施N对不同水稻品种N肥利用率及根际硝化作用和硝化微生物的影响

发生在水稻根际的硝化作用对水稻的氮素（N）营养受到人们越来越大的关注。在田间条件下研究了不同N效率粳稻品种（4007、武运粳7号和Elio）在无肥（0kgN/hm^2）、中肥（180kgN/hm^2）和高肥（300kgN/hm^2）水平下籽粒产量、吸N量、N肥利用率、根际土壤铵态氮（NH4^＋-N）和硝态氮（NO3^--N）含量、硝化强度和氨氧化细菌（AOB）数量。结果表明不同水稻品种的籽粒产量在3个N处理中差异极显著，4007在中肥处理中获得最高产量11117kg/hm^2，而Eilo在所有处理中籽粒产量均最低。各品种地上部吸N量随施N量增加而增加，但各品种之间差异不显著。不同水稻品种N肥利用率差异显著，4007显著高于武运粳7号和Elio。本试验根据不同品种水稻在不施N肥水平下的籽粒产量与N肥利用率的大小，将3个品种分为N肥高效敏感型（4007）、N肥高效不敏感型（武运粳7号）和N肥低效不敏感型（Elio）。在水稻中后期干湿交替的水分管理条件下，无肥和中肥区的水稻根际土壤以NO3^--N为主;而在高肥区则以NH4^＋-N为主。随着施N量增加，水稻根际土壤铵、硝态N含量也随之增加。NH4^＋-N含量在无肥、中肥和高肥水平下分别为0.88、0.94mg/kg和13.5mg/kg，而NO3^--N含量分别为1.61、1.73mg/kg和2.33mg/kg。不同水稻品种根际土壤硝化强度之间差异极显著，在3个施N水平下均表现为4007〉武运粳7号〉Elio。其平均值分别为6.94、5.46μg/（kg·h）和2.42μg/（kg·h）。在3个施N水平下，Elio根际土壤AOB数量均显著低于4007和武运粳7号。4007根际土壤AOB数量在高肥水平下达最大值2.02×106个/g土，而最小值为中肥水平下Elio的根际土壤（1.89×105个/g土）。相关性分析表明，水稻根际土壤硝化强度在无肥、中肥和高肥条件下与产量呈极显著正相关关系（r=0.799，0.877，0.934），而且在中肥条件下与水稻N肥利用率显著相关（r=0.735）。水稻根际土壤AOB数量分别和硝化强度以及水稻籽粒产量呈极显著正相关关系。试验结果表明，水稻根际的硝化作用较大程度上决定着水稻籽粒产量或水稻N肥利用率。

Effect of N application on fertilizer-N use efficiencies, nitrification and nitrifying microorganisms in rhizosphere soil growing with different lowland rice cultivars

More and more evidence shows that nitrification happened in rhizosphere soil of rice is of significance to nitrogen (N) nutrition of rice plants. Three japonica rice cultivars (4007, Wuyunjing7 and Elio) with different N use efficiencies were used to study rice grain yields, total N accumulation and the nitrification characteristics under three N treatments, such as zero N level (0 kg N/hm²), moderate N level (180 kg N/hm²) and high N level (300 kg N/hm²) in field conditions. The results obtained were described as follows. There were significant differences of rice grain yields among the three rice cultivars under different N application rates. The maximal and minimal grain yields were obtained in 4007 in the moderate N level and in Elio in the zero N level, achieved 11117 kg/hm²and 5322 kg/hm2, respectively. There were significant differences of the total N accumulation among the three N treatments, and the total N accumulation increased with the increase of the N fertilizer application rates. Significant differences were found in the fertilizer-N use efficiency and rice grain yields among the three rice cultivars under different N application rates. For example, the fertilizer-N use efficiency of 4007 was always significantly higher than those of the Wuyunjing 7 and Elio in both moderate and high N level treatments, and the average fertilizer-N use efficiency in the high N level treatment was 42.2% lower than that of the moderate N level treatment. Based on the fertilizer-N use efficiency and grain yield at zero N fertilization level, the three rice cultivars could be defined as efficient and responsive (4007), efficient and nonresponsive (Wuyunjing7) and nonefficient and nonresponsive (Elio).
Under the water management of alternation of wetting and drying during the middle-late rice growing stages, the main N form in the rice growing rhizosphere soil was nitrate (NO₃^--N) in the zero and moderate N level treatments, while ammonium (NH₄⁺-N) was the main N form in the high N level treatment. The contents of NH₄⁺-N and NO₃^--N in the rhizosphere soil increased with the increase of the N fertilizer applications. For example, the average contents of NH+4-N at the zero, moderate and high N level conditions were 0.88, 0.94 mg/kg and 13.5 mg/kg, respectively, while those of NO₃^--N were 1.61, 1.73 mg/kg and 2.33 mg/kg, respectively. The nitrification potential in the rice growing rhizosphere soil represented significant differences among the three rice cultivars, and the average values were 6.94, 5.46 g/(kg•h) and 2.42 g/(kg•h) for 4007, Wuyunjing 7 and Elio, respectively, under all the N application levels. The abundance of ammonia-oxidizing bacterial (AOB) in the rhizosphere soil of Elio was significantly lower than those of 4007 and Wuyunjing 7 under the different N application rates. The maximal abundance of AOB was 2.02×106/g soil in the rhizosphere soil of 4007 at high N level, while the minimal one was 1.89×105/g soil in the rhizosphere soil of Elio at moderate N level. The nitrification potentials in rhizosphere soil were significantly correlated with the rice grain yield at zero, moderate and high N levels (r=0.799**, 0.877** and 0.934**, respectively), and also they were significantly correlated with the N physiological efficiency at moderate N level (r=0.735*). Furthermore, the abundances of AOB in the rhizosphere soil were correlated with the nitrification potentials and the grain yields. These results inferred that there should be a relationship among rice yields, fertilizer-N use efficiency and nitrification potential in rhizosphere of rice plants.