rainfall was low on both ends of the island, although it was high in winter. Table 43 shows 

 the effect of postplanting irrigation on survival— there was little or no improvement in 

 survival of either species. In July, plantings were irrigated heavily for 10 days after planting 

 to test the possibility that the amount of irrigation of winter and spring plantings was too 

 light. Results (Table 44) show no difference in survival of either species. These data agree 

 with the conclusion from preliminary 1972 trials that postplanting irrigation does not 

 improve plant survival sufficiently to warrant the time and expense. This conclusion may 

 not be valid during extended drought, but with average or above average rainfall, natural 

 precipitation is sufficient. 



The reason irrigation had little effect on transplant survival is probably because it did not 

 increase subsurface soil moisture (Table 45). On elevated surfaces (2-foot sand fence), soil 

 moisture was usually near field capacity. Excess water drained through the soil pores and 

 was not retained. Here, irrigation brought the surface layer of dry sand up to field capacity, 

 but the subsurface layer was unaffected. On the backshore, the soil was not freely drained, 

 and the soil moisture, usually in excess of field capacity, was partly dependent upon the 

 water-table depth, normally about 2 feet beneath the surface. Water added by irrigation 

 appeared to drain through the sand without affecting the water table. Only by raising the 

 water table with heavy rainfall can backshore soil moisture be increased for longer than a 

 few hours. However, irrigation partially leached heavy salt concentrations out of the 

 backshore soil, which had occurred as a result of inundations not followed by rain 

 (Table 45). On the elevated sand-fence dune, irrigation slightly increased soil salinity, since 

 the irrigation water was moderately saline (3,000 micromhos per centimeter). 



b. Nutrients. Several reports indicate windborne sand from the beach is higher in plant 

 nutrients than stable sand or old dunes (Gorham, 1958; Wagner, 1964; Woodhouse, Seneca,- 

 and Cooper, 1968). Wagner found that sea oats grew more vigorously on foredune sites with 

 accumulating sand than on interdunes and hind dunes. This could be attributed to higher 

 nutrient content of the fresh sand and the additional area of sand from which nutrients may 

 be drawn. A stabilized dune would presumably have lower nutrient content, and the root 

 system of dune plants would be curtailed by increased competition. 



Contrary to the above references, project analysis of Padre Island sands indicated a low 

 level of many nutrients regardless of island location (Table 6). In June 1970, vegetative 

 characteristics of sea oats were measured as an index of vigor to compare fertilized beach 

 areas with nonfertilized plants growing on foredunes, interdunes, and hind dunes (Table 46). 

 Vigor was evaluated by the weight of flowering culms per plant. This was chosen over 

 number of leaves per shoot (Wagner, 1964) as Hyder and Sneva (1963) reported that the 

 relative number of seed stalks is a better indicator for most species. Vigor measurements for 

 this study were obtained by multiplying weight per flowering culm by number of flowering 

 culms per plant. 



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