Comparison of mineralization rates and nitrogen potentials in foreshore reclamation long-term cultivated paddy soils and adjacent upland soils

Foreshore land reclamation is one major way to expand land area in coastal lines. Soil nitrogen mineralization parameters can reveal the evolution of reclamation lands, which are the indicators for soil fertility and nitrogen supply. However, the knowledge is rarely available in foreshore reclamation soils in China. An intermittent leaching method was used to investigate nitrogen mineralization rates and potentials of four paddy soils, and adjacent another four upland soils originated from foreshore reclamation before 520 years in Cixi city on the plain of marine at the south bank of Hangzhou Bay. A first-order kinetic model derived from curve fitting to laboratory incubation data can be used to predict N mineralization as a function of time［Nt=N0(1-e-kt), where Nt is the cumulative mineralized N at time t, N0 is the potential mineralizable N pool, k is the first order rate constant, and t is incubation time］. The potentially mineralizable N pool (N0) ranges from 82.7 to 161.9 mg/kg (av.114 mg/kg) for paddy soils, accounting for 7.3% of SON, and 63.9-104.4 mg/kg (av.83.4 mg/kg) for upland soils, accounting for 7.3% of SON. The k value of paddy soils is 0.033-0.114/d (av. 0.064/d), and 0.007-0.023/d (av. 0.020/d) for upland soils. The N0k ranges from 3.84 to 18.46 mg/(kgd)［av.8.0 mg/(kgd)］for paddy soils, and 0.54-2.66 mg/(kgd)［av. 1.6 mg/(kgd)］for upland soils. Total N concentration is 1.4-2.0 g/kg (av. 1.6 g/kg) for paddy soils, and 0.87-2.0 g/kg (av. 1.3 g/kg) for upland soil. It can be concluded that soil N pool, potentially mineralizable N pool and mineralizable N rate constant of paddy soils are all greater than those of upland soils. Therefore, paddy soil originated from foreshore reclamation could be highly sustainable land use compared to uplands.