Effects of enhanced NH4+-N supply and concomitant changes in the concentrations of other nutrients needed for ion balance on the growth, yield, and nutrient status of eggplants grown on rockwool

SummaryEggplants (Solanum melongena L.) grown on rockwool in a glasshouse were supplied with a nutrient solution (NS) containing 1.0 mM NH4+-N, or three NS containing 4.0 mM NH4+-N. In one of the high NH4+-N treatments, the K, Ca, Mg, and NO3–-N concentrations were reduced to maintain the same electrical conductivity (EC; 2.0 dS m–1), total-N (14.25 mM), and K:Ca:Mg ratio as in the low NH4+-N treatment. In the other two high NH4+-N treatments, the K, Ca and Mg levels were not altered, thus the extra NH4+-N elevated the EC to 2.3 dS m–1, while the NO3–-N was either reduced to maintain the same total-N as in the low NH4+-N treatment, or not altered, in which case the total-N rose to 17.25 mM. The concentrations of P, Fe, Mn, Zn, Cu, B, and Mo were identical in all four treatments, while in the high NH4+-N treatments, ion balance was achieved by adjusting the concentration of SO42–. The increase in NH4+-N from 1.0 mM to 4.0 mM in the NS resulted in similar increases in NH4+-N in the root zone, as indicated b...