Establishment requirements of Leucaena leucocephala (Lam.) de Wit cv. Cunningham

Abstract

The role and relative importance of vesicular arbuscular mycorrhiza (VAM), Rhizobium, weed competition, water stress and soil fertility (nitrogen, phosphorus and Ph) on early growth and establishment of leucaena were examined in a series of field and pot trials conducted in Central and Southeast Queensland from December 1987 to June 1990. Leucaena was found to be highly dependant on VAM for phosphorus extraction from the soil. Plants growing in soils low in mycorrhizal activity suffered a period of phosphorus deficiency until 15-20% root length was infected. Large differences in rate of infection were observed between soils. Activity of indigenous mycorrhiza able to infect leucaena varied among eight soils collected in Southeast and Central Queensland and accounted for over 65% of height differences in 4 and 6 week old leucaena grown in pots. This is the first documented evidence of growth differences in leucaena linked with varying levels of VAM in Australian soils. Other factors however appeared to have an over-riding importance in leucaena grown at 5 sites in the field. Phosphorous concentration in plant tissues were generally above critical nutrient concentrations 6-8 weeks after planting. Best final yield occurred in a well structured soil from Redland Bay (lowest in mycorrhizal activity). A soil higher in mycorrhizal activity on the other hand produced poor growth due to waterlogging. Early growth of leucaena in soils low in mycorrhizal activity could be increased by application of phosphorus fertilizer in pots and some field sites. Very high rates however were needed to stimulate early growth of plants. For example, 1200 kg P/ ha was required to significantly increase growth and tissue phosphorus concentration of leucaena prior to week 5 in a low activity podzolic soil from Mt. Cotton. As infection of the roots increased, however, response to phosphorus decreased and final yield at 75 kg P/ ha in the field and at 100 kg P/ ha in pots, was similar to that at the 1200 kg P/ ha rate. Very little response was found to application of nitrogen in either the field or in pots. A new Rhizobium strain CB3060 (TALI 145) was found to effectively nodulate leucaena in a number of soils. It was found to be persistent and accounted for greater than 90% nodules 12 months after planting at a site at Crows Nest.