Abstract: 【Objective】In arid regions, agricultural plantation is mainly restricted by water and fertilizer. To explore a optimal water/phosphorus ratio and provide a theoretical basis for the high yield of quinoa in arid land. In this study, the effects of water and phosphorus coupling on root growth, biomass allocation and high yield of quinoa (Chenopodium quinoa Willd) were studied. 【Method】 Guinoa was taken as an experimental material and pot-culturing experiment were carried out at 3 levels of water irrigation (W1, W2 and W3 represented 35%-45%, 55%-65% and 75%-85% soil moisture content) and 4 levels of phosphorus fertilizer (P₂O₅ application rates of P0, P1, P2, P3 were 0, 0.1, 0.2 and 0.4 g·kg^-1), and root morphological and physiological indexes, biomass allocation and yield under the conditions of 12 different water and phosphorus coupling treatments were compared. 【Result】 At the same water irrigation level, the root parameters (root area, total root length, maximum root length, root diameter and root volume) were the highest under P2 treatment. At the same phosphorus level, the maximum root length and total root length reached the maximum under W2 treatment, and root area showed W2P0＞W3P0 and W2P1＞W3P1 under low phosphorus treatment (P0, P1). Under high phosphorus treatment (P2, P3) root area showed W2P2＜W3P2 andW2P3＜W3P3. Root diameter and root volume increased with the increasing of water content. Under the severe drought stress (W1) with P1 treatment, root activity were highest; but it was the highest under other water irrigation levels with P2 treatment. POD and SOD activities were highest and MDA was lowest under P2 (0.2 g P₂O₅·kg^-1) treatment across all irrigations; The appropriate phosphorus fertilizer (P2) significantly reduced the soluble sugar and proline content. The appropriate ratio of water and phosphorus (W3P2, W3P1) was beneficial for  biomass of stem and leaf weight, and yield of quinoa, while the weight of root and panicle were the highest under W2P3 treatment. High water irrigation benefited for biomass allocation between stems and leaves; Low water irrigation was beneficial for biomass allocation between root and panicle at 3 water levels, P2(0.2 g P₂O₅·kg^-1) treatment was suitable for formation of apical spike; Low phosphorus promoted the number of branch and spike, 1000-grain weight and grain weight, while they were specific under high phosphorus conditions, and at various levels of phosphorus with W3 treatment gain weight reached the maximum, respectively. 【Conclusion】 The suitable phosphorus supplement (P2, 0.2 g P₂O₅·kg^-1) improved root activity, root growth, increased area of the root contacting and soil, strengthened antioxidant ability of root, and therefore enhanced the drought resistance of quinoa. and the optimal ratio of water and phosphorus (W3P2) was suitable for biomass accumulation and high yield of quinoa.

Key words: quinoa, water and phosphorus coupling, root system, biomass, yield