Dry matter production by a subtropical grass (Makarikari grass) grown in association with a temperate annual legume (barrel medic) and nitrogen fertilizer in southern Queensland

Abstract

The effects of a temperate annual legume, barrel medic (Medicago truncatula) cv. Cyprus, and five levels of fertilizer nitrogen (N), from 0 to 400 kg/ha.year, on the dry matter (DM) production and N economy of Makarikari grass (Panicum coloratum var. makarikariense) cv. Pollock, were investigated in a cutting experiment between 1973 and 1979. Each year, N fertilizer on grass alone increased both DM production and N uptake, up to N application rates of 200 and 400 kg/ha.year respectively. The mean annual effect of medic was to increase DM production and N uptake of associated grass each year by 90 and 130% respectively, and of the grass-medic system by 230 and 530%, respectively, for fertilizer rates between 0 and 100 kg N/ha.year. The increased DM production of associated grass occurred in summer and autumn; grass DM production was suppressed in spring, probably by competition with the medic. A trend for the DM yield of grass grown without medic to decline with time was most evident in the treatment without N fertilizer; in the comparable grass-medic pasture, grass DM production was as great in the sixth year as in the first. Medic DM yield varied with winter season rainfall. When the study concluded, the amount of N in the soil (0-10 cm depth) was higher after grassmedic than grass alone, except at the highest level of N fertilizer application. It was estimated that medic had fixed about 71 kg N/ha.year.