Leaf spectral characteristics of ‘Yarkent’ almond and its sensitivity to N, P, K at different growth periods in Xinjiang

【Objectives】 The sensitive period of leaf spectral index was studied by analyzing the leaf spectral reflectance in the response to nitrogen (N),phosphorus (P) and potassium (K) fertilizer at different growing stages of ‘Yarkent’ almond in Shache of Xinjiang aiming to provide a non-invasive,simple and rapid nutrition diagnosis of N,P,K. 【Methods】 Using “3414” fertilizer experiment and ‘Yarkent’ almond as tested material,the leaf spectral reflectance was measured using Unispec-SC spectrometer at fruiting,expanding,stone hardening and maturing stages of almond tree under different N,P,K fertilizer levels. 【Results】 The fluctuation of leaf spectral reflectance of ‘Yarkent’ almond depended on the wavelengths at all the growing stages,and the least variation was in the range of visible wavelength. The leaf spectral reflectance was generally in the order of stone hardening stage fruiting stage expanding stage maturing stage. The leaf spectrum indexes (ND705) of ‘Yarkent’ almond was significantly (P0.05) and extremely significantly (P 0.01) different among different N,P,K fertilizer levels at all growing stages. The spectral sensitive band of foliar N concentration was 815-894 nm,375-398 nm,608-616 nm and 429-437 nm at fruiting stage,expanding stage,stone hardening stage and maturing stage,respectively. The spectral sensitive band of foliar P concentration was 766-802 nm,1023-1063 nm,708-713 nm and 1130 nm at above 4 stages. For foliar K concentration,the spectral sensitive band was 815-894 nm,345-368 nm and 475-491 nm at fruiting stage,expanding stage and maturing stage,respectively.【Conclusions】 The sensitive periods for leaf spectral nutrition diagnosis of N, P and K in ‘Yarkent’ almond are at mature stage and stone hardening stage. The spectral sensitive bands for N are 815-894 nm,375-398 nm,608-616 nm and 429-437 nm at fruiting stage, expanding stage, stone hardening stage and maturing stage, respectively; those for P are 766-802 nm, 1023-1063 nm, 708-713 nm and 1130 nm; and those for K are 815-894 nm,345-368 nm and 475-491 nm at fruiting stage,expanding stage and maturing stage,respectively.