The world production of grain and meat over 1961-2001 grew quicker than the population that almost doubled. The per capita production of grain increased by 20% and that of meat by 67%. The world production of milk grew slower and in 2001, expressed per capita, was 14% lower than in 1961. The progress in food output was achieved mainly by intensification of agricultural production; in the years 1961-2001 the area of agricultural land grew only by 11.8% and that of arable land by 10.7%, but irrigated area almost doubled and grain yields grew nearly 2.5 times. In a majority of countries of Europe, North America, Oceania, and in some countries of Latin America a high level of food production, exceeding internal demand, was achieved. A particularly quick growth of agricultural output took place in many countries of South and East Asia where the per capita production of grain, meat and milk considerably increased. A decline in food production, on the other hand, occurred in Africa and in the Middle East, where agricultural production did not keep pace with the population growth. In the countries of the former Soviet Union the decrease in arable land area took place and the nutrition level of the population worsened as compared with the 1961 level. In Poland, in the years 1961-2001 the area of agricultural land decreased especially that of arable land (by 13.4 percent). At the same time cereal yields grew by 70 percent, which resulted in an increase in per capita grain production. The production of meat grew slower than the European average and the per capita production of milk decreased, as a result of drop in number of dairy cows, not compensated by their higher milk yields.

The study analyses the effect of bacterial endophytes on different crop species. It describes how endophytes live in the host tissues of different plants and how endophytic bacteria affect the plant health status. The effect can be both direct, by producing different plant growth stimulators and making the fixed nitrogen available, or indirect when the bacteria act as biological control agents.

The empirical data used in the present research cover the results of winter wheat cultivar experiments carried out over 1971-1995 and the weather observations reported by local meteorological stations in the north-eastern Poland. The study analysed the relations between winter wheat yielding and meteorological variables, including the yield linear trend, as well as relations between the beginning dates of full development stages of plants and the number of days at a given stage and the temperature and precipitation. Having defined the standard fitting method (R², R²_adj, E), each multiple regression model was verified with Cross Validation (CV) test, the LOO version, to obtain an independent evaluation method. The CV test showed an effective tool as it disqualified almost half of the equations. The significant effects showed a greater impact of weather conditions on plant development than on plant yield.

Three-year field experiment (1999-2001) was conducted to determine the effectiveness of Treflan 480 EC herbicide (trifluraline) for common windgrass (Apera spica-venti) control applied directly after winter wheat sowing in mixtures with herbicides for grass and/or dicotyledonous weed control: Afalon Dyspersyjny 450 EC (linuron), Glean 75 DF (chlorsulfuron) and Stomp 330 EC (pendimethaline). Treflan 480 EC applied directly after winter wheat sowing followed by Mustang 306 SE (2,4-D + florasulam) applied in spring at wheat tillering period constituted the control. The best common windgrass and dicotyledonous weed control, yield increase and net profit were recorded for the mixture of Treflan 480 EC (1,25 dm³∙ha^-1) with Glean 75 DF (15 g∙ha^-1) applied in autumn, directly after winter wheat sowing.

The aim of the studies carried out in 1997-2002 was a comparison of weed infestation and spring wheat yielding when organic and conventional fertilisation was applied. It was observed that fertilisation with compost limited spring weed emergence, while spring nitrogen fertilisation increased their density. Biodynamic preparations enhanced weed infestation in spring and at full vegetation. Organic fertilisation significantly decreased spring wheat grain yields.

In field trial the effects of different methods of fungal disease control on growth, development and yield of ‘Bogo’ winter triticale were studied. The following treatments were compared: full control, integrated control and no control of fungal diseases. Over the research years the plantations were infected by leaf and husk septoria. In the second research year there was also observed, however at low intensity, ear fasariosis. The method of fungicide application showed significant differences in the degree of plant infection. The fungicide applied twice during the vegetation period was the most effective method of protection. When no fungicide was applied, the yield decreased by 15%.

The aim of the experiment carried out in 1994-1996 was to determine the effect of the intensity of weed control in winter triticale with the use of Granstar 75 DF herbicide applied in 3 doses: 24.0; 18.0 and 12.0 g(ha^-1 on the yield and nitrogen agricultural productivity. It was shown that the effectiveness of Granstar 75 DF depended on the herbicide dose applied and the highest effectiveness was obtained for the maximum dose of 24 g(ha^-1 (76.7%). After 8 weeks the effectiveness increased on average to 79.2%. The Granstar 75 DF had a significant effect on the crop yield and agricultural effectiveness of nitrogen, regardless of the dose applied.

The application of different soil cultivation methods before sowing increased the values of investigated physical soil properties when simultaneously the depth of cultivation and soil compaction were reduced. However, it did not affect the spring triticale yield. Pre-sowing soil compaction by means of the Campbell and ring rollers significantly decreased plant emergence and the number of spikelets per ear. The grain yield was modified in 32% by out-of-control factors in the years and in 8% by nitrogen fertilisation.

Nitrogen fertilisation is one of the most effective yield-increasing factors but also one of the most critical items of cereal production costs. The aim of the present study was an attempt at defining the optimum nitrogen fertilisation rate for winter barley, factoring in the production, economic and energy effectiveness. The highest yield, profit and profitability ratio was obtained at the nitrogen rate of 90 kg N·ha^-1, while the most favourable value of energy effectiveness – at 60 kg N·ha^-1.

The aim of the present studies carried out over 1994-1998 was to define the effect of multi-year fertilisation with straw + NPK, NPK only, manure only, manure with: PK, NK, NP, NPK, NPK + Ca and no fertilisation on the weed infestation of cereals cultivated in crop rotation. The weed infestation was evaluated in a static fertilisation experiment established in 1948 at Mochełek in the vicinity of Bydgoszcz on typical lessive soil, IVa valuation class, of very good rye complex. Weeds dominating in spring barley included Spergula arvensis and Chenopodium album, and in winter wheat Viola arvensis and Apera spica – venti. The lowest amount of air-dry matter of weeds in spring barley was observed for multi-year fertilisation with manure and with NPK + Ca and with no fertilisation. In winter wheat, however, low weed infestation was also recorded for fertilisation with manure only and with manure + PK.

This paper attempts at defining and comparing winter and spring barley economic effectiveness. The analysis was based on long-term crop rotation experiment and grain prices in the second quarter of 2003. The profits obtained per area unit were 88.7% higher for winter barley. The profitability ratio for winter barley reached 1.70; and for spring barley – 1.3. Smaller differences were found for energy efficiency index; 2.94 for winter barley and 2.37 for spring barley. The comparative analysis of winter and spring barley production on the stand after potato shows a higher energy efficiency and more favourable economic results for winter barley.

The paper presents the results of a study on sowing value of spring barley and oats grain obtained from pure crop and mixture. The grain of both cereals originated from a strict static field experiment carried out during the years 1996-1998 on medium soil of a very good rye complex. The scope of analyses and tests conducted annually covered the major features that determine the sowing value of grain. The results obtained indicate that barley found more favourable conditions in a mixture obtaining in that case higher 1000 grain weight values, uniformity, germination energy and capacity as well as vigour and health status than in monoculture. Different results were obtained for oats where in the majority of the parameters examined its grain originating from monoculture showed a significant advantage over that from the mixture applied, in particular, germination energy and capacity, vigour and health status. Similarities to barley, i.e. better results in case of a mixture were recorded only for 1000 grain weight, their uniformity and contents of offal.

This paper presents a study on the effect of a 26- to 31-year monoculture on the weed infestation of two oat cultivars with and without chemical control. The 6-year study was carried out in a static field experiment on podzolic soil formed of medium dusty clay at the Bałcyny Experimental Station. The control was made up of oat grown in a 6-field crop rotation: potato – oat – fibre flax – winter rye – horse bean – winter triticale. The oat cultivation in a 26-to-31-year monoculture resulted in a heavy weed infestation. In comparison to oat grown in crop rotation, the number of weeds per 1 m² in the uncontrolled oat monoculture was over 3-fold greater, while their biomass was over 4-fold greater. The herbicides applied had a similar effect on weed reduction in both fields (namely in crop rotation & monoculture), while their effect on the reduction in weed biomass was 68% greater in crop rotation than in monoculture (36% greater). We found similar weed infestation for the two oat cultivars grown in monoculture.

The aim of the experiment was to analyse bacterial strains of Arthrobacter ssp. isolated from rhizosphere, rhizoplane and endorhizoplane of winter rye. The enzymatic and antagonistic activities against phytopathogenic fungi were studied. A high activity of isolated strains in protein, starch, pectins, lecithin hydrolysis was observed. Numerous strains showed a potential for benefiting from organic rather than mineral sources of phosphorus. All the strains examined were catalase positive. Mycoantagonism of Arthrobacter ssp. bacteria was investigated towards Fusarium genus fungi. The results obtained from microbiological and statistical analyses show that very antagonistic strains of Arthrobacter genus bacteria occur in the soil rhizosphere. The correlation analysis shows that protein hydrolysis can be involved in antagonistic mechanisms, and that pectinolytic strains are less effective in growth inhibition of pathogenic fungi.

The objective of the study was to evaluate the productivity of five fodder crops (white mustard, radish, winter rape, sunflower and tansy phacelia) cultivated as a stubble intercrop after winter wheat depending on the fertilisation method: cattle slurry, straw-and-mineral fertilisation and mineral fertilisation only. The field experiment was conducted over 1996-1998, at the Mochełek Experimental Station in the vicinity of Bydgoszcz, on a very good rye complex soil. Over three research years high yields of fresh and dry matter were noted. However a great variation among species in their productivity was observed and ranged from 4.53 t D.M.·ha^-1; 4.36t D.M.·ha^-1 to 4.32 t D.M.·ha^-1 for radish, tansy phacelia and white mustard respectively, to 2.74t D.M.·ha^-1 for sunflower. The method of straw-mineral fertilisation resulted in a lower yielding of aboveground parts of radish, rape and sunflower. Over low-rainfall years after sowing a lower seed emergence was recorded for objects fertilised with straw than for the other objects.

This study compared the production of several cereal and legume combinations that were grown on light complex soils. The evaluation of these combinations was based on yield calorific value, survival of perennial species, lodging, and maturation uniformity. Multi-characteristics comparison analysis showed the best effects of mixtures of yellow lupine with spring triticale or with oats.

The research was conducted in 1999-2002 at the Brody Experimental Station of the Poznań Agricultural University. The aim of this study was to determine the effect of tillage systems (conventional, reduced and direct drilling) on yield, weed infestation of maize and physical and chemical soil properties. Reduced tillage and direct drilling systems caused a decrease in the number and height of plants and total dry matter yield of maize as compared to conventional tillage. A continuous use of reduced tillage systems had negative effect on soil physical properties, but increased the weed infestation of maize. A change from conventional system to reduced or direct tillage system causes an accumulation of C, N, K and Mg in the topsoil.

The study was based on a field experiment carried out at the Experimental Station at Zawady over 1995-1997 and aimed at determining the effect of some herbicides on the iron and manganese contents in table potato tubers. The experimental factors included 6 weed control methods and 4 cultivars of potato. The iron and manganese contents in potato tubers were determined with the AAS method. The content of iron depended significantly on the weed control methods, cultivar-specific characteristics of potato and the weather conditions in vegetation periods, while the concentration of manganese – on the cultivar and weather conditions.

Over 1995-1997 a two-factor experiment was carried out which aimed at defining whether and, if so, to what extent magnesium fertilisation affects the content of organic acids and potato tuber blackening right after reaching full maturity and after autumn-winter storage. ‘Mila’ table potato cultivar was researched. The experimental factors included: 2 evaluation dates (after harvest and after 6 months of storage) and 5 magnesium fertilisation rates (15, 35, 50, 70, 85 kg MgO·ha^-1) against fixed nitrogen, phosphorus and potassium fertilisation. In the experiment the degree of raw and cooked tuber blackening was evaluated as well as the content of organic acids which cause blackening. Magnesium fertilisation shows a significant effect on the content of organic acids in tubers. The most favourable effect on the content of chlorogenic and citric acid was recorded for 70 kg MgO·ha^-1, while a concentration of ascorbic acid was the highest for 50 kg MgO·ha^-1. Magnesium fertilisation, to the satisfaction of consumers, decreases tuber blackening.

In laboratory studies there was observed no positive effect of azadirachtin on PVY^N retention in Myzus persicae (Sulz.) which, having contracted the pathogen, were starved and next they were feeding on Physalis floridana test plants. Aphids feeding on protected plants retained active virus for 64 minutes, which was even longer than aphids feeding on unprotected test plants (16 min.). A positive effect of azadirachtin was found in aphids feeding directly after contracting the virus. In two study series only, out of a total of 12, further (the third and fourth) plants were infected out of 10 successively inoculated in the series. In all the other series only the first plants were infected. In some non-protected series also even further plants were infected (the fifth, sixth and even eighth out of 10 inoculated plants). Similarly the total plant infection in the non-protected combination was higher (15%) than in the protected one (5%).

The paper presents the results of a 6-year investigation in a crop-rotation experiment on lessive soil (Orthic Luvisols) of a good wheat complex and of a very good rye complex. There was evaluated yielding of field pea cultivars, Ergo and Agat, grown in a 6-field crop rotation and an increasing 1-6 year monoculture with three pea protection variants. The field pea seed yield in the crop rotation amounted to an average of 3.99 t∙ha^-1, while in the continuous cropping – it was 47% lower. In monoculture there was a decrease in the plant density by 12.1%, the number of pods by 44.2% and the number and 1000 seed weight by 48.9 and by 21.9%, respectively. The field pea cultivars reacted similarly to both the kind of crop sequence (crop rotation, monoculture) and the crop protection levels (herbicides, fungicides). The application of herbicides and fungicides in crop rotation is not justifiable, while in monoculture it increases the seed yield.

This paper presents a 2-year study on the effect of no exposure to light during soil cultivation and sowing on weed infestation in winter rape. Light exposure was limited in two ways: soil cultivation and sowing at daytime with tools with tightly covered working parts (light-resistant shields) and soil cultivation and sowing at night. The control field was cultivated and sown at daytime. Pre-sowing cultivation was done as ploughing and disc-tillage. The results showed that the amount of weeds was lower under a limited light exposure during soil cultivation and sowing than in the soil cultivation at daytime. A reduction in the abundance of weeds on objects treated with shielded tools, depending on the research date and the tillage tool, ranged from 8 to 16%, while after the night tillage and sowing – from 9 to 19%. As compared with plough tillage, the application of disc-harrow in each variant and sowing of winter rape increased the stand weed infestation.

In the pot experiments two cultivars of Trifolium ambiguum, Rhizo and Monaro, were grown. The plant weight and the content of nitrogen in plants were higher after inoculation of the seeds with the isolated bacterial strain of Rhizobium leguminosarum bv. trifolii than after applying soil from Trifolium ambiguum rhizosphere as a source of bacteria. The best development of kura clover was recorded at the soil moisture of 50 and 75% of the total water capacity.

The turf-type perennial ryegrass, Stadion, was sown in the autumn and spring of 1998 and in 1999 in pure stand and as an undersown crop with spring barley cultivated for green matter and for grain. The intensity of Heteroptera, Homoptera and Thysanoptera pests occurrence in the first year of perennial ryegrass growth for seeds depended on different sowing methods. The plantations set up in autumn showed a greater intensity of the occurrence of Thysanoptera and Aphididae. The perennial ryegrass sowing method affected the intensity of the occurrence of neither Cicadellidae nor Aelia acuminata.

A 3-year field study evaluated the effect of various rates of nitrogen fertilisers (0, 75, 150, 225 and 300 kg^.ha^-1 N) on total and true protein, as well as crude fiber contents in stinging nettle plants harvested at three development stages: before budding (the so-called ‘vegetative phase’), at full budding and full flowering. The results obtained show that increasing rates of nitrogen fertilisers increased the content and yield of protein, much higher in plants harvested at vegetative phase than over budding or flowering. Plant harvest at subsequent development stages increased the dry matter and crude fiber percentage in nettle plants but decreased that of protein. Leaves contained considerably more protein, however much less fibre than stems.

The effect of various rates of nitrogen fertilisers on macro- (N-NO₃, P, K, Mg, Ca) and microelement (Fe, Cu, Zn, Mn) contents in nettle plants harvested at three development stages was evaluated in 3-year field and laboratory study. The results obtained show an increase in nitrate and manganese contents in stinging nettle plants along with an increase in nitrogen fertiliser rate applied. Plant harvest at subsequent development stages (vegetative, budding and flowering) decreased the K, Ca, Mn and Cu contents. Plant harvest at full budding may be considered as the optimum one for P, Fe, Cu and Zn contents. Under the conditions of the experiment, the stinging nettle plant contents of K and Mn were too high, while the content of Ca – too low. Additionally the results of the analysis show a considerably higher content of minerals in leaves than in shoots.