Contents of N, P, K+, Ca2+ and Mg2+ in the amaranth (Amaranthus spp) under saline stress and mulch

The saline stress can affect the absorption of nutrients by plants causing reduction of the production potential. A study was carried out, in greenhouse, in the experimental area of the Centro Federal de Educacao Tecnologica do Rio Grande do Norte, in Natal-R-N, Brazil, from July to November 2006, to evaluate the contents of nutrients in the amaranth tissue. Columns of PVC with 30 kg of a silt loam soil were used. A completely randomized arrangement with eight treatments and four replications was tried to test the use or not of mulch and four levels of salinity (0.15; 1.50; 3.00 e 4.50 dS m(-1), a 25 degrees C), totalizing 32 plots. The use of the mulch increased the contents of K+ and P in the roots, of Cl- in the leaves the same time that reduced N and Na+ in the dry biomass of the amaranth stem. The dry biomass production of plants was increased due to use of mulch, when compared to that obtained in the, soil without mulch. The increase of the irrigation water salinity caused reduction in the contents of N, K+ and Mg2+ in the roots, also increased Cl- in the stems and Na+ in different parts of the plants but didn't affected the others nutrients. The dry biomass production of amaranth was affected by the increase in saline concentration of the irrigation water up to the level of 4.50 dS m(-1) (P < 0.05). The average content of protein in the dry biomass of the amaranth makes possible its potential use as animal food.