[Effects of planting density on root spatiotemporal distribution and plant nitrogen use efficiency of winter wheat]

Taking winter wheat cultivars Tainong 18 (TN18) and Shannong 15 (SN15) as test materials, a field experiment was conducted to study the effects of planting density (135 x 10(4), 270 x 10(4), and 405 x 10(4) plants x hm(-2) for TN18; 172.5 x 10(4), 345 x 10(4), and 517.5 x 10(4) plants x hm(-2) for SN15) on the root spatiotemporal distribution and plant nitrogen use efficiency of the varieties. For TN18, its root length density, total root absorbing area, and active root absorbing area increased with increasing planting density, and peaked at planting density 405 x 10(4) plants x hm(-2) during the whole growth period. For SN15, its root length density, total root absorbing area, and active root absorbing area achieved the highest values at planting density 345 x 10(4) plants x hm(-2) at booting and late grain-filling stages. The grain yield, nitrogen uptake efficiency, nitrogen partial factor productivity, and nitrogen use efficiency of TN18 were the highest at planting density 405 x 10(4) plants x hm(-2), and those of SN were the highest at planting density 345 x 10(4) plants x hm(-2) but had less differences between the densities 345 x 10(4) and 517.5 x 10(4) plants x hm(-2). The inorganic nitrogen accumulation in different soil layers decreased with increasing planting density at maturity stage. Taking grain yield and nitrogen use efficiency into consideration, the appropriate planting density of TN18 and SN15 would be 405 x 10(4) and 345 x 10(4) plants x hm(-2), respectively.