EFFECTS OF PARTIAL ROOT EXCISION AT THE RE-GREENING STAGE OF WINTER WHEAT ON ROOT/SHOOT RATIO, YIELD AND WATER USE EFFICIENCY IN LOESS PLATEAU REGION, CHINA

Background and Aims It is important for water conservation that suitable agricultural measures are used to improve the water use efficiency (WUE) of crop production. Water_conserving irrigation has improved WUE of crops, but is difficult to practice in arid and semi_arid areas of Loess Plateau, especially those areas lacking water for irrigation. Therefore, water_conserving agriculture in these areas focuses on increasing the rainfall_use efficiency of crops. This study examines whether root_cutting can increase grain yield and WUE of winter wheat in rain_dependent farmland on Loess Plateau. Methods The field experiment was conducted in 2004 and 2005 at the Changwu Experimental Station of the Chinese Academy of Sciences. The cultivar of winter wheat was `Changwu135' (Triticum aestivum cv. Changwu135), which is widely used by farmers in the region. Roots were partially cut off vertically to 13 cm depth along two sides, 2 cm away from the main stems at the re_greening stage (March 14, 2004). Soil water content was measured at 10 cm depth intervals at different developmental stages. Root respiration rate was measured at the flowering stage. Grain yield, aboveground biomass, spike number per unit area, grain weight and harvest index were measured at the maturity stage. We studied effects of partial root_cutting on root/shoot ratio (R/S), yield and WUE. Key Results Partial root_cutting at the re_greening stage of winter wheat significantly decreased upper root biomass: root biomass to 20 cm soil depth at the flowering stage was 249.70 g·m~ -2 for root_cutting treatment and 307.52 g·m~ -2 for intact plants, and total root biomass was 305.53 g·m~ -2 for cutting treatment and 368.73 g·m~ -2 for intact plants. Root_cutting reduced root respiration rate by 25.57% compared with intact plants. Spike number was reduced to 590.33 m~ -2 , compared to 646.33 m~ -2 for intact plants, but 1 000 kernel weight increased significantly after partial root_cutting (45.99 g compared to 41.47 g for intact plants), and harvest index also increased. Yield was little affected by root_cutting, but water consumption was greatly reduced. Biomass water use efficiency and yield water use efficiency were increased by 32.52% and 29.98%, respectively, compared with intact plants. Conclusions Root_cutting reduced the root system of winter wheat, restraining population density which reduced water consumption and improved soil water content after anthesis. It is favorable to grain development in wheat. Root_cutting lowered root respiration rate and decreased the amount of dry matter consumed by the root system, which raised the proportion of dry matter allocated to aboveground organs. Dry weight of shoot was unaffected by root_cutting, but water consumption was greatly reduced. Therefore, WUE of winter wheat can be increased on dry lands by partial root_cutting at the re_greening stage. More study, especially on timing and intensity on root_cutting, is needed to synchronously increase grain yield and WUE of wheat.