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Effects of Soil Water Deficit on Leaf Nitrogen, Chlorophylls and Spad Chlorophyll Meter Reading on Growth Stages of Soybean

SHAKIL UDDIN AHMED
Department of Soil, Water and Environment, University of Dhaka, Dhaka

Abstract/ Executive Summary:

Soybean leaf Nitrogen (N) status correlated linearly with the amount of chlorophylls and SCMR at flowering stage in response to water deficit levels. In addition, SCMR showed significant positive correlation with chlorophylls at flowering stage. Grain yield significantly correlated to the leaf nitrogen as well as to the chlorophylls and SCMR at flowering stage in response to water deficit levels. These relationships indicated that the water stress decreased leaf nitrogen, chlorophylls and SCMR which in turn caused decreased grain yield of soybean. The results from the study suggest that, flowering stage is the best time for prediction on the adverse effects of water stress on leaf nitrogen assimilation, chlorophylls and SCMR on potential yielding ability of soybean.

Keywords: Soil water deficit, Leaf nitrogen; Chlorophyll (a+b), Growth stages, Soybean

Location:

Start Date:

End Date:

Program Area: Knowledge Management

Commodity: Soybean

Objectives:

The present study aimed at selecting the best time of evaluating SCMR at different growth stages for prediction of adverse water stress effects on leaf nitrogen status and chlorophylls in determining potential yielding ability of soybean grain.

Methodology:

This research was conducted in a vinyl house (surrounding sides were open). The soil was clay loam in texture (0.40g/g sand, 0.27g/g silt and 0.33g/g clay). The bulk density was 1.07 (g/cm³). Soil water content at field capacity (34.7kPa) was 0.516 m3/m³ and wilting point (185 kPa) was 0.296 m³/m³^. Therefore, the total available water (TAW) was 0.220 m3/m3. Five water deficit (D) treatments viz. D₁(0 - 20%), D₂(20 - 40%), D₃(40 - 60%), D₄ (60 - 80%) and D₅(80 - 100%) of total available water (TAW) were arranged in a completely randomized block design with 12 replications. The TAW is defined as the water content between field capacity (θFC) and permanent wilting point (θPWP). The water deficit level of D₂(20-40%), for example, meant that the available water deficit was maintained between 20 and 40% of TAW throughout the growing season. When the maximum allowable depletion of available water came close to 40% of TAW, water was applied to restore the available water to the deficit level of 20% of TAW. Plastic pots (10 liters volume and 23.8 cm diameter) with no drainage holes were filled with 7 kg air-dried soil. Then five soybean seeds [Glycine max (L.) Merrill] were sown in each pot. Prior to planting, uniform water was applied to all the pots to bring them to field capacity (θFC) for uniform germination. The soil moisture for all pots was maintained at field capacity (θFC) until 14 days after sowing (DAS) and then the deficit irrigation treatments were initiated. The irrigated period of soybean was 20 weeks from June 16 to November 3. The plants were thinned to one per pot at the 2- to 3-leaf-stage. Three replicate pots of each water deficit (D) level were sampled at 49 DAS (development stage), 77 DAS (flowering stage), 105 DAS (seed growth stage) and 140 DAS (maturity stage) during the experiment. Three plants per treatment were used for final yield analyses. Leaf disks and SPAD meter readings were taken in parallel from a minimum of ten leaves starting at the tip of a shoot and moving basipetally along the same shoot. SPAD meter readings (SCMR) were conducted on the same leaves directly next to, and immediately after, leaf disks had been excised for chlorophylls.

Source of Information: Bangladesh J. Bot. 40(2): 171-175, 2011 (December)

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Achievement/Findings:

Results indicate that water deficit had significant effect on the relationships among the leaf N accumulation, chlorophylls, SCMR and grain yield at flowering stage, because physiological maturity might reach maximum at that time. A critically important period for fixation and assimilation of nitrogen in soybean production is at the pick of the flowering stage. It appeared that SPAD chlorophyll meter reading (SCMR) and determining of leaf N and chlorophylls during flowering stage is the best time for the prediction of adverse water stress effects on potential yield capacity of soybean grains

Knowledge Management: Journal