Using root DNA to assess responses to phosphorus by surface roots in wheat and barley

Abstract

Most phosphorus (P) in agricultural soils is found in the surface layers and topsoil foraging is often considered to be important for P recovery. The aim of this work was to examine how the amount and distribution of roots in the surface soil layer affects growth and response to P fertiliser in wheat and barley. Between 10 and 20 varieties of wheat and barley were grown at 0 kg P/ha and 30 kg P/ha at P responsive sites over two years. The amount of roots in the surface 10 cm of soil between and within sowing rows and their ratio were assessed using the concentration of root DNA in the soil at Zadok’s growth stage (ZGS) 30–31. Shoot biomass and P concentration were measured at the time of root sampling and plots were harvested for yield. Adding P increased root DNA density with the greater response observed in the seeding row. Significant differences in root DNA density were measured among varieties and these showed some consistency over sites. The degree of lateral spread of roots did not differ between barley and wheat, but within-row root growth of barley showed a greater response to P than that of wheat. Biomass production, yield and yield response to P were not related consistently to root DNA density nor to the ratio of root DNA between and within rows. Genetic differences in root growth in the top 10 cm can be identified but the root DNA density in the soil and the distribution of roots within and between rows were not consistently associated with P uptake, yield or yield response to P.