Management of oilseed rape to balance root and canopy growth

Abstract

Eleven commercial crops of oilseed rape were sampled in 2004 for root length density and total biomass, post flowering. Root length densities declined with depth, and were on average higher than values previously recorded in the UK for oilseed rape, but lower than those in winter wheat. Substantial variation between sites was in part attributed to cultivation and soil type differences. No relationship between crop biomass and root length density was found, suggesting that it might be possible to modify root systems maximise below ground resource capture whilst avoiding excessively large canopy sizes.
 
In 2005, replicated experiments at ADAS Boxworth and Rosemaund, tested single factor comparisons of sowing date, seed rate, sulphur, nitrogen, plant growth regulators, and cultivations on rooting and yield.  53% of the variation in yield at ADAS Boxworth was attributable to differences in root length density between 40 and 100cm depth in the soil. This highly significant relationship suggests that rooting is limited at depth in oilseed rape, and improving root length density at depth may improve drought tolerance and yield. 

Of the treatments affecting root length density below 40cm, only spring-applied metconazole, significantly improved root length density, and only at one site. Ploughing, subsoiling, and not delaying sowing significantly increased root length density near the surface (mainly the top 20cm). There was no similar effect on rooting at depth (below 60cm).

Low seed rates and delaying N strategies may improve the profile of rooting at depth; however each effect was only seen at one of the two sites, and as such would require further verification. Canopy size measurements in the second year again showed this was not linked to root length density, supporting the conclusion from the first season, that it is possible to affect root shoot balance in oilseed rape.