江汉平原农田土壤有机碳分布与变化特点:以潜江市为例

以地处江汉平原腹地的潜江市农田土壤(水田、旱地)为研究对象,于2011年实地采样分析表层土壤(0~20 cm)有机碳的分布现状,并对比第二次土壤普查(1983年)资料,探讨28 a来江汉平原农田土壤有机碳的分布与变化特点.结果表明,2011年潜江市农田表层土壤有机碳密度为30.50 t·hm-2,碳储量为452.82×104t,与1983年相比有明显下降,下降速率分别为0.10 t·(hm2·a)-1和1.53 t·a-1,碳储量共损失了9%.两个时期水田土壤有机碳密度均明显高于旱地土壤,分别是旱地土壤的1.6倍和1.3倍,但是经过28年的常规耕作管理,水田土壤有机碳密度呈下降趋势,下降速率为0.23 t·(hm2·a)-1,导致的有机碳损失为52.83×104t,损失比例达16%;而旱地土壤有机碳则以0.05 t·(hm2·a)-1的速率缓慢增长,碳储量共增加了8.57×104t,增加比例为5%,远不能抵消水田土壤的有机碳损失.水田土壤碳储量的损失主要来自于低产潜育型水稻土碳密度的大幅下降所致(尽管其所占面积比例较小),其碳损失量占水田碳损失量的比例达80%;其次为占水田面积比例最大的潴育型水稻土,其碳损失量占水田碳损失量的15%.旱地土壤碳储量增长缓慢,完全来自于面积占96%的灰潮土有机碳密度的增长.因此,江汉平原区水田土壤有机碳的变化决定了农田土壤有机碳的整体动向,今后需着力提升有机碳下降迅速的低产水田以及面积较大的土壤类型的有机碳积累和固持能力.

Distribution and Dynamics of Cropland Soil Organic Carbon in Jianghan Plain: A Case Study of Qianjiang City

Taking an example of Qianjiang City in Jianghan Plain, the distribution and dynamics of soil organic carbon (SOC) in croplands was studied in present study. The cropland included both paddy field and dry land. SOC contents were analyzed by taking soil samples of topsoil (0-20 cm) in 2011 according to land uses and soil types, and then compared with the initial SOC conducted in the period of the second soil survey (1983). The results showed that SOC density and storage in 2011 was 30.50 t ·hm^-2and 452.82×10⁴ t, respectively. During the past 28 years, the cropland SOC density was decreased at a rate of 0.10 t ·(hm² ·a)^-1, and SOC storage was reduced by 9% with the decreasing rate of 1.53 t ·a^-1. SOC density and storage in paddy field was about 1.6 and 1.3 times over that in dry land in the two selected periods. However, the dynamics of SOC in paddy field and dry land were quite the opposite. In paddy field, SOC was lost by 16% (52.83×10⁴ t), with a decreasing rate of 0.23 t ·(hm² ·a)^-1; whereas in dry land, SOC was increased by 5% (8.57×10⁴ t), with an increasing rate of 0.05 t ·(hm² ·a)^-1. The loss of SOC in paddy field was mainly resulted from gleyed paddy soil, which suffered a fast decrease of SOC density and accounted for 80% of SOC lost in paddy field. In addition, Hydromorphic paddy soil, accounting for 50% of the area of paddy field, tended to loss another 15% of SOC in paddy field. While in dry land, the minor SOC storage increased was dominantly attributed to grey fluvo aquic soil, which accounted for 96% of the area of dry land. Thus, the dynamics of cropland SOC in Jianghan Plain was dominantly controlled by SOC changes in paddy field. Our findings suggest that effective management should be considered to enhance the capacity of SOC accumulation and sequestration in the low-yield paddy field and the types of soils that are large in area.