proportion of acres fertilized were used to estimate 

 the total fertilizer use in the Chenier Plain (table 

 3.13). Probably tire major use is in rice cultivation 

 where the fertilizer blend of 18-18-9 (percent 

 N-PjOj-KjO) is commonly applied at planting time. 

 The resultant nutrient load (expressed as phosphorus) 

 to basin waters and its contribution to eutrophication 

 are discussed later. 



Use of agricultural areas by wildlife: Although 

 the creation of agricultural land destroys natural 

 habitat (for instance, the loss of the grassland habitat 

 of the Attwater prairie chicken), it also provides an 

 important concentrated food source that is available 

 to some wildbfe, particularly migratory birds. The use 

 of rice fields and pastures by waterfowl is discussed 

 in part 5.0. The agricultural areas appear to be 

 especially valuable when conditions are unfavorable 

 in adjacent wetlands. 



Surface- and Ground-water Use. Rice irrigation 

 puts severe seasonal demands on the freshwater 

 supply in the Chenier Plain. Since over 95% of the 

 water used for agriculture (fig. 3-6) in Louisiana 

 is for rice production (98% in the southwest por- 

 tion of tlie state, including tlie Louisiana portion 

 of the Chenier Plain (Louisiana Department Public 

 Works 1971), other agricultural uses will be ignored. 

 Considering the rice area in the Chenier Plain basins, 

 the freshwater usage for rice ranges from 0.7 niilUon 

 m^ (24.7 million ft-') in the Chenier Basin to 320 



million m^ (1 1,301 million ft^) in the Mermentau 

 Basin (fig. 3-7) for an estimated total of 571 million 

 m^ (20,165 ft-') (based on 3.11 acre-feet per acre, 

 Louisiana Department Public Works 1970). The 

 timing of this withdrawal is ecologically important 

 since it corresponds with the hottest months of the 

 year when water demand by natural vegetation is also 

 at its peak (fig. 3-8). 



In the southwestern part of Louisiana (including 

 Vernon, Beauregard, Allen, Evangeline, St. Landry, 

 and Acadia parishes as well as the Chenier Plain 

 parishes), 38% of the required water is purchased 

 from commercial suppliers, 28% is self-suppUed from 

 surface water, and the rest is pumped from ground- 

 water by the rice growers (table 3.14). Overall, 

 about 66% of the water is drawn from the surface, 

 the rest from wells. The Vermilion River and the 

 Gulf Intercoastal Waterway (GIWW) supply about 

 26% of the total irrigation surface water used in 

 southwestem Louisiana. Other principal water 

 sources for surface water in the Chenier Plain region 

 are tabulated by the Louisiana Department of Public 

 Works (1970). 



The use of surface and ground water for agri- 

 cultural irrigation is only one demand on this re- 

 newable resource. The total demand and environ- 

 mental impUcations are discussed in part 3.5.3. 



Table 3.13. .'Vrea of agricultural lands, fertilized lands, and tons of fertilizer used for each Chenier Plain basin. 



^Fertilizer ratio not stated in U.S. Department of Agriculture (1975), but the common ratio for rice is 18-18-9 (N-P2OJ-K2O). 



Calculated from the parish percentage of fertilized land (U.S. Department of Agriculture 1975) converted to basin values using 



agriculture factors developed from the rural population figures (appendix 6.2). 

 ''At a rate of 0.173 + .019 short tons/a (0.379 metric tonnes/ha) (U.S. Department of Agriculture 1975). 



37 



