soaking rain. The factor determining irrigation need is the amount of dry surface sand 

 overlaying the moist sand. Except during droughts, moist sand on the backshore is less than 

 6 inches deep. Hand planting requires less than 2 inches of dry surface sand; otherwise, the 

 dry sand fills each hole when dug. Therefore, hand planting is time consuming and costly. 

 Machine transplanting can be successful with several inches of dry surface sand. 



In hand planting 1,800 linear feet of a south Padre fence-built dune (North Section 

 Fence) in 1973, all sites were irrigated before planting, with satisfactory results. Although 

 the winter was wetter than normal, irrigation was essential except for a few sections planted 

 soon after a soaking rain. 



The irrigation system consisted of sprinklers spaced at 40-foot intervals along a line of 

 1.5-inch flexible plastic pipe. The freshwater source was a series of pits, each about 40 feet 

 square and 5 feet deep, dug with a backhoe behind the artificial dune line, and protected 

 from blowing sand with fencing around the perimeter of the pit. Average time of excavation 

 was 3 to 5 hours; pit capacity was about 18,000 gallons, but this varied during periods of 

 rainfall or drought. Pits excavated in 1973 had partially filled with sand but still contained 

 water in 1974, even though drought conditions prevailed from November 1973, to the 

 summer of 1974. In 1973, a pit pumped dry at the end of the first day was more than half 

 full the second day, and completely full of water on the third day. Salinity of the irrigation 

 water varied and was not predictable; therefore, it was essential to test a water sample from 

 the site before excavating the pit. Ideal irrigation water salinity (undiluted) is less than 

 2,000 micromhos per centimeter (about 5 percent seawater); however, up to 5,000 

 micromhos per centimeter is tolerable. Irrigation water with a salinity of 15,000 micromhos 

 per centimeter caused salt damage to leaves of both sea oats and bitter panicum, and most 

 plants died, although soil salinity did not exceed 600 micromhos per centimeter 

 (2:1 dilution). 



A single irrigation line with 10 sprinklers effectively watered a strip 40 to 50 feet wide 

 by 400 feet long at an equivalent precipitation rate of 0.22 inches per hour. Mean output 

 per sprinkler was 3.5 gallons per minute, with a range of 3.2 to 3.8 depending on distance 

 from the pump. For a five-sprinkler system, 200 feet long, the average output was 3.8 

 gallons per minute. Moistening a 6-inch layer of dry surface sand usually takes 1 day of 

 irrigation. 



/. Preparing the Field for Planting: Grading. The backshore often has irregular low 

 drifts of shifting sand and low dunes temporarily stabilized by sea purslane, which cause 

 undulations in the planting surface and form localized areas where dry sand is too deep for 

 planting. The problem was eliminated on several plantings by grading the planting surface 

 with a bulldozer before planting. However, this is unnecessary unless low dunes of dry sand 

 are common. 



m. Mulch-Netting. On south Padre, plantings were made in 1972-73 on the slopes of 

 barren dunes budt with sand fencing. Plantings not protected from wind were eroded and 



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