Nitrogen nutritional status in Aruana grass in a controlled environment

Aruana grass (Panicum maximum cv. Aruana) is well adapted to pastures, especially those grazed by sheeps, but knowledge on mineral nutrition of this grass is scant. In order to evaluate the nutritional status of this forage in relation to nitrogen, Aruana grass was grown in a nutrient solution with N six rates (14; 112; 210, 294; 378 and 462 mg L-1). The experiment was carried out in a greenhouse in the Spring, from October to December 2000. Each experimental unit consisted of one pot with ground quartz as substrate. Plants were harvested twice. The first harvest occurred 35 days after transplanting to the pots, while the second one was 28 days after the first harvest. Right after the second harvest the roots were separated from the substrate and collected. Visual symptoms off deficiency appeared on the 10(th) day after seedling transplanting. Results showed significant effects off rates on N concentration and N distribution in the plant parts, on nitrate reductase activity as well as the SPAD values. At the first harvest, SPAD values ranged from 32.0 to 52.6 and from 25.1 to 42.1 at the second harvest, respectively, from the lowest to the highest N rate. The critical levels off concentration and SPAD values determined in the recently expanded leaf blades were, respectively, 28.4 g kg(-1) and 49.0 at the first harvest, and 34.1 g kg(-1) and 42.8 at the second harvest.