Responses of Nitrogen Status Indicators to Nitrogen Rates and Soil Moisture in Corn (Zea mays L.)

The present study compared the sensitivity of tissue nitrogen (N) concentration, SPAD readings, Dualex readings, and SPAD/Dualex ratios for assessing the N status of corn (Zea mays L. cv. Pioneer 38B84) under different water supply conditions. A greenhouse trial was conducted with 4 rates of N fertilizer (0, 50, 50+75, and 200 kg ha−1) and 3 watering levels (drought, drought followed by rewatering, and fully-watered). Tissue N concentration, SPAD, Dualex, and SPAD/Dualex values were influenced significantly by N rates and soil water content (SWC). Tissue N concentration, SPAD value, and SPAD/Dualex ratio increased with N rates, whereas Dualex value decreased. In the first phase of reaction to drought, tissue N concentration, SPAD value, and SPAD/Dualex ratio decreased rapidly, but Dualex value increased; however, the opposite pattern of response was observed in the long term. Under rewatering, tissue N concentration, Dualex value, and SPAD/Dualex ratio gradually recovered, whereas SPAD values did not change significantly as they did in the drought treatment. There were highly significant relationships between tissue N concentration and SPAD reading (r = 0.92, P ≤ 0.001), Dualex value (r = (0.86, P ≤ 0.001), or SPAD/Dualex ratio (r = 0.63, P ≤ 0.001). However, SPAD and Dualex values were better predictors of tissue N concentration under drought condition (r= 0.90, P ≤ 0.001 for SPAD; r = −0.83, P ≤ 0.001 for Dualex) than under fully-watered condition (r = 0.39, P ≤ 0.05) for SPAD; r = −;0.44, P ≤ 0.05 for Dualex) at the end of the trial. Among the indicators, Dualex is better to discriminate N treatments with consistent results across SWC levels.

摘要SPAD-502叶绿素仪与Dualex-3多酚仪均可诊断作物的氮素营养状况, 为了探讨不同水分条件下该指标对作物施氮量的响应, 以玉米品种Pioneer 38B84为研究对象, 在温室盆栽条件下, 研究3个土壤水分水平(干旱、干旱后复水和水分良好)和4个施氮水平(0、50、50+75和200 kg hm−2), 即12个处理对植物含氮量、SPAD值、Dualex值以及SPAD/Dualex比值的影响。结果表明, 植物含氮量、SPAD值和SPAD/Dualex比值均随施氮量的增加而增加, Dualex值随施氮量的增加而减少。干旱胁迫初期, 植物含氮量、SPAD值和SPAD/Dualex比值迅速下降, Dualex值迅速增加; 随着干旱胁迫时间的推进, 各指标逐渐呈相反趋势变化。干旱复水后, 植物含氮量、Dualex值和SPAD/Dualex比值逐渐恢复, 然而SPAD值恢复较小。SPAD值(r = 0.92)、Dualex值(r = −0.86)及SPAD/Dualex值(r = 0.63)与植物含氮量呈极显著的相关性, 但试验后期, 由于生长阶段的不同, SPAD值和Dualex值与植物含氮量在干旱条件下(SPAD: r = 0.90; Dualex: r = −0.83)的相关性高于在水分良好条件下(SPAD: r=0.39; Dualex: r = −0.44)。通过比较不同水分条件下, SPAD值、Dualex值和SPAD/Dualex值对不同施氮量的响应, 发现Dualex值在不同水分条件下均能较好地反应施氮水平。