Can salt cause erectile dysfunction? Today there is no study that has actually looked at this. However, such a study is likely to come out soon and below I give you reason after reason that salt is going to be hard on erections, both in the short term and in the long. Salt raises many of the key risk factors for erectile dysfunction and so it's just a matter a time before the researchers find that sodium actually plays dirty and punches below the belt.
Salt is abundant in almost all packaged and processed foods, making it very difficult to avoid. Most of us have grown up addicted to heavy sodium content in our diet and food seems dull and uninteresting without it. Most of us have become salt addicts and, as I'll show below, that will likely prove to be deadly to your sex life.
Here are many key reasons that salt will lead to loss of erectile strength:
1. Nitric Oxide. Salt is yet another of what I call an "anti-Viagra." By that I mean a food or substance that does the opposite of Viagra and lowers endothelial nitric oxide. Salt is just such a player and is the last thing you want to allow into your bedroom.
Many men believe that salt raises blood pressure by pulling water into the vessels and arteries. This is a partial explanation at best. The truth is that, according to several animal studies, if you have enough salt, it actually makes NOS (nitric oxide synthase) "less active".  NOS is the very enzyme that Viagra works on to allow nitric oxide to persist in your blood stream longer, which in turn relaxes your arteries and allow more blood to flow into your penis.
Significant salt will do the opposite, constrict your arteries and can lead to hypertension. This is why, as I cover in my link on Erections and High Blood Pressure, that hypertension is a risk for erectile dysfunction.
2. Acetylcholine. Acetylcholine is another artery-relaxer that plays a role in increasing blood flow throughout the body. Although not as potent of a vasodilator as nitric oxide, it nevertheless plays a role. One study found that when salt whacked nitric oxide levels, it also took acetylcholine with it. 
NOTE: Acetylcholine is known as the "memory neurotransmitter." Anything that hammers acetylcholine is likely to be hard on mental performance. This may be why several studies link salt to decreased cognitive function. 
3. Inflammation and Hardening of the Arteries. I covered this in my link on Deadly Salt: salt boosts both arterial inflammation and arterial stiffness. Neither of these are going to help you in the bedroom and will, over time, lead to loss of erectile strength. Think of this way: inflammation leads to damge on the delicate inside of the arteries where nitric oxide is produced. And hardening of arteries damages the entire artery!
>ONE FINAL NOTE: watch out when you eat out. One of the quick and dirty ways to make any food taste better is to add a lot of salt and most restaurants do it without conscience. In fact, this is absolutely necessary to keep a salt-addicted public happy and paying customers returning to the tables. If you eat out, you'll almost for sure end up with too much salt in your diet and that could set you up for long term erectile dysfunction.
1) Am J Hypertens, 2001 Feb, 14(2):155-63, "Effect of salt loading on nitric oxide synthase expression in normotensive rats"
2) American J of Physiology: Heart and Circulatory Physiology, Published online before print March 2002, "High-salt diet depresses acetylcholine reactivity proximal to NOS activation in cerebral arteries"
3) Neuroscience, 2001, 103(2):351-63, "Dahl salt-sensitive and salt-resistant rats: examination of learning and memory performance, blood pressure, and the expression of central nicotinic acetylcholine receptors"