Field research was conducted in Poland from 2019–2021 to determine the effect of the bacteria Azospirillum lipoferum Br17 and Azotobacter chroococcum, as well as companion red clover on the total protein content and yield in the grain of spring barley cultivated in a system of organic agriculture. Two factors were examined in the field experiment: I. bacterial formulations: 1—control, 2—nitrogen-fixing bacteria (Azospirillum lipoferum Br17, Azotobacter chroococcum), 3—nitrogen-fixing bacteria (Azospirillum lipoferum Br17, Azotobacter chroococcum) + phosphorus-releasing bacteria (Bacillus megaterium var. phosphaticum, Arthrobacter agilis), and 4—nitrogen-fixing bacteria (Azotobacter chroococcum) + plant growth-promoting rhizobacteria (PGPR) (Bacillus subtilis, Bacillus amyloliquefaciens, Pseudomonas fluorescens); II. companion crop: control without a companion crop, red clover, and red clover + Italian ryegrass. In spring barley grain, the total protein content was determined and the total protein yield was calculated. The obtained study results demonstrated that the growing season conditions significantly affected the total protein content and yield in the spring barley grain. The highest total protein content was recorded in the grain of spring barley following an application of nitrogen-fixing bacteria (Azotobacter chroococcum) combined with PGPR (Bacillus subtilis, Pseudomonas fluorescens) and grown with companion red clover.

The objective of the work was to determine the effect of undersown catch crops, which were either autumn-incorporated or left on the soil surface as mulch for spring incorporation, on the microelement content in the tubers of potato cultivated in the integrated and organic production system. Field research was conducted at the Zawady Experimental Farm owned by Siedlce University of Natural Sciences and Humanities, Poland (52° 03′ 39″ N, 22° 33′ 80″ E). The following two factors were examined in the study: (i) organic fertilisation, control, farmyard manure, serradella, westerwolds ryegrass, serradella applied as mulch and westerwolds ryegrass applied as mulch and (ii) production system, organic and integrated. Microelements (B, Cu, Fe, Mn, Zn) were determined in potato tubers samples. The tubers of potato manured with autumn-incorporated serradella had the highest iron and zinc contents, whereas tubers following autumn-incorporated serradella and spring-incorporated serradella mulch had the highest boron content. Manuring with undersown catch crops and farmyard manure contributed to a decline in the potato tuber content of copper and manganese. Potato cultivated in the integrated production system contained more copper, manganese and zinc, whereas organic tubers had more iron and boron.

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The paper presents the results of a 2016–2018 study to determine the effect of the share of components in the mixture and the harvest date on the weed infestation and yield of mixtures of field pea with spring triticale. Two factors were studied in the experiment: the proportion of components in the mixture: field pea – clean sowing 100%, spring triticale – clean sowing 100%,  field pea 75% + spring triticale 25%, field pea 50% + spring triticale 50%, field pea 25% + spring triticale 75%; harvesting date: flowering stage of field pea (BBCH 65), flat green pod stage of field pea (BBCH 79). The results obtained allow us to conclude that the cultivation of pea in mixed sowings with spring triticale reduces the weed infestation in the canopy compared to pea grown in pure sowing. The highest fresh matter yield was obtained from the mixture of field pea and spring triticale with 50% share of both components, harvested at the stage of flat green pod of field pea.

The paper presents the results from the studies carried our in 2009-2011. The objective of the research was to evaluate the influence of the share of components in the mixtures of blue lupine and oat, and the harvest date on the yield, and weed infestation. Two factors were taken into account: I-the share of components in the mixture: blue lupine (pure stand) 100%, oat (pure stand) 100%, blue lupine 75% + oat 25%, blue lupine 50% + oat 50%, blue lupine 25% + oat 75%, II-the harvest date: flowering stage of blue lupine, flat green pod stage of blue lupine. The results showed that the blue lupine and oat mixtures were less infested with weeds than blue lupine cultivated in a pure stand. The less mass of weed was observed in the mixtures that were harvested at the flowering stage of blue lupine than at the flat green pod stage of blue lupine. The highest yield of green matter was obtained from the blue lupine and oat mixture with the share of components 50% + 50% and the oat cultivated in a pure stand, and harvested at the flat green pod stage of blue lupine.