In 2005-2007 at the Education and Research Station Krasne (50^o03’ N; 22^o06’ E) near Rzeszów, on brown soil formed from loess classified as the good wheat complex, a study was carried out on the effect of cultivation methods on the weed infestation and yield of two-species mixtures with 50% of spring wheat, spring barley and oat. The mechanical and chemical method using harrowing and ½ dose of the herbicide Chwastox Trio 540 SL was characterized by the highest effectiveness in limiting the total number and mass of weeds, especially in the oat-barley mixture. Applying each method of cultivation resulted in a significant increase in the mixture grain yield as compared with the control treatment. Significantly lower grain yields were obtained on the treatments after the application of harrowing and the full dose of the herbicide as compared with the herbicide application at a smaller dose after earlier harrowing. The oat-barley mixture was characterized by a higher yield-forming potential. Its yield amounted to 4.42 t·ha^-1 and was significantly higher, on average by 0.45 t·ha^-1, than the yield of the other mixtures.

Contamination of soils artificially polluted with polycyclic aromatic hydrocarbons (PAHs) and soils aged polluted with crude oil in the phytoremediation process were compared. The plant used in the tests was maize (Zea mays L.). In chamber tests with soils artificially polluted (chernozem, calcareous rendzina, and lessives), selected three PAHs (anthracene, phenanthrene, and pyrene) were used at the doses of 100, 500, and 1000 mg·kg^-1 d.m. of soil and diesel fuel at the doses of 0.1%, 0.5%, and 1% (v/v). The soil naturally, aged polluted with crude oil chosen for the experiment was brown soil from crude oil refinery. Additionally, in the bioremediation process, the inoculation of plants with the mixture of bacteria strains Azospirillum and Pseudomonas stutzeri was used in the amount of 1 ml·500 g^-1 of soil. Chamber pot-tests were carried out in controlled conditions (temperature, humidity) during four weeks of plant growth period. Physical properties of soils polluted with PAHs, diesel fuel, and crude oil and the degree of PAHs degradation were analyzed in the study. The amounts of anthracene, phenanthrene, and pyrene were determined in soils artificially polluted and Σ15 PAHs in soils artificially polluted with diesel fuel, as well as in brown soil aged polluted with crude oil. The obtained results showed a statistically important increase in the physical properties of soils polluted with PAHs, diesel fuel, and crude oil compared with the control and also an important decrease in the content of PAHs in soils (both artificially and aged polluted) inoculated with Azospirillum and Pseudomonas stutzeri after maize growth. The bioremediation processes were especially intensive in calcareous rendzina artificially polluted with PAHs and in brown soil aged polluted with crude oil.

Contamination of soils artificially polluted with PAHs and aged polluted with crude oil in the phytoremediation process were compared. The plant used in the tests was maize (Zea mays L.). In chamber tests with soils artificially polluted (chernozem, calcareous rendzina, and lessives), selected three PAHs (anthracene, phenanthrene, and pyrene) were used at the doses of 100, 500, and 1000 mg·kg^-1 d.m. of soil and diesel fuel at the doses of 0.1%, 0.5%, and 1% (v/v). Brown soil from crude oil refinery was chosen as the soil naturally, aged polluted with crude oil. Additionally, plant inoculation with the mixture of bacteria strains Azospirillum and Pseudomonas stutzeri was applied in the bioremediation process in the amount of 1 ml·500 g^-1 of soil. Chamber pot-tests were carried out in controlled conditions (temperature, humidity) during a four-week-long plant growth period. Physical properties of soils and the dry mass of above- and underground parts of plants were analyzed in the work. The obtained results showed a statistically significant increase in the dry mass of the above- and underground parts of plants (both artificially and aged polluted) inoculated with Azospirillum and Pseudomonas stutzeri after maize growth.

A two-factorial pot experiment was carried out in 2005 to estimate the effect of soil moisture on competition intensity between oat and yellow lupine plants in mixtures Factor I was soil moisture: 40, 60, 80% of field water capacity, and factor II: the composition of oat and lupine mixture (pcs·pot^-1) respectively – 30 + 5, 20 + 5, 10 + 5, 0 + 5 (pure sowing of lupine), 10 + 0, 20 + 0, 30 + 0 (pure sowings of oat). Indexes worked out by Rudnicki and Kotwica [2007] were applied for the assessment of competition intensity. Competitive effect of oat on lupine increased along with a growing oat plant density in mixtures, in inverse proportion to the soil humidity. Lupine plants exerted a weaker competitive pressure on oat plants than vice versa, which resulted from their smaller density. Single oat plants turned out to be weaker competitors than single lupine plants in the mixture.

The results of two-factorial field experiment conducted in 2002, 2004 and 2005 at the Research Station Mochełek near Bydgoszcz (53^o13’ N; 17^o51’ E) were applied to estimate mutual interactions between oat and yellow lupine. The factors were: sowing rate of oat (0, 140, 280, 420, 560 grains·m^-2) and lupine (0, 25, 50, 75, 100 seeds·m^-2). Combinations of levels of both factors gave 16 mixtures and four pure sowings of each of the species. Assessment of competition intensity was made based on indexes worked out by Rudnicki and Kotwica [2007]. Competition between oat and lupine in mixture stands is characterized by strong asymmetry. Oat was the dominant species and its competitive advantage over lupine resulted from a greater plant density. The competitive potential of a single yellow lupine plant towards oat turned out to be higher than that of a single oat plant towards lupine. Relations of the competitive strength of a single plant in mixtures were arranged according to the regularity that the stronger was competition between plants of species B and the weaker between plants of species A, the stronger competitors single plants of species A were for single plants of species B.

The field experiment with mixtures of barley, husked oat and naked oat with field pea was conducted in 2005-2007 at the Podlasie Centre for Agricultural Consultancy in Szepietów (53^o7’ N; 22^o9’ E). One experiment was established on the soil of the good wheat complex (soil pH above 5.5; in the stand after wheat), and the other on the soil of the good rye complex (soil pH 4.8-5.5; in the stand after triticale). The effect of nitrogen rates: 0, 25 and 50 kg·ha^-1 on seed yield, total protein content in seeds of both mixture components, protein yield and mass fraction of the components in seed and protein yield were studied. Barley was more suitable for cultivation in mixture with pea than oat (especially in better soil conditions), due to higher yields of seeds, protein and net energy. For mixtures of barley and oat with pea the rate of N – 25 kg·ha^-1 turned out to be sufficient. Percentage of pea in seed yield of mixtures with cereals was small (16-32%), and in protein yield – 24-41%. Higher percentage of protein deriving from pea was found in the mixture with naked oat than in mixtures with husked cereals.

The study was carried out in 2007-2009 at the growth chamber of the Institute of Soil Science and Plant Cultivation – National Research Institute in Puławy, in Mitscherlich pots containing a mixture of 5 kg of hortisol and 2 kg of sand. 1^st order factor was soil moisture: 30 and 60% of field water capacity (FWC), and 2^nd order factor – a way of sowing: pure sowing of lupine – 5 plants, mixed sowing – 3 lupine plants and 6 barley plants and pure sowing of barley – 10 plants∙pot^-1. Blue lupine of the cultivar Sonet and barley of the cultivar Johan were sown in the experiment. The aim of this study was to estimate the response of a determinate cultivar of blue lupine grown in pure sowing and in mixture with barley to drought stress occurring in the flowering period. A lower sensitivity to drought of the lupine-barley mixture than of lupine cultivated in pure sowing was observed. Under conditions of the optimal soil moisture (60% FWC) sowings of lupine with barley gave the highest yield, whereas under conditions of water deficiency in soil barley grown in pure sowing gave the highest yield. For the reason of a larger yielding stability, under conditions of expected water deficiency in soil it is better to cultivate blue lupine with barley than in pure sowing. Planing such sowings, it should be taken into account that in spite of high yields they provide less lupine seeds than pure sowings of this species.

An experiment was carried out at the Experimental-Didactic Station in Swadzim (52^o26’ N; 16º45’ E), which is part of the Poznań University of Life Sciences, in years 2006-2008. The aim of the research was to examine the effect of weather conditions on the yield of ten sugar maize hybrids. Length of growth period, yield size, first class cobs share, number of grains in the cobs, and cob length were defined. It was found that the length of growth period and weather conditions have an effect on yield size and first class cobs share. The best sugar maize hybrids for processing proved to be ‘Sweet Wonder’, ‘Rebecca’, and ‘Sweet Nugget’. The best for direct consumption were ‘Sweet Wonder’, ‘Rebecca’, and ‘Sweet Talk’.

In the experiment, the productivity of winter wheat grown with diversified nitrogen fertilization as a cover crop for the undersowns crop of seradella and white clover, as well as their mixture were compared. After wheat harvest, stubble crops of white mustard and fodder pea and their mixtures were sown. Field experiment was conducted in two growth seasons – 2004/2005 and 2005/2006 on Eutric Gleyic Cambisol, quality class IIIb and very good rye complex. Winter rape was the forecrop for winter wheat. Wheat fertilization with P and K amounted to, respectively, 33.4 and 74.7 kg. Wheat sowing was carried out annually in the third decade of September. The highest grain and wheat straw yield were obtained with nitrogen fertilization in the amount of 90 kg·ha^-1. The number of grains per spike and thousand grain mass increased under the influence of nitrogen fertilization, which consequently increased grain yield. Winter wheat created favourable growth and development conditions for the undersowns crop of seradella and white clover, as well as their mixtures, regardless of the nitrogen dose. Stubble crop growth after winter wheat harvest increased the amount of manurial biomass, and the amount of accumulated nitrogen depended on the biological properties of the grown species. Species mixtures within the range of undersowns and stubble crops made it possible to obtain a high yield of dry mass and in a better way met the idea of the introduction of biodiversity into sustainable agriculture in comparison with monocrops.

This study compares the effectiveness of fertilization of spring barley of the cultivar Orthega relative to varied nitrogen fertilization rates in 2001, 2002 and 2004. Analysis of economic effectiveness was made on the basis of a record of measures and types of technological equipment used and outlays of labor and tractive force and material outlays, and the energy effectiveness of production on the basis of the ratio of energy contained in the obtained crops to energy outlays incurred in production. On the basis of determination of economic and energy effectiveness it was indicated that the optimal fertilization of fodder spring barley amounts to 80 kg N·ha^-1. Cost analysis indicated that the main cost generator is work of tractors and machines. Additionally, growing nitrogen fertilization resulted in an increase in profitability index from an economic perspective and a decrease in value of production energy profitability index.