[Nitrogen - potassium - calcium and magnesium contents in the roots of the herbaceous plants growing in a semiarid climate [in Spain]]

analisi statistica analyse statistique analytical methods azote azoto calcio calcium espagne herbaceous plants magnesio magnesium metodi analitici nitrogen piante erbacee potasio potassio potassium racine radici roots semiarid zones spagna spain statistical analysis technique analytique zone semiaride