JOURNAL OF PLANTNUTRTIlON, 20(10),1255-1266 (1997) Changes in Nitrate Accumulation and Growth of Endive Plants During Light Period as Affected by Nitrogen level and Formi P. Santamaria,. A. Elia,b and M. Gonnellab a/nst;tute 01 Agronomy and F;e/d Crops, Un;vers;ty 01 Bar;, Bar; 70/26, /ta/y b/nstitute olVegetab/e Cropslor Process;ng, CNR. Bar; 70126, /ta/y ABSTRACT Endive plants (C;choriumendivia L. varocrispum Hegi) were bydroponicatly grown in a growth chamber to asse55, 7 and 14 days after beginning of treatments (DAT), the variation ofleafnitrate (NO) accumulation and growth during the Iight period in relation to both nitrogen (N) availability (8 and 16 mM) and form percentage ratio [50:50 and O:100ammonium (NH4):NO)]in the nutrient solution. 80th 7 and 14 DAT, fresh weight and leaf area linearly increased during the lig~t period without influence of N treatments. Dry matter (d.m.) percentage increased over the 12 hours of Iight. Leaf NO) concentration decreased during the Iight period more with 50:50 than with O:100 NH4:NO)ratio: 7 DAT NO) decreased by 25% with the former N treatment and only by 4% with the latter. After 7 days more, the difference between the two N form ratios was more evident: NO) decreased by 12% with the mixed N fonn, while increased by 10% with 100% NO)-N in the IThe work was carried out at tbe Institute ofVegetable Crops for Processing oftbe Italian National Research Council (CNR), Director Prof. Vito V. Bianco. 1255