不同施肥处理稻田系统磷素输移特征研究

磷是水体富营养化限制性元素,近年来由于磷肥的过量施用,农田迁移的磷素已成为水体磷素的主要来源。本研究通过野外测坑定位试验,研究有机肥处理(OT)、混施肥处理(MT)和化肥处理(CT)3种施肥处理下,稻田中磷素的迁移流失特征及这3种处理对水稻产量和磷素利用率的影响,以探求稻田系统的最佳施磷方式。结果表明,CT、MT和OT 3种施肥方式的磷径流流失负荷分别为0.56 kg(P)·hm-2、1.13 kg(P)·hm-2和4.20 kg(P)·hm-2,渗漏流失负荷分别为0.42 kg(P)·hm-2、0.44 kg(P)·hm-2和0.45 kg(P)·hm-2;磷的径流流失占流失总量的56.86%~90.38%,是水稻田磷素流失的主要途径。磷的径流流失主要受施肥和降雨的影响,50%左右磷的流失发生在第1次径流过程;磷素渗漏流失特征不受施磷处理的影响,80%以上的流失发生在施肥后的前30 d。在磷素流失形态上,坑面水、渗漏水和径流水中磷素的主要形态均为可溶性磷;在土壤方面,MT处理和OT处理能保证土壤磷营养,CT处理的土壤有效磷和有机质含量则显著下降。3种施肥处理的水稻产量显著高于空白对照,且MT最高,为6 728.84 kg·hm-2;磷肥利用率CT和MT处理显著高于OT,CT和MT间差异不显著。综合比较,混施肥处理在磷素流失、土壤养分利用和水稻产量等方面更符合我国生态农业发展的要求。

Phosphorus loss and migration characteristics in paddy fields under different fertilization treatments

Anaerobic ammonium oxidizing (anammox) bacteria of phylum Planctomycetes origin have been identified to be responsible for N removal in terrestrial and aquatic environments through combined NH₄⁺ oxidation and NO₂ reduction. Anaerobic ammonium oxidation mediated by anammox bacteria has been noted to be a key process of biogeochemical N cycle in various ecosystems. It was also possible to have anammox processes in flooded paddy fields because of the low oxygen habitat conditions. To investigate the existence of anammox bacteria and the bacteria community diversity response to applied N fertilizer in paddy fields, anammox bacteria community structures in paddy fields were investigated with the aid of denaturing gradient gel electrophoresis and cloning sequencing by assay 16S rRNA gene in the third year of N fertilizer experiment in the field. DGGE images of 16S rRNA gene in surface or root-zone soil showed rich anammox bacteria in paddy soils. The numbers of DGGE band in the images of surface soil or root-zone soil under high N level treatment N3: 225 kg(N)·hm^-2] were greater than those under other N levels N2: 150 kg(N)·hm^-2, N1: 75 kg(N)·hm^-2 and CK: without fertilizer]. The Shannon-Wiener index based on the number and density of DGGE band showed significantly (P < 0.05) higher diversity of anammox bacteria in surface soil or root-zone soil under N3 treatment than N2, N1 or CK treatments. At the same time, Shannon-Wiener index of anammox bacteria in surface soil was markedly (P < 0.05) higher than in root-zone soil under N3 treatment. Redundancy discriminate analysis (RDA) based on 16S rRNA gene DGGE profiles showed significant correlation (P = 0.006) of anammox bacteria community structure in surface soils of paddy fields with different levels of N fertilizer application. RDA plot depicted that anammox bacteria community structure in surface soil under N3 treatment obviously differed from that under N1 or CK treatment. Furthermore, 18 DNA sequences cloning from DGGE band was obtained and logged in GenBank. The findings demonstrated that anammox bacteria community structure in paddy soils strongly responded to intensive N fertilizer use especially in surface paddy soils. Anammox bacteria possibly played a critical role in N cycle in paddy soil ecosystem.