Effects of initial and maintenance phosphorus levels on the establishment of four legumes oversown into Setaria anceps swards

Abstract

The re-establishment of four legumes, Stylosanthes guianensis cv. Schofield, Lotononis bainesii cv. Miles, Desmodium intortum cv. Greenleaf and Macroptilium atropurpureum cv. Siratro by oversowing into a Setaria anceps cv. Kazungula stand was studied in plots with different phosphate (P) levels. Half the plots had received different levels of initial P only, seven years previously, the other half received initial and maintenance P plus a further application at oversowing. At 15 weeks after sowing all species had similar seedling densities (10 to 23 plants m-2). The densities of stylo and siratro declined over the 88 week trial, and desmodium also declined except at the highest rate of P. Lotononis density increased except at Nil P where all legumes, except stylo, were almost eliminated. In terms of legume survival and growth, setaria tiller density, and P concentration in plant tops, residual effects of P applied seven years previously were clearly evident, particularly at the higher rates (44 and 88 kg P ha-1). P and N concentrations in tops were linearly related.