Increased plant density of winter wheat can enhance nitrogen-uptake from deep soil

Increased plant density improves grain yield and nitrogen (N)-use efficiency in winter wheat (Triticum aestivum L.) by increasing the root length density (RLD) in the soil and aboveground N-uptake (AGN) at maturity. However, how the root distribution and N-uptake at different soil depths is affected by plant density is largely unknown. A 2-year field study using the winter wheat cultivar Tainong 18 was conducted by injecting (15) N-labeled urea into soil at depths of 0.2, 0.6, and 1.0 m under four plant densities of 135 m(-2), 270 m(-2),405 m(-2), and 540 m(-2). We observed significant RLD and (15) N-uptake increases at each soil depth as the plant density increased from 135 to 405 m(-2). (15) N-uptake increased with plant density as the soil depth increased, although the corresponding RLD value fell with depth. The (15) N-uptake at each soil depth was positively related to the RLD at the same depth. The total AGN was positively related to RLD in deep soil, especially at 0.8-1.2 m. Increasing the plant density from 135 m(-2) to the optimum increases AGN primarily by increasing the RLD in deep soil and therefore increasing the plant density of winter wheat can be used to efficiently recover N leached to deep soil. Moreover, the total root numbers per unit area and RLD still increased at supraoptimal density while shoot number and N uptake stagnated.