Maize is a crop that is characterized by a high level of herbicide consumption, due to its efficiency and fastness of chemical control performance. Cultivation of maize is more profitable than cereals. The research conducted in 2004-2007 in western Poland on weed infestation in maize showed the negative aspect of maize cultivation in monoculture. At the beginning of the study, the following weed species occurred: Echinochloa crus galli, Chenopodium album, Agropyron repens, Galium aparine, Viola arvensis, Thlaspi arvense, Capsella bursa-pastoris, Anthemis arvensis and different dicotyledonous weeds present in field experiments. Four years later, the following taxons predominated in maize monoculture: Echinochloa crus-gali, Chenopodium album and new weed species which occurred in trials: Solanum nigrum, Aethusa cynapium. Therefore, experiments were performed in the Institute of Soil Science and Plant Cultivation in Wrocław (50^o58’ N; 16^o56’ E), using herbicides and the following mixtures: Lumax 537,5 SE – applied preemergence, Callisto 100 SC + Milagro 040 – applied postemergence at the 3-4 leaf stage of maize, Maister 310 WG + Actirob 842 EC + Mustang 306 SE – applied postemergence in split doses, limiting weed infestation in maize monoculture crop in direct sowing variant and simplified tillage variant, in ploughing cultivation. Long-term research showed that the effectiveness of herbicides present at farming market should be improved through, for example, postemergence herbicide choice to secondary weed infestation, and the application of mixtures of sulfonylurea herbicides used at the divided fractional doses for weed infestation control at postemergence time. The system of weed control using glyphosate to overwintering species and the ones germinating before a cultivated plant and additionally, the mixture of Maister 310 WG + Actirob 842 EC + Mustang 306 SE applied postemergence in split doses for the secondary weed control, made it possible to eliminate undesired plants on that soil stand in the most efficient way and to achieve the highest grain yield.

Three-year field experiments (2005-2007) were conducted at the Didactic and Experimental Station in Brody (52^o26’ N; 16^o18’ E) of Poznań University of Life Sciences. The aim of the study was to determine the effect of the herbicides Callisto 100 SC (mesotrione) and Maister 310 WG (foramsulfuron + iodosulfuron) applied with oil adjuvant (Actirob 842 EC) and mineral adjuvant – liquid fertilizer (UAN) on the efficacy of weed control and cob yield in the maize cultivar Fido. The herbicides were applied at recommended rates (1.5 dm³·ha^-1 and 150 g·ha^-1 respectively, without adjuvants) and reduced rates (0,75 or 0,50 dm³·ha^-1 and 75 or 50 g·ha^-1) with adjuvant Actirob 842 EC (methylated rape seed oil) at a rate of 1.5 dm³·ha^-1 and with liquid mineral fertilizer UAN (28% N urea-ammonium nitrate) at rates of 2, 4, and 8 dm³·ha^-1. The weed control efficacy of herbicides applied was determined based on the evaluation of weed infestation. Herbicides Callisto 100 SC and Maister 310 WG applied at recommended rates controlled Chenopodium album up to 90%, and Echinochloa crus-galli up to 60%; total weed control was 89 and 93%, respectively. Weed control using mixtures of herbicides at reduced rates with oil adjuvant and UAN was similar to weed control with herbicides applied at recommended rates. Cob yields on the treatments were at similar level; however, they were much higher than that on the control.

In 2006-2008 strict, one-factorial field experiments were established in randomized block design with the control in four replications at three fields situated in Kurowo (52^o07’ N; 16^o39’ E), Czerniejewo (52^o26’ N; 17^o29’ E) and Winna Góra (52^o12’ N; 17^o27’ E). The main goal of the presented paper was to evaluate the selected herbicide selectivity and effectiveness in cultivation of the sorghum cultivar Sucrosorgo 506. Sorghum is considered a minor crop in Poland. There are no registered herbicides, so it is necessary to provide management options for weed control in sorghum. The following active ingredients were tested: s-metolachlor (Dual Gold 960 EC 1.5 dm³·ha^-1), acetochlor (Trophy 786 EC 2.5 dm³·ha^-1), dicamba (Banvel 480 SL 0.5 dm³·ha^-1), florasulam + 2,4D (Mustang 306 SE 0.6 dm³·ha^-1), fluoroksypyr + 2,4D (Aminopielik Gold 530 EW 1.25 dm³·ha^-1), mesotrione (Callisto 100 SC 1.5 dm³·ha^-1), MCPA (Chwastox Extra 300 SL 3.0 dm³·ha^-1), MCPA + dicamba (Chwastox Turbo 340 SL 2.0 dm³·ha^-1), foramsulfuron + iodosulfuron methyl sodium (MaisTer 310 WG 0.15 kg·ha^-1). Dual Gold 960 EC and Trophy 768 EC were applied directly after crop sowing and the other herbicides at the 3-4 leaf stage of sorghum. Weed control effectiveness was assessed 3-4 weeks after herbicide application. Before harvesting, the fresh weight of five sorghum plants and plant density were determined. The research indicated that years of experiments significantly influenced the herbicides selectivity. Fresh weight of 5 sorghum plants was significantly higher in comparison with the control plants after Trophy 786 EC (in 2006) and Chwastox Turbo 340 SL (in 2008) application, while sorghum density was influenced by Chwastox Turbo 340 SL (in 2006 and 2007) and Banvel 480 SL (in 2007). Maister 310 WG applied with adjuvant Actirob 842 EC caused the total destruction of sorghum.

Two series of pot experiments were conducted in 2004 in the greenhouse of the University of Warmia and Mazury in Olsztyn. Meadow fescue (cultivars Skra and Skawa) and timothy (cultivars Kaba and Karta) were grown at the optimum level of soil moisture (80% of field water capacity) and at moisture deficiency (40% of field water capacity).  Soil moisture content was differentiated after emergence. In order to maintain the appropriate soil moisture, water losses were made up on a daily basis, to achieve a specified weight of the pot with soil. Kick-Braukmann pots were filled with 8 kg peat-muck soil containing 29.7% organic matter. The available nutrient content of the soil was as follows: 320 mg P, 540 mg K and 300 mg Mg, and 5 mg Cu, 28.6 mg Zn, 88.6 mg Mn and 112.6 mg Fe·kg^-1 soil. Soil reaction in 1 n KCl was pH 4.9.  During the growing season, the rate of photosynthesis was determined with a LI-COR 6400 portable gas analyzer and leaf greenness was measured with a SPAD 502 chlorophyll meter (Minolta). The plants were cut down three times. The concentrations of total protein, crude fiber, ash, phosphorus, potassium, calcium and magnesium were determined in the biomass. It was found that water deficit reduced photosynthesis rate by 44%, on average. The meadow fescue cultivar Skawa showed the strongest response to moisture deficiency, manifested by a decrease in photosyntesis rate reaching 47%. SPAD values, representing the chlorophyll content of leaves, increased in all cultivars grown under water deficit conditions. Chlorophyll concentration was significantly higher in meadow fescue plants (by approx. 14 SPAD units, on average) than in timothy plants. The drop in soil moisture from 80% to 40% caused a decrease in dry matter yield. Of the investigated cultivars, the highest yield decrease was reported for the timothy cultivar Karta, while the lowest – for the meadow fescue cultivar Skawa. All cultivars grown under soil moisture deficiency conditions contained more total protein and calcium and less crude fiber and phosphorus, compared with control treatment plants. No significant changes were observed with respect to the levels of crude ash, potassium and magnesium. The results of the study indicate that the meadow fescue cultivar Skawa was the most resistant to water deficiency in soil. Despite a considerable decrease in the rate of photosynthesis, the yield of this cultivar dropped only slightly under water deficit conditions.

In the period of 2004-2005 researches were done at the Agricultural Experimental Station in Bałcyny (53^o35’ N; 19^o51’ E) of the University of Warmia and Mazury to determine the results of conversion of oat growing from the conventional system to the organic one. In the first crop rotation it was cultivated according to the principles of the conventional cropping system, applying mineral fertilizers and pesticides. In the second one, a two-year period of conversion of crops to the organic system was realized. In the conventional cropping and in the plot being converted to the organic one naked-grain oat cultivar was sown in the fields after winter wheat. In the conventional crop rotation, as mean from 2 years, 4.81 t∙ha^-1 of oat grain was obtained. The conversion of its growing to organic system decreased the yield by 28.7%. The decrease in grain yield was accompanied by the worsening of all the morphometric elements of the crops and yield structure. The content of protein and P in oat grain in the field of cropping converted to organic system was lower, whereas the contents of K and Mg were higher than those in the field with conventional cropping. The content of Ca was identical in oat grains coming from the two cropping systems.

Abstract: The paper presents the results of a study conducted during the years 2000 – 2002 at the Production and Experimental Station in Bałcyny (53^o35’ N; 19^o51’ E). The objective of this study was to determine the suitability of two maize hybrids, Wilga (FAO 190) and Bzura (FAO 239), for the production of silage as dependent on sowing time (the last ten days of April – early sowing, the first ten days of May – sowing delayed by two weeks) and density of sowing (8, 12 or 16 plants per m²). It was demonstrated that the yield of silage raw material was determined by weather conditions in particular years of the study. The mid-early hybrid Bzura was found to be more suitable for silage production under climate conditions of the Province of Warmia and Mazury, due to a higher yield of both green matter and dry matter, and a higher quality of raw material. Sowing in the first ten days of May, as compared with sowing in the last ten days of April, provided more favorable conditions for plant growth and development, which resulted in a significant increase in the yield of green matter, dry matter and total protein, and in gross energy value. The density of sowing of 16 plants per m² ensured attaining the highest yield of green matter, while the highest yield of dry matter and total protein as well as the highest gross energy value were reported for the density of sowing of 12 plants per m².

In the recent years, traditional methods combined with molecular techniques have been used in many modern breeding programs. This gives the opportunity to introduce more objective selection criteria and parental material selection. It can also allow the time needed to breed a new hybrid to be significantly shortened. Many scientists tried to foresee the effect of heterosis by examining the genetic distance between the parental lines. The experiment was established in 2006 at the Agricultural Experiment Station in Dłoń (51° N; 17° E) of Poznań University of Life Sciences. The aim of this study was to prove the relation between the heterosis effect of the generation F₁ of corn and the molecular level genetic distance between the parental components, with respect to their origin. Proving those relations could make it possible to choose the parental forms which take part in the creation of a new hybrid, and to decrease the number of lines tested in nature. This shortens the breeding cycle and decreases the cost of breeding. The molecular markers: AFLP and RAPD can be useful in selecting the parental components for the purpose of corn hybridization.

In the years 2004-2006 a field experiment was conducted at the Maize Breeding Station in Kobierzyce (50o99’ N; 16o95’ E) on changeability of selected maize hybrid yields in relation to the dose and kind of herbicide applied. The experiment was established according to split plot method in four replications. The first factor in the experiment was herbicides Mustang 306 SE, Callisto 100 SC, Maister OD introduced in a basic dose and in a doubled one. Within the frames of each first factor treatment there was analyzed yield changeability of 8 maize hybrids considerably differing in earliness of maturing and origin: Gazelle, Sastra, Tripoli, Monumental, Claudia, PR39H32, Lober and Anju 248. Discriminatory and cluster analysis of maize hybrid yield changeability under the influence of selected herbicides revealed profound differentiation among the hybrids analyzed. Out of 6 differentiated environments, taking into account chemical protection, the hybrids Sastra and Monumental featured the highest yields, while Claudia and Tripoli were characterized by the lowest yields. Differentiated herbicide doses did not reduce yields of the examined maize hybrids, except for Mustang 306 SE applied in the dose of 1.2 dm3.ha-1 , which resulted in lower yield values than those following the variant recommended by the producer. The most considerable effect on maize hybrid yield changeability was recorded for herbicides Callisto 100 SC in 3.0 dm3.ha-1 dose, as well as Mustang 306 SE in the dose of 1.2 dm3.ha-1. The hybrid Claudia reacted in a different way to herbicide doses used as compared to the remaining treatments. The yields of maize hybrids PR39H32, AN JOU248, PR39H32 and Sastra proved to be very similar, which was confirmed by insignificant Mahalanobis distances between those treatments.