硝酸盐反射仪和SPAD法对玉米氮素营养诊断的比较

Comparison of RQ flex and SPAD methods of diagnosing maize(Zea mays) nitrogen nutrient

精准的营养诊断是了解作物氮素营养及推荐施肥的基础。本文在田间滴灌条件下利用SPAD叶绿素仪(SPAD-502 Plus)和硝酸盐反射仪(RQ flex10)两种诊断方法对玉米关键生育时期的氮素营养诊断进行研究,旨在筛选出适宜的诊断方法,并依据诊断值建立滴灌玉米不同生育时期的施肥模型。试验设置0 kg(N)·hm^(-2)(N0)、225 kg(N)·hm^(-2)(N225)、330 kg(N)·hm^(-2)(N330)、435 kg(N)·hm^(-2)(N435)和540 kg(N)·hm^(-2)(N540)5个施氮水平,在不同生育时期测定了玉米叶片SPAD值和叶鞘NO_3^-含量,并分别与施氮量、植株全氮含量、产量进行方程拟合,比较两种诊断方法对玉米氮素营养的响应。研究结果表明:1)玉米叶片SPAD值和叶鞘NO_3^-含量均随施氮量的增加而显著升高,且在拔节期对施氮量的响应最敏感。叶鞘NO_3^-含量对施氮量变化的响应较SPAD值大,其与施氮量及玉米产量的拟合度均高于SPAD值,说明硝酸盐反射仪法对滴灌玉米氮素丰缺的反应更灵敏。2)玉米全氮含量与叶片SPAD值呈显著线性关系,而与叶鞘NO_3^-含量则以线性加平台表示。当叶鞘NO_3^-含量小于186 mg·L^(-1)时,植株全氮与NO_3^-间呈显著线性相关;当叶鞘NO_3^-含量大于186 mg·L^(-1)时,植株全氮随NO_3^-含量增加趋于不变。3)本农作区滴灌玉米最佳经济施氮量为402.5 kg·hm^(-2),对应的玉米产量为17 049 kg·hm^(-2)。玉米拔节期、抽雄吐丝期和灌浆期的临界叶鞘NO_3^-含量分别为729.3 mg·L^(-1)、536 mg·L^(-1)和81.2 mg·L^(-1)。SPAD叶绿素仪和硝酸盐反射仪均可对滴灌玉米进行氮素营养诊断,但硝酸盐速测值能更敏感地反映氮素丰缺状况,基于硝酸盐反射法进行作物氮素营养诊断及推荐施肥具有较好的准确性与适用性。

Precise and prompt approach of crop nutrient diagnosis is the prerequisite in determining crop N content and the recommendation of reasonable amount of N fertilizer. In this study, a field experiment was carried out under drip irrigation condition, the chlorophyll equipment （SPAD-502 Plus） and nitrate reflectrometer （RQ flex10） was employed in terms of diagnosis of maize N nutrition during key growth stages. The aim of the study was to build maize fertilization mode by using the most suitable diagnosis approach. Five N fertilizer application rates were arrayed, including N0 [0 kg（N）·hm^-2], N225 [225 kg（N）·hm^-2], N330 [330 kg（N）·hm^-2], N435 [435 kg（N）·hm^-2] and N540 [540 kg（N）·hm^-2]. The difference of diagnostic effect between SPAD-502 Plus and RQ flex10 methods on maize plant N nutrient were compared based on correlation analysis.＆amp;nbsp;The analysis compared the relationships between corn leaf SPAD and leaf sheath NO3^- concentration for various N fertilizer application rates, plant total N content and yield during different maize growth stages. Also the sensitivities of the RQ flex 10 and SPAD methods of diagnosis of maize plant N nutrient were compared. The results were as follows： 1） Maize leaf SPAD and leaf sheath NO3^- concentration significantly increased with increasing N fertilizer application rate and the most sensitive period was from jointing stage to either tassel-emergence stage or grain-filling stage. The response of sheath NO3^-concentration to N application rate was more sensitive than that of SPAD. This resulted into a higher degree of fit between NO3^-concentration determined by RQ flex 10 method and N application rate or maize yield. RQ flex 10 method was more sensitive in diagnosis of maize N nutrition. 2） The total N content in maize had a significant linear correlation with leaf SPAD, while there was linear and then a constant correlation between the total N and sheath NO3^- concentration. That was, total N content was linearly correlated with NO3^- concentration as corn sheath NO3^- concentration less than 186 mg·L^-1, however, total N content varied slight when sheath NO3^- concentration exceeding 186 mg·L^-1. 3） The recommended economic fertilizer application rate in maize under drip irrigation was 402.5 kg·hm^-2, which produced a yield of 17 049 kg·hm^-2. The critical NO3^-concentration was 729.3 mg·L^-1 at jointing stage, 536 mg·L^-1 at tassel emergence stage and 81.2 mg·L^-1 at grouting stage, respectively. In conclusion, our study showed that both the chlorophyll meter and RQ flex 10 were suitable for maize N nutrient diagnosis. Moreover, the RQ flex 10 approach was a more sensitive method than the chlorophyll meter in diagnosing maize N nutrient status. The study suggested that the RQ flex method was highly suitable for the recommendation of N fertilizer as well as better N resource management in maize fields.