Leaf Spectral and Pigment Responses to Phosphorus and Nitrogen Deficiencies in Wheat.

Remote sensing has become an important tool for assessment of nutrients in plants. Nitrogen (N) and phosphorus (P) are major macronutrients whose deficiency drastically influences wheat growth. Due to deficiency of either N or P, plants exhibit changes in concentration of leaf pigments. Hence we investigated whether changes in leaf reflectance caused by N and P deficiencies could be related to changes in leaf pigment concentrations. A three way factorial glasshouse experiment was conducted at two growth stages (tillering Z20 and early stem elongation Z30), with three nitrogen levels (25, 50 and 100% of normal growth), and four levels of phosphorus (25, 50, 75 and 100%). The hyperspectral leaf reflectances were taken from the youngest fully emerged leaf with spectrophotometer (StellerNet Inc) in the range of 200-1100 nm at 0.5 nm interval. The specific leaf area, tiller number, leaf biomass (fresh and dry), leaf water content and leaf thickness were measured for each leaf. The pigments were extracted and the concentrations of chlorophyll a, chlorophyll b, anthocyanins, and carotenoids were measured. The absorbance readings of pigment extract were taken to show the absorbance of light in the spectrum range 200-1100 nm by the HPCHEM software. The low P and N treatment had shown dark green leaves with fewer tillers than the higher level of P and N. Leaf reflectance was high for low N and P treatment in the blue, green and red regions of spectrum but less in near infrared (NIR) region. Most of the treatments could be separated in these regions because of the increase or decrease of pigment concentration. The relationships between nutrient deficiency, leaf reflectance, pigment concentrations and physiological parameters are described in the paper.