First, I'm a Soil Scientist with USDA. Secondly, I am in a somewhat similar situation in that I live on very sandy soils and am also an avid vegetable gardener. Some recomendations to consider are, just how deep is the "sand" on your land before you hit more loamy or clayey soil? In my instance, I have bored down as deep as 10 feet and hit nothing but sand. I finally hit a water table around 10 to 11 feet. Why is this important? The loamy and clayey layers will restrict and conserve the downward flow of water. If these layers occur within a foot or so of the surface, you are in good shape because roots will be able to extract moisture and nutrients from these depths. If, however, your soil is like mine, with no loamy or clayey layers anywhere in sight, the measures I am about to discuss become even more critical. Secondly, I would suggest you have a soil test run. Many states offer testing for lawns, gardens, and cropland through their county Ag Extension Service.
Now, for the things you can do yourself. Sandy soil most certainly DOES leach many nutrients. First and formost of concern is lime. (assuming your soil is acidic) Lime helps regulate pH. Having a pH somewhere in the vacinity of 6 is usually desirable. Many nutrients are unavailable to plants without the proper pH level. I generally recommend applications of dolomitic limestone AT LEAST every other year on sandy soils. Lime can be added anytime and will not harm plants. However, it takes 5-6 months for the lime to break down enough to begin to work, so the sooner the better. The soil test I mentioned should give you a recommendation as to the amount needed. Personally, if I knew my soil is acidic, I'd go ahead and apply some now.
Your next concern should be to incorporate organic matter. Sandy soils are usually conspiciously devoid of OM. OM will do several good things. First, it will increase the water holding capacity of your soil. Secondly, it will increase the Cation Excahnge Capacity whick exxentually is a fancy way of saying it will hold larger amounts of nutrients that are available to plants, instead of allowing them to leach downward. Finally, it will improve soil tilth. I use a lot of tree leaves. I rake them up in the fall, and run them through a mulcher right into my garden space. I do NOT recommend using grass clipping. They often contain weed seed that will infest your garden. Same goes for some manures. Chicken litter from poultry houses is usually ok, but there is some worry about heavy metal toxicity from the feed they eat. Do this in the fall or winter and get it incorporated through tillage before spring.
When planting time comes, do not use ridged up rows. The main purpose to ridging rows is to allow soil to dry out and warm up quicker than the surrounding soil so the seed can get a head start. On sandy soils, this is not necessary and actually detramental. Sandy soils stay TOO dry. The ridges only function to shed water to the surrounding soil, and sometimes don't allow the seed to get enough moisture to germinate and grow. They will also prevent the plants from getting the most out of your irrigatgion water. Therefore, the solution is to plant a "flat" garden.
As for irrigaton, in your case, it appears you are in an arid area of the country. Evapotransporation is of big concern there. I use a sprinkler system here, but I am located in the humid southeast. In your situation, I'd suggest a soaker hose, or drip emitter irrigation to lessen the amout of water you lose to the atmosphere. I'd water long enough that the soil is moist 3 to 4 inches deep. I usually water my garden every other day (unless it rains) during the hotest part of the summer. If possible and practical, mulching on top around your plants with organic material will also help conserve and hold in moisture.
I hope this helps. Good luck!
