Nurseries for tree legumes containing up to 80% rock phosphate - Preliminary results

Abstract

An experiment was performed to investigate the effect of increasing proportions of rock phosphate (0-80% by volume) in the substrate for growing "bracatinga" (Mimosa scabrella Benth), "sabiá" (Mimosa caesalpiniaefolia Benth) and "algaroba" (Prosopis juliflora D.C.) inoculated with their specific Rhizobium spp. in nurseries. The mixture of rock phosphate in a proportion of 4:1 with sandy soil (75% coarse sand) produced the best growth in terms of height and dry weight of algaroba. The dry matter production of "bracatinga" was similarly favoured by this mixture. In both cases with this treatment dry matter production was higher than when a conventional dose of triple superphosphate was applied. The percentage infection of the roots of algaroba with vesicular arbuscular mycorrhizas was reduced in the presence of high concentrations of rock phosphate, but the infection of "bracatinga" was unaffected. There were no significant effects of any treatment on the number or dry weight of nodules of any of the species although there was a tend of decreasing in algaroba in the treatments with 40 to 80% (by volume) of rock phosphate in the growth medium. No significant differences between any of the treatments were observed for any of the parameters studied in the case of sabiá. The results demonstrate the possibility of producing seedlings in substrates containing high concentrations of rock phosphate which may serve as a source of phosphorus for later plant growth.