Assessing the drought risk of oilseed rape to target future improvements to root systems (PhD)

Abstract

It has been suggested that root length density in the subsoil of many UK oilseed rape crops may be insufficient to fully explore the soil horizon and therefore limit supply of water to the crop (HGCA Project Report 402). Information on water relations of oilseed rape is, however, lacking.

The aim of the current project was to compare the water relations of oilseed rape and wheat. In an experiment to test the hypothesis that oilseed rape was more sensitive to drying soil than wheat, irrigated oilseed rape mini-crops transpired more water than wheat crops and showed a greater reduction in growth when water was withheld. In a separate experiment, the root hydraulic conductance of oilseed rape was about twice that of wheat. These results suggest that oilseed rape needs a less dense root system for water extraction than wheat.

When soil dries it also hardens and high soil strength is known to impede root growth and alter plant-water relations. At low soil strength, oilseed rape had a greater stomatal conductance than wheat but, as soil strength increased, stomatal conductance decreased to a greater extent in oilseed rape, indicating a more sensitive response.

Plants often rely on pores to explore the soil and to reach soil and water stored below a plough pan. The ability of oilseed rape and wheat to exploit soil pores to penetrate hard soil layers was compared in a pot experiment. Presence of pores in the hard layer led to a significant increase in number of roots in the deeper soil, of 29% for wheat and 54% for oilseed rape, compared to when no pores were present. This suggests that oilseed rape is better able to exploit soil pores than wheat.

This project has shown that the growth and distribution of oilseed rape roots under a range of soil conditions was similar to, if not better than, that of wheat, but that stomatal conductance and biomass production of oilseed rape reacted more sensitively to soil drying. Oilseed rape would therefore probably benefit from improved soil management to ensure greater access to deep soil water in the same way as wheat in drought prone areas. Additionally, using or developing oilseed rape varieties that maintain canopy function longer during a period of water limitation may also decrease yield loss to drought in future.