Studies on competition between Macroptilium atropurpureum and Crotalaria goreensis

Summary: Experiments were conducted at Walkamin, Queensland, Australia on the competitive effects of Crotalaria goreensis Guill. & Perr. on Macroptilium atropurpureum (DC.) Urb. cv. Siratro. In one experiment it was shown that varying C. goreensis densities of 10, 20, 40 and 200 plants/m 2 produced successive reductions in M. atropurpureum yields and successive increases in C. goreensis yields. Varying the M. atropurpureum density from 2.3 to 6 plants/m 2 did not significantly affect the yield of either species. Two hundred C. goreensis plants/m 2 produced approximately 500 10 6 seeds/ha. In three time of emergence experiments it was shown that the competitive ability of one species relative to the other varied with environmental factors. In one of these experiments with equal numbers of each species C. goreensis lowered M. atropurpureum top dry matter yield only when the former species emerged 2 weeks prior to the M. atropurpureum . When there were many more plants of C. goreensis present, emergence of both species at the same time lowered M. atropurpureum top dry matter yield in one experiment and emergence of C. goreensis 2 weeks after the M. atropurpureum lowered the dry matter yield of the latter species in a third experiment. In a time of weeding experiment it was shown that under the particular environmental and plant density conditions prevailing removal of C. goreensis for 12 days after planting was sufficient to prevent a reduction in M. atropurpureum dry matter. In this experiment it was also shown that under these conditions the two species were not mutually exclusive. In mixtures the C. goreensis provided physical support to the M. atropurpureum , enabling the latter species to intercept more light energy than it could when growing in monoculture.