**1. Introduction**

Cereal–legume mixtures are usually cultivated for grain or green fodder, sometimes as a green manure. Compared to their pure sowing, cereal and legume mixtures are characterized by a higher total protein yield, more stable yielding, especially in unfavorable habitats, a better legume health, and higher nutritional value [1,2]. An additional advantage of the mixture is soil enrichment by legumes with symbiotically fixed nitrogen [3–5]. In the research mixtures of oats with common vetch were tested.

Oat (*Avena sativa* L.) is a cereal with phytosanitary properties in the crop rotation because it is rarely infested by fungal pathogens of stem base and roots [6]. The tolerance of oats to soil acidification, poor soil conditions, low temperature, and higher soil humidity make them a frequent component of many crop rotations, especially in mountainous regions, with a higher share of rainfall [7]. Oats' grain is an excellent feed for horses and dairy cattle because of its chemical composition. Depending on the cultivar, grains of oats contain ca. 100 g kg−<sup>1</sup> dry matter (d.m.) of total protein, 40–50 g kg−<sup>1</sup> d.m. of crude fat, 100 g kg−<sup>1</sup> d.m. of crude fiber, 60 g kg−<sup>1</sup> d.m. of nitrogen-free extract [8–10]. The biological value of oat protein is not high, but it contains many valuable amino acids, such as lysine and arginine [10]. Of all cereals, oats have the most fiber, mainly in their husks, which

**Citation:** Puzy ´ ˙ nska, K.; Puzy ´ ˙ nski, S.; Synowiec, A.; Bocianowski, J.; Lepiarczyk, A. Grain Yield and Total Protein Content of Organically Grown Oats–Vetch Mixtures Depending on Soil Type and Oats' Cultivar. *Agriculture* **2021**, *11*, 79. https://doi.org/10.3390/ agriculture11010079

Received: 15 December 2020 Accepted: 15 January 2021 Published: 18 January 2021

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reduces their digestibility and energy value [11,12]. Oat products and grain quality can be improved by mixing with legumes [13,14].

Common vetch (*Vicia sativa* L.) contains high amounts of protein in seeds (approx. 33% of dry matter) and vegetative parts, i.e., in straw (approx. 60–120 g kg−<sup>1</sup> d.m.) and green fodder (150–250 g kg−<sup>1</sup> d.m.) [15]. Vetch seeds can be used as a supplement for animals' feed in the absence or limited access to soybean or cornmeal [16]. Ceglarek et al. [17] underline the high content of thiamine acids and methionine in its protein, in comparison to other legume species. Common vetch is ideal for green forage as it has thin stems rich in fine leaves. The slender shoots of vetch can reach a length of up to 150 cm, so it can easily lodge [18]. Common vetch, like oats, is a good forecrop [19]. However, unlike oats, it has high soil demands. It is also characterized by high water requirements, especially during flowering due to the pile root system and a high transpiration rate [20].

The oat–vetch mixture for grain or green forage production combines the advantages of two different species, e.g., reduced fertilization needs due to symbiotic nitrogen fixation. When mixed with oats, vetch plants are less prone to lodging so that harvesting can be done in one step with a combine harvester. The oat and vetch mixture improves soil structure and growth of succeeding crops. In the mixture, the oat protein complements the vetch's sulfur amino acids, and the vetch protein has a positive effect on the quality of the feed [19,20].

The share of vetch seeds in the mixture with oat is variable [20,21], and for that reason, it is not very popular in cultivation. Moreover, with low rainfall, vetch cannot withstand competition for water with oat, and its share in the mixture yield is small [22]. Another important factor influencing the yield of the mixture are different soil requirements of its components. A proper selection of cultivars for the mixture is essential, especially cereal cultivars characterized by lower competitiveness toward the legume component [21]. To date, there are very few reports in the literature on the effect of cultivar choice on the yield of the cereal and legume mixtures in conditions of organic farming. For this reason, this study aimed to analyze the yield, its components and protein content of grain of four oat cultivars grown organically in a mixture with Hanka's vetch on two different soils.

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

#### *2.1. Field Site and Experiment Descriptions*

The research was carried out in 2012–2014 in the Experimental Station Mydlniki-Krakow (50◦05 N 19◦51 E) in the southern Poland. The experiment was set up in a randomized block design, with four replications on two types of soils: Stagnic Luvisol (S.L.) and Haplic Cambisol (H.C.) [23], located about 1 km apart. The area of the experiment was under organic farming managemen<sup>t</sup> since 2009. The description of the soils is given in Table 1. The preceding crop was winter spelt (*Triticum spelta* cv. 'Frankenkorn').


**Table 1.** Characteristic of the soils.

The mixtures of oat with common vetch (*Vicia sativa*, cv. 'Hanka'; breeder: FN Granum, Wodzierady, Poland) were cultivated for grain. The common vetch was mixed with one of the four oats' cultivars, namely 'Celer', 'Grajcar', 'Kasztan', or 'Furman'. A characteristic of the oats' cultivars is presented in Table 2. The mixtures were sown on 23 March 2012; 16 April 2013; and 20 March 2014, on plots of 18 m<sup>2</sup> (3 × 6 m) area, using plot drill (Hege 80) at row space 13.0 cm. A total of 32 plots were established each year. The planned density


of crops was 500 plants m<sup>−</sup><sup>2</sup> of oat and 75 plants m<sup>−</sup><sup>2</sup> of vetch. Crops were cultivated organically.


#### **Table 2.** Characteristics of oats' cultivars.
