The main objective of this work was to investigate the effect of soil bulk density on nutrient (N, P, K) content and uptake, and also cellular fluid pH of spring barley (Hordeum vulgare L.) and weeds with different levels of fertilization. Data were collected from the Estonian University of Life Sciences research fields (58º23xN, 26º44xE) with four different levels of soil compaction on sandy loam Stagnic Luvisol from 2003 to 2005. The soil was compacted by tractor MTZ-82 (with loader; total weight 4.9 Mg) before spring sowing. Four levels of fertilization (N0P0K0, N40P7K20; N80P14K40; N120P21K80) were applied using N20: P3.5: K10 fertilizer. Results of our experiments showed a high positive correlation between soil bulk density and cellular fluid pH (average r=0.87) and negative correlation between soil bulk density and nutrient content (average r=–0.88) at highest rates of fertilization (N80P14K40; N120P21K80) and positive correlation (r=0.84) at lower rates of fertilization (N0P0K0, N40P7K20) in earing phase of barley. If the soil bulk density increased up to level 1.56 Mg m–3, there was a sudden increase of cellular fluid pH without fertilizers use. Use of fertilizers decreased the barley stress. A sudden increase of cellular fluid pH started after soil bulk density 1.61 Mg m–3. The greatest impact of soil compaction was on nitrogen and potassium content in barley dry matter in all fertilization levels. The nitrogen and potassium content in barley dry matter decreased up to 37% by high soil bulk density depending on fertilization. Soil compaction decreased competiveness of barley and increased the share of weeds from 20% up to 53%. The most widespread weed species were common lambsquarters (Chenopodium album L.), field pennycress (Thlaspi arvense L.), common fumitory (Fumaria officinalis L.), red dead nettle (Lamium purpureum L.) and common chickweed (Stellaria media (L.) Vill.) in all fertilization treatments. Soil compaction decreased nutrient content in weeds, but increased weeds role in nutrient uptake, especially at highest doses of fertilizer. The highest share of nutrient accumulation by weeds was on the N40P7K20 treatment, where the total biomass of weeds was also the highest. Without fertilizer use the uptake of nutrients by roots was higher than uptake by shoots in case of nitrogen and phosphorus. Soil compaction increased nutrient content in roots but fertilization had no significant effect on it. The experiment showed that the higher decrease of nutrient content and the sudden increase of cellular fluid pH started at the same soil bulk density value.