rates, particularly of nitrogen, to obtain the same result and are 

 more convenient in that they require fewer applications. However, 

 they are far more expensive and where cost is a factor, as on large 

 plantings, only the conventional forms appear to be practical. 



Placement of soluble fertilizers appears to be of little conse- 

 quence on sandy substrates. Ammonium sulfate and triple superphosphate 

 applied on the bare soil surface at low tide can be very effective and 

 remain in place suprisingly well with little evidence of lateral move- 

 ment (Woodhouse, Seneca, and Broome, 1974). However, surface applica- 

 tion may be very ineffective on compact soils. In the comparison shown 

 in Fig. 29 both the soluble and slow-release materials applied subsur- 

 face produced a fivefold to tenfold increase in growth over the surface- 

 applied slow release. Soluble as well as slow-release fertilizer mate- 

 rials should be applied in the planting holes, or furrows and covered 

 prior to reflooding on heavy-tejctured soils. 



Split applications of nitrogen (ammonia forms) are likely to result 

 in more efficient utilization than large single applications on sandy 

 soils. Three applications of 30 to 50 kilograms of nitrogen (N) per 

 hectare and one application of 30 to 50 kilograms of phosphate (P2O5) per 

 hectare may be warranted during the first growing season on sands. The 

 phosphate and the first nitrogen application should be made 2 to 4 

 weeks after planting or as soon as new growth appears. The other 

 nitrogen applications should follow at 6-week intervals. 



A possible acceleration of eutrophication by the addition of fertil- 

 izers to estuaries should be considered. Although there are no data 

 bearing directly on this problem, the judicial use of fertilizers in 

 marsh establishment is unlikely to contribute significantly to the 

 pollution load of most estuaries for the following reasons: 



(a) Applied nitrogen utilization by marsh plantings can be 

 quite efficient. Apparent recovery in aboveground growth in the year 

 of application has been as high as 50 percent, comparable to that of 

 upland crops (Woodhouse, Seneca, and Broome, 1976) . 



(b) The amount of nitrogen applied in a planting, encompassing 

 only a small part of an estuary, is usually insignificant in comparison 

 with the nitrogen regularly entering estuaries from other sources (agri- 

 cultural, municipal, and industrial). 



(c) Little fertilizer phosphorus is likely to leave a planted 

 area because of the affinity of marsh sediments for this nutrient. 



(d) Fertilization will normally be a one-season event, applied 

 only in the year of establishment. The resulting marsh will be capable 

 of immobilizing much larger quantities of pollutants in succeeding years. 



71 



