气候因子和地表覆盖对沿海滩涂土壤盐分动态的影响

为探明气候因子对沿海滩涂表层土壤盐分季节性变化规律的影响,并探讨植被和秸秆覆盖对滩涂土壤脱盐效果及控盐的作用。2014年5月—2015年5月,在江苏沿海滩涂盐碱地(中重度盐分),设置4种处理进行田间试验,分别为对照(裸地,CK)、秸秆覆盖(覆盖量为15 t·hm-2,SM)、植被覆盖(PC)和植被+秸秆覆盖(覆盖量为7.5 t·hm-2,PC+1/2SM),监测了气候因子和表层土壤盐分的季节性动态变化。结果表明:1)在沿海滩涂裸地中,土壤盐分具有一定程度的季节性规律,表现为在10—12月具有明显的积盐效果,且在10月EC1︰5达到最大值为3.90 d S·m-1。2)相关分析表明:采样前7 d降雨累积量与土壤盐分变化有着极密切负相关关系;气候因子的多因子及互作逐步分析表明:降雨量增加可以促进土壤脱盐作用,大气温度升高可加剧土壤盐分表聚,降雨量和大气温度的互作效应增加会对土壤盐分累积产生正效应。3)地表覆盖(包括PC和SM)显著地改变了气候因子对土壤盐分动态变化的影响,累积降雨量和大气平均温度与土壤盐分无显著相关性,且大量秸秆覆盖对滩涂表层土壤脱盐具有更明显的效果。因此,在沿海气候向暖湿方向发展的趋势下,综合考虑脱盐及控盐作用,选择适量秸秆覆盖(如覆盖量15 t·hm-2)或适量秸秆覆盖结合植被种植覆盖,同时充分利用沿海地区降雨量集中的特点,可能是未来滩涂盐碱盐渍土快速脱盐和土壤改良的重要措施。

Climatic factors and mulching affect soil salinity dynamics in coastal areas

To clarify the impact of climatic factors on seasonal variations in soil salinity and to explore the effects of vegetation cover and straw mulching on soil desalination and salinity control in coastal areas, a field experiment was conducted in the medium-heavy saline coastal area of Rudong, Jiangsu Province. Four treatments were set in the study-control (bare land, CK), straw mulch (at 15 t·hm^-2, SM), vegetation cover (PC) and PC combined with SM (at 7.5 t·hm^-2, PC+1/2SM). Climatic factors (rainfall and air temperature) and topsoil salinity dynamics were determined for the period from May 2014 to May 2015. The results showed that:1) seasonal variations of soil salinity to some extent occurred in bare lands in coastal areas, with obvious salt accumulation during the period from October to December with the highest EC_1:5 (3.90 dS·m^-1) in October. 2) Correlation analysis showed that change in soil salinity under CK treatment was significantly negatively correlated with 7-day cumulative rainfall before sampling (P< 0.01) and also with 15-day cumulative rainfall before sampling (P< 0.05), but no so obvious significant correlation were found under SM, PC and PC+1/2SM treatments (P> 0.05). Under CK treatment, multi-factor interphase analysis of climatic factors indicated that increase in rainfall promoted soil desalinization (P< 0.01) and increase in air temperature exacerbated soil salt accumulation in surface soil (P< 0.01). Simultaneously, interaction between rainfall and air temperature had a positive effect on soil salt accumulation (P< 0.01). 3) Surface mulching (including PC and SM) significantly altered the effects of climatic factors on seasonal variations in soil salinity. Under PC and PC+1/2SM treatments, the relationship of the change in soil desalinization ratio (Y) with treatment time (X) followed the quadratic functions of Y_PC=0.001X²-0.345X + 54.41 (R²=0.456, P< 0.01) and Y_PC+1/2SM=0.001X²-0.293X + 57.121 (R²=0.526, P< 0.01), respectively. Under SM treatment, the relationship was a Logistic curve with an equation of Y_SM=94.912/(1+e^1.482-0.052X) (R²=0.980, P< 0.001). In addition, soil desalination rate increased rapidly after 29 days of SM treatment (that is June to August) and the trend stabilized as the rate reached 94.91% in 70-80 days after straw mulching. Moreover, large amount of straw mulch (15 t·hm^-2) had a more obvious effect on soil desalination, but also caused more obvious alkalinity problems. To therefore control desalination and salinity, a suitable amount of straw mulching (such as straw cover of 15 t·hm^-2) or suitable amount of straw mulching combined with vegetation cover (such as Sesbania cannabina Pers. and Brassica juncea L. Czern. et Coss.) were recommended in coastal area with seasonal concentrated high rainfall. This promoted soil desalinization and future soil reclamation under warming-wetting climate in coastal areas.