The effectiveness of a subsurface asphalt moisture barrier in increasing yields of vegetable crops grown on loamy sand soils was investigated. Six vegetable crops were grown under conditions of irrigation and no irrigation with and without a barrier. Average yield increases of all crops over the barrier without irrigation were 46%, 58% and 55% for 1967, 1968 and 1969 respectively. With irrigation, yield increases were 35%, 16% and 30% for 1967, 1968 and 1969. Yield increases were due to a combination of increased water retention and a reduction in nitrate leaching due to excessive rainfall. The barrier increased the water holding capacity of the soil in top 2 feet by approximately 1.25 inches or an additional 70% in available water. In laboratory leaching studies with simulated barriers using high rates of nitrogen, 2 1/2 times as much nitrate remained in the top 2 feet of the soil compared to no barrier with a 5 inch application of water. A summary of yields by crop and graphs of the movement of nitrate, ammonium and potassium are included. The asphalt moisture barrier has proven to be an effective production practice with sandy soils where irrigation is not feasible. (Author)