treatments were half the plant weight. Sea oats were potted 1 to 2 months earlier, which 

 probably contributed to the difference. The 120-60-120 treatment produced the highest 

 bitter panicum shoot weight and second highest root weight, while highest tillering occurred 

 at 60-60-60. The least productive treatments were the control and 180-120-120, the 

 treatments with the least and the most nutrients added. 



Both sea oats and bitter panicum responded to fertilizer but yields were increased no 

 more than 2.5 times. Similar pot studies by Barr (1971) in Australia revealed that Spinifex 

 hirsutus and Ammophila arenaria increased 23 to 40 times, respectively, with fertilizer. 



(2) In Field. Field fertilizer trials were conducted in summer 1973, on established 

 north Padre dunes. A randomized block design was used, with three blocks and seven 

 treatments for sea oats and three blocks with six treatments for bitter panicum. The sea oats 

 treatments were applied on the foreslope of the 1,200-foot sea oats dune, which was over 

 4 years old when fertilized. Bitter panicum treatments were on the foreslope of the 

 1,200-foot dune- width panicum plot (two blocks), which was 15 months old when 

 fertilized, and the hind part of the Pan Am panicum site (one block), 38 months old at 

 fertilization. Plot size in all blocks was 50 by 50 feet, but was reduced to 50 by 25 feet 

 before the growth was randomly clipped. Fertilizer was applied in May, June, and July, with 

 one-third total application each month. Aerial growth was clipped in October for bitter 

 panicum and early November for sea oats. 



Results of the field trials (Table 49) were different than the greenhouse results. Bitter 

 panicum increased aerial growth in direct response to increased nitrogen. The heaviest 

 application of nitrogen (180 pounds per acre) yielded nearly 4 times that of the control; 



Table 49. Dry yield of bitter panicum and sea oats in response to fertilizer in field trials. 



Fertilizer treatment 



Sea oats 



Bitter panicum 



Pounds per acre 



Block 



Total 



Block 



Total 



Nitrogen 



Phosphorus 



Potassium 



1 



2 



3 



1 



2 



3 









60 



120 



120 







120 



6*0 



60 



120 



60 



120 





 60 

 60 

 120 

 120 

 60 

 60 



1,861 

 695 

 1,818 

 1,615 

 1,184 

 938 

 1,401 



588 

 1,458 

 1,020 

 1,020 

 1,002 

 1,052 



724 



1,041 

 1,373 



934 

 1,095 

 1,333 

 1,323 



948 



1,162 

 1,177 

 1,259 

 1,244 

 1,173 

 1,104 

 1,024 



2,278 

 3,797 

 2,824 



1,626 

 2,253 

 4,635 



4,485 

 5,826 

 3,794 



984 

 3,049 

 4,500 



5,345 

 6,068 

 4,364 



1,629 a 

 3,033 a, b 

 3,986 a, b, c 



120 

 180 

 180 



5,534 



6,436 



10,201 



5,121b, c 

 6,111c 

 6,118 c 



1. Treatment plots 50 by 25 feet; 10 random 0.25 square meter samples clipped per plot. 



2. Three blocks, seven random treatments per block; 1,200-foot sea oats dune. 



All data from foreslope (0- to 24-foot basal). Treatment means are not significantly different (P ). 



3. Three blocks, six random treatments per block: 0- to 600-foot dune-width panicum blocks 1 and 2); 



data from foreslope (0- to 25-foot basal); Pan Am panicum (block 3) data from backslope (no sand accumulation). 

 Treatment means sharing a common letter are not significantly different (P ). 



138 



