配施有机肥减少太湖地区稻田土壤硝态氮淋失的机理研究

采用田间小区试验,设计两种无机氮肥梯度,研究配施有机肥对太湖地区水稻季土壤氮素淋失的影响,并从水/土NO_3~-–N迁移研究其对土壤NO_3~-–N淋失的影响机制。设置的处理有:对照(CK)、常规施氮(CT)、减氮施肥(RT)、常规施氮下配施有机肥(CT+M)、减氮施肥下配施有机肥(RT+M)。结果发现:①除去2015年的CT处理,两年里30 cm处配施有机肥和单施无机肥处理之间的土壤NO_3~-–N淋失均没有显著差异;80 cm处,CT+M处理的NO_3~-–N淋失较CT处理减少41%,RT+M处理较RT处理减少12%。②无机肥处理的田面水NO_3~-–N和土壤淋溶水NO_3~-–N之间存在极显著线性相关,但是有机肥的参与会削弱二者之间的相关性。③配施有机肥有利于土壤有机质含量的提高,CT+M处理的有机质含量较CT处理提高6.7%。0～20 cm土层,配施有机肥处理土壤NO_3~-–N含量明显高于无机肥处理;而20～40 cm土层,二者之间的土壤NO_3~-–N含量差异很小。这表明配施有机肥是通过提高土壤有机质含量,增强土壤表层对NO_3~-–N的吸附固持,从而抑制土壤NO_3~-–N的向下迁移,而不是通过减少田面水NO_3~-–N浓度来实现的。此外,配施有机肥还可以提高土壤质量和水稻产量,促进作物对土壤氮素的吸收,这也是稻田土壤NO_3~-–N淋失减少的一个原因。研究结果为减少农田土壤NO_3~-–N淋失提供了科学依据。

Study on Mechanism of Reducing Nitrate Leaching with Organic Addition from Paddy Field in Taihu Lake Region

Field plot experiment with two N rates was adopted to study the effect of organic addition on nitrogen (N) leaching in rice season of Taihu Lake Region, and the mechanism was also studied through nitrate (NO3--N) migration of water and soil. The results showed that: (1) There was no significant difference of soil NO3--N leaching between organic addition and inorganic fertilizer treatments at 30 cm depth during the two seasons except CT treatment in 2015. NO3--N leaching at 80 cm depth in CT+M was 41% lower than in CT, and RT+M produced 12% lower NO3--N leaching loss compared to RT. (2) Floodwater NO3--N under chemical N treatments was in significant relationship with soil NO3--N leaching, while the involvement of organic fertilizer would weaken the relationship between floodwater NO3--N and soil NO3--N leaching. (3) Organic addition could increase soil organic matter content, and CT+M achieved 6.7% higher SOM than CT. Organic N treatments showed higher soil NO3--N content at 0-20 cm compared to chemical N treatments. And soil NO3--N content at 20-40 cm differed little between organic N and chemical N treatments. These indicated that organic addition enhanced the absorption and fixation of NO3--N by soil through the improved SOM and thus inhibited the migration of NO3--N to deep soil. The reduced NO3--N leaching under organic addition was not achieved by reducing floodwater NO3--N concentration. Additionally, organic addition improved soil quality and rice yield, promoted crop N uptake, and thus could also explain the reduced NO3--N leaching loss. The results provided scientific basis for decreasing NO3--N leaching in farmland.