A rapid diagnosis of nitrogen nutrition status in the soil is fundamental for precise fertilization during the remediation and safe use of heavy metal polluted paddy soils. Determination of leaf chlorophyll content using the SPAD (soil and plant analyzer development) Chlorophyll Meter has been widely used as nitrogen nutrition diagnosis for corn, wheat and cotton. However, its applicability in rice plant is unclear for the different types of paddy soils under cadmium (Cd) pollution. In this study, twenty-one types of paddy soils collected in the main rice-planting regions of China were used for a pot experiment with a rice variety (DN 2000). Three Cd pollution treatments were established: without Cd addition (no Cd pollution), low dose Cd addition (slight Cd pollution), and high dose Cd addition (severe Cd pollution). Rice leaf SPAD values and nitrogen concentrations in soil solutions were measured at seedling, tillering, jointing, heading and mature stages. The results showed that soil type had a significant impact on the response of rice leaf SPAD value to Cd pollution, and soil pH played an important role (with an average relative contribution of 20%) on the variation of SPAD value. SPAD values were significantly correlated to rice grain nitrogen concentrations, with the highest correlation coefficient in the jointing stage. At the same time, SPAD values were significantly correlated with the total nitrogen and ammonium nitrogen concentrations in soil solutions at seedling and tillering stages, which was independent of Cd pollution level and soil type. In general, rice leaf SPAD value during rice growth season, especially at the jointing stage, could characterize the impact of soil nitrogen supply on nitrogen nutrition status of rice plant in different paddy soils under Cd pollution.%治理和安全利用重金属污染水稻土过程中,氮素营养的快速诊断是制定合理施肥措施的基础.叶绿素测定仪SPAD已广泛应用于非污染耕地土壤中玉米、小麦和棉花等作物的氮素营养诊断,然而针对镉污染条件下的不同类型水稻土,SPAD在诊断水稻氮素营养的适应性方面仍然缺乏系统研究.本研究采集了我国水稻主产区的21种典型水稻土,以德农2000为供试水稻品种,设置无镉污染、轻度镉污染、重度镉污染处理的水稻盆栽试验,研究水稻叶片SPAD值对镉污染水稻土氮素供应诊断和水稻产量预测的能力.结果表明:水稻土类型影响了水稻叶片SPAD值对不同水平镉污染的响应,土壤pH是主控因子,其相对影响的平均值为20%.水稻叶片SPAD值与不同生育期水稻籽粒氮素含量显著正相关,其中拔节期的相关系数最大;同时水稻叶片SPAD值与水稻营养生长期(苗期至拔节期)土壤溶液总氮和铵态氮含量呈显著正相关,且不受镉污染程度和土壤类型的影响.总体上,不同生育期(尤其是拔节期)水稻叶片的SPAD值可以表征镉污染条件下不同类型水稻土氮素养分供应对水稻氮素营养的影响.
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