Testing the hypothesis on estimating field maize height and above-ground biomass using tower-based gradient wind data

Abstract

Abstract Maize height and dry above-ground biomass (AGB) are of great significance for farmland ecosystems, agricultural yield and production statistics, greenhouse gas emissions and climate change. Traditional approaches of estimating these parameters are labour-intensive, destructive, and with high uncertainties. This paper describes a challenging attempt to estimate field maize height and dry AGB through aerodynamic parameters of Zero Plane Displacement (ZPD), aerodynamic roughness length (ARL) and the combination index (CI) of ZPD and ARL, which are used to characterize the interaction between vegetation and atmosphere. ZPD/ARL was calculated from gradient wind data based on the Monin-Obukhov Similarity Theory. The experiment was conducted at Daman Irrigation District in the Heihe River Basin with continuous observations during three maize growing seasons. Although the CI based height estimation shows a high R2 of 0.97 and a low RMSE of 0.14 m, the error analysis of the model shows a high error of -0.59 m∼+0.739 m. The ZPD and CI based biomass estimations in power fitting show high R2 of 0.98 and 0.97 with low RMSE under 5% and 7% of the maximum dry AGB, however, the steep curve in the middle and late growing stages shows serious sensitivity to the variations of ZPD and CI. Considering the high sensitivity and uncertainties in estimating crop biomass or crop height, it is concluded that this micrometeorology based method is difficult and cumbersome to be practicable. It will always need assistance of the simple traditional sampling.