Study on estimating cotton LAI and aboveground fresh biomass using fractional interception of photosynthetically active radiation data.

【Objective】 This paper analyzed the correlation of the fractional interception of photosythetically active radiation(FPAR) and leaf area index(LAI),aboveground fresh biomass of cotton canopy respectively,and established modelings for estimating LAI and aboveground fresh biomass.Finally,an experimental approach was taken to prove that the FPAR can be actively used to monitor cotton growing status.【Method】 The photosythetically active radiation data were recorded by utilizing linear quantum sensor at cotton key growth stages in a field experiment including two cultivars of Xinluzao No.19 and Xinluzao No.13 with four planting patterns,meanwhile LAI and aboveground fresh biomass were tested at the same sites.The function models for FPAR against cotton LAI and aboveground fresh biomass were established respectively.The differential values were compared between tested data and estimated data for LAI and aboveground fresh biomass respectively.【Result】 There were a similar variation of FPAR on two varieties at different growth stages:with a rapid increase from full squaring stage to blooming stage,their maximum value were both at blossom stage or full boll stage,afterwards it gradually declined;the best modeling correlation between FPAR and LAI,aboveground fresh biomass of cotton canopy,was power function(RFPAR-LAI=0.851 3**,RFPAR-aboveground Fresh biomass=0.746 9**,n=80).The estimated function for LAI,estimated by using FPAR,had higher precision than aboveground fresh biomass.Correlation between tested LAI and estimated LAI,tested aboveground fresh biomass and estimated aboveground fresh biomass respectively were significant(Rtested LAI-estimated LAI=0.818 0**,Rtested aboveground fresh biomass-estimated aboveground fresh biomass=0.739 6**,n=80).【Conclusion】 The study shows that it is a simple,effective and non-destructive method to estimate the cotton canopy LAI and aboveground fresh biomass by the fractional interception of photosythetically active radiation data.