The experiments were conducted in 1998-2000 at the Research Station in Wierz- chucinek, belonging to the University of Technology and Life Science in Bydgoszcz. The two-factor field experiment was made and the effect of diverse nitrogen dosages (0, 60, 120, 180 kg N∙ha^-1) on the content of total nitrogen and amino acid composition was analysed in the consecutive plant growth phases. Nitrogen fertilization significantly reduced nitrogen content in the green mass of winter barley in each phase of its growth. An essential decrease in the contents of the most exogenous amino acids was shown, which may suggest some decline in the protein biological value.

It was attempted to determine and characterize selected quality characteristics of edible potato sold in the trade network of Siedlce by means of the variability and relationship analyses. The research material consisted of potato samples of tubers harvested during three successive years, bought once a month from October to June in five shops in Siedlce. The starch content and peeling productivity (both expressed as percentages) were determined in all samples. Moreover, an organoleptic evaluation of outer and inner characteristics of potato tuber quality was done. It was found that, apart from the regularity of tuber shape and depth of eyes, all the characteristics met the quality requirements defined by the standards. The highest variability was characteristic of the culinary and usable type, starch content and average tuber weight, which proves that the potatoes provided by suppliers vary greatly. The research carried out showed that many significant and highly significant relationships found between the quality characteristics of potato tubers were determined by the years, months and purchase places. Variation in the relationships between the examined characteristics in individual months and shops as well as a marked variation in years resulted from genetic (varietal) differences and physiological changes taking place in tubers, being modified by the storage conditions.

An experiment was carried out to examine the forecrop value (weight of post-harvest residue and accumulation of total nitrogen, phosphorus and potassium) of spring wheat, spring triticale, field pea, and spring wheat-field pea and spring triticale-field pea mixtures in the respective proportions of 80 + 20% and 40 + 60%. An impact of these forecrops on winter wheat was determined. The field experiment was set up at the Experimental Farm in Zawady over 2001-2004. The soil was the rye very good complex. The largest and the smallest amounts of post-harvest residue were produced by spring triticale and field pea, respectively. The weight of post-harvest residue of the spring triticale-field pea mixture was significantly higher and the accumulation of total nitrogen, phosphorus and potassium was also higher than the accumulation by the post-harvest residues of spring wheat-field pea mixture. Winter wheat grain yield, yield structure components and grain total protein content were significantly impacted by weather conditions and forecrop. Field pea and spring wheat- and spring triticale-field pea mixtures more beneficially influenced the yield level of spring wheat than the cereals which were mixture components. An increased share of field pea in the spring wheat- and spring triticale-based mixtures from 20 to 60% significantly increased grain yield and total protein content in winter wheat grain. Choosing grain yield as an assessment criterion, field pea and the mixture of spring triticale and field pea in the respective proportions of 40 and 60% were found to be the best winter wheat forecrop under the soil and climatic conditions of central-eastern Poland.

The authors investigated the impact of the Sinorhizobium inoculum density on the plant development of alfalfa, nodulation and nitrogenase activity. It was found that plants inoculated with a 10% inoculant (4.9 x 10⁶ CFU) were characterized by the best growth, more profuse fresh material and a very well developed root system and, additionally, they revealed higher nitrogenase activity.

The subject of research conducted in 2002-2005 at the University of Agriculture Experimental Station at Prusy near Krakow was an assessment of the effect of two cultivation technologies, diversified in respect of intensity, on yielding, grain protein concentrations and its yield from several selected winter wheat cultivars. The compared cultivation technologies: medium intensive and intensive had a significant influence upon protein content in grain of the analyzed cultivars, as well as on the yield of grain and protein. Wheat cultivation using the intensive technology caused an increase in grain yield by 1.5 t∙ha^-1, in grain protein content by 0.9 percentage point and protein yield by 230 kg∙ha^-1 in comparison with the medium-intensive technology. The effect of cultivation technology on the quantity of the analyzed features depended on the weather conditions and the cultivar. The analysed winter wheat cultivars were yielding on a very high level. From among compared cultivars, the lowest yielding wheat was Kobra Plus, and remaining cultivars yielded from 11 to 17% higher. Finezja and Soraja were characterized by the highest grain protein concentrations, whereas Turnia, Soraja and Finezja had the best protein yield.

The grain yield and technological quality of two winter wheat cultivars Sukces and Tonacja depending on nitrogen fertilization doses and way of N application were determined and described in the field experiment conducted in Puławy Experimental Station in 2004-2006. Three nitrogen fertilization doses 0, 120, 180 kg N·ha^-1 and two ways of nitrogen application (two times and tree times) were applied in this experiment. The biggest grain yield was obtained with nitrogen fertilization at a dose of 180 kg N·ha^-1 and 120 kg N·ha^-1 applied in two doses during growing period. Nitrogen fertilization applied at a dose of 120 kg N·ha^-1 three times during the growing period of winter wheat caused an increase in protein and gluten content and sedimentation value compared with two times. The way of nitrogen fertilization applied at a dose of 180 kg N·ha^-1 had no significant influence on grain quality.

The contents of nitrogen, potassium, phosphorus, calcium, magnesium and sodium were estimated in tubers of Jerusalem artichoke Helianthus tuberosus coming from the field experiment conducted over 2003-2005. The experimental factors were the cultivars of Jerusalem artichoke Albik and Rubik and different nitrogen fertilization levels, against phosphorus and potassium fertilization and the full dose of manure. The cultivar Rubik proved to be more abundant in mineral elements than Albik. The latter was cha-racterized by a higher stability of characteristics. The highest content of nitrogen, calcium and sodium in Jerusalem artichoke tubers was found at the plots fertilized with a dose of 50 kg N·ha^-1.

The aim of the study was to compare the festulolium suitability in mixtures with meadow clover. The first factor was the share of red clover (40, 60 and 80%), the second factor was the level of nitrogen fertilization (0, 60, 120 and 180 kg·ha^-1). The study from years 2005-2007 found that yields of dry matter and total protein were significantly dependent on the percentage of mixture components and doses of nitrogen fertilization. The combination where red clover was sown in 80% and a dose of nitrogen was 60 kg·ha^-1 gave the highest yields of dry matter and total protein. The mixture containing 40% of red clover without nitrogen fertilization was the least advisable.

The purpose of the study conducted in 2005-2006 in Kruszyn Krajeński near Bydgoszcz was to determine the root mass of millet cultural varieties Gierczyckie and Jagna and the vertical distribution of the roots in a very light soil under sprinkling irrigation and diverse nitrogen fertilization. The mass and distribution of roots in the soil depended on sprinkling irrigation and nitrogen fertilization. Sprinkling irrigation contributed to an increase in the root mass of Gierczyckie and Jagna varieties by 11 and 53% respectively; it also promoted root growth in the upper soil layer. Nitrogen fertilization significantly increased the root mass of millet, where the highest increase was observed in Gierczyckie variety for nitrogen fertilization doses 80 and 120 kg·ha^-1 (increase by 80 and 52%), while in Jagna variety for nitrogen fertilization doses 40 and 80 kg·ha^-1 (increase by 43 and 51%). Sprinkling irrigation increases the ratio of P : K index, which defines the relation between grain yield (P) and root mass (K), whereas nitrogen fertilization decreases this ratio.

The aim of this research was to determine the influence of nitrogen fertilization doses and time of its application on the grain yield, yield components and grain quality of spring wheat cv. Nawra. The field experiment was conducted in 2004-2006 at the Research Station Kepa in Pulawy, Poland. The experiment was conducted in three replications using block methods. Two nitrogen fertilization doses (90 and 180 kg N·ha^-1) and two ways of nitrogen application plus control were used. It was found that the nitrogen fertilization dose affected the grain yield. The lowest grain yield was found for nitrogen application at three times during the vegetation phase, compared with two-time application. This was connected with a smaller number of kernels, lower grain yield per plant and lower productive tillering. The best grain quality parameters were found for a dose of 180 kg N·ha^-1 applied three times during the vegetation period (60 kg before sowing + 60 kg in shooting phase + 60 kg in heading phase).The correlation coefficient indicated a strong relationship between nitrogen fertilization and the grain yield, number of heads, protein content and gluten content in spring wheat grain.

The field experiments on the efficacy of weed control of some herbicides: Azoprim 50 WP (atrazine), Maister 310 WG (formasulfuron + iodosulfuron), Dual 960 EC (metolachlor), Chwastox Turbo 340 SL (MCPA + dicamba), Aminopielik Gold 530 EW (fluroxypr + 2,4 D), Mustang 306 SE (florasulam + 2,4 D), Titus 25 WG (rimsulfuron), Emblem 20 WP (bromoxynil), Cadu Star SC (isoksuflutol + flufenacet), Successor 600 (pethoxamid) and Pledge 50 WP (flumioxazin) or their mixtures used in sugar maize cultivation have been conducted in 2004-2006 at the Experimental Station Swadzim near Poznań. On control plots, main species of weeds were: Viola arvensis, Brassica napus, Chenopodium album, Polygonum convolvulus, Echinochloa crus-galli and Galium aparine. The tested herbicides and their mixtures differently affected the reduction of fresh weight of weeds. The most useful for applying in sugar maize appeared Maister 310 WG with Aminopielik Gold 530 EW. Pledge 50 WP with Successor 600 gave good control of Viola arvensis, Chenopodium album and Galium aparine. The least useful for applying in sugar maize appeared Dual 960 EC + Emblem 20 WP. The highest yields of cobs were obtained after Maister 310 WG + Aminopielik Gold 530 EW application.

Field experiments on the reaction of 10 sugar maize varieties – Candle, Challenger, Comanche, Dickson, GSS 5022, GSS 9377, Jubilee, Shaker, Shimmer and Sweet Trophy to herbicides Milagro 040 SC, Maister 310 WG, Mustang 306 SE, Titus 25 WG, Dual 960 EC and Chwastox Turbo DF were carried out in the years 2004-2006. The herbicides were applied in recommended doses at the three ? four-leaf growth stage. Not all herbicides tested were selective to the sugar maize varieties. The herbicide that proved specially not selective was Titus 25 WG. Two varieties, Candle and Sweet Trophy, proved totally resistant to the applied herbicides. GSS 50 22 and GSS 9377 were the least resistant to the herbicides. The highest yield of cobs was observed after Maister 310 WG with Actirob 842 EC application. The lowest yield of cobs was observed after Dual 960 EC with Chwastox Turbo DF application.