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

Abstract

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.