The simplification of crop rotation systems, an increase in the concentration of cultivated cereals, and intensification of animal production in litter-free farms have drastically reduced the pig manure production. The consequences include negative organic matter balance and considerable leaching of mineral components from fields. The objective of this paper is to assess the effect of high doses of pig slurry on plants, and to analyse the ionic balance of white mustard. The experiment was conducted in four replications. Test plots were treated with pig slurry at doses of 0, 30, 60, and 90 tonnes fresh mass per hectare. Then, white mustard was sown. After the harvest, the plant material was separated into grains, husks, and stalks. The following were determined in the organic material: total nitrogen, cations (Ca, Mg, K, Na), phosphorus, and total organic acids. The ionic composition of particular parts of plants showed considerable differences associated with different life functions of these plant organs. In grains and stalks of mustard, the ratio of bivalent (Ca+Mg) to monovalent cations (K+Na) showed no considerable variations and was approximate to one. It was only in husks that bivalent cations were three times more abundant that monovalent cations. A considerable increase in yields was observed with an increase in pig slurry doses. The analysis showed the highest accumulation of Ca and K in husks, and the accumulation of mostly N, P, and Mg in grains. During the crop cultivation, approximately 20% of nutrients absorbed by plants from the soil are removed in the form of useful yield, that is grains. The remaining plant parts are ploughed as organic matter, providing nutrients to successive crops through its slow mineralisation over several years.