**1. Introduction**

The cultivation of spring cereal mixtures (SCMs) is an element of crop rotation typical for Polish agriculture [1]. In 2015, cereals accounted for 73.3% of the total crop area of Poland, including 10.7% of SCMs. In 2017 and 2018, cereals accounted for 70.1% and 72.1%, respectively, and in the same years, the SCMs accounted for 11.6% and 12.7%, respectively [2].

The spring cereal mixtures are applied both in organic and sustainable agricultural systems [3–5], mainly as a source of feed (grains) for livestock [6–8]. This method of crop cultivation involves the simultaneous sowing of usually two di fferent species of spring cereals, in di fferent proportions [9,10]; their grains are mixed before sowing.

Cultivation of SCMs has many advantages and is desirable in sustainable agriculture owing to current ecological trends related to reducing the amount of mineral fertilizers and pesticides, as a part of integrated pest managemen<sup>t</sup> [11–13]. It results in less environmental pollution and lower outlays on agronomic practices [14]. This is because of the fact that SCMs are less infested by pathogens and insect pests than pure sowings [15,16], which results from a reduced number of plants of a given species susceptible to a particular pest [17]. The components of mixtures are characterized by a di fferent growth pattern [10], and as a result, they better cover soil, protecting it from water loss. This also results in a reduced weed infestation, as species in the mixture compete more e ffectively with weeds [18] and promote biodiversity in a canopy [19].

Many authors [20–22] confirmed the relationship between grain yield and leaf area index (LAI). LAI is referred to as the ratio of the surface of assimilation organs of a crop, mainly leaves, to the surface of soil. The LAI value depends on genetic characteristics and habitat factors [23]. For various crops, the LAI is several times larger than the surface of the soil, for example, for small-seeded legumes, 4–5 times, and for other crops, 2–4 times [24].

The SCMs are characterized by greater yield stability than pure sowing [25]. This is because of, among others, the fact that, in the adverse weather and soil conditions (e.g., drought) for the first species (component), the second component of the SCM finds more favorable conditions and increases the yield, compensating for the lower yield of the first one [26,27]. This compensation is also associated with the complementary use of soil resources, that is, nutrients and water, which results from the diverse architecture of the root systems of SCMs. Mixtures are an important element in increasing species diversity in crop rotation [28,29], which is supportive to stabilizing the yield of following crops [30].

A common component of SCMs is oats, called a phytosanitary plant [31]. Oats are a cereal species with a very well-developed root system, capable of taking water and nutrients from deeper layers of soil. Moreover, as an allelopathic crop, they influence, by root exudates, the abundance and composition of soil-pests, as well as the composition of soil microorganisms, which together contribute to the soil biological activity [32]. In this way, oats also stimulate the growth and development of the other component of SCM [33].

The available literature lacks current studies on the yield, competitiveness of components, and economic aspects of the cultivation of SCMs in di fferent cropping systems, especially in the long term and in the extensive conditions of mountainous agriculture. Decisions related to the selection of the production structure are made based on both the production/quality characteristics and economic results [34], also including the system of agricultural subsidies [35]. Moreover, subsidies in the mountainous areas of southern Poland are one of the most important and motivating factors for a farmer to produce organically [3]. All of this became a reason for undertaking our research. The profitability of cultivation is determined by the relation between the value of the obtained crop and the incurred production costs, which include all elements throughout the production process. For this reason, our research also included economic analysis of standard gross margin of SCMs' cultivation.

The aims of our study were to (i) analyze the yield, competitiveness, and leaf area index (LAI); and (ii) assess the economic indicators of spring cereals in pure or mixed sowings in integrated or organic crop rotations, over nine years (three rotations of crops) in the mountainous area of southern Poland.

#### **2. Materials and Methods**

A field experiment was carried out in the years 2011–2019 in the Mountainous Experimental Station in Czyrna near Krynica Górska, southern Poland (545 m a.s.l.; 49◦25', N 20◦58' E). The soil was acid (pHKCl = 5.1), brown soil—Cambisol [36], formed from weathered flysch material, composed of loam with a medium skeleton content. The chemical composition of soil was as follows: 0.22% Ntot.; 46.2 mg kg−<sup>1</sup> soil P; 203.3 mg kg−<sup>1</sup> soil K; 1.84% Corg. The experiment was set up in a two-factorial split-block design, with four replications. The total area of a single plot was of 30.8 m2, with 22 m<sup>2</sup> of a harvested area. Three full rotations of the crops (nine years) were included in the results.

There were two systems (first factor) of the experiment: (1) integrated, with mineral fertilization and chemical pesticides; and (2) organic, without any synthetic additives. Each of the systems was composed of six three-field crop rotations (second factor): (1) potato fertilized with manure (33 t ha−1); (2) spring cereal pure sowing or a spring cereals mixture—six variants in total (Table 1); and (3) spring vetch. The density of cereals in the mixture was reduced by 50%, in relation to the pure sowings. All of the systems and crops were present each year, which means that each crop was grown nine times throughout the whole study period. Three full rotations of the crops (nine years) were included in the results.

**Table 1.** Species composition and number of grains (pcs. m-2) for pure and mixed sowings of spring cereals.


1 Breeders: oats, Małopolska Hodowla Ro´slin-HBP sp. z o.o. (Krakow, Poland); spring barley, Hodowla Ro´slin (HR) Smolice Sp. z o. o. Grupa Instytut Hodowli i Aklimatyzacji Ro´slin (IHAR) (Smolice, Poland); spring triticale, HR Strzelce Sp. z o. o. Grupa IHAR (Strzelce, Poland).

In the integrated crop rotation, a mineral fertilization for cereals in pure sowings and their mixtures was balanced, based on the content of nutrients in soil, quality of the preceding crop, and forecasted yield. In autumn, 34 kg ha−<sup>1</sup> P and 55.6 kg ha−<sup>1</sup> K were applied before a deep ploughing in October. For cereals in spring, a total dose of 72.0 kg ha−<sup>1</sup> N was divided into two equal doses, one applied before sowing and a second in the shoot formation. Grains were coated with karboxine + thiram (60 g + 60 g per 100 kg of grains). Weeds in the pure sowings and mixtures were controlled by tribenuron methyl (12 g ha−1).

In the organic crop rotation, no chemical fertilizers nor pesticides were applied. Weeds in the cereals were mechanically controlled by a Weeder harrow, run two times in by the end of tillering/beginning of shooting (BBCH 29–30 [37]).

In the stage of grains development (BBCH 70–71), samples of cereals were collected from each plot from 1 m2. An area of leaves was measured from 20 shoots per sample, using an LI-COR 3100 Area Meter (LI-COR Biosciences GmbH, Bad Homburg vor der Höhe, Germany). Next, the average area of leaves per shoot was multiplied by the total number of shoots per 1m<sup>2</sup> [24]. On this basis, a leaf area index (LAI) was calculated:

$$\text{LAI} \equiv \text{Leaf area (m}^2\text{)} / \text{Ground cover (m}^2\text{)},\tag{1}$$

At harvest, the grain was collected from each plot (22 m2). The yield was expressed as per ha at 15% of seed moisture content.

To assess the competition between the components of the mixtures, two competition indices were calculated: land equivalent ratio (LER) (2) [38] and competitive ratio (CR) (3) [39].

$$\text{LER} = \text{LERi} + \text{LERj},\tag{2}$$

$$\text{LERi} = \text{Y}i\text{j}/\text{Y}i\text{i},\tag{3}$$

$$\text{L.ERj} = \text{Y} \text{ji} / \text{Y} \text{j},\tag{4}$$

where Y*ii*—yield of species *i* in a pure sowing, Y*jj*—yield of species *j* in a pure sowing, Y*ij*—yield of species *i* in a mixed sowing with a species *j*, and Y*ji*—yield of species *j* in a mixed sowing with a species *i*.

If LER value is greater than one (LER > 1), it means that the mixture is more e ffective than the pure sowing [40,41].

$$\text{CRi} = (\text{LERi} / \text{LERj}) \text{ (Zji} / \text{Zij}),\tag{5}$$

$$\text{CRj} = \text{(LERj / LERi)} \ (\text{Zij / Zji}), \tag{6}$$

where *Zij*—proportion of species *i* in the mixture with species *j* and *Zji*—proportion of species *j* in the mixture with species *i*.

If CR = 1, it means that there are equal competitive abilities of species *i* and *j*. If CR*i* > 1, it means that species *i* is more competitive than species *j*. If CR*i* < 1, it means that species *j* is more competitive than species *i* [40–42].

The economic indicators were calculated. The amount of cash outlay on the means of production was taken as the basis for the agricultural techniques used in the experiment, as well as the consumption of pesticides, fertilizers, and seeds. The values were calculated per area of 1 hectare. The commodity value of the harvested crops and the prices of the means of production were according to data contained in the market analyses developed at the Department of Market Research IERiGZ-PIB, Warsaw, Poland [43]. An additional source of data was the farm production calculations compiled by the Department of Economics and Agricultural Management MODR, Karniowice, Poland [44]. All calculations took into account the prices of the last, that is, the year 2019. The average yield of crops during the 2011–2019 study period was included in the calculations. The amount of human labor expenditure was adopted [45]. The costs of agrotechnical operations were determined using the method [46]. The standard gross margin was calculated from the di fference between the value of products obtained and the direct costs incurred. The direct profitability index, which characterizes the relation of production value to direct costs, was determined [47]. The labor consumption in the cultivation of cereals and cereal mixtures was 9.5 working hours per ha−<sup>1</sup> and was based on the workload involved in the experiment.

The mean value of nine years was used in the statistical analysis. Before the examination, the results of the experiment were tested for normality of distribution as well as homogeneity of variance by Shapiro–Wilk and Brown–Forsythe tests (Statistica PL ver. 13.1, StatSoft, Krakow, Poland). Both tests turned insignificant values (*p* = 0.1 for both tests), a basis for performing the analysis of variance (ANOVA). The results were subjected to a two-factor ANOVA for a split-block design with four replications, using FR-ANALWAR-4.3 Microsoft Excel-based package (author: Prof. F. Rudnicki; UTP University of Science and Technology, Bydgoszcz, Poland). The significance of di fferences between means was tested using the Tukey test (*p* ≤ 0.05).
