NITROGEN USE EFFICIENCY IN QUINOA. WHERE ARE WE STANDING?

AGUIRRE CASTRO, P.; GOMEZ, M.B.; BERTERO, H. D

Pullman, WA

Simposio; International Quinoa Research Symposium; 2013

Washington State University

Quinoa is usually mentioned as a crop able to grow and produce high protein seeds in environments strongly limited by water and nutrients. Few works analyze the yield vs. nitrogen (N) availability relationship and, generally, are based on empirical relationships between yield and applied N (Napl, agronomic efficiency) or between yield and absorbed N (Physiological Efficiency (PEyield)). From the absorbed N perspective, Yield = absorbed N during the crop cycle (Nabs) x N harvest index (NHI, grain N x Nabs-1) x % grain N (% Ng)-1 ad PEyield = NHI x % Ng-1. As % Ng is a critical quality component, higher PEyield and yield should arise from increases in NHI and Nabs and/or NHI, respectively. N absorption and partitioning dynamics, PEyield and some of their determinants were analyzed in two cultivars (NL-6 and 2-Want) under irrigation and high N availability (100 kg N ha-1). Cultivars differed in cycle duration determining significant differences in yield and Nabs (3970 vs 5570 kg ha-1 and 164 vs 205 Kg N ha-1 for NL-6 y 2-Want). NL-6, the earliest to flower, accumulated a higher % of total Nabs compared to 2-Want (81 vs 63 %). In both cultivars the highest Nabs proportion was absorbed between visible floral buds and end of flowering, when the highest crop growth rates were observed. Considering grain N, an elevated proportion of it came from retranslocation from other organs in NL-6 (62 %) and post flowering absorption in 2-Want (75%). [N] in biomass decreased with biomass accumulation leading to a higher biomass physiological efficiency ((PEbiomass). Two factors explain the increase of PEbiomass during the crop cycle, the lower relative importance of leaf biomass –with high [N]- and the increase in radiation use efficiency leading to a higher growth per unit intercepted radiation and eventually N in biomass. No significant difference in PEyield was detected between NL-6 and 2-Want. Unlike % Ng, NHI is positively associated with PEyield (r2= 0.52) and harvest index (HI) (r2= 0.72). Compared to other crops, quinoa exhibited a low NHI (~ 0,5). Our results also show an “ortodox” behavior for PEbiomass under high N availability although it is mandatory to evaluate N physiological responses under a range of N availability. Furthermore, the low NHI observed in this and other works pose a limit to PEyield; a breeding strategy based on selection for higher NHI or HI could simultaneously increase yield and PEyield.