ABSTRACT

Salt-affected reclaimed tidelands (RTLs) in coastal areas of South Korea are commonly used for rice (Oryza sativa L.) cultivation as excessive salts are removed through leaching by irrigation during rice growth. However, changes in soil properties and rice growth in RTLs by continuous rice cultivation are not well understood. In the present study, we investigated soil salinity indices (EC_e, electrical conductivity of soil extracts; SAR, sodium adsorption ratio; ESP, exchangeable sodium percentage), fertility (mineral nitrogen (N), and available phosphorus (P) concentrations), and carbon (C) content as well as rice biomass and yield in 72 paddy fields within 10 RTL areas, which have been cultivated for different time periods (13–35 years). Continuous rice cultivation decreased EC_e by 0.36 dS m⁻¹ per year, indicating desalinization, but ESP and SAR were not changed. Available P concentration increased but mineral N concentration did not change with rice cultivation years. There was also an indication of increased soil organic C (SOC) concentration with rice cultivation. However, rice biomass and yield were not different among the RTLs. Instead, rice biomass and yield as well as SOC concentration were negatively correlated with EC_e when all individual measurements from 72 sampling sites within the 10 RTLs were pooled, suggesting that salinity is a constraint for both rice production and SOC sequestration at field scales. Interestingly, soil mineral N concentration was positively correlated with EC_e but negatively with rice biomass and yield. This result implies that heavy application of N fertilizer in highly saline soils may not benefit rice growth due to salinity stress. Our results show that long-term rice cultivation with fertilization and irrigation decreases salinity while increasing P availability. However, SOC content and rice biomass and yield were more responsive to the salinity status of each paddy field than during cultivation years, highlighting the need for field-specific soil management for improved rice production and enhanced SOC sequestration.

摘要

韩国沿海地区受盐影响的复垦潮地 (RTL) 通常用于水稻 ( Oryza sativa L.) 种植，因为在水稻生长过程中通过灌溉浸出去除了过量的盐分。然而，通过连续水稻种植在 RTLs 中土壤特性和水稻生长的变化尚不清楚。在本研究中，我们调查了土壤盐度指数（EC _e，土壤提取物的电导率；SAR，钠吸附率；ESP，可交换钠百分比）、肥力（矿物氮 (N) 和有效磷 (P) 浓度）， 10 个 RTL 区域内 72 个稻田的碳 (C) 含量以及水稻生物量和产量，这些稻田已经种植了不同的时间段（13-35 年）。连续水稻栽培降低EC_e每年增加 0.36 dS m ^-1，表明海水淡化，但 ESP 和 SAR 没有改变。有效磷浓度随水稻种植年限增加而矿质氮浓度没有变化。也有迹象表明，随着水稻种植，土壤有机碳 (SOC) 浓度增加。然而，水稻生物量和产量在 RTL 之间没有差异。相反，当汇集 10 个 RTL 内 72 个采样点的所有个体测量值时，水稻生物量和产量以及 SOC 浓度与 EC _e呈负相关，这表明盐度是大田规模水稻生产和 SOC 封存的制约因素。有趣的是，土壤矿物质 N 浓度与 EC _e呈正相关但对水稻生物量和产量不利。该结果表明，由于盐分胁迫，在高盐度土壤中大量施用氮肥可能不利于水稻生长。我们的结果表明，通过施肥和灌溉的长期水稻种植降低了盐度，同时增加了磷的可用性。然而，与耕作年份相比，土壤有机碳含量和水稻生物量和产量对每个稻田的盐度状况的响应更大，这突出表明需要进行田间特定土壤管理以提高水稻产量和增强有机碳封存。