Evaluating quinoa stem lodging susceptibility by a mathematical model and the finite element method under different agronomic practices

Abstract

Stem lodging, mainly caused by wind force, is a major constraint in quinoa production. Therefore, it is of great importance to reduce lodging susceptibility when developing attainable yield of quinoa under different agronomic and environmental conditions. A mathematical crop lodging model (GCLM) and a finite element model (FEM) via software ANSYS were applied to evaluate the quinoa lodging susceptibility with measured lodging percentages under field experiments in arid area of Northwest China in 2018 and 2019. The experimental treatments consisted of three factors: (1) irrigation threshold based on soil matric potential (SMP) (−15, −25, and −55 kPa), (2) nitrogen fertilizer rate (80, 160, and 240 kg ha−1), and (3) plant density (20, 30, and 40 plants m−2). Results showed that both the GCLM and FEM could be satisfactorily used to evaluate the quinoa lodging incidence. Increasing SMP and plant density would significantly (P < 0.05) decrease the critical wind speed (CWS, higher CWS means greater lodging resistance) mainly due to the great plant height and low stem strength, respectively. The effect of increasing plant height with greater nitrogen rates on CWS was counteracted by an increase in stem strength, resulting in the insignificant (P> 0.05) difference in CWS among nitrogen treatments. Quinoa height and stem strength were the two main factors that affected lodging susceptibility compared to spike mass and Young's modulus. The CWS of quinoa ranged from 3.5 m s−1 to 4.5 m s−1, and it would decrease by 1.8–2.3 m s−1 for every 0.1 kg m−2 increase of estimated yield. Therefore, the attainable yield needs to be maintained within a proper range in consideration of the local wind conditions to avoid dramatic yield loss caused by lodging.