80% of the total protein content in the grain. They determine the parameters and qualities of bread and other products obtained from wheat flour [3,4].

The accumulation of gluten proteins that takes place in the grain-filling period depends, to the highest degree, on genotype [5]. However, it is also modifiable by agrotechnical factors, particularly by fertilization with nitrogen, and other environmental effects, including predominantly weather [6]. The shortage of water, high temperatures, and stress duration time during the growing season exert a considerable effect on the content of protein fractions and their interrelationships [7]. Stress associated with drought and high temperatures usually changes the protein quality. Nevertheless, no modifications in the number of protein fractions and no worsening of protein quality were observed under the influence of merely high temperatures [8].

Despite previous failures in cultivation works, hybrid wheat varieties have been ultimately introduced to be grown with success in Europe, the USA, China, India, and Pakistan [9,10,11]. Hybrid wheat varieties are grown in order to obtain satisfactory grain yield and quality in the context of numerous environmental stressful factors, adapting them to desired agronomic conditions [12].

In Poland, as in other European countries, wheat is grown both in the conventional tillage (CT) and reduced tillage (RT) systems. Reduced tillage improves the soil structure and bioactivity and increases the water-holding capacity in the arable layer. Therefore, under reduced tillage conditions, it is possible to obtain a high yield of wheat grain with favorable quality parameters [13]. The studies on the effect of tillage systems on wheat grain yield and quality are ambiguous. The results of some of these studies indicate an increase in grain yield, protein and gluten content, and the sedimentation index under conventional tillage (CT) [14]. Other studies confirm that conventional tillage (CT) and reduced tillage (RT) have no effect on grain yield and the above-mentioned quality parameters [15]. Studies of some authors show that under no-tillage (NT) and reduced tillage (RT) conditions, higher wheat grain yields can be obtained compared to conventional tillage (CT), which is determined by the higher water holding capacity under NT and RT than under CT [16]. The competitive ability of cereal species and varieties, including wheat, against segetal flora varies and due to this, weeds occurring directly contribute to a reduction in grain yield and quality [17,18].

Reducing the amount of plant protection products used, including herbicides, is justified economically, agronomically, and environmentally, which has been confirmed in some studies both with regard to cereals and other plant species [19,20,21,22,23,24]. Combined mechanical and chemical methods using lower herbicide rates are one of the elements of integrated weed control methods preventing decreased effectiveness of reduced herbicide doses in cereals [25]. The advantages of these methods include lower contamination of the environment and plant products with residues of active substances, good weed control efficacy, and lower herbicide application costs [26,27]. Moreover, the use of integrated weed control methods in cereal crops meets the requirements of sustainable agriculture, which is a method for farmers to produce safe food [28].

The aim of this study was to determine to what degree tillage reductions and the use of different weed management methods affect the crop and protein quality and quantity as well as other quality characteristics of wheat hybrid grain grown under the environmental conditions of south-eastern Poland.

2. Materials and Methods

2.1. Studied Area

The field experiment was carried out at the Advisory Centre in Boguchwała (south-eastern Poland; 49°59′ N, 21°56′ E; altitude 222 m) during three consecutive growing seasons between the years 2017 and 2020.

The experiment was set up on brown alluvial soils classified as a Fluvic Cambisol (CMfv) of silt loam (SiL) with the granulometric composition considered as a good wheat soil complex and of slightly acidic pH [29]. The soil was rich in available phosphorus and potassium forms and with medium levels of magnesium and organic matter (

Table 1. Selected chemical properties (layer of 0–30 cm).

Years	Soil Textural Classes (%)			pH in 1 mol dm−3 KCl	Humus Content (%)	Content of Available Forms (mg kg−1 soil)
	Sand	Silt	Clay			Phosphorus	Potassium	Magnesium
2017/2018	40.5	33.9	25.6	5.58	1.59	173	222	53
2018/2019	38.5	38.0	23.5	5.70	1.62	194	258	59
2019/2020	39.2	33.1	27.7	5.84	1.79	198	261	56

). The soil samples were analyzed in an accredited laboratory of the District Chemical and Agricultural Station in Rzeszów, Poland. The study area is located in the temperate climate zone of northern latitude, in the type of transitional climate.

Weather conditions during the autumn growing season were favorable (Figure 1). The amount of precipitation was lower relative to the long-term mean rainfall only in the 2019/2020 season. The winter rest period had a similar temperature and amount of precipitation compared to the long term. However, the 2019/2020 season was warmer than average compared to the long-term data. With regard to the periods of spring–summer vegetation, hydrothermal conditions [30] for wheat cultures were optimal in 2019 and excessively humid in 2018 and 2020 (

Table 2. The hydrothermal Sielianinov Index (K) in the experimental period.

Year	Spring-Summer Period				Mean
	April	May	June	July
2017/2018	3.48 (e/m)	2.60 (e/m)	0.75 (s/d)	0.85 (s/d)	1.92 (e/m)
2018/2019	0.50 (d)	1.11 (o)	0.91 (s/d)	1.55 (e/m)	1.02 (o)
2019/2020	2.35 (e/m)	3.21 (e/m)	0.40 (d)	0.58 (s/d)	1.64 (e/m)
1980–2016	1.62 (e/m)	1.45 (o)	1.30(o)	1.55 (e/m)	1.48 (o)

K ≤ 0.5—drought (d); 0.5 < K ≤ 1.0—semi-drought (s/d); 1.0 < K ≤ 1.5—border of optimal moisture (o); >1.5—excessive moisture (e/m).

). In turn, extremely unfavorable hydrothermal conditions in the form of drought occurred in April 2018 and June 2020. Conversely, excessively humid conditions were recorded in April–May 2018 and 2020.

2.2. Experimental Design and Agronomic Management

Winter wheat cv. Hybiza (breeder: Saaten Union Recherche SAS, Estrées-Saint-Denis, France) was the study subject. The cv. Hybiza (quality class A) is characterized by good technological parameters of grain (protein and gluten) and protein quality. The average proportions of gluten fractions in the grain are as follows: albumins and globulins—20.2%; gliadins—47.5%; and glutenins—32.3%. Additionally, this cultivar yields consistently well under varied agronomic and environmental conditions.

The experiment was based on a two-factorial split-plot design in three replicates. There were 24 plots with an area of 20.0 m² (12.5 × 1.6 m) for a total net experimental area of 480 m².

The study factors were as follows: tillage system (TS)–factor one: CT or RT. CT involved shallow plowing (depth 11–12 cm) and harrowing and pre-sowing tillage (depth 18–20 cm). In turn, RT involved disc harrowing (2.8 m wide; 14–15 cm deep), and, prior to sowing, combined cultivating (cultivator + string roller + harrow; 2.8 m wide).

Weed control method (WCM)–factor two: mechanical (M) and mechanical and chemical treatments with the recommended doses of herbicides at a level of 100%, 75%, and 50%, i.e., denoted as (MH100), (MH75), and (MH50), respectively.

Mechanical weeding (M) of the wheat crop was carried out three times, i.e., in autumn (3–4 leaf stage, BBCH 13–14), in spring at the beginning of the growing season, and the tillering stage (BBCH 24–25).

In using the mechanical and chemical method (MH100), M was performed only in autumn (3–4 leaf stage, BBCH 13–14). For chemical weed control (tillering stage, BBCH 24–25), commonly used herbicides Chwastox Trio 540SL (mecoprop, MCPA, dicamba; 2.0 L ha⁻¹) and Huzar Activ 387OD (iodosulfuron-methyl-sodium +2,4-D; 1.0 L ha⁻¹) were applied. In treatments MH75 and MH50, herbicide rates were reduced by 25% (doses 1.5 and 0.75 L ha⁻¹) and by 50% (doses 1.0 and 0.50 L ha⁻¹) in relation to the recommended dose (MH100).

Soybean was the previous crop for wheat. Wheat was sown at a rate of 200 seeds per m² in the first 10 days of October 2017, 2018, and 2019. It was harvested in the third 10 days of July 2018, 2019, and 2020. The other agrotechnical practices are presented in

Table 3. Agricultural practices in the experiment.

Specification	Fertilization and Plant Protection
Nitrogen–N (ammonium nitrate, 34%)	180 kg ha−1 (30 kg—presowing; 60 kg—start of vegetation; 60 kg—BBCH 32–33; 30 kg—BBCH 54–56)
Fungicides	Soligor 425 EC (protioconazole + spiroksamin + tebuconazole) 1.0 L ha−1 (BBCH 32–33); 3Artea 330 EC (propiconazole+cyproconazole) 0.5 L ha−1 (BBCH 54–56)
Insecticides	Karate Zeon 100 CS (lambda-cyhalothrin) 0.35 L ha−1 (BBCH 54–56)
Growth regulator	Moddus 250 EC (trinexapac-ethyl) 0.35 L ha−1 (BBCH 54–56)
Foliar fertilizer	FoliQ Mikromix (microelements in g dm−3: B—4,35; Cu—7,25; Fe—14,50; Mn—21,75; Mo—0,15; Zn—14,50) 1.0 L ha−1 (BBCH 54–56)

. Fertilization with phosphorus (superphosphate, 46%) at a dose of 100 kg ha⁻¹ and with potassium (potassium salt, 60%) at a dose of 130 kg ha⁻¹ was used once prior to wheat sowing. Nitrogen fertilization and other plant protection products were applied at adequate growth stages of wheat in accordance with the BBCH scale [31].

2.3. Grain Yield and Yield Components

Wheat grain was harvested at the fully ripe stage (BBCH 89–92) using a plot harvester. The grain yield from the plots was calculated per 1 ha at a 15% grain moisture content. Prior to the winter wheat harvest, the number of ears per m² was determined for two randomly selected areas (1 m × 0.5 m) of each plot. The mean number of grains per ear was calculated based on 25 wheat ears harvested from each plot. Thousand-grain weight (TGW) at a moisture content of 15% was calculated using a grain counter (Sadkiewicz Instruments, Bydgoszcz, Poland) [32].

2.4. Analytical Methods

The crude protein content of wheat grain was determined by the Kjeldahl method [33]. The wet gluten content and gluten index (GI) were determined using a Glutomatic 2200 Gluten System and a Glutomatic Centrifuge 2015 (Perten Instruments, Huddinge, Sweden) [34]. The GI value expresses the weight percentage of the wet gluten remaining on sieves after automatic washing in salt solution and centrifugation.

Protein fractions were analyzed using the RP-HPLC technique, described by Konopka et al. [35], with the help of a solvent system [36]. Albumins and globulins were twice extracted with 1 mL of 0.4 mol L⁻¹ NaCl containing 0.067 mol L⁻¹ HKNaPO4 (pH 7.6). Gliadins were extracted with 1 mL of 60% ethanol (a three-fold extraction). Glutenins were twice extracted with 1 mL of 50% 1-propanol, 2 mol L⁻¹ urea, 0.05 mol L⁻¹ Tris-HCl (pH 7.5), and 1% DTT (dithiothreitol) under nitrogen. Detection was carried out by an HP 1050 detector (Palo Alto, CA, USA) using a reading at a wavelength of 210 nm. The identification of protein subunits was based on their retention times and the second derivative of their UV spectra. The results were analyzed using the HPLC 3D ChemStation computer program (Palo Alto, CA, USA). The content of each protein fraction was expressed in mAU s⁻¹ (milli-absorbance units).

2.5. Statistical Analysis

The findings were statistically processed using a three-factorial variance analysis (ANOVA) in order to determine the effects of tillage systems, weed control methods, and study years on the following variables: yield, yield structure parameters, protein content and quality, and other quality characteristics of hybrid wheat grain. In total, 72 results (2 tillage systems, 4 weed control methods, 3 years, and 3 replicates) were used for statistical calculations with regard to the analyzed parameters. Calculations were made by means of a statistical programme Statistica 13.3.0. (TIBCO Software Inc., Palo Alto, CA, USA). The Shapiro–Wilk W-test was employed to ascertain the normality of variable distributions, while Levene’s test was utilized to validate the homogeneity of variance. The significance of differences between the treatments was verified using Tukey’s test at the significance level p ≤ 0.05.

3. Results

3.1. Yield and Yield Components

The choice of the tillage system had no significant effect on wheat grain yield, with a trend of increased grain yield in the CT system compared to the RT system (

Table 4. Hybrid wheat grain yield and yield components depend on the tillage system, weed control method (mean for 2017–2020), and years of research.

Factor		Grain Yield (t ha−1)	Number of Ears (no. m−2)	Number of Grains per Ear (no.)	Thousand Grain Weight (g)
Tillage System (TS)	Weed Control Method (WCM)
CT	M	7.37 ± 0.28 b	575.2 ± 4.9 c	33.7 ± 3.5 c	37.8 ± 3.2 d
	MH100	8.20 ± 0.41 a	602.6 ± 8.4 a	36.3 ± 5.3 a	42.5 ± 4.6 a
	MH75	8.00 ± 0.35 a	588.8 ± 7.4 b	34.6 ± 4.6 b	41.2 ± 4.4 b
	MH50	7.24 ± 0.23 b	571.6 ± 5.6 c	34.4 ± 4.2 b	38.6 ± 3.2 c
RT	M	7.06 ± 0.22 bd	570.5 ± 5.8 c	31.5 ± 3.0 c	37.3 ± 3.4 d
	MH100	7.94 ± 0.36 a	595.4 ± 8.1 a	35.6 ± 5.1 a	41.6 ± 4.2 b
	MH75	7.62 ± 0.30 b	583.1 ± 7.2 b	33.8 ± 3.7 c	39.9 ± 3.7 c
	MH50	6.82 ± 0.25 d	560.0 ± 4.6 d	33.6 ± 3.5 c	36.0 ± 3.5 e
CT		7.70 ± 0.28 a	584.6 ± 8.3 a	34.7 ± 4.4 a	40.0 ± 3.6 a
RT		7.36 ± 0.24 a	577.3 ± 6.4 b	33.6 ± 3.2 a	38.7 ± 3.0 a
	M	7.18 ± 0.25 b	572.9 ± 5.4 b	32.6 ± 3.4 c	37.6 ± 2.9 c
	MH100	8.07 ± 0.38 a	599.0 ± 9.1 a	36.0 ± 5.2 a	42.1 ± 3.8 a
	MH75	7.81 ± 0.32 a	586.0 ± 8.0 a	34.2 ± 4.8 b	40.6 ± 3.4 b
	MH50	7.03 ± 0.20 b	565.8 ± 4.1 b	34.0 ± 4.5 b	37.3 ± 3.1 c
Year (Y)	2017/2018	7.37 ± 0.28 b	576.4 ± 5.2 b	33.5 ± 3.8 b	39.0 ± 3.4 ab
	2018/2019	8.20 ± 0.41 a	587.2 ± 7.8 a	35.1 ± 4.6 a	40.3 ± 3.9 a
	2019/2020	8.00 ± 0.35 a	579.1 ± 4.9 ab	34.0 ± 4.9 ab	38.8 ± 2.8 b
Mean		7.53	581.0	34.2	39.4
TS		ns	F = 267.0 p < 0.0001	ns	ns
WCM		F = 181.9 p < 0.0001	F = 287.3 p < 0.0001	F = 90.3 p < 0.0001	F = 72.7 p < 0.0001
Y		F = 125.6 p < 0.001	F = 15.5 p < 0.01	ns	ns
TS x WCM		F = 19.0 p < 0.01	F = 18.6 p < 0.01	F = 16.1 p < 0.01	F = 32.4 p < 0.001
TS x Y		F = 7.6 p < 0.05	ns	ns	ns
WCM x Y		F = 12.4 p < 0.05	F = 20.9 p < 0.01	ns	ns
TS x WCM x Y		ns	ns	ns	ns

CT—conventional tillage; RT—reduced tillage; M—mechanical; MH100—mechanical and dose of herbicides 100%; MH75—mechanical and dose of herbicides 75%; MH50—mechanical and dose of herbicides 50%; The data shown are mean ± standard deviation (SD). Different letters in the same column indicate significant differences according to Tukey’s test at p < 0.05; ns—not significant.

). When CT was further compared with RT, the former revealed a slightly greater number of ears per square meter; however, this was with no significant differences in the number of grains per ear and thousand-grain weight (TGW) (Table 4). The highest grain yield was found in the mechanically and chemically weeded plots using either MH100 or MH75 treatments. The mean yield difference between them was 0.34 t ha⁻¹ and was statistically insignificant. The crop productivity for wheat weeded only mechanically (M) was lower by 0.89 and 0.63 t ha⁻¹ compared to treatments MH100 and MH75 and close to MH50 treatments, in which the crop productivity was the lowest (7.03 t ha⁻¹).

The number of grains per ear and TGW in MH100 were higher, particularly when compared to M treatments (by 9.5 and 10.7%) and MH50 (by 5.6 and 11.4%), respectively. The wheat developed the lowest number of ears per square meter in treatments MH50 and M, while the highest one was in MH100 and MH75 treatments, respectively. In comparison with the years 2018 and 2020, a higher wheat grain yield (by 0.69 and 0.96 t ha⁻¹, respectively) was achieved in 2019. The number of ears per m² and the number of grains per ear were the lowest in 2018. These parameters increased by 1.8 and 4.6% in 2019. In 2020, compared to 2018, that difference was insignificant. TGW was similar in 2018 and 2020 and higher in 2019 compared to 2018 and 2020.

It was demonstrated that the interaction between the particular tillage system (TS) and weed control method (WCM) affects grain yield and yield components (Table 4). The greatest grain yield was obtained in the CT and RT systems for the MH100 treatments. Furthermore, compared to MH100, the use of MH75 in the CT system did not lead to a significant decrease in grain yield. No such relationship was demonstrated for the RT system. However, the wheat crop responded with a drop in grain yield both in the CT and RT systems for M treatments, while the lowest yield drop was found in the RT system with MH50 (Table 4).

Also, wheat weeding in the CT or RT systems with MH100 treatment favored a significantly greater number of ears per m² and the number of grains from a single ear. Compared to MH100, the use of treatment MH50 gave rise to a reduction in the number of ears per m² in the CT and RT systems by 5.2 and 6.0%, respectively. In contrast with the number of ears per m², the mechanical weeding (M) in the CT and RT systems resulted in the lowest mean number of grains per ear. TGW was considerably determined by the TS x WCM interaction, too. In the case of treatment M, TGW values were similar both in the CT and RT systems. However, they were significantly greater in the other weed management treatments, i.e., by 2.1 (MH100), 3.2 (MH75), and 6.7% (MH50), when CT was compared with the RT system.

3.2. Quality Parameters

The content of protein in wheat grain significantly differed depending on the tillage system. A greater amount of this component was found in the CT system relative to RT; the difference was 15.2 g kg⁻¹ (

Table 5. Selected quality parameters, sum albumins, and globulins of hybrid wheat grain depending on the tillage system, weed control method (mean for 2017–2020), and years of research.

Factor		Protein (g kg−1)	Wet Gluten (%)	Gluten Index (%)	Albumins Globulins (mAU s−1)
Tillage System (TS)	Weed Control Method (WCM)
CT	M	129.3 ± 1.3 c	25.2 ± 1.2 c	90 ± 2 b	10.5 ± 0.3 a
	MH100	148.3 ± 2.5 a	30.4 ± 2.6 a	93 ± 1 a	11.1 ± 0.4 a
	MH75	138.5 ± 1.6 b	27.1 ± 1.8 b	94 ± 2 a	11.4 ± 0.2 a
	MH50	128.5 ± 0.9 c	25.7 ± 1.3 c	86 ± 3 c	10.8 ± 0.4 a
RT	M	116.7 ± 0.7 e	25.2 ± 0.7 c	85 ± 4 c	10.6 ± 0.3 a
	MH100	124.1 ± 1.6 d	28.7 ± 1.4 b	92 ± 1 a	11.0 ± 0.6 a
	MH75	123.9 ± 1.4 d	25.7 ± 1.2 c	90 ± 2 b	10.9 ± 0.1 a
	MH50	119.5 ± 0.9 e	24.1 ± 0.9 c	86 ± 1 c	10.0 ± 0.3 a
CT		136.2 ± 2.3 a	27.1 ± 2.1 a	91 ± 4 a	10.9 ± 0.2 a
RT		121.0 ± 0.9 b	25.9 ± 1.5 a	88 ± 2 b	10.6 ± 0.3 a
	M	123.0 ± 1.0 c	25.2 ± 0.8 b	87 ± 2 b	10.5 ± 0.3 a
	MH100	136.2 ± 2.0 a	29.5 ± 1.5 a	93 ± 4 a	11.0 ± 0.5 a
	MH75	131.2 ± 1.5 b	26.4 ± 2.0 b	92 ± 2 a	11.1 ± 0.4 a
	MH50	124.0 ± 1.4 c	24.9 ± 1.2 b	86 ± 1 b	10.4 ± 0.1 a
Year (Y)	2017/2018	128.3 ± 1.2 b	26.1 ± 1.2 a	90 ± 1 a	11.4 ± 0.2 a
	2018/2019	127.2 ± 1.0 b	26.3 ± 0.9 a	87 ± 1 b	9.6 ± 0.1 b
	2019/2020	130.3 ± 1.9 a	27.0 ± 1.8 a	92 ± 3 a	11.3 ± 0.4 a
Mean		128.6	26.5	90	10.8
TS		F = 45.3 p < 0.001	ns	F = 114.8 p < 0.0001	ns
WCM		F = 68.9 p < 0.0001	F = 40.8 p < 0.0001	F = 125.031 p < 0.0001	ns
Y		F = 10.4 p < 0.05	ns	F = 13.3 p < 0.05	F = 41.6 p < 0.05
TS x WCM		F = 78.4 p < 0.0001	F = 34.0 p < 0.001	F = 85.0 p < 0.01	ns
TS x Y		ns	ns	ns	ns
WCM x Y		ns	ns	ns	ns
TS x WCM x Y		ns	ns	ns	ns

CT—conventional tillage; RT—reduced tillage; M—mechanical; MH100—mechanical and dose of herbicides 100%; MH75—mechanical and dose of herbicides 75%; MH50—mechanical and dose of herbicides 50%; The data shown are mean ± standard deviation (SD). Different letters in the same column indicate significant differences according to Tukey’s test at p < 0.05; ns—not significant.

). The lowest significant content of protein was recorded in the grain harvested from the plot weeded either only mechanically (M) or mechanically with a 50% dose of herbicides (MH50). Treatments MH100 and MH75 exerted a positive effect on the protein content in the grain. The difference in the protein content between these treatments was 3.7%. The grain harvested in 2020 had a significantly greater protein content than the grain harvested in 2018 or 2019. Tillage systems and years did not influence the gluten content in the wheat grain. Among the weed control methods, the grain from treatment MH100 had a significantly higher content of gluten than that from treatments MH75, M, and MH50 by 10.5, 14.6, and 15.6%, respectively.

Gluten index values were modified by the tillage systems, weed control methods, and study years. A higher value of the parameter discussed was found for the CT system, when compared with RT, and in treatments MH100 and MH75. The grain harvested both from the treatments M and MH50 showed a lower value of this parameter. The gluten index turned out to be the lowest in 2019. It was higher in 2018 and 2020 when similar values were found.

The interaction between a given tillage system and weed control method had a significant effect on protein and gluten content, as well as on the gluten index value (Table 5). In comparison with the RT system, in the CT system, treatments MH100 and MH75 exerted a more beneficial effect on the grain quality characteristics under investigation. In the CT system, protein and gluten content was significantly higher for treatment MH100 compared to MH75, i.e., by 9.8 g kg⁻¹ and 3.3%. Under RT, in turn, the difference in the grain protein and gluten content between these weeding treatments was insignificant for protein and significant for gluten. The wheat grain from the RT system with mechanical weed management (M) alone showed the lowest protein, gluten index, and gluten values in treatment MH50. Furthermore, the amount of gluten in the grain for the CT and RT systems did not statistically differ between M, MH50, and MH75 for RT. No effect of the studied parameters and their interactions on the grain content of albumins and globulins in the grain was found. Similar values of the analyzed protein fractions were shown for 2018 and 2020. However, their decrease was observed in 2019.

3.3. Protein Composition

Protein fraction composition was significantly dependent on TS, WCM, the study year, and the relationships among the experimental variables (

Table 6. Values of gliadins of hybrid wheat grain depending on the tillage system, weed control method (mean for 2017–2020), and years of research.

Factor		Total GLI	α/β GLI	γ GLI	ω GLI
Tillage System (TS)	Weed Control Method (WCM)
		(mAU s−1)
CT	M	28.0 ± 1.5 a	14.9 ± 0.8 b	8.8 ± 0.8 a	4.3 ± 1.9 b
	MH100	29.2 ± 1.8 a	16.1 ± 0.9 a	8.1 ± 2.3 a	5.0 ± 0.9 a
	MH75	29.1 ± 1.4 a	15.8 ± 1.2 a	8.5 ± 1.0 a	4.8 ± 1.1 a
	MH50	25.4 ± 2.5 d	14.2 ± 1.7 b	6.6 ± 2.3 c	4.5 ± 0.8 b
RT	M	24.0 ± 2.6 d	13.4 ± 2.1 c	6.7 ± 0.5 c	4.0 ± 1.6 b
	MH100	27.6 ± 1.2 b	15.4 ± 1.3 a	7.7 ± 3.0 b	4.4 ± 1.5 b
	MH75	26.6 ± 1.8 b	14.6 ± 2.3 b	7.8 ± 1.5 b	4.2 ± 1.0 b
	MH50	24.4 ± 3.5 d	13.8 ± 2.8 c	6.8 ± 0.9 c	3.8 ± 0.7 b
CT		27.9 ± 1.6 a	15.2 ± 0.9 a	8.0 ± 1.8 a	4.7 ± 1.3 a
RT		25.6 ± 2.1 b	14.3 ± 1.4 b	7.2 ± 2.5 b	4.1 ± 1.0 a
	M	26.0 ± 1.8 b	14.1 ± 2.4 b	7.7 ± 1.5 ab	4.2 ± 0.9 a
	MH100	28.4 ± 1.9 a	15.8 ± 1.9 a	7.9 ± 0.7 a	4.7 ± 0.8 a
	MH75	27.8 ± 2.0 a	15.2 ± 0.9 a	8.2 ± 1.6 a	4.5 ± 2.3 a
	MH50	24.9 ± 3.2 b	14.0 ± 2.2 b	6.7 ± 1.5 b	4.2 ± 1.6 a
Year (Y)	2017/2018	26.9 ± 1.5 b	14.9 ± 1.8 ab	7.6 ± 0.7 ab	4.4 ± 2.2 ab
	2018/2019	25.1 ± 2.8 b	14.0 ± 2.5 b	7.2 ± 1.9 b	3.9 ± 1.4 b
	2019/2020	28.4 ± 1.4 a	15.5 ± 1.4 a	8.1 ± 1.4 a	4.8 ± 1.8 a
Mean		26.8	14.8	7.6	4.4
TS		F = 76.7 p < 0.0001	F = 11.7 p < 0.01	F = 65.4 p < 0.001	ns
WCM		F = 185.4 p < 0.0001	F = 10.9 p < 0.01	F = 86.3 p < 0.0001	ns
Y		F = 96.5 p < 0.001	F = 4.4 p < 0.05	F = 8.7 p < 0.05	F = 4.8 p < 0.05
TS x WCM		F = 89.0 p < 0.001	F = 15.0 p < 0.001	F = 29.5 p < 0.001	ns
TS x Y		F = 12.4 p < 0.05	F = 5.6 p < 0.05	ns	ns
WCM x Y		ns	ns	ns	ns
TS x WCM x Y		ns	ns	ns	ns

GLI—gliadins; α/β GLI—α/β-gliadins; γ GLI—γ-gliadins; ω GLI—ω-gliadins. CT—conventional tillage; RT—reduced tillage; M—mechanical; MH100—mechanical and dose of herbicides 100%; MH75—mechanical and dose of herbicides 75%; MH50—mechanical and dose of herbicides 50%; The data shown are mean ± standard deviation (SD). Different letters in the same column indicate significant differences according to Tukey’s test at p < 0.05; ns—not significant.

). Compared to RT, the use of the CT system caused a substantial increase in the sum of gliadins by 9.2%, and in the content of α/β and γ gliadin subunits by 6.0 and 10.0%, respectively. No statistical differences in the content of ω gliadin subunits between the CT and RT systems were noted. The mean percentages of α/β, γ, and ω gliadin subunits in the gliadin fraction of hybrid wheat grain were 55.3, 28.3, and 16.4%, respectively. The contents of gliadin subunits, excluding ω gliadins, and of total gliadins were significantly greater for the treatments MH100 and MH75 compared to treatments M and MH50. The differences in total gliadins and in the percentage of gliadin subunits between MH100 and MH75 were non-significant and ranged from 0.2 to 0.6 mAU s⁻¹. Compared to MH75 and MH100, the use of MH50 resulted in a reduction in total gliadins by 11.6 and 14.0%, respectively. It was also manifested by drops in the quantity of γ, α/β, and ω gliadin subunits to the greatest and lowest degree, respectively.

The relationship between TS and WCM revealed that the sum of gliadins and the content of γ gliadin in the CT system were similar in the context of treatments M, MH100, and MH75 (Table 6). Additionally, under CT, the comparisons of the α/β and ω gliadins contents in treatments MH100 and MH75 also showed statistically insignificant differences. In the RT system, higher total numbers of gliadin molecules and sums of gliadin subunits were found in the case of treatment MH100, while the lowest ones occurred in the cases of M and MH50. Under RT, no significant differences were revealed between treatments MH100 and MH75 for the sum of gliadins and the content of γ gliadin. The selected WCM method had no significant effect on ω gliadin content under RT. A more favorable grain content of gliadins and their sum were found in the 2020 season, particularly if compared to 2019 when the values of these parameters were the smallest.

In the CT system, compared to RT, the sum and content of glutenin subunits significantly increased within the range from 20.9 (LMW) to 29.8% (HMW), while for the sum of gliadins, the increase was 22.6% (

Table 7. Values of glutenins of hybrid wheat grain depending on the tillage system, weed control method (mean for 2017–2020), and year of research.

Factor		Total GLU	HMW-GS	LMW-GS	GLI/GLU
Tillage System (TS)	Weed Control Method (WCM)
		(mAU s−1)
CT	M	23.9 ± 3.5 b	5.4 ± 1.2 b	18.5 ± 3.2 a	1.24 ± 0.6 c
	MH100	27.7 ± 3.2 a	7.8 ± 2.5 a	19.9 ± 2.3 a	1.01 ± 0.5 d
	MH75	22.9 ± 2.5 c	5.6 ± 1.4 b	17.4 ± 2.4 b	1.29 ± 0.4 c
	MH50	19.1 ± 4.3 d	4.1 ± 1.5 c	15.0 ± 2.0 c	1.64 ± 0.4 a
RT	M	16.2 ± 2.9 e	3.2 ± 1.9 c	13.0 ± 1.8 d	1.45 ± 0.2 b
	MH100	19.0 ± 4.8 d	4.3 ± 1.0 c	14.6 ± 1.9 c	1.40 ± 0.1 b
	MH75	21.5 ± 3.9 c	5.1 ± 2.4 b	16.4 ± 2.0 b	1.27 ± 0.3 c
	MH50	15.7 ± 2.7 e	3.5 ± 2.0 c	12.1 ± 3.0 d	1.69 ± 0.6 a
CT		23.4 ± 3.3 a	5.7 ± 1.7 a	17.7 ± 3.2 a	1.30 ± 0.5 a
RT		18.1 ± 3.0 b	4.0 ± 1.9 b	14.0 ± 4.5 b	1.45 ± 0.8 b
	M	20.1 ± 1.9 b	4.3 ± 1.2 b	15.8 ± 4.1 b	1.34 ± 0.9 b
	MH100	23.3 ± 2.0 a	6.1 ± 1.8 a	17.3 ± 2.4 a	1.20 ± 0.2 a
	MH75	22.2 ± 2.2 a	5.4 ± 2.2 a	16.9 ± 2.9 a	1.28 ± 0.5 a
	MH50	17.4 ± 1.8 c	3.8 ± 2.5 b	13.6 ± 3.0 c	1.66 ± 0.6 c
Year (Y)	2017/2018	21.0 ± 3.5 ab	5.1 ± 1.4 a	15.9 ± 3.2 ab	1.36 ± 0.5 a
	2018/2019	19.7 ± 3.9 b	4.3 ± 1.8 b	15.5 ± 2.8 b	1.35 ± 0.9 a
	2019/2020	21.5 ± 4.2 a	5.3 ± 1.8 a	16.2 ± 2.4 a	1.41 ± 0.8 a
Mean		20.7	4.9	15.8	1.37
TS		F = 156.6 p < 0.0001	F = 147.7 p < 0.0001	F = 85.9 p < 0.0001	F = 8.1 p < 0.01
WCM		F = 112.9 p < 0.0001	F = 201.4 p < 0.0001	F = 49.6 p < 0.001	F = 5.0 p < 0.05
Y		F = 7.4 p < 0.05	F = 10.0 p < 0.05	F = 8.6 p < 0.05	ns
TS x WCM		F = 75.3 p < 0.0001	F = 35.6 p < 0.001	F = 7.5 p < 0.05	F = 6.6 p < 0.05
TS x Y		ns	ns	ns	ns
WCM x Y		ns	ns	ns	ns
TS x WCM x Y		ns	ns	ns	ns

GLI—glutenins; HMW-GS—high molecular weight glutenin subunits; LMW-GS—low molecular weight glutenin subunits; GLI/GLU—gliadin/glutenin ratio; CT—conventional tillage; RT—reduced tillage; M—mechanical; MH100—mechanical and dose of herbicides 100%; MH75—mechanical and dose of herbicides 75%; MH50—mechanical and dose of herbicides 50%. The data shown are mean ± standard deviation (SD). Different letters in the same column indicate significant differences according to Tukey’s test at p < 0.05; ns—not significant.

). Out of the total polymeric glutenin content, the mean percentages of HMW and LMW protein subunits were 23.7 and 76.3%, respectively. No significant differences in the total number of glutenin molecules, as well as of HMW and LMW glutenin subunits, were demonstrated between treatments MH100 and MH75. The differences in the content of HMW and LMW glutenins for the treatments MH100 and MH75 were 0.70 and 0.40 mAU s⁻¹, respectively, and the glutenin sum was 1.10 mAU s⁻¹. The grain from the treatment MH50 showed the lowest content of glutenins. Treatment M, compared with MH50, was distinguished by a significantly higher content of glutenin sum and LMW glutenins, whereas the difference in HMW glutenin content was insignificant.

The TS x WCM interaction demonstrated a significantly high content of glutenins in the CT system and treatment MH100, while under RT in MH75 treatment (Table 7). Decreasing the herbicide dose by 25% (MH75) did not cause a significant difference in glutenin content in the CT system compared to the RT system. The content of HMW glutenin subunits in the CT system was similar for treatments M and MH75, whereas, in the RT system, it was similar for treatments in M, MH100, and MH50. On the other hand, the content of LMW glutenin subunits was similar in the CT system in treatments M and MH100, while under in RT it was similar in treatments M and MH50. Herbicide dose reduction by half (MH50) in the CT and RT systems caused a significant decrease in total glutenin molecules, while under RT, the value of this parameter did not statistically differ compared to treatment M.

The highest gliadin values were noted in 2020, whereas in 2018 and 2019, their decrease occurred. Compared to 2020, in 2019, a drop in the sum of glutenins and in the numbers of HMW and LMW glutenin subunits took place by 9.1, 23.2, and 4.5%, respectively. In relation to the RT system, the grain from the CT system presented a better GLI/GLU ratio. A more beneficial GLI/GLU ratio was found in the treatment MH100, especially compared to MH50. In both tillage systems, treatment MH50 caused a significant increase in the GLI/GLU proportion, while in the case of MH100, it was 38.4% under CT, and in the case of MH75, it was 24.9% under RT. The study calendar years did not cause a significant difference in the GLI/GLU proportion.

4. Discussion

4.1. Grain Yield and Yield Attributes

For the hybrid wheat, grain yield and the elements of yield structure were determined mainly by WCM and study years, while to a lesser extent by TS. No significant differences, especially in the case of the CT system, were found in the grain yield achieved both in MH100 and MH75. In their study on the efficacy of lower herbicide doses used in wheat, Hussain et al. [37] also achieved an optimum grain yield using only 75% of the recommended herbicide dose with an addition of an adjuvant. Wesołowska et al. [38] demonstrated that using herbicides with spelt, both in recommended and reduced doses, caused a significant increase in grain yield within the range of 0.59–1.63 t ha⁻¹ compared to mechanical weed control.

In our own study, the wheat responded with a drop in the grain yield for treatments M and MH50, both in the CT and RT systems. In turn, an experiment conducted by Cacak-Pietrzak et al. [39] revealed that the use of herbicides in recommended doses with spring wheat had no effect on yield. Under the influence of their higher doses, however, a significant reduction in the grain yield occurred compared to the control plot weeded mechanically. Also according to Didace et al. [40], the application of different herbicides at recommended doses and doses reduced by 50% in wheat did not cause any differences in grain yield, but the combination of the herbicides with a growth regulator improved the yield structure elements and enhanced the grain quality. As reported by Javaid et al. [41], the effectiveness of weed management in wheat increased after the application of the recommended rate of metribuzin combined with an adjuvant since the highest TGW, as well as the highest biological yield and grain yield, were obtained in this treatment.

The hybrid wheat harvested from the plots in treatment MH75 was characterized by a similar number of ears per m² compared to the use of MH100. However, it showed a significantly higher number of ears per m² relative to treatments MH50 and M. In their study, Khaliq et al. [42] introduced the wheat spray in the treatments MH100 and MH75. In each instance, it caused an increase in the number of ears per square meter and the number of grains per ear; however, it did not differentiate the TGW parameter. According to Zhang et al. [43], the use of reduced herbicide doses, although ecologically justified, may be burdened with a greater risk of their lower efficacy than the use of recommended doses.

Based on Swanton et al. [44] and Sheikhhasan et al. [45], the efficacy of herbicides, used in doses reduced by 25–50% in relation to the recommended doses, is dependent on numerous factors, such as the competitiveness of varieties, degree of weed infestation in a field, the growth stage of weeds, the herbicide active substance, or weather conditions.

Excessive rainfall in April and May 2018 and 2020 caused a reduction in the grain yield and the elements of yield structure, if compared to 2019 when hydrothermal conditions were optimal. Moreover, a lower soil moisture content in 2019 resulted in lower competitiveness of weeds, which, in turn, led to a higher stability in the hybrid wheat yields. Wesołowska et al. [38] reported that high precipitation in the spring–summer period can affect the efficacy of weed control methods, both in mechanically weeded experimental plots and in treatments with a reduced dose of herbicides. A strong negative correlation between the wheat yield and total rainfall in the growing season was observed by De Vita et al. [46].

Our findings demonstrated that the particular tillage systems did not significantly affect the grain yield. This accounts for the possibility of growing hybrid wheat crops both in CT and RT systems without plowing. In relation to the CT system, comparable wheat yields in the RT system may be due to a positive response of wheat to an enhanced capacity for water retention in the soil in reduced systems, as mentioned in the study by Wesołowska et al. [38]. Similarly to our study, where the difference in the yield between the CT and RT systems was 0.34 t ha⁻¹, De Vita et al. [46] also demonstrated that the mean wheat yield was almost identical in the CT and NT systems, with the difference amounting to 0.52 t ha⁻¹ and being statistically insignificant. A study by Małecka et al. [47] revealed that a reduction in wheat yields in the treatments with no-tillage crops was associated, first and foremost, with a drop in ear density per m², and, to an inconsiderable degree, with a drop in the number of grains per ear and TGW. Woźniak and Rachoń [14] proved that the individual tillage systems had no effect on the following: grain weight per ear, TGW, the number of ears per square meter, and wheat grain yield, both under CT and RT systems, while a significantly lower number of ears per square meter and grain yield were found in the NT system compared to the CT system.

4.2. Grain Quality Parameters

Our study demonstrated a significantly higher content of protein and a higher gluten index in the hybrid wheat grain in the CT system when compared to the RT system. The amount of gluten did not statistically differ between the CT and RT systems. According to Šip et al. [48], the CT system favors a more beneficial use of nitrogen, which results in a better quality of the wheat grain, especially a higher protein content than in the RT system. Jaskulska et al. [49] revealed that the use of CT and RT systems had no effect on the following: protein content, quantity of gluten, sedimentation index, and other quality parameters of wheat grain, whose increase was determined by a higher rate of 200 kg N ha⁻¹ and flour. No effect of tillage systems on the basic parameters of wheat grain quality has also been demonstrated in other studies [50,51,52].

The dietary value of wheat is extremely important because wheat occupies an important place among cultivated species, which are commonly grown as a basic source of food [2]. A study by Mehmeti et al. [53] demonstrates that after the application of herbicides (triasulfuron + dicamba), compared to mechanical weed control, the protein content in wheat grain was higher by 15.3 g ha⁻¹. According to Kieloch and Domaradzki [54], the use of herbicides in mixtures with retardants, both at the tillering stage of winter wheat and at the flag leaf stage, contributed to lower seed uniformity but did not disqualify the grain in terms of its protein and gluten content. Khan et al. [22], in turn, draw attention to the fact that weeds compete with the crop plant for minerals and hinder their uptake as well as disturb soil microbiological activity, which in combination decreases the nutritional value of plants, in particular by reducing the nitrogen and protein content in seeds.

In the present study, the wheat grain obtained in the RT system, especially that harvested from the plot with mechanical weeding (M) alone, was characterized by the lowest values of protein content and gluten index as well as by the lowest gluten content for treatment MH50.

In order to achieve a good baking quality of wheat products, the required content of wet gluten in the grain should be at least 25% and the flour ought to have a gluten index within the range of 75–90 [55,56]. In our studies, gluten content above 25% and gluten index above 90 were achieved in the CT and RT systems for the treatment MH100, while only for the treatment MH75in the CT system. Likewise, the study by Wesołowska et al. [38] showed that spelt, weeded with a 100% and 75% dose of herbicide, demonstrated a higher level of grain quality parameters, including the content of protein and gluten, and a falling number and sedimentation index. A paper by Andruszczak [57] revealed that chemical plant protection caused a substantial increase in protein content and sedimentation index in the spelt; however, it did not differentiate the amounts of gluten and starch it in.

As far as the protein fraction composition is concerned, the study on hybrid wheat led to the observation that there was a higher content of total gliadins, including α/β and γ gliadins as well as glutenins and their LMW and HMW subunits in the CT system compared to RT. However, experiments conducted by Peigné et al. [52] demonstrated only a tendency for a higher content of gliadins under RT compared with CT, with no effect on the number of glutenins and their subunits. In agreement with the study by Godfrey et al. [58], the quality characteristics and protein proportions of wheat grain are linked predominantly to fertilization with nitrogen, used particularly just before wheat flowering. Dupont and Altenbach [59] reported that the use of nitrogen at the end of the wheat growing period, under perfect circumstances, should exert a positive effect on the elevation of the protein concentration in the grain because nitrogen directly participates in the synthesis of cereal proteins. Furthermore, the amount of protein in the wheat grain is, to a considerable degree, determined by the nitrogen content in the soil. This chemical element is not only delivered to the plant as a result of fertilization: its incorporation in the cereal’s amino acid residues also stems from the mineralization of post-harvest remains, especially if leguminous plants are the previous crop for wheat [60].

A less favorable fractional content of protein under RT in relation to the CT may be associated with a greater soil density and infestation with weeds, which, in turn, may lead to poorer nitrogen uptake by the wheat [48,52,61]. Our experimental findings indicate that, both for the CT and RT systems, mechanical and chemical weed control either in a recommended dose (MH100) or a dose reduced by 25% (MH75) yielded grain of better fractional protein content than only mechanical methods (M) or mechanical methods with a 50% baseline dose of the herbicide (MH50). According to Hernández Plaza et al. [62], in the case of a relevant limitation of a reduction in herbicide doses, the appearance of a greater number of weeds and their more numerous species composition may affect the quality of the wheat grain, modifying protein content, but it does not exert any effect on GLI/GLU proportions. Marti et al. [63] reported that the GLI/GLU ratio constitutes a balanced index between the elasticity and extensibility of dough, and its optimum value ranges from 1.0 to 1.3. In our own study, the range of such GLI/GLU values was achieved in the CT and RT systems for treatment MH75 and in the CT system both for treatment MH100 and M. Weather conditions during the filling up of the grain affect the accumulation of proteins and the development of caryopses. Additionally, they have the potential to change the functional properties of flour [7].

Protein constituents are very sensitive to drought and thermal shock at later stages of grain filling up. Importantly, under such conditions, it is common to record an increase in protein content, yet it does not have to entail an improvement in its quality [64,65]. The hybrid wheat grain had a higher protein content and a more favorable composition of protein molecules and their subunits in 2020 and 2018 when in June and July, i.e., in the period of the grain filling up, periodical droughts occurred. However, an unequivocal study year on the amount of gluten and the gliadin to glutenin ratio was not demonstrated. Stress associated with drought exerts a particular impact on the speed and duration time of accumulation of gliadin and glutenin as well as their composition [8,66]. In our study, from among the gliadin and glutenin fractions, the highest increase was recorded in 2020 in relation to 2019 specifically for ω gliadin and HMW glutenin by 18.8% and 18.9%, respectively. The scientific works by Rekowski et al. [8] show that strong drought-induced stress during the filling up of the grain has a positive effect on the wheat grains, while under such conditions, the quality of a bread baking batch may more strongly depend rather on ω gliadin fractions than, as was expected before, on HMW glutenins.

5. Conclusions

The selection of the tillage system did not have a significant effect on hybrid wheat grain yield and yield structure elements (except for an increase in the number of ears per m² under CT). The use of the RT system decreased the protein content and the glutenin (GLU) fraction. The amount of gluten and ω gliadin (GLI) subunits did not differ between the CT and RT systems. A higher productivity and quality of hybrid wheat grain can be achieved by using mechanical and chemical weed control with both the recommended dose of herbicide (MH100) and a dose reduced by 25% (MH75).

A reduction in the herbicide dose by 25% (MH75), compared to the recommended dose (MH100), improved the glutenin (GLU) fraction composition particularly in the RT system, without causing significant differences in the protein content. The stability of hybrid wheat yields was promoted by optimal hydrothermal conditions during the spring/summer growing season. On the other hand, short-term rainfall deficiency during the wheat ripening period contributed to a higher protein content and a more favorable composition of proteins and their subunits in the grain.

Given the unfavorable effect of herbicides on the natural environment and grain quality, research on reduction in herbicide doses in different wheat varieties and species, grown especially under no-tillage (NT) and reduced tillage (RT) conditions, should be continued.