Field research was conducted in Poland from 2019–2021 to determine the effect of the bacteria Azospirillumlipoferum 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 (Azospirillumlipoferum Br17, Azotobacter chroococcum), 3—nitrogen-fixing bacteria (Azospirillumlipoferum 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.

The objective of the study was to establish the effect of component share in mixtures and harvest date on concentrations of selected heavy metals in the green fodder of field pea, oat, and their mixtures. The research hypothesis assumed that the cultivation of peas and oats in pure sowing, and in mixtures will also allow to choose combinations from which the forage will have the lowest content of heavy metals. Field research was conducted at the Zawady Experimental Farm (52° 03′ 39″ N, 22° 33′ 80″ E) which belongs to Siedlce University of Natural Sciences and Humanities. Two factors were tested in the study: I—component share in the mixture: field pea—pure stand 100%, oat—pure stand 100%, field pea 75% + oat 25%, field pea 50% + oat 50%, field pea 25% + oat 75%; II—harvest date: field pea flowering stage, field pea flat pod stage. Plant material was sampled to determine the following elements: Cu, Zn, Cd, Pb, Cr, and Ni. The results of the study demonstrated that field pea grown in pure stand had the highest copper and zinc contents, and the lowest chromium and nickel contents. Field pea mixed with oat significantly reduced heavy metal content in green fodder. Cadmium and lead contents in the green fodder of field pea/oat mixtures were too low to be determined by means of the spectrometer Perkin Elmer Optima 8300. Regular checks of heavy metal contents are recommended in spite of their low amounts in the green fodder of field pea/oat mixtures.

In order to protect and remediate soils, organic farming methods have grown in popularity. The aim of the study was to evaluate the effect of rhizobacteria (Bacillus subtilis, Bacillus amyloliquefaciens, Pseudomonas fluorescens) and catch crops (undersown red clover alone, undersown Italian ryegrass alone and a mixture of clover and ryegrass) on the microbiological activity of the soil under organic spring barley. In 2019–2021, a field experiment was carried out on an organic farm, randomly in eight variants, each in three repetitions. The following parameters were analyzed: enzymatic activity of dehydrogenases (DHA), acid phosphatase (PAC) and catalase (CAT), soil fertility index (BIF), and a number of selected physiological groups of microorganisms (molds, bacteria, and actinomycetes). Compared to the control variant (without catch crops and bacteria), the values of DHA, CAT, and BIF increased significantly in the variant in which rhizobacteria and catch crops were used simultaneously. The highest BIF, of 32, was obtained in 2019, after the application of red clover catch crop + Italian ryegrass + rhizobacteria. PAC activity dropped significantly after the application of the bacterial consortium alone and was lower than the control by an average of 30%.

Field research was conducted in Poland in 2019–2021 to determine the effect of microbial products and living mulches on grain yield and grain yield structure elements as well as the biological index of soil fertility (BIF) in spring barley grown in organic agriculture. Two factors were examined: I. microbial products: control (no treatment with microbial products), inoculation with phosphorus-releasing bacteria (Bacillus megaterium var. phosphaticum, Arthrobacter agilis), and co-inoculation (simultaneous inoculation) with phosphorus-releasing bacteria (Bacillus megaterium var. phosphaticum, Arthrobacter agilis) and nitrogen-fixing bacteria (Azospirillum lipoferum Br17, Azotobacter chroococcum); II. living mulch: control (no living mulch—spring barley grown in a pure stand), red clover, red clover and Italian ryegrass, and Italian ryegrass. The study results demonstrated that the highest grain yield at 4.5 t ha⁻¹ with superior structure was produced by spring barley following co-inoculation with phosphorus-releasing bacteria (Bacillus megaterium var. phosphaticum, Arthrobacter agilis) and nitrogen-fixing bacteria (Azospirillum lipoferum Br17, Azotobacter chroococcum). The highest value of the biological index of soil fertility (BIF II) determined at the flowering stage was obtained in plots with spring barley cultivated with the living mulch of red clover mixed with Italian ryegrass or red clover following inoculation with phosphorus-releasing bacteria and nitrogen-fixing bacteria 6.9 and 5.7, respectively.

Research was conducted in Poland in 2017–2019 at Siedlce University of Natural Sciences and Humanities in Siedlce. It aimed at determining the effect of the bacteria Bacillus megaterium var. phosphaticum, the amino acid L-alpha proline, and the mineral nitrogen fertiliser regime on iron content in soil during the period of rapid growth of spring wheat plants, as well as in spring wheat grain and straw. The following two factors were examined: (I) biological products: untreated control, Bacillus megaterium var. phosphaticum, L-alpha proline, Bacillus megaterium var. phosphaticum + L-alpha proline; (II) mineral nitrogen fertiliser regime: nonfertilised control, 60 kg N·ha⁻¹, 90 kg N·ha⁻¹, 90 kg N·ha⁻¹ + foliar fertilisation. The study demonstrated that, during the period of rapid spring wheat plant growth, Fe content was the highest in the soil following an application of Bacillus megaterium var. phosphaticum + L-alpha proline + mineral nitrogen fertiliser applied at the rate of 90 kg N·ha⁻¹. This combination resulted in the highest concentration and uptake of iron by spring wheat grain, whereas for straw, the same result was also achieved following mineral nitrogen fertiliser at a rate of 90 kg N·ha⁻¹ + foliar fertilisation.