Spelt in Diversified and Spelt-Based Crop Rotations: Grain Yield and Technological and Nutritional Quality

Abstract

A properly designed crop rotation contributes to the equilibrium of the agro-ecosystem and the volume and quality of the yield. The cultivation of spelt in crop rotations enriches its biodiversity and provides grains with many different types of nutritional value. The aim of this current study was to investigate how the distribution of winter spelt in different positions and after different forecrops in four-field crop rotations would affect the technological quality of the grain, the nutrient content of the grain, and the grain yield. A 6-year field experiment, designed in a randomised block, was conducted from 2012 to 2018 in north-eastern Poland (53°35′47″ N, 19°51′20″ E). This study provides the results from a 6-year (2013–2018) field experiment. The spelt was cultivated in four crop rotations: CR1—winter rape + catch crop (blue tansy), spring barley, field pea and winter spelt; CR2,—winter rape, winter spelt + catch crop (blue tansy), field pea and winter spelt; CR3—winter rape + catch crop (blue tansy), field pea, winter spelt and winter spelt; and CR4—winter rape, winter spelt + catch crop (blue tansy), spring barley and winter spelt. This study evaluated grain yield and the following grain parameters: the total protein, wet gluten and starch contents, the Zeleny index, the falling number, the weight of 1000 grains, the N, P, K, Mg, Ca, Cu, Fe, Zn and Mn contents, and the grain yield. The results were assessed at the significance level p < 0.05. It was demonstrated that the cultivation of spelt in all four crop rotations after winter rape and after field pea was characterised by higher protein and wet gluten contents, Zeleny index value and falling number, a greater weight of 1000 grains, higher N, P, Fe and Zn contents, and greater grain yield than those harvested from the crop rotations CR3 and CR4 after spelt and after barley. It was demonstrated that the cultivation of spelt in crop rotations CR3 and CR4, in succession after spelt and after barley, caused deterioration in grain quality (lower protein and gluten contents, a lower Zeleny index value, a lower falling number, and a smaller weight of 1000 grains, and the N, P, Fe and Zn contents). In addition, a smaller grain yield was obtained from these crop rotation fields. Regardless of the type of crop rotation, the cultivation of spelt after winter rape and after pea produced a high yield and a good quality yield of this cereal. Due to the lower yield of grain and its lower quality, it is not recommended that winter spelt is grown after each other or after spring barley.

1. Introduction

A properly functioning, sustainable, and biodiverse agro-ecosystem guarantees that high and qualitatively good yields are obtained. It has a beneficial effect on the fertility of the soil and its biological life, and protects crops against the excessive spread of diseases, pests and weeds, which is very important for ensuring food security [1,2,3]. Meanwhile, modern, conventional agriculture is increasingly focused on the cultivation of fewer species and fewer varieties within each species [4], with wheat being the dominant species in fields under cultivation [5]. The breeding progress in the cultivation of this cereal has considerably increased yields, although it has reduced its genetic diversity and deteriorated the grain quality [6]. In order to obtain high yields with high protein contents, the application of high-input means of production, such as fertilisers (particularly those that are nitrogen based) and plant protection agents, is required in the cultivation of wheat.

An alternative solution is to introduce ancient cereals to the production, such as spelt, einkorn wheat and Khorasan wheat [7,8]. The cultivation of old wheat species is a holistic and sustainable method for increasing cereal biodiversity [9]. This enriches the diversity of foods by incorporating valuable nutritional substances [10]. The most common ‘old cereal’ in cultivation is spelt wheat [11]. Its grains are superior to the common wheat grains in terms of the protein content, soluble dietary fibre, fat and minerals, such as phosphorus (by approximately 10%), copper (by approximately 20%), potassium (by approximately 7%) and zinc (by approximately 70%), as well as iron and magnesium [12,13,14]. Moreover, it is a rich source of bioactive compounds and micronutrients [6,15,16,17]. Spelt is, however, characterised by a lower gluten quality as well as poorer dough stability and strength [18,19]. Where the soil is well supplied with nutrients, spelt produces lower yields than modern wheat varieties [20].

Currently, two types of spelt are cultivated: traditional (pure) spelt and modern spelt, derived from hybridisation with common wheat. The technological quality of the grain and flour of hybrid varieties does not differ from the quality of traditional varieties [21]. Due to the increasing consumer awareness of high-quality (healthy) foods, there is a growing demand for food products made from spelt (bread, biscuits, pasta, etc.). For this reason, there is more and more research into the quality of this cereal grain [22].

In sustainable agriculture, crop rotation serves an important role [1,23,24]. It is one of the oldest, most environmentally friendly, input-free factors of production. Crop rotation has a favourable effect on the volume and quality of the yields obtained and is a natural method for reducing weeds, diseases and pests [1,25]. Its long-term effect is noticeable after many years (several crop rotation cycles) [26]. The cultivation of different species, one after another, on the same field provides (physical, chemical and biological) properties of the soil environment, which are favourable for crops. This contributes to the availability and efficient utilisation of nutrients by crops [1,26,27,28,29,30,31,32,33,34]. The inclusion in crop rotations of plants that have a favourable effect on the soil, such as sugar beet, potato, rape, legumes and catch crops, results in greater yields and higher yield quality of the successive crops (mainly cereals) [5,35,36,37,38,39]. The inclusion of spelt in crop rotations also increases the biodiversity of the agro-ecosystem [40], which contributes to sustainable agricultural production [22,41].

Recent years have seen a simplification in crop rotations, involving a reduction in the number of species under cultivation to two or three and even their cultivation in monoculture [42]. However, the frequent cultivation of the same species in succession on the same field, and especially cultivation in monoculture, has an adverse effect on the agro-ecosystem, resulting in the excessive development of weeds, pathogens and pests [1,38,43]. In the soil environment, an accumulation of secondary metabolites of plants and microorganisms takes place, the excessive concentration of which disturbs the biological equilibrium of the soil [2,44,45]. These factors are considered to be among the main causes of a reduced yield and the deterioration of the yield quality in short crop rotations and in monocultures. This has been confirmed by the research of Darguza and Gaile [46], who showed that the decrease in yield of wheat grown after wheat was almost 30%, relative to crop rotation. There was also a 10% decrease in the weight of 1000 grains and a 7% decrease in the protein content of the grain. Babulicova [47], growing spelt in a rotation with 80% cereals, found a reduction in grain yield by 6%, the weight of 1000 grains by 8%, gluten by 7%, and Zeleny index and falling number by 8%, compared to a rotation with 60% cereals. Similarly, Wanic et al. [48], growing spelt in a field after spelt, observed a reduction in grain yield by 16%, weight of 1000 grains by 5%, protein by 7%, gluten by 5% and Zeleny index by 8%, relative to its cultivation after pea. The consequences of such practices vary and are largely determined by the cereal species and varieties, natural (mainly soil and climate) conditions, and the agricultural practices applied [42]. This problem has led to a reduction in the number of crop rotation species in Europe and Poland for the past 50 years. It is cereals, and wheat in particular, that have become the dominant species in crop rotations.

Scientific literature provides a wealth of information on the effect of crop rotation on common wheat grain yield and quality. However, there has been little research on spelt, especially its hybrid varieties. Moreover, this information has been acquired across short (2–3 years) research periods. Our research adds to the knowledge on the above topic. It is based on six years of research results. The aim of this study was to investigate how the crop rotation type, forecrop (winter rape, field pea, winter spelt and spring barley) and the frequency of the cereals in crop rotation would affect grain yield, the technological properties of the grain and the macro- and micronutrient contents of the grain. This study put forward the research hypothesis that the share of winter spelt in crop rotations and the cultivation of winter spelt after different forecrops (winter rape, field pea, winter spelt and spring barley) would not bring about changes in the qualitative characteristics of the grain and the yields of this cereal. The hypothesis was verified based on the results obtained from the 6-year field experiment.

2. Materials and Methods

2.1. Site, Soil and Climate

This study was based on a field experiment located in north-eastern Poland at the research centre of the University of Warmia and Mazury in Olsztyn (53°35′47″ N, 19°51′20″ E) and conducted in the years 2012–2018. This paper presents the results obtained in the years 2013–2018, representing years 2, 3, 4, 5, 6 and 7 of this experiment.

Soil experimental fields were classified as Luvisols [49]. In its 0–30 cm layer, the soil contained 64.7% sand, 15.4% coarse silt, 16.5% fine silt and 3.4% clay. It was characterised by a slightly acidic reaction (pH KCl of 6.0), a SOC content of 6.7 g∙kg⁻¹, a total N content of 0.66 g kg⁻¹, a phosphorus content of 63.5 mg∙kg⁻¹, a potassium content of 170.0 mg∙kg⁻¹ and a magnesium content of 45.7 mg∙kg⁻¹.

During the winter spelt growth period (from October to July), the average air temperature was (

Table 1. Air temperature and precipitation in the growing seasons of winter spelt (2012/2013–2017/2018).

Season	Months
	Sep	Oct	Nov	Dec	Jan	Feb	Mar	Apr	May	Jun	July	Aug
Air temperature (°C)
2012/2013	14.0	7.9	4.9	−3.3	−4.5	−0.8	−4.0	6.3	15.0	17.4	17.9	18.0
2013/2014	11.5	9.3	4.9	2.3	−3.5	2.0	5.5	9.5	13.3	14.8	21.0	17.9
2014/2015	14.5	9.5	4.4	−0.6	0.6	0.3	4.6	7.2	12.1	15.7	18.0	21.3
2015/2016	13.0	8.1	2.8	−1.0	−2.4	−1.6	1.8	7.7	13.2	15.8	18.3	17.7
2016/2017	14.1	6.9	2.5	1.0	−3.2	−1.2	5.1	6.7	13.1	16.7	17.3	18.7
2017/2018	13.5	9.4	4.3	1.9	0.0	−4.1	−0.5	11.9	16.5	17.9	20.0	20.4
Precipitation (mm)
2012/2013	41.0	57.6	48.5	15.1	34.6	21.3	14.0	22.5	46.2	45.4	163.8	25.3
2013/2014	69.3	15.4	23.2	34.1	44.0	11.4	55.7	26.1	24.9	72.2	20.4	59.2
2014/2015	30.8	21.3	21.2	56.6	28.5	8.8	46.0	23.4	25.4	43.0	71.0	13.0
2015/2016	56.2	51.2	46.1	42.6	30.1	23.1	30.7	29.8	62.3	72.9	81.2	70.6
2016/2017	17.1	96.3	78.2	77.8	15.8	40.5	53.0	52.1	34.0	109.9	106.1	54.8
2017/2018	211.1	160.3	49.0	53.8	37.6	2.0	25.0	28.1	41.0	64.7	140.7	31.2

) as follows: in the 2012/2013 period, +5.7 °C; in 2013/2014, +7.9 °C; in 2014/2015, +7.2 °C; in 2015/2016, +6.3 °C; in 2016/2017, +6.5 °C; and in 2017/2018, +7.7 °C. In all of the years of this study and all of the months of the spelt growth period, the air temperature was similar to the average multiannual temperature for this region, and was not a limiting factor in the growth and development of spelt.

Precipitation between October and July was as follows: in the period of 2012/2013, 469.0 mm; 2013/2014, 327.4 mm; 2014/2015, 345.2 mm; 2015/2016, 470.0 mm; 2016/2017, 663.7 mm; and in 2017/2018, 602.2 mm. The highest levels of precipitation were noted for the season of 2012/2013 in July (34.9% of the total amount); for 2013/2014 in June (22.1% of the total amount); for 2014/2015 in July (20.6% of the total amount); for 2015/2016 in May, June and July (14.9, 17.4 and 19.4% of the total amount, respectively); for 2016/2017 in June and July (19.4 and 18.7% of the total amount, respectively); and for 2017/2018 in July (31.8% of the total amount). Heavy rainfall in September and October during the 2017/2018 season delayed the spelt sowing date (the cereal was sown as late as 20 October), which resulted in its reduced yield. During that season, very heavy rainfall in June had no effect on the yield and its quality, as it occurred in the second ten-day period of that month (with the spelt already being in the ripening stage). Excessive precipitation in July 2013 and in June and July 2017 was the cause for the reduced quality of the cereal grain. In contrast, evenly distributed rainfall in April, May, and June 2018, combined with a higher air temperature than in previous years, had a favourable effect on spelt grain quality.

2.2. Experimental Design

This experiment was established as a single-factor study in the autumn of 2011. It was designed in a completely randomised block in 4 replicates. The experiment assessed four crop rotations, as follows:

CR1

—winter rape + catch crop (blue tansy), spring barley, field pea and winter spelt (CR1-P); 50% cereals, including 25% spelt (control).

CR2

—winter rape, winter spelt (CR2-O) + catch crop (blue tansy), field pea and winter spelt (CR2-P); 50% spelt.

CR3

—winter rape + catch crop (blue tansy), field pea, winter spelt (CR3-P) and winter spelt (CR3-S); 50% spelt.

CR4

—winter rape, winter spelt (CR4-O) + catch crop (blue tansy), spring barley and winter spelt (CR4-S); 75% cereals, including 50% spelt.

The forecrops for winter spelt were field pea (crop rotations CR1, CR2 and CR3), winter rape (crop rotations CR2, CR4), winter spelt (crop rotation CR3) and spring barley (crop rotation CR4). The plant varieties employed were ‘Rokosz’ (a hybrid variety) for winter spelt, ‘Califorium’ for winter rape, ‘Batura’ for pea and ‘Mercada’ for spring barley.

In each year, the experiment was carried out on all crop rotation fields simultaneously. In each year, this included 64 plots (4 fields/crops in crop rotation x 4 crop rotations, x 4 replicates), each with a harvestable area of 16 m² (Table S1). Detailed research was conducted on the plots sown with winter spelt.

In the years 2012, 2013, 2014, 2015 and 2016, winter spelt was sown in autumn within the optimal agrotechnical time frame (on 17 September, 21 September, 12 September, 21 September and 17 September, respectively) In 2017, due to the very high water content of the soil (caused by heavy rainfall in September and October) the sowing was carried out later (20 October). The spelt was sown at a germinating kernel density of 450 seeds∙m⁻², at a depth of 3 cm. The NPK mineral fertilisation rates were determined based on the soil abundance and the estimated values of their uptake by the crops, and for N, they also depended on the forecrops. For the winter spelt, N (ammonium nitrate 34%) was applied at the following rates: 160 kg ha⁻¹ on the fields following the cultivation of winter rape, winter wheat and spring barley, and 130 kg ha⁻¹ on the fields following the cultivation of field pea. Doses of P (superphosphate 18%) and K (potassium salt 60%) were identical for all the plots sown with spelt (they were not differentiated depending on the forecrop). They were applied in autumn, a few days prior to the sowing of spelt, at the rate of K—91.3 kg∙ha⁻¹ and P—35.2 kg∙ha⁻¹ of pure component. The entire N dose was divided into four parts and applied before sowing (20 kg∙ha⁻¹); at the tillering stage, BBCH 25–29 (80 kg∙ha⁻¹); at the stem elongation stage, BBCH 30–31 (40 kg∙ha⁻¹); and at the heading stage, BBCH 56 (20 kg∙ha⁻¹).

The following preparations were used against weeds. Mustang 306 SE (florasulam and 2.4-D) at a rate of 0.5 dm³ ha⁻¹ at BBCH 12–32 and Lancet Plus 125 WG (florasulam, pyroxsulam and aminopyralid) at a rate of 0.2 kg∙ha⁻¹ at BBCH 21–31. Aphids were controlled using a preparation of Karate Zeon 050 CS (lambda-cyhalothrin) at a rate of 0.12 dm³ ha⁻¹ (BBCH 57–59). The cereal leaf beetle was controlled using preparations of Decis Mega 50 EW (deltamethrin) at a rate of 0.1 dm³ ha⁻¹ and Sherpa 100 EC (cypermethrin) at a rate of 0.2 dm³ ha⁻¹ (BBCH 55–59).

The grains of the spelt were harvested from each plot using a plot harvester at the full kernel ripeness stage (BBCH 89) as follows: in 2013, on 28 July; in 2014, on 23 July; in 2015, on 4 August; in 2016, on 28 July; in 2017, on 3 August; and in 2018, on 24 July.

2.3. Measurements

2.3.1. Grain Yield Determination

Each year, after harvesting, the spelt grains from each plot were de-hulled, dried to a water content of 12% and weighed. The results obtained in kg per plot were converted to t per ha. A sample of 1 kg of the grain from each plot was weighed out. In the laboratory, the weight of 1000 grains (TGW) was determined for these samples. Fully developed grains with a diameter of more than 2 mm were analysed. Analyses were carried out each year on 500 grains from each plot. The results were converted into 1000 grains. The measurements were made using an electronic seed counter (LN-S-50A, Unitra Cemi, Zumpi, Szczytno, Poland).

2.3.2. Grain Quality

Analyses were performed to ascertain the technological properties of the grain, including the total protein, wet gluten and starch contents of the grains, the Zeleny sedimentation index and the falling number. Furthermore, the nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), copper (Cu), iron (Fe), zinc (Zn) and manganese (Mn) contents in the grain were determined. The technological properties of the spelt grain were determined using a NIR System InfratecTM 1241 Analyzer (Foss). The mineral content of the spelt grain was determined following the wet mineralisation of plant material in concentrated sulfuric acid (H₂SO₄) using the following methods: the Kjeldahl method for N, the spectrophotometric method for P, the flame photometry method for K, and flame atomic absorption spectrometry (FAAS) for Mg, Ca, Fe, Zn and Mn [50]. The analyses were carried out each year (2013–2018) on grain samples derived from each plot.

2.4. Statistical Analysis

In the statistical processing of the results, a two-way analysis of variance (ANOVA) at a probability p < 0.05 was applied. The factors included crop rotations and the years of study. Homogeneous groups were then determined using Tukey’s test (HSD) at p < 0.05. This analysis was conducted using the Statistica 13.3 program.

3. Results

3.1. Effect of Crop Rotation on Grain Yield of Spelt and Weight of 1000 Grains

This study demonstrated a significant effect of crop rotations (p = 0.002) and years (p = 0.001), as well as the interactions between them (p = 0.003) on spelt grain yield and the weight of 1000 grains (p < 0.001, p < 0.001 and p = 0.011, respectively) (

Table 2. Significance testing (p-values) for spelt grain yield and weight of 1000 grains (TGW) depending on crop rotation, years and the interaction between crop rotation and years.

Grain Yield and Weight of 1000 Grains	Crop Rotation (CR)	Year (Y)	Interaction (CR × Y)
Grain yield	0.002	0.001	0.003
TGW *	<0.001	<0.001	0.011

* weight of 1000 grains.

).

On average, across the years, no significant changes in grain yield were noted between the sites of spelt cultivation in crop rotations CR1, CR2, in CR3 after pea, and in CR4 after rape (Figure 1). The cultivation of spelt in succession after spelt (CR3-S) and after barley (CR4-S) resulted in a reduction in grain yield (on average across the years by 17.3–21.8%). The magnitude of the yield reduction after spelt and barley was similar in most of this study years. A reduction in grain yield at the site of spelt cultivation after spelt (CR3-S) and after barley (CR4-B) was noted in all the years of this study. The greatest reduction took place in 2016 (over 50%) and the smallest was in 2013, in the field of spelt cultivation in succession after spelt (7%).

The greatest weight of 1000 grains (TGW) was exhibited by the grain harvested from the fields CR1-P, CR2-O CR3-P and CR4-O (

Table 3. Weight of 1000 grains (TGW) of spelt.

Years	Fields in Crop Rotations							Mean
	CR1-P	CR2-O	CR2-P	CR3-P	CR3-S	CR4-O	CR4-B
2013	45.2 a	45.3 a	43.8 c	45.0 a	43.3 c	44.9 b	43.4 c	44.4 B
2014	43.3 ab	43.9 a	41.8 bc	43.0 b	42.0 a-c	42.6 a-c	40.6 c	42.5 B
2015	43.7 a	43.1 a	41.2 b	43.2 a	42.0 b	43.0 a	40.1 c	42.3 B
2016	40.8 a	40.2 a	37.8 b	40.3 a	37.5 b	39.9 a	36.4 b	39.0 C
2017	43.2 a	43.9 a	43.8 ab	44.2 a	43.8 ab	43.7 a	42.6 c	43.6 B
2018	45.4 c	45.7 c	45.3 c	47.8 a	44.8 d	46.5 b	44.0 d	45.6 A
Mean	43.6 A	42.3 A	42.3 B	43.9 A	42.2 B	43.4 A	41.2 C

Abbreviations: CR1-P—crop rotation CR1, forecrop pea; CR2-O—crop rotation CR2, forecrop oilseed rape; CR2-P—crop rotation CR2, forecrop pea, CR3-P—crop rotation CR3, forecrop pea; CR3-S—crop rotation CR3, forecrop spelt; CR4-O—crop rotation CR4, forecrop oilseed rape; CR4-B—crop rotation CR4, forecrop barley. Uppercase letters (normal font) in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for crop rotation fields. Uppercase letters (italic font) in the columns denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for years, lowercase letters in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for crop rotation fields rotational fields in each year.

). At these sites, the TGW values were the highest, as compared to the least effective site after barley, i.e., CR4-B, on average across the years of this study (by 5.3–6.6%). The interaction between crop rotations and the years showed that the grain with a significantly higher TGW value (in relation to the field CR4-B) was harvested from the above-mentioned fields in most of the years of this study.

3.2. Effect of Crop Rotation on Grain Quality

This study showed the significant effects of crop rotations, years and the interactions between crop rotations and years (

Table 4. Significance testing (p-values) for grain quality depending on crop rotation, years and interaction between crop rotation and years.

Technological Properties	Crop Rotation (CR)	Year (Y)	Interaction (CR × Y)
Total protein content	<0.001	<0.001	<0.001
Wet gluten content	0.002	<0.001	0.003
Starch content	0.275	0.146	0.066
Zeleny index *	0.002	<0.001	0.006
Falling number	<0.001	0.005	0.001

* The grain intended for flour production should have a Zeleny index value of >25 cm³. The higher the value of this index, the better the quality of the flour. Grain with a Zeleny index value < 25 cm³ is not suitable for consumption.

) on the following spelt grain parameters: total protein content (p < 0.001, p < 0.001 and p < 0.001, respectively), wet gluten content (p = 0.002, p < 0.001 and p = 0.003, respectively), Zeleny index (p = 0.002, p < 0.001 and p = 0.006, respectively), the falling number (p < 0.001, p = 0.005 and p = 0.001, respectively) and the weight of 1000 grains (p < 0.001, p < 0.001 and p = 0.011, respectively). No effects of crop rotation, years or their interactions on the starch content of the grain were demonstrated.

The highest total protein and wet gluten contents, as well as Zeleny index values, were noted in the spelt grain harvested in 2018 (Table 4 and

Table 5. Content of total protein, wet gluten and starch in winter spelt grain.

Years	Fields in Crop Rotations							Mean
	CR1-P	CR2-O	CR2-P	CR3-P	CR3-S	CR4-O	CR4-B
Total protein content (g kg−1)
2013	114 a	110 b	115 a	111 ab	104 c	103 c	103 c	109 D
2014	108 ab	106 a	109 a	100 ab	100 ab	103 ab	94 b	103 E
2015	113 ab	117 a	115 a	115 a	110 b	117 a	111 b	114 C
2016	127 a	126 a	121 b	123 ab	115 b	129 a	126 a	124 B
2017	106	104	107	108	100	102	102	104 D
2018	146 a	134 b	142 a	142 a	137 ab	138 ab	131 b	139 A
Mean	119 A	116 A	118 A	117 A	111 B	115 A	111 B
Wet gluten content (g kg−1)
2013	245 ab	243 b	256 a	250 a	236 c	239 c	234 c	243 C
2014	233 ab	237 a	234 ab	234 ab	235 ab	230 b	229 b	233 D
2015	256 b	255 b	255 b	261 a	244 c	255 b	244 c	253 C
2016	297	286	293	279	262	287	263	281 B
2017	247	247	242	240	239	245	235	242 C
2018	338 a	315 b	323 ab	328 ab	296 c	318 b	308 bc	318 A
Mean	269 A	264 AB	267 A	265 A	252 B	262 AB	252 B
Starch content (g kg−1)
2013	674	674	664	664	669	672	669	669
2014	661	661	664	662	659	661	662	661
2015	725	717	713	712	718	713	716	716
2016	699	696	696	693	688	694	686	693
2017	688	689	689	685	689	687	687	688
2018	699	696	696	693	688	694	686	693
Mean	691	689	687	685	685	687	684

Abbreviations: CR1-P—crop rotation CR1, forecrop pea; CR2-O—crop rotation CR2, forecrop oilseed rape; CR2-P—crop rotation CR2, forecrop pea; CR3-P—crop rotation CR3, forecrop pea; CR3-S—crop rotation CR3, forecrop spelt; CR4-O—crop rotation CR4, forecrop oilseed rape; CR4-B—crop rotation CR4, forecrop barley. Uppercase letters (normal font) in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for crop rotation fields. Uppercase letters (italic font) in the columns denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for years, lowercase letters in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for crop rotation fields rotational fields in each year. No letters next to numbers—not significant.

). Grains with the significantly lowest protein and gluten contents were obtained in 2014, those with the lowest Zeleny index value in 2013 and 2014, and those with the lowest falling number in 2017.

On average, for the years 2013–2018, no significant differences in total protein content (Table 5) were noted between the crop rotation fields CR1, CR 2 and CR3—at the site of spelt cultivation after pea (CR3-P) and CR4—at the site of spelt cultivation after rape (CR4-O). A significant protein content reduction (by 3.5–6.7%) was shown in grain from fields of spelt cultivation in succession after spelt (field CR3-S) and those of spelt cultivation after barley (field CR4-B). Throughout the 6-year study period, a significant reduction was noted for the field of spelt cultivation in succession after spelt in year 3 and after barley in year 4 of the six years of this study. In addition, in 2013, the significantly lowest protein content was found in grains originating from the field of spelt cultivation after rape in crop rotation CR4 (field CR4-O), and in 2018, also in grains from the field of spelt cultivation after rape in crop rotation CR2 (field CR2-O). The values for the wet gluten content of the grain were similarly arranged. On average, across the years, significantly lower wet gluten content values (by 4.9–5.6%) were noted for grain from fields CR3-S and CR4-B, as compared to fields CR1-P, CR2-P and CR3-P. This decrease was observed in the years 2013 and 2014 (except for field CR3-S), as well as 2015 and 2018. In 2013, the significantly lowest gluten content was also found in grain harvested from field CR3-S. On average, across the years, the cultivation of spelt at site CR4-B significantly reduced the Zeleny index value (by 6.2–7.4%) in relation to that in fields CR1-P, CR2-O and CR2-P (

Table 6. Zeleny sedimentation index and falling number in winter spelt grain.

Years	Fields in Crop Rotations							Mean
	CR1-P	CR2-O	CR2-P	CR3-P	CR3-S	CR4-O	CR4-B
Zeleny sedimentation index (cm3)
2013	33.1 b	33.7 b	34.7 a	33.1 b	34.0 a	33.1 b	32.3 c	33.4 D
2014	31.9 a	32.4 a	31.8 a	32.4 a	32.2 a	32.1 a	31,0 b	32.0 D
2015	44.5 a	44.6 a	44.5 a	44.7 a	43.4 b	42.4 c	41.2 d	43.6 C
2016	51.3 a	48.8 ab	50.9 a	48.4 ab	43.7 b	51.0 a	44.2 b	48.3 B
2017	46.4	46.6	46.3	47.0	50.2	45.1	44.1	46.5 B
2018	67.3 a	65.3 b	65.2 b	65.8 b	64.4 c	62.7 cd	61.3 d	64.6 A
Mean	45.8 A	45.2 A	45.6 A	45.2 A	44.7 AB	44.4 AB	42.4 B
Falling number (s)
2013	426.0 a	422.8 a	419.0 b	429.8 a	407.8 c	393.0 d	402.8 d	414.5 A
2014	398.3 b	399.8 a	383.5 b	401.5 a	391.3 b	390.5 b	374.0 c	391.3 A
2015	398.9 a	399.6 a	393.5 b	398.3 a	388.5 bc	390.5 b	374.0 d	391.9 A
2016	347.8 a	338.5 ab	314.5 b	333.0 ab	334.3 ab	341.5 ab	301.8 c	330.2 AB
2017	284.3	283.3	276.0	282.0	280.3	279.5	271.5	279.6 B
2018	417.0	397.5	395.5	409.0	404.8	392.0	381.0	399.5 A
Mean	378.7 A	373.6 A	363.7 BC	375.6 A	367.8 AB	364.5 BC	350.9 C

Abbreviations: CR1-P—crop rotation CR1, forecrop pea; CR2-O—crop rotation CR2, forecrop oilseed rape; CR2-P—crop rotation CR2, forecrop pea; CR3-P—crop rotation CR3, forecrop pea; CR3-S—crop rotation CR3, forecrop spelt; CR4-O—crop rotation CR4, forecrop oilseed rape; CR4-B—crop rotation CR4, forecrop barley. Uppercase letters (normal font) in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for crop rotation fields. Uppercase letters (italic font) in the columns denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for years, lowercase letters in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for crop rotation fields rotational fields in each year. No letters next to numbers—not significant.

). In this field, a significant reduction in this index was noted in year five of this study. In 2016, a significant reduction in Zeleny index value was also observed in field CR3-S. In contrast, in 2017, no significant differences between the crop rotation sites under assessment were noted. Significant differences in the falling number values between plots were noted in the first four years of this study (2013–2016). Its significant reduction was noted in grain from two crop rotation fields CR4 (CR4-O and CR4-B) and from the field after pea in crop rotation CR2 (CR2-P), as compared to the most favourable fields CR1, CR2-O and CR3-P. This reduction ranged from 2.4 to 7.3%. The significantly largest reduction in this index was also noted in 2013 in the field CR3-S.

3.3. Effect of Crop Rotation on Macro- and Micronutrient Content

The crop rotation sites had a significant impact on the spelt grain N (p < 0.001), P (p = 0.003), Fe (p < 0.001) and Zn (p < 0.001) contents (

Table 7. Significance testing (p-values) for the nutrient content of spelt grain and of spelt grain yield depending on crop rotation, years and the interaction between crop rotation and years.

Nutrients	Crop Rotation (CR)	Year (Y)	Interaction (CR × Y)
N	<0.001	<0.001	0.001
P	0.003	<0.001	0.004
K	0.436	0.430	0.478
Mg	0.616	0.310	0.507
Ca	0.124	0.274	0.337
Cu	0.235	0.179	0.446
Fe	<0.001	<0.001	<0.001
Zn	<0.001	0.003	0.004
Mn	0.135	0.192	0.614

). However, they had no effect on the K (p = 0.436), Mg (p = 0.616), Ca (p = 0.124), Cu (p = 0.235) and Mn (p = 0.135) contents. This study demonstrated a significant effect of the years and the interactions between crop rotation and the years on the N (p < 0.001, p < 0.001, respectively), P (p < 0.001 and p = 0.004, respectively), Fe (p < 0.001 and p <0.001, respectively) and Zn (p = 0.003 and p = 0.004, respectively) contents.

The significantly highest N, P and Zn contents were found in the spelt grain harvested in 2018. In addition, the P content was significantly the highest in 2016, and the Zn content in 2017. On the other hand, the grain richest in Fe was obtained in 2013. The lowest N content was noted for the grain harvested in 2014, while the lowest Fe content was in 2017, as well as the P and Zn contents in the remaining years.

The spelt cultivated on crop rotation fields CR1-P, CR2-O, CR2-P, CR3-P and CR4-O was characterised by a significantly higher N content than that on fields CR3-S and CR4-B, on average, across the years by 6.9–8.1%, with deviations ranging from 1.8% in 2017 to 15.8% in 2013 (

Table 8. Content of nitrogen, phosphorus, potassium, magnesium and calcium in winter spelt grain.

Years	Fields in Crop Rotations							Mean
	CR1-P	CR2-O	CR2-P	CR3-P	CR3-S	CR4-O	CR4-B
N (g kg−1)
2013	18.3 a	17.6 b	17.7 b	17.7 b	16.6 c	17.4 b	15.8 d	17.3 D
2014	15.6 a	15.9 a	15.7 a	16.0 a	15.0 b	15.6 ab	15.0 b	15.5 E
2015	18.8 a	18.2 b	17.8 c	18.1 bc	16.7 e	18.6 a	17.3 c	17.9 C
2016	20.2 a	20.2 a	20.0 a	19.0 b	17.9 c	20.6 a	18.5 bc	19.7 B
2017	17.0 a	17.0 a	17.4 a	17.4 a	16.7 ab	17.8 a	16.1 b	17.1 D
2018	22.5 a	22.8 a	22.6 a	22.7 a	21.1 b	22.1 a	21.0 b	22.1 A
Mean	18.7 A	18.6 A	18.5 A	18.5 A	17.3 B	18.7 A	17.3 B
P (g kg−1)
2013	2.71 a	2.48 b	2.60 a	2.70 a	2.70 a	2.60 a	2.50 b	2.61 C
2014	2.53 a	2.32 b	2.38 ab	2.38 ab	2.35 b	2.38 ab	2.48 ab	2.40 C
2015	2.90 a	2.40 bc	2.22 c	2.50 bc	2.68 ab	2.58 ab	2.50 bc	2.54 C
2016	3.00	3.18	3.00	3.12	2.90	3.18	3.15	3.08 A
2017	2.88 a	2.68 b	2.68 b	2.90 a	2.48 c	2.80 ab	2.53 c	2.71 B
2018	2.98 a	2.75 ab	3.00 a	3.00 a	2.65 b	3.00 a	2.60 b	2.85 A
Mean	2.83 A	2.64 B	2.65 B	2.77 A	2.63 B	2.76 A	2.63 B
K (g kg−1)
2013	4.60 a	4.32 ab	4.63 a	4.58 a	4.25 b	4.25 b	4.30 b	4.42
2014	4.90 a	4.25 b	4.58 ab	4.30 b	4.33 b	4.60 ab	4.30 b	4.47
2015	4.98 a	4.55 b	4.32 b	4.50 b	4.55 b	5.03 a	4.18 c	4.59
2016	4.98	4.85	4.95	4.60	4.56	4.58	4.30	4.69
2017	4.60	4.6 0	4.55	4.58	4.60	4.58	4.60	4.59
2018	5.13 a	5.08 a	4.83 a	4.68 ab	4.28 b	4.63 ab	4.30 b	4.70
Mean	4.87	4.61	4.64	4.54	4.43	4.61	4.33
Mg (g kg−1)
2013	1.10	1.15	1.18	1.20	1.10	1.18	1.05	1.14
2014	1.08	1.03	1.03	1.03	1.03	1.00	0.93	1.02
2015	1.05	0.98	0.75	0.95	0.95	0.95	0.85	0.93
2016	0.75 b	1.10 ab	1.05 ab	0.98 ab	1.18 a	1.08 ab	1.05 ab	1.03
2017	1.12	1.15	1.18	1.20	1.18	1.18	1.10	1.16
2018	1.30	1.25	1.30	1.28	1.28	1.27	1.25	1.28
Mean	1.07	1.11	1.08	1.11	1.12	1.11	1.04
Ca (g kg−1)
2013	0.49	0.49	0.59	0.59	0.60	0.50	0.60	0.55
2014	0.50	0.59	0.55	0.55	0.60	0.55	0.49	0.55
2015	0.64	0.44	0.40	0.55	0.60	0.50	0.45	0.51
2016	0.53	0.60	0.60	0.59	0.60	0.60	0.60	0.59
2017	0.65	0.64	0.64	0.70	0.65	0.70	0.66	0.66
2018	0.65	0.55	0.58	0.70	0.65	0.50	0.51	0.59
Mean	0.57	0.55	0.56	0.61	0.62	0.56	0.55

Abbreviations: CR1-P—crop rotation CR1, forecrop pea; CR2-O—crop rotation CR2, forecrop oilseed rape; CR2-P—crop rotation CR2, forecrop pea; CR3-P—crop rotation CR3, forecrop pea; CR3-S—crop rotation CR3, forecrop spelt; CR4-O—crop rotation CR4, forecrop oilseed rape; CR4-B—crop rotation CR4, forecrop barley. Uppercase letters (normal font) in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for crop rotation fields. Uppercase letters (italic font) in the columns denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for years, lowercase letters in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for crop rotation fields rotational fields in each year. No letters next to numbers—not significant.

). Such results were obtained across all the years of this study (with the exception of fields CR2-P in 2015 and CR3-S in 2017). On average, for the 6-year period, the highest P content of the grain was noted in fields CR1-P, CR3-P and CR4-O. The cultivation of spelt on the two crop rotation fields CR2 (CR2-O and CR2-P), as well as on the fields CR3-S and CR4-B, significantly reduced the P content of the grain in relation to the above-mentioned sites (by 4.0–7.1%). However, in individual years, the effects of the crop rotations under assessment on the P content of the grain varied. In 2016, no significant differences between crop rotations were observed. In the remaining five years, the greatest P concentration was noted for the grain derived from crop rotation CR1-P.

In addition, in 2013, a similar P contents were found in grain from fields CR2-P, CR3-P, CR3-S and CR4-O; in 2017, in the grain from field CR3-P; and in 2018, in the grain from fields CR2-P, CR3-P and CR4-O. The lowest content of this element in 2013 was noted for grains derived from fields CR2-O and CR4-B. In 2014, the P content was most unfavourably affected at sites CR2-O and CR3-S; in 2015, site CR2-P; and in 2017 and 2018, sites CR3-S and CR4-B. The cultivation of spelt in succession after spelt in crop rotation CR3, and following the cultivation of barley in crop rotation CR4, was the cause of a significant reduction in the Fe content of the grain (

Table 9. Content of copper, iron, zinc and manganese in winter spelt grain.

Years	Fields in Crop Rotations							Mean
	CR1-P	CR2-O	CR2-P	CR3-P	CR3-S	CR4-O	CR4-B
Cu (mg kg−1)
2013	1.95 b	1.95 b	2.35 a	2.35 a	2.38 a	1.98 b	2.38 a	2.19
2014	2.00 b	2.35 a	2.20 ab	2.20 ab	2.40 a	2.20 ab	1.97 b	2.19
2015	2.55 a	1.75 cd	1.60 d	2.20 abc	2.40 ab	2.00 c	1.80 d	2.04
2016	2.10 b	2.39 a	2.38 a	2.37 a	2.40 a	2.40 a	2.39 a	2.35
2017	2.58 b	2.57 b	2.55 b	2.80 a	2.60 b	2.80 a	2.62 b	2.65
2018	2.58 b	2.20 c	2.30 c	2.80 a	2.60 b	2.01 d	2.02 d	2.36
Mean	2.29	2.20	2.23	2.45	2.46	2.23	2.20
Fe (mg kg−1)
2013	92,2 a	93,6 a	96,6 a	96,4 a	76,5 b	72,8 b	63,0 c	84.4 A
2014	71.4 a	66.6 b	65.6 b	72.4 a	64.0 c	69.2 b	60.1 c	67.0 C
2015	72.0 b	74.0 ab	76.0 a	74.2 ab	61.0 c	76.6 a	60.2 c	70.6 B
2016	72.6 a	72.9 a	72.6 a	73.0 a	68.6 c	70.8 b	70.0 c	71.5 B
2017	57.4 b	64.0 a	57.0 b	52.4 b	49.2 c	57.8 b	49.8 c	55.4 E
2018	64.0 b	62.0 b	64.8 b	70.0 a	55.5 c	63.6 b	58.6 c	62.6 D
Mean	71.6 A	72.2 A	72.1 A	73.1 A	62.5 B	68.5 AB	60.3 B
Zn (mg kg−1)
2013	26.0 a	24.5 b	24.2 b	23.6 c	23.7 c	24.2 b	23.0 c	24.2 B
2014	22.8 b	22.5 b	22.8 b	24.0 a	21.4 c	20.6 c	20.5 d	22.1 B
2015	22.4 b	22.6 b	22.4 b	20.8 d	20.6 d	23.2 a	21.4 c	21.9 B
2016	24.4 b	24.6 b	22.4 d	25.4 a	22.4 d	25.4 a	24.0 c	24.1 B
2017	29.4 b	27.6 e	29.0 c	28.2 d	27.0 f	30.8 a	26.2 g	28.3 A
2018	32.3 b	31.8 bcd	32.0 bc	34.0 a	31.2 d	29.8 e	31.4 cd	31.8 A
Mean	26.2 A	25.6 A	25.5 A	26.0 A	24.4 B	25.7 A	24.4 B
Mn (mg kg−1)
2013	38.0	30.3	37.9	30.0	29.8	30.0	34.0	31.4
2014	35.2	31.6	30.4	34.6	32.2	33.2	33.4	32.9
2015	30.0	31.8	29.0	31.2	29.0	29.0	26.4	30.9
2016	32.8	30.6	32.3	34.8	30.2	32.6	30.6	32.0
2017	38.4 a	37.6 a	38.2 a	33.4 b	36.4 a	36.1 a	34.4 b	36.6
2018	32.4	33.0	28.6	33.1	33.2	32.8	29.4	31.8
Mean	34.5	32.5	32.7	32.9	31.8	32.3	31.4

Abbreviations: CR1-P—crop rotation CR1, forecrop pea; CR2-O—crop rotation CR2, forecrop oilseed rape; CR2-P—crop rotation CR2, forecrop pea; CR3-P—crop rotation CR3, forecrop pea; CR3-S—crop rotation CR3, forecrop spelt; CR4-O—crop rotation CR4, forecrop oilseed rape; CR4-B—crop rotation CR4, forecrop barley. Uppercase letters (normal font) in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for crop rotation fields. Uppercase letters (italic font) in the columns denote homogeneous groups in Tukey’s HSD test (p < 0.05) for the mean value from 2013 to 2018 for years, lowercase letters in the rows denote homogeneous groups in Tukey’s HSD test (p < 0.05) for crop rotation fields rotational fields in each year. No letters next to numbers—not significant.

). This reduction, in relation to crop rotations CR1 and CR2, and the field after pea in CR3, on average across the years, amounted to 12.7–17.5%. The greatest reduction (34.8%) was noted in 2013, while the smallest reduction (2.4%) was in 2014. The sites left after the cultivation of spelt and barley (fields CR3-S and CR4-B) had a similar effect on a reduction in Fe content, except in 2013, when significantly less iron was found in the grain of spelt cultivated after barley than in that cultivated after spelt. In the remaining crop rotation fields CR1, CR2 and CR3, the Fe content was significantly higher, with no clear indication of an advantage for any of them. The values showing the Zn content were similarly arranged. In this case, a significant contribution of cereal forecrops to a reduction in the Zn content of the grain of this cereal was also found. The Zn content of the grain from fields CR3-S and CR4-B was lower than that on crop rotation sites CR1, CR2 and CR3 on average across the years by 4.3–7.0%. In 2013 and 2015, a negative effect of the pea forecrop cultivated in crop rotation CR3 was noted; in 2016, the same effect was also noted for the pea forecrop cultivated in CR2; and in 2014, a negative effect of the rape forecrop in CR4 was noted. The reduction in the Zn content in individual years, in the fields after spelt (CR3-S) and after barley (CR4-B), was similar.

4. Discussion

4.1. Spelt Grain Yield

In this present study, the negative effect of spelt cultivation after spelt and after barley was found across all years of study. After these forecrops, the largest yield reductions were noted in 2016 and 2018, when the lowest grain yield was obtained. The reason for the decrease in yield in 2016 was a strong infection of spelt by fungal pathogens and large weed infestation (caused by heavy rainfall in May, June and July). In 2018, a delayed sowing date (due to a very wet autumn) and the low temperature in February (−4.1 °C) caused mortality among the plants, reducing their density. Thus, in unfavourable weather conditions, the negative impact of cereal forecrops is more visible than in conditions favourable to spelt vegetation. This confirms the significant role of diversified crop rotation in mitigating the effects of crop cultivation in unfavourable habitat conditions [23,51].

4.2. Grain Quality

This study showed that the spelt grain derived from crop rotations, in which this cereal was cultivated after spelt (field CR3-S) and after barley (field CR4-B), exhibited a significantly lower total protein and wet gluten contents, and a lower TGW value, while, after barley in crop rotation CR4 (field CR4-B), it also exhibited a Zeleny index value lower than the other crop rotation plots. The grain harvested from the two crop rotation fields CR4 (CR4-O and CR4-B) was characterised by a significantly lower falling number, with that harvested from the CR4-B field additionally exhibiting a lower Zeleny index.

An earlier study by Wanic and Parzonka [40] showed that wheat grown in analogous rotations following each other and following barley was characterised by lower photosynthesis than that grown following rape and pea. The direct reason for this was the development of leaves with a smaller surface area and lower chlorophyll and N contents. Biological synthesis and the translocation of assimilates from the vegetative parts to the grain were therefore weaker (data not published). In sites with wheat following wheat and other cereals, soil degradation occurs due to the accumulation of harmful metabolites in the soil, leading to an imbalance in the biological balance of the soil, the destruction of soil structure and the depletion of nutrients. This results in less uptake of water and nutrients from the soil, manifesting itself in poorer growth of both above-ground parts and roots.

The obtained results were confirmed in studies by other authors [47,52,53], who demonstrated that grain of lower quality (a lower Zeleny index and falling numerical values, as well as lower gluten content) is obtained from crop rotations with a large cereal share. A study by Podolska et al. [52] showed that the spelt of the ‘Rokosz’ variety exhibited a significantly lower gluten index in the crop rotation with an 80% cereal share than that in the crop rotation with a 60% cereal share. Also, Tomczyńska [54] and Nemeiksiene et al. [55], in studies on wheat, and Wanic [48], in a study on spelt, demonstrated that these cereals were cultivated in succession, and after barley, they exhibited the lowest protein content. A different view is presented by Woźniak et al. [56], who demonstrated that the highest protein content was noted for wheat cultivated in monoculture

In this study, the spelt grain harvested from fields after rape and after pea exhibited higher TGWs than that after barley and after spelt, higher protein and gluten contents, and higher sedimentation index and falling number values. After harvesting rape and pea, a large mass of crop residue, rich in N and other elements, remains in the soil. The well-developed root systems of these crops loosens the soil and facilitates the transfer of nutrients from deeper soil layers. In addition, legumes fix atmospheric nitrogen (BNF) and leave crop residues with a narrow C:N ratio, which increases the rate of their mineralisation as well as the release of N and other elements [57,58]. Legume residues stimulate the microbiological and enzymatic activity of the soil as well as the overall rate of nutrient circulation in the soil. They also improve nitrogen mineralisation and reduce its immobilisation [59,60]. This facilitates the uptake of nitrogen and other elements by the wheat, improves photosynthesis, and consequently increases cereal yields [40,61,62]. A positive relationship between the activity of the enzymes involved in C, N and P circulation and the wheat yield was confirmed by a study by Liu et al. [57]. On the other hand, the organic acids secreted by rape roots dissolve water-insoluble compounds, thereby releasing nutrients to be utilised by successive crops [37,63]. These sites are favourable to the growth of successive crops [40,64]. This was confirmed by a study by Podolska et al. [65], which demonstrated that the nitrogen contained in the soil had a positive effect on the protein and gluten contents of the grain and the sedimentation index in winter spelt of the ‘Rokosz’ variety. At sites after rape and after pea, Babulicova [24], as well as Darguza and Gaile [46], noted grain with higher TGW values than that after cereals. A higher TGW is usually associated with a greater amount of nutrients in the grain. This was confirmed by the present research, in which the spelt grain harvested from the fields after rape and after pea exhibited higher TGWs than that after barley and after spelt, higher protein and gluten contents, and higher sedimentation index and the falling number values. In addition, Liu et al. [57], as well as Darguza and Gaile [46], showed that crop rotations with a legume share had a positive effect on the protein content of the grain. A different view was presented by Wozniak [43] and Woźniak et al. [56], who demonstrated that the protein and gluten contents of the grain, as well as the sedimentation index, were lower at the site after the cultivation of pea than that after the cultivation of wheat.

On the other hand, Carr et al. [66], Podolska et al. [52], Jankowski et al. [67] and, in another experiment, Babulicová [47] demonstrated no effect of crop rotation on protein content, falling number or sedimentation index values.

4.3. Macro- and Micronutrient Content of Spelt Grain

In this present research, the succession of spelt after spelt in crop rotation CR3 (despite two very good forecrops, rape and pea, preceding its cultivation) and after barley in crop rotation CR4, with a 75% share of cereals, significantly reduced the N, P, Fe and Zn contents of the spelt grain. In the other crop rotation fields, the contents of these elements were higher and exhibited no major differences between them. A previous study conducted by Wanic et al. [48] showed that rape and pea, as forecrops, increased the Fe and Mn contents of spelt grain, with rape additionally increasing the Fe content in relation to the cultivation of this cereal in succession. According to Stankowski et al. [68], a site rich in nitrogen is favourable for the N content of spelt grain while reducing the potassium and magnesium contents, without differences in the P, Ca and Mn contents, and Wozniak [69] reported that such soil reduces the P, K, Ca and Fe contents. In this present research, however, the forecrops (rape, pea, spelt and barley) did not differentiate the P, K, Mg, Ca and Cu contents, while in a study by Dragicevic [23], Mg and Zn were not differentiated. Kraska [70], when cultivating spelt in succession after spelt, noted a reduction in the Mg, Zn, Cu, Mn and Fe contents of the grain with no significant changes in the P content. In addition, Sharma et al. [71] claim that the preceding crop (soybean) contributed to the increased Zn, B, Fe and Mn contents of the grain. It follows from a study by Lollato et al. [72] that at the sites of spelt cultivation after rape and after pea, the soil is characterised by a higher SOC content as well as higher microbiological and enzymatic activity. This contributes to a greater availability of mineral nutrients and their uptake by crops, which results in a greater accumulation of elements in the spelt grain. The nitrogen released from residues rich in this element may have an effect on the uptake and accumulation in the grain of both N and other elements, such as P, Ca, Mg, Fe and Cu. In contrast, cereal forecrops leave behind very little crop residue that is not very rich in nutrients. Their decomposition is slower due to the lower biological activity of the soil. The factors limiting their uptake are the less developed root system with less suction power and allelochemicals with toxic properties, released during the decomposition of residues. According to Houx [26], crop rotation had no effect on the elemental content of the plants. In this current study, this was confirmed by the K, Mg, Ca and Cu contents, while in a study by Dragicevic [23], this was confirmed by the Mg and Zn contents.

5. Conclusions

The yield of winter spelt grain and the quality of the grain were found to be dependent on the forecrop, but not on the crop rotation type (selection of species, distribution in crop rotation and the frequency of the cereals in crop rotation). The yields of grain harvested from the fields of spelt grown after winter rape and after pea were higher, with the grain exhibiting greater weights of 1000 grains, higher protein and wet gluten contents, and higher Zeleny index and falling number values, as well as higher N, P, Fe and Zn contents. The yield of winter spelt grain and the grain quality were found to be lower and significantly worse, respectively, when the crops were grown after a forecrop of winter spelt and spring barley. The inclusion of spelt after forecrops of winter rape and field pea (even in a crop rotation with a 75% cereal share) allows a high and qualitatively good yield of this cereal to be obtained.

Given the lower yield of grain and its inferior quality, it is not advisable to cultivate winter spelt succeeding spelt and spring barley. Further detailed studies, which should be extended to other quality characteristics of this cereal grain and carried out under different climatic and soil conditions, are recommended. Additionally, studies on spelt forecrops, including yield, weight and quality of this crop residues, as well as chemical properties of the soil, represent a valuable area for further investigation.