Nitrogen and phosphorus fertilizer application to Elephant grass (<i>Cenchrus purpureus</i> syn. <i>Pennisetum purpureum</i>) cultivar ‘Cameroon’ in an arenosol in Rio Grande do Norte, Brazil
Elephant grass (Cenchrus purpureus syn. Pennisetum purpureum) stands out for its high dry matter production per unit area and good nutritional value and is cultivated throughout Brazil. This study aimed to evaluate the performance of elephant grass cultivar ‘Cameroon’ fertilized with nitrogen (N) and phosphorus (P) at different rates. The experimental design was in randomized blocks with 10 treatments and 4 replicates. The treatments consisted of 5 doses of N (0, 200, 400, 600 and 800 kg N/ha) all with 66 kg P/ha and 5 doses of P (0, 22, 44, 66 and 88 kg P/ha) all with 600 kg N/ha. The variables evaluated during 3 harvests were: shoot dry matter (DM) yield, N and P concentrations in shoots, and uptakes of N and P in forage. Results showed that, in the arenosol of the experimental area, high doses of N and P could produce high yields of the grass (40‒41 t DM/ha) over 260 days. The grass extracted large amounts of N (on average, 800 kg N/ha over 260 days) and P concentrations were significantly affected by P fertilization only in the last harvest, where it increased from 0.27 to 0.78 g P/kg DM. However, application of only 200 kg N/ha will produce more than 60% of the DM yield response achieved with 800 kg N/ha. Similarly, there seems little merit in applying more than 22 kg P/ha with the N. Longer-term studies are needed to test these hypotheses along with economic assessments to determine the financial soundness of such decisions.