Effects of Water Stress on Soil Plant Analytical Development (SPAD) Chlorophyll Meter Reading and its Relationship to Nitrogen Status and Grain Yield of Soybean under Different Soil Types

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An experiment was conducted in a vinyl house at Gifu University, Japan, from June to November 2007 to elucidate the water stress effects on Soil Plant Analytical Development (SPAD) chlorophyll meter reading (SCMR) and its relationship to nitrogen status and grain yield of soybean under the three soil types. The first factor was the three soil types, comprising clay loam, sandy clay loam, and sandy loam, classified as Inceptisol, Ultisol, and Andisol, respectively. Water deficit (D) was the second factor with four levels including D_1(0-25%), D_2(25-50%), D_3(50-75%) and D_4(75-100%) of total available water (TAW). The soybean grain yield showed linear relationships with ET and LAI among the three soil types. On the other hand, soybean grain yield correlated with SCMR, leaf N and grain N status with significant differences among the three soil types in response to different water deficit levels. The highest soybean grain yield was in Inceptisol, followed by Ultisol, and Andisol in response to the same water deficit levels. The results of SCMR suggest that, seed formation stage is the best time for prediction of adverse water stress effects on nitrogen assimilation in potential yielding ability of soybean.