EVALUATING QUINOA LODGING RISK AND YIELD UNDER DIFFERENT IRRIGATION THRESHOLDS, NITROGEN RATES AND PLANTING DENSITIES IN NORTH-WESTERN CHINA

A moderate irrigation threshold of −25 kPa gave the greatest actual yield. ● Nitrogen rates of 80−160 kg·ha−1 reduced lodging risk without yield decrease. ● Planting density of 30 plants·m−2 provided both high yield and lodging resistance. ● A lower-stem lodging index was best for prediction of quinoa lodging risk. Lodging is a major yield-limiting factor of quinoa production. In 2018 and 2019, the orthogonal field experiments were conducted to investigate the responses of quinoa lodging risk and yield to irrigation threshold (soil matric potential of −15, −25 and −55 kPa), nitrogen rate (80, 160 and 240 kg·ha−1) and planting density (20, 30 and 40 plants m−2). Results showed that high irrigation thresholds and nitrogen rates significantly (P < 0.05) increased plant height and fresh weight per plant, and high planting densities reduced stem diameter and strength, all of those led to significantly ( P < 0.05) high lodging risks. The −15 and −55 kPa treatments gave the lowest actual yield ( P < 0.05) in 2018 and 2019, respectively. Higher lodging rate with a nitrogen rate of 240 kg·ha −1 resulted in a lower actual yield than 80 and 160 kg·ha−1 in both years. Planting density of 30 plants m−2 gave a significantly (P < 0.05) greater estimated yield than 20 plants m −2 and had a lower lodging rate than 40 plants m−2, resulting in the maximum actual yield among planting densities. In conclusion, a moderate irrigation threshold of −25 kPa, a nitrogen rate of 80−160 kg·ha−1 and an intermediate planting density of 30 plants m−2 were determined to be best for quinoa cultivation in North-western China. In addition, the lower-stem lodging index (quarter plant height) could evaluate lodging risk more accurately than middle-stem (half plant height) or upper-stem (three quarters plant height) lodging indexes.