Silvoarable agroforestry (the intercropping of trees and arable crops) can diversify farm incomes, increasing tree planting and improve farm biodiversity. In 1992 a silvoarable experiment, comprising three replicate blocks of four poplar (Populus spp.) hybrids (at a spacing of 10 m x 6.4 m) and three arable treatments, was established by Cranfield University in Bedfordshire, Leeds University in West Yorkshire, and the Royal Agricultural University in Gloucestershire. The attached report describes the results from the experiment for the four-year period from April 1999 to April 2003. It covers the effects on tree growth, crop yields, economics, understorey vegetation, and the number and diversity of ground invertebrates.