Modelling Cereal Root Systems for Water and Nitrogen Capture: Towards an Economic Optimum

Abstract

A quantitative model of wheat root systems is developed that links the size and distribution of the root system to the capture of water and nitrogen (which are assumed to be evenly distributed with depth) during grain filling, and allows estimates of the economic consequences of this capture to be assessed. A particular feature of the model is its use of summarizing concepts, and reliance on only the minimum number of parameters (each with a clear biological meaning). The model is then used to provide an economic sensitivity analysis of possible target characteristics for manipulating root systems. These characteristics were: root distribution with depth, proportional dry matter partitioning to roots, resource capture coefficients, shoot dry weight at anthesis, specific root weight and water use efficiency. From the current estimates of parameters it is concluded that a larger investment by the crop in fine roots at depth in the soil, and less proliferation of roots in surface layers, would improve yields by accessing extra resources. The economic return on investment in roots for water capture was twice that of the same amount invested for nitrogen capture.

Breeding for Improved Nitrogen Use Efficiency in Oilseed Rape

“…Measurements of rooting have shown that the root length density of oilseed rape is greater than 1cm per cm 3 of soil within the top 40 cm of soil and averages 0.74 cm/cm 3 below 40cm depth (Blake et al, 2006). Studies on wheat have shown that a root length density of 1cm/cm 3 is required for the roots to extract all available water from soil (King et al, 2004). If this is the same for oilseed rape then its root system is generally not dense enough below 40 cm depth to extract all of the mineral N. If the root length density below 40 cm could be increased to 1cm/cm 3 then it is estimated that oilseed rape could take up an additional 8 kg N/ha using assumptions described in King et al (2004) and a typical mineral N content below 40 cm depth of 30 kg N/ha.…”

Changes in durum wheat root and aerial biomass caused by the introduction of the Rht-B1b dwarfing allele and their effects on yield formation

“…In the Mediterranean Basin, one of the largest durum wheat producers in the world, more than 50 % of the total grain of durum wheat is produced in arid and semi-arid conditions, with severe drought most years (Loss and Siddique 1994;Araus et al 2003;García del Moral et al 2005). In dryland agricultural systems, a large root system that promotes access to soil water and nutrients is regarded as beneficial for plant growth (Richards 2008), although under terminal drought a greater investment in fine roots at depth would improve yield due to the better access to water and nitrogen (King et al 2003). Accordingly, root dry weight at depth has been related to drought adaptation (Lopes and Reynolds 2010).…”

Uptake of mineral nitrogen from subsoil by winter wheat

“…The utilization of nitrogen supply from subsoil layers is determined chiefly by crop demand for nitrogen, root morphological and physiological traits (King et al 2003), forms, amount and distribution of available N in a soil, and soil moisture (e.g. Svoboda et al 2000, Gastal and Lemaire 2002, Jeuffroy et al 2002.…”