The supplies of water and nitrogen to a plant during its critical stages of growth are the main factors that define crop yield. A crop experiences irregular water deficits during its life cycle in rainfed agriculture. An effective anti-stress-oriented approach therefore ought to focus on increasing the units of water productivity. The main objective of this conceptual review is to confirm that adequate K management can be used as an important tool to alleviate the negative effects of water deficit on plant growth, yield-component formation, and yield. The French and Schultz approach of using the water-limited yield (WLY) was modified in this review into a graphical form and was used to discriminate between yield fractions that depended on the volume of transpired water from those that were induced by K fertilizer. By using this method, it was possible to demonstrate the extent of several crop (winter wheat, spring triticale, maize, sugar beet) responses to the K supply. Yield increases resulting from K application mostly appeared under conditions of mild water deficit. As described for sugar beet, finding the critical period of crop K sensitivity is a decisive step in understanding its impact on water-use efficiency. It has been shown that an insufficient supply of K during crucial stages in the yield formation of cereals (wheat, spring triticale), maize, and sugar beet coincides with a depressed development in the yield components. The application of K fertilizer to plants is a simple agronomic practice used to increase crop tolerance to a temporary water shortage. It may be that the improvement of a plant's access to K during mild water-deficiency stress will increase water uptake by the root cells, which in turn increases their osmotic potential and thereby allows extension growth. This growth in turn promotes access to other mineral elements (including nitrogen) and water, which favor plant growth and yield.

Nowadays, the main objectives of plant crop growers aim at two targets (i) increasing food production and (ii) simultaneously, reducing the environmental impact of increasing fertilizer nitrogen consumption. On a global scale, fertilizer nitrogen recovery ranges from 33 to 50%. The required efforts stimulating production but protecting the environment focus on increasing unit productivity of fertilizer N. Magnesium, owing to its biological functions in plants, should play a much more important role In modern agriculture controlling N economy of crop plants and, consequently, nitrogen dispersion in the environment. In Poland, arable soils are generally poor in total and available magnesium. This state can be considered as indicating the necessity of applying magnesium and then maintaining a wellfeed plant nutritional status of growing crops. Crops well supplied with magnesium since the beginning of their growth, as seen from studies on the response of sugar beets and maize, are in a position to increase nitrogen unit productivity. Cereals respond to Mg supply when a dressing treatment takes place just before the onset of flowering. Another factor significantly affecting fertilizer nitrogen recovery in Poland is soil pH. Acid soils fertilized with Mg contain increased soil exchangeable Mg levels, which in turn depress the pressure of toxic aluminum on growing crops. Improvement of the plant Mg nutritional status enables plants to incorporate some of potentially residual N into biomass, increasing biomass yield. It can therefore be concluded that magnesium, owing to its ameliorating function in arable soils, meets the main requirement of sustainable nitrogen management, both in agriculture and in the environment. AbstraktG³ówne zadania stawiane wspó³czeoenie producentom rooelin uprawnych skupiaj¹ siê na dwóch celach: (i) zwiêkszeniu produkcji ¿ywnooeci, i (ii) jednoczeoenie zmniejszeniu ujemnego wp³ywu wzrastaj¹cego poziomu nawo¿enia azotem na oerodowisko. W skali globalnej wykorzystanie azotu szacuje siê od 33 do 50%. Wymagane dzia³ania proprodukcyjne i proekologiczne skupiaj¹ siê na zwiêkszeniu jednostkowej produkcji azotu stosowanego w nawozach. W nowoczesnym rolnictwie magnez, ze wzglêdu na funkcje biologiczne w rooelinie, powinien odgrywaae du¿o wiêksz¹ rolê w kontroli gospodarki azotowej rooeliny, a tym samym rozproszenia azotu w oerodowisku. W Polsce gleby uprawne s¹ ogólnie ubogie w ca³kowity i przyswajalny magnez, co stwarza koniecznooeae stosowania nawozów magnezowych w sposób zabezpieczaj¹cy odpowiedni poziom od¿ywienia rooeliny. Rooeliny dobrze zaopatrzone w magnez od pocz¹tkowych faz rozwoju, jak wynika z reakcji buraków lub kukurydzy, s¹ w stanie istotnie zwiêkszyae jednostkow¹ produktywnooeae azotu. Zbo¿a reaguj¹ na nawo-¿enie magnezem wówczas, gdy zabieg odbywa siê tu¿ przed kwitnieniem. Drugim istotnym czynnikiem ograniczaj¹cym wykorzystanie azotu przez rooeliny uprawiane w Polsce jest odczyn gleb. Traktowanie gleb kwaoenych nawozami magnezowymi, w nastêpstwie wzrostu koncentracji wymiennego magnezu...

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The impact of industrial heavy metal pollution on Scots pine (Pinus sylvestris L.) and black pine (Pinus nigra Arn.) populations was investigated. Sampled pine stands, which were located in Upper Silesia (southern Poland) in an area strongly polluted by heavy metals, consisted of resistant and sensitive trees. To evaluate the adaptation process, genetic structure and diversity was tested using isozyme analysis. Higher levels of Zn, Pb, Cd and Cu were detected in needles of sensitive trees compared with resistant ones. With respect to morphology, Scots pines were more distinctly impaired than black pines. Although black pines had lower heavy metal concentrations, levels in 1-year-old needles, other than Cu, significantly exceeded “reference plant” values (Markert 1994). In both species, resistant trees demonstrated a lower degree of genetic variation than metal-sensitive trees with respect to some enzyme loci (SHDH A, PGI, PGM, MDH C and DIA). This observation was corroborated in sensitive trees by the smaller number of identified alleles and alleles per locus, absence of private alleles and significant excess of homozygotes in relation to expected Hardy–Weinberg equilibrium values. Assuming that only resistant trees of both species survive under conditions of prolonged soil contamination, the observed genetic structure implies that remaining populations will be depleted of some alleles of unknown adaptive value to future selection pressures. Genetic changes induced by heavy metals suggest an important role for specific enzymes—FEST, SHDH A and B, GOT B and PGI—in the adaptation process. Our results may serve as a basis for selection and propagation of individuals appropriate for re-cultivation of areas chemically degraded by industrial activity.