COMPETITION EFFECTS BETWEEN LEUCAENA AND MAIZE GROWN SIMULTANEOUSLY IN AN ALLEY CROPPING SYSTEM IN SUBTROPICAL AUSTRALIA

A field experiment was conducted to assess the effect of competition b etween a leucaena hybrid and maize (Zea mays L.) when planted simultan eously in an alley cropping system. The leucaena hybrid (a cross betwe en L. diversifolia and L. leucocephala) was planted at hedgerow spacin gs of 3 and 5.25 m, while maize was planted in rows 75 cm apart betwee n the hedgerows. The spacing between the leucaena hedgerow and maize w as varied by removal of 0, 1 or 2 rows of maize to give three spacing treatments of 37.5, 75 or 112.5 cm between leucaena and maize. A contr ol plot of leucaena alone was also included in the treatments. The gro wth and yield of individual maize rows were virtually unaffected by ti le presence of leucaena, but maize had a significant influence on the growth and yield of leucaena. At full maize canopy development, photos ynthetically active radiation reaching the leucaena was reduced in all treatments, resulting in a 75% yield reduction in leucaena at the clo sest spacing. Overall, maize grain yield reached 10.3 t ha(-1) in the continuous maize plots (37.5 cm treatment). This was reduced by up to 40% after removal of two maize rows in the closest, leucaena row spaci ng treatment. The implications of these results for the practical esta blishment of leucaena hedgerows with a maize crop are discussed.