Effects of sowing time on agronomic characteristics and yield of quinoa

Quinoa is rich in nutrient and has a wide range of adaptability to climatic conditions. In recent years, it was successfully introduced and planted in Inner Mongolia, and the planting area was increasing year after year. There is a little rainfall in the farming-pastoral zone, however, evaporation in the region is excessive and climatic conditions highly complicated in the northern foothills of Yinshan Mountains, which limit research on the introduction and biological characteristics of quinoa. To explore the effects of sowing time on the growth and climatic conditions of quinoa in the northern foothills of Yinshan Mountains, a field experiment was conducted for the period 2014-2016. On the base of the research results of 2014-2015, in 2016, 10 different sowing times were selected (S1-S10) and the treatments divided into three sowing stages-early sowing (S1-S3 for 18-28 April), conventional sowing (S4-S7 for 3-18 May) and late sowing (S8-S10 for 23 May to 2 June). The growth, physiological and yield characteristics of quinoa were compared in all the 10 treatments. The results showed that:1) accumulated temperature of ≥ 10℃ for the whole life cycle of quinoa was 2 112-2 214℃, and growth period of quinoa was 114-150 days. 2) Early sowing treatments (S1-S3) had a longer period of vegetative and reproductive growth stages than the conventional (greater by 7.8-14.4 d) and late sowing (greater by 9.0-17.8 d) treatments. 3) Dry matter accumulation and leaf area index in treatments S1-S5 were high, with those in treatment S2 significantly higher than in conventional and late sowing treatments. 4) There was midday depression in quinoa photosynthesis at flowering stage and treatment. S2 had a significantly higher ability in terms of photosynthetic performance. Photosynthetic rate, stomatal conductance and transpiration rate of treatment S2 were respectively 3.22-6.32 μmol(CO₂)·m^-2·s^-1, 0.01-0.26 mol(H₂O)·m^-2·s^-1 and 1.52-2.51 mmol(H₂O)·m^-2·s^-1 higher than those of other treatments. 5) The highest spike grain weight (151.78 g per plant) and yield (4 097.97 kg·hm^-2) were obtained in treatment S2, which were significantly higher than in the other treatments. Yield in treatment S2 was 2.87 times higher than in treatment S9. 6) In terms of quinoa growth and yield, accumulated temperature was a more critical factor than rainfall in the study area. Accumulated temperature affected yield mainly by regulating the number of spikes and single panicle weight from grain-filling stage to maturity stage of quinoa. Therefore, early sowing was beneficial for good biological morphologic development and it increased leaf area index. Accumulated temperature during grain-filling stage of quinoa was needed for high gain yield and economic coefficient. Our results suggested that the optimum sowing time of quinoa was from mid April to early May in the northern foothills of Yinshan Mountains. Sowing time was the most important factor in quinoa production. Accumulated temperature greatly affected growth and yield formation, which required a specific attention in order to avoid low temperature conditions at later growth stages of quinoa.