Prediction of soil nitrogen (N) and phosphorus (P) availability in highly saline-submerged soils is crucial to optimize the growth of algae and to sustain Artemia cyst production in the solar saltwork in coastal areas of the Mekong Delta. This study was carried out to aim at revealing the effects of hypersaline conditions on soil N and P availability and finding the correlation between the amounts of dissolved N and P released from the pond sediment and the pools of these nutrients present in soil.

Our results from laboratory incubation experiments showed that the hypersaline conditions existing in Artemia ponds have an effect on both N and P availability. Increasing salinity to 80 g L^-1 (EC 108 dS m^-1) resulted in less mineral N accumulation at the early stage of submergence. However, adverse effects of high salinity on N mineralization are short-lived. In the later stages of submergence, the rate of net N mineralization recovered. On another hand, extremely high salinity enhanced P availability and mobility. At saline concentration of 70 g L^-1 (EC 84-94 dS m^-1), the concentrations of dissolved reactive P (DRP) present in the water column were 1.5 to 2 fold above the concentrations of DRP in the extracts with lower salinity (EC 11-23 dS m^-1). Disturbing soil by daily raking of the pond bottom sediment to feed Artemia offered favorable conditions for the release and maintenance of available N and P. Under these conditions, the availability of N and P to algae utilization can be reliably predicted based on some soil chemical properties: the presence of available inorganic N (DIN) after submergence can be predicted from the fractions of soil labile organic N extractable by hot KCl; whereas the pools of Olsen-P and/or 24-h DRP in equilibrium can be used as indicators to estimate the availability of P.

Keywords: nitrogen, phosphorus, hypersaline, saline-submerged soils, dissolved reactive P, available inorganic N, algae, Artemia.