I found an interesting article telling about nitrogen form effect on calcium deficiency. In the past i used NPK fert that probably consisted urea. Using the fert i didn't have any stunted tips, deformed leaves etc. despite of very low Ca (about 10..15 ppm). Having switched to NO3 - i got into terrible troubles.
http://www.pubmedcentral.gov/picrend...3&blobtype=pdf
(pdf file format)