Spatial soil water and nutrient distribution affecting the water productivity of winter wheat

Abstract

Understanding the effects of the spatial distributions of soil water and nutrients on crop growth and yields is important for optimizing their management to achieve high water productivity (WP) under water deficit conditions. In this study, three spatial distributions of irrigation and nutrients were set up to winter wheat (Triticum aestivum L.) grown in 1 m deep tubes (19.2 cm inner diameter) in 2017/18 and 1.4 m deep tubes in 2018/19 buried in the field. The three treatments included: both irrigation water and nutrients applied to the surface soil layer (NS+WS); nutrients in the surface soil layer and irrigation applied to deep soil layer (60 cm below soil surface) (NS+WD); and nutrients and water both applied to the deep soil layer (ND+WD). For the three main treatments, each was supplied with two irrigation levels, i.e., deficit irrigation and full irrigation at 160 mm and 240 mm, respectively, divided into four applications at different growing stages of winter wheat. The results showed that the wheat grain yield and WP at grain yield level (WPg) under NS+WD were the highest under deficit irrigation, with yields 7.7% and 20.9% higher, and WPg 9.2% and 20.4% higher than those of NS+WS and ND+WD averagely for the two seasons, respectively. The NS+WS treatment resulted in the highest grain yield and WP at both grain and biomass levels (WPb) under full irrigation, with yields 17.7% and 31.8% higher, and WPg 23.4% and 38.0% higher than those of NS+WD and ND+WD averagely for the two seasons, respectively. Treatments with nutrients located in deep soil layer produced the lowest yield and WP under both irrigation levels. Therefore, nutrients should be located in the top soil layer to increase their availability for crop use anytime during the growing season. Water applied in the deep soil layer could benefit grain production and WPg under deficit irrigation, possibly related to the increase in the proportion of the water use during reproductive growing stage to achieve higher harvest index (HI). Under full irrigation, water and nutrients matched in the topsoil layer, where the roots were mostly distributed, increased the availability of water and nutrients for root uptake and reduced the dry-matter allocation to root growth in acquiring resources, which resulted in a lower root/shoot ratio, higher biomass production and higher WPb. The spatial soil water and nutrient distribution affected their availability for crop use during different growing stages, and influenced the allocation of dry matter to above- and below-ground parts. Optimizing the spatial distribution of nutrients and water based on water availability would benefit crop production and water productivity.