Need some help keeping my navel orange healthy. The first image shows the (semi-dwarf) navel orange shortly after I planted it in September 2012 (around 8 to 9 months ago from writing this post). The following image is from June 2013 (a couple of days ago). As you can see it originally had a healthy dark leaf but the leaf is now looking a lot paler and I'm not sure if that's a sign of some sort of deficiency. The tree is in Phoenix, AZ so gets plenty of sun (and heat) but is well watered to compensate.