Does earlier sowing of winter wheat improve root growth and N uptake?

Abstract

Nitrate leaching from agricultural land is a major environmental concern. Earlier sowing of winter wheat (Triticum aestivum L.) could be a tool to reduce nitrate leaching loss, as deeper root penetration and increased biomass production might increase the N uptake during autumn. Quantitative estimates of the effect of sowing time are needed.A two-year field experiment was conducted on sandy loam soils. During the season, the effects of early, normal and late winter wheat sowing were studied on root development and soil nitrogen to 2.3m soil depth. Root depth and density were studied by means of minirhizotrons and effects on aboveground biomass and nitrogen uptake were measured.Advancing sowing time increased the root depth by the onset of winter in December by up to 18mm day−1 of earlier sowing and the rooting depth increased up to 0.7m, reaching up to 0.9m average maximum root depth. The total root density was 9–16 times higher in early than in late sown wheat. Root depth penetration rates estimated from November (late autumn) until anthesis in June were 0.9–1.2mm°C day−1 and no significant differences were observed between the sowing treatments.In November, soil N reductions of early sown wheat compared to normal and late sown wheat were on average 20kg nitrate N ha−1.Sowing time affected root growth, aboveground growth and N relations during the entire growth season, though it had little effect on yield. Sowing time affected root depth throughout the season. Late sown wheat continued to increase its root depth after anthesis and reached up to 1.5m average maximum root depth, but it never reached the root depth of early and normal sown wheat reaching up to 1.8 and 2.0m average maximum root depth, respectively.The results show that earlier sowing can be an important tool to reduce the amount of soil N during autumn and winter and hence the potential leaching. In addition, it will improve the root growth of the wheat during its main growing season. However, promoting earlier sowing may interact with other agronomic factors.