among the five fertilizer treatments, but the unfertilized plots trapped nearly 1 cubic yard 

 per linear foot more than the plots with the highest fertilizer applied. Composite cross 

 sections of the two control plots and two 180-120-60 pounds per acre fertilized plots with 

 the heaviest application and the greatest response showed distinct differences (Fig. 42). The 

 unfertilized plots trapped sand more evenly across the dune, and the heavily fertilized plots 

 trapped sand primarily at the front of the dune, forming a steep foreslope and backslope. 

 This was also observed at several test plots on south Padre, e. g., the north 100 feet of a 

 panicum dune (1,800 to 2,000 feet, North Section Fence) which was fertilized in 1972. 

 A year later, the fertilized section had a high crest with steep slopes, but the unfertilized 

 portion was lower, broad and even. These differences are still apparent 2 years after 

 fertilization. Two fertilized 50- by 50-foot plots on the Pass No. 4 panicum planting (2-foot 

 sand fence) show the same response. Apparently, the 300 to 400 percent increase in cover 

 traps sand too effectively— the sand is trapped at the front of the dune rather than spreading 

 over the entire dune width. Consequently, fertilization does not improve the sand trapping 

 ability of an established bitter panicum planting, and may cause an undesirable situation by 

 building a steep and narrow dune rather than a flatter, broader one. 



e. Fertilizer Application Recommendations. Based on laboratory and field data, the 

 following recommendations are made for fertilization: 



(1) Recent Planting. Both species benefit by fertilization beginning the spring after 

 planting, or 2 to 3 months after a spring planting. Fertilization at this time enables the 

 planting to fill weak spots and to develop sand-trapping cover by mid-summer. Early 

 transplant growth of unfertilized plantings is slow and sand may move through the planting 

 which could be trapped with denser cover. Tins increase in cover is illustrated in the lower 

 photo in Figure 41; the foreground section was fertilized from 4 to 6 months after planting 

 while the background section was not fertilized. Fertilizer should be applied in two or three 

 equal applications, spread over several months, preferably in late spring to summer. The best 

 rates, from greenhouse data, would be 120-60-60 pounds per acre for sea oats, and 

 120-60-120 pounds per acre for bitter panicum. However, field data for bitter panicum 

 indicate that any complete fertilizer with 120 to 180 pounds per acre of nitrogen will be 

 satisfactory. Field data from an established sea oats dune showed no response to any 

 fertilizer level, but observations from nurseries and recently transplanted beach plantings 

 indicated that the same rates should be applied. 



(2) Established and Growing Dunes. Sea oats did not respond to fertilizer; bitter 

 panicum responded, but sand-trapping ability was not improved. Therefore, fertilizing a 

 planting after the first summer is not necessary, except possibly for localized areas with 

 poor cover. 



(3) Nursery. In a nursery, both species should be fertilized annually with the same 

 rates as suggested for a recent planting. If unfertilized, bitter panicum stands thin out after 

 2 to 3 years and the culms become small. Fertilization will restore size and density within a 

 few months. 



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