Narrow‐Waveband Reflectance Ratios for Remote Estimation of Nitrogen Status in Cotton

Abstract

Tailoring nitrogen (N) fertilizer applications to cotton (Gossypium hirsutum L.) in response to leaf N status may optimize N use efficiency and reduce off-site effects of excessive fertilizer use. This study compared leaf and canopy reflectance within the 350 to 950 nm range in order to identify reflectance ratios sensitive to leaf chlorophyll (Chl), and hence N status, in cotton. Plants were grown outdoors in large pots using half-strength Hoagland's (control) solution until some three-row plots received a restricted supply of N. Treatments comprised control, 20% of control N at first flower bud (square) onward; 0 and 20% of control N at first flower onward; and 0% of control N at fruit-filling onward. Despite leaf N values ranging from 51 to 19 g kg-1 across treatments and sampling dates, a weak correlation was obtained between Chl and N (r2 = 0.32, df = 70). In general, N stress led to increased reflectance at 695 +/- 2.5 nm (R695) and decreased reflectance at R410, and changes in leaf N were best correlated with either R695 or R755 in leaves and either R410 or R700 in canopies. The strongest associations between leaf constituent and canopy reflectance ratio were Chl vs. R415/R695 (r2 = 0.72), carotenoids vs. R415/R685 (r2 = 0.79), and N vs. R415/R710 (r2 = 0.70). The R415 measure appears to be a more stable spectral feature under N stress, as compared with more pronounced changes along the reflectance red edge (690-730 nm). Multiple regression identified a three-waveband canopy reflectance model that explained 80% of the variability in leaf N. Results indicate that remote sensing of N status in cotton is feasible using narrow-waveband reflectance ratios that involve the violet or blue region of the spectrum (400 to 450 nm) and the more commonly featured red-edge region.

Assessing Hyperspectral Vegetation Indices for Estimating Leaf Chlorophyll Concentration of Summer Barley

“…But these SRs were reported somewhere explained more than 90 % of the variation in chlorophyll (Gitelson and Merzlyak, 1996;Blackburn, 1998;Daughtry et al, 2000;Read et al, 2002), and 85 % of the variation in leaf N accumulation (Xue et al, 2004). The SR 11 explained 61 % of the variation in total LCC across several species as reported by Sims and Gamon (2002), but explained only 52 % of the LCC variation across the 7 varieties in this study.…”

“…However, almost all these studies were conducted in controlled environmental conditions with artificial N nutrient gradients, and some plants even faced N deficiency as well as stress caused by disease, insects and other nutrients deficiency. It is noted that not only N deficiency causes reflectance increase in the visible spectral region (Read et al, 2002), but also other stresses may result in an increased reflectance due to the reduced amount of chlorophyll (Carter and Knapp, 2001). Therefore, the determination of leaf chlorophyll concentration in one field environment without an artificial nutrient gradient is required for improving our knowledge of the relationship between the hyperspectral reflectance data and the investigated plant physiological variables.…”

“…In the last decades numerous VIs have been developed for estimating biomass (Rouse et al, 1974), LAI (Jordan, 1969;Asrar et al, 1985;Haboudane et al, 2004), LCC (Chappelle et al, 1992;Haboudane et al, 2002) and N concentration (Peñuelas et al, 1994;Read et al, 2002). Two categories of the most widely used VIs are the simple ratios (SR, or called ratio vegetation indices, RVI) and the normalized difference vegetation indices (NDVI, or called NDI).…”

Produção de almeirão em função de níveis de fertirrigação nitrogenada e disposição de mangueiras gotejadoras nos canteiros

“…A resposta das culturas à aplicação de nitrogênio é fortemente dependente do suprimento de água durante o desenvolvimento das plantas (HAVLIN et al, 2005). Conforme relataram READ et al (2002), com a deficiência de N, ocorre diminuição da concentração de clorofila e do conteúdo de proteína solúvel, da taxa de expansão foliar, e também do desenvolvimento da planta. Nesse sentido, observouse que, nos canteiros que utilizaram a irrigação subsuperficial, o teor de clorofila das folhas de almeirão apresentou uma resposta quadrática às doses de N aplicadas, obtendo-se a maior eficiência técnica na dose de 120kg ha -1 de N na água de irrigação.…”

Índice de vegetação no algodoeiro sob diferentes doses de nitrogênio e regulador de crescimento

“…Entretanto, observou-se resposta do NDVI em relação às doses de N aplicadas, sendo obtido ajuste quadrático (Figura 3). Com a deficiência de N, ocorre a diminuição da concentração de clorofila e do conteúdo de proteína solúvel, bem como da taxa de expansão foliar e desenvolvimento da planta (READ et al, 2002). Como a refletância na região do visível do espectro eletromagnético varia em função da concentração de clorofila no tecido foliar, quanto menor o suprimento de N na planta, menor será o nível de clorofila e, consequentemente, menor será a absorção da radiação na região do visível, o que causa a redução do NDVI.…”