Good explanation on fitting competition models in forest genetic trials using asreml:
Competitive Genetics: Exploring the impact of direct and indirect genetic effects in tree breeding. https://vsni.co.uk/blogs/competitive-genetics
Based on the work by Joao Costa e Silva and Richard Kerr “Accounting for competition in genetic analysis, with particular emphasis on forest genetic trials” https://link.springer.com/article/10.1007/s11295-012-0521-8