Effect of nitrogen form on trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) plants grown under saline conditions

The objective of this study was to scrutinize the possible relation of the applied N form with the alleviation of salt stress effects on two citrus rootstocks, C. aurantium and P. trifoliata. One-year-old trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) plants were irrigated with nutrient solutions containing three forms of nitrogen (NO3--N, NH4+-N, and their combination). At the end of the experiment (57 days), it was ascertained that sour orange exhibits higher dry matter weight of leaves and roots compared to trifoliate orange. The dry matter weight of the roots and stems of sour orange is not greatly affected by the addition of NaCl, while the concentration of N in its leaves increases due to the increasing NaCl rate. The application of NaCl led to an increase in the absorbed quantity of N and a reduction in the quantity of K and P, which was taken in by both genotypes. At the same time, an increase in the K use efficiency was noted. As far as photosynthetic parameters are concerned, these exhibited their highest values when administering NO3--N to trifoliate orange and NH4+-N to sour orange without NaCl. On the whole, the combination of NO3--N and NH4+-N favored the plant tissue weight and N content of the leaves in both genotypes when NaCl was added.