Submitted to: European Journal of Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2004
Publication Date: 5/3/2005
Citation: Zhao, D., Reddy, K.R., Kakani, V.G., Reddy, V. 2005. Nitrogen deficiency effects on plant growth, leaf photosynthesis, and hyperspectral reflectance properties of sorghum. European Journal of Agronomy.22:391-403. Interpretive Summary: Sorghum is one of the important grain crops cultivated in 40.2 million hectares with a production of 54.7 million metric tons of grain. Soil nitrogen supply and plant nitrogen concentration have been found to affect various physiological processes and grain yield in sorghum. A study was conducted to determine the effects of nitrogen deficiency on growth, development and various physiological processes of sorghum. Nitrogen deficiency decreased leaf area, leaf chlorophyll content and photosynthesis. The decrease in leaf nitrogen and chlorophyll concentration resulted in changes in light reflectance properties of the sorghum leaves resulting in overall decrease in dry matter. The results of this study help in developing improved nitrogen application strategies for increased yields of sorghum crops. The quantitative data developed from this study are also useful for the development of a process level, mechanistic corn simulation model.
Technical Abstract: An experiment was conducted under outdoor pot-culture conditions to determine effects of N deficiency on sorghum growth, development, physiological characteristics, and leaf spectral reflectance properties. Sorghum (cv. DK 44C) was seeded in 12-L pots filled with fine sand. All pots were irrigated with half-strength Hoagland's nutrient solution from emergence to 25 days after sowing (DAS). Thereafter, pots were separated into three identical groups (120 pots each) and the following treatments were initiated: (1) the control (100% N) with the half-strength nutrient solution, (2) reduced N to 20% of the control (20% N), and (3) withheld N from the solution (0% N). Photosynthesis, chlorophyll (Chl) and N concentrations, and hyperspectral reflectance of the uppermost, fully-expanded leaves were determined 3-4-day interval from 21 to 58 DAS during the N treatments. Plants were harvested 58 DAS to determine effects of N deficiency on leaf area (LA), biomass accumulation and partitioning. Nitrogen deficiency significantly reduced LA development, leaf Chl content and photosynthetic rate, resulting in lower biomass production. Decreased leaf photosynthesis due to N deficiency was mainly associated with lower stomatal conductance. Among plant component dry parts, leaf dry weight had the greatest and root dry weight had the smallest decrease under N deficiency. Nitrogendeficit stress mainly increased leaf reflectance at 555 (R555) and 715 nm (R715). Leaf N and Chl concentrations were linearly related to the reflectance ratios of R405/R715 (r2 = 0.68***) and R1075/R735 (r2 = 0.64***), respectively. These specific reflectance ratios may be used to estimate sorghum leaf Chl and plant N status.