| Abstract: | Marine benthic macrophytes were examined as possible nitrogen (N) sources for agriculture in Greece in terms of N mineralization and available standing stocks. Net N mineralization patterns were determined over a 30‐week incubation period under aerobic conditions. Ulva sp., Cystoseira barbata C. Agardh, and Posidonia oceanica (L.) Delile storm‐cast material (SC) and harvested leaves (L) were incorporated into acidic, slightly acidic after liming, and alkaline soils and incubated at 35°C. From the initial stage until the 12th week of incubation, ammonification was higher than nitrification in most cases. The decreasing order of mineralized N originating from macrophytes was: Ulva sp. > P. oceanica (SC) > C. barbata > P. oceanica (L). Rates of net N mineralization of the macrophytes were the highest in the alkaline soil, whereas the lowest values were recorded in the strongly acidic soil. Application of Ca into the acidic soil revealed a considerable increase of N mineralization. Immobilization and ammonification were observed after incorporation of Ulva sp. into the acidic soil. As Ulva sp. proved to be the only potential alternative N source for arable crops, its standing stocks in two geographically different Greek lagoons, the Vassova Lagoon (N Greece) and Papas Lagoon (S Greece) were estimated. It was estimated that 2 ha of Ulva could supply adequate N to cultivate approximately 1 ha cotton. Posidonia and Cystoseira did not show potential as an alternative N source for agriculture and especially in plant nutrition. |
