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f;:') co f'- '. .i salt marsh crops (Salicornia o~ Sporobolus, for planted in soil with a low ion exchange capacity, over the richer soils of most stagnant bogs, example) , eg, sands, <...::> .b~" '-~ Glenn and O'Leary (1985) measured irrigation requirements and yields of halophytes grown on seawate~ in the Sonoran desert. Using a soil consisting of 95 % medium-to-fine textured quartz and feldspa~ sand, with 5% clay, they found that the productivity 0~2Salac~rnia bi~elovii could be maintained at 1539 g Dry wt m yr and soil salinity stabilized, They concluded that the overall feasibility of seawater agriculture depended on developing high-frequency, low-volume irrigation systems suitable fo~ seawater applications, The STEP process is not concerned with efficient water use, or with water conservation; as a pollution control p~ocess, its principal objectives is to concentrate salts through the evaporation and transpiration of wate~. This modifies the objective from low-volume to high-volume irrigation, Irregardless, these data clea~ly show that the ~etention of good drainage, the maintenance of a low ion exchange capacity in the soils, and p~ovisions fo~ flow-through, flushing, and volume turnovers will be needed in STEP ponds, Selecting either species or conditions' that encourage shallow rooting will also be advantageous. Smalley and Thien (1976) report that 65% of the roots of Deschampsia cespitosa, Grindelia inte~rifolia, and Salicornia vir~inica occur in the upper 10 em,: most of the roots of Spartina alterniflora, one of the deepe~ rooted species according to Gallagher (1980), can be found in the upper 30 em (Hanson. 1980), This range of 10 - 30 em permeable bottom soil depth is indicated appropriate for planning purposes in STEP ponds. c. Yield Estimates for Grand Junction Region Applications Because production is one of the major determinants of operating revenues in the STEP process. careful estimates of yield under operating conditions are essential, This is done here as a first step by reviewing historical yields reported for one of the most cosmopolitian and well studied salt marsh plant species in the United States, Spartina alterniflora, and drawing comparisons with the latitude, growth season, and average daily solar radiation linked with that data, The relationships established th~ough this procedure are then applied to the characteristics of the Grand Junction region, The historical yield data fo~ Spartina alte~niflora is p~esented in Table VI, along with respective location and climate information. All yields are standardized fo~ the totals recorded over a 365 day period in grams dry weight per square meter, Most reports presented a range of yields, eithe~ from replicate plots or study years, The lowest annual yield was ~ecorded in Connecticut. equivalent to 2,8 tons per acre. and the highest were reported in Georgia (20,9 tons per acre) and Massachusettes (18,1 tons per acre), 21.