Nitrogen nutrition index and morphogenesis in Alexandergrass of the Central Depression of Rio Grande do Sul

ABSTRACT: This study assessed the nitrogen nutrition index, morphogenic characteristics and tiller structure of Alexandergrass (Urochloaplantaginea (LINK) Hitch) pasture submitted to different nitrogen (N) levels (zero, 150 or 300 kg ha-1 of N). The experimental design was entirely randomized with repeated measures arrangement. The experimental animals were Angus heifers under rotational stocking grazing method. The number of animals was variable to keep 30±5 cm post-grazing sward height. Nitrogen nutrition index increased linearly according N levels (Ŷ = 59.8 + 0.1216N; P < 0.0001; r²=0.53). The leaf appearance rate adjusted to a positive linear regression model according the thermal sum (TS) with zero of N (Ŷ0N = 0.0077 + 0.0000087TS; P = 0.0308; r² = 0.72) and 150 kg ha-1 of N (Ŷ150N = 0.0020 + 0.000021 TS; P = 0.0022; r² = 0.92). The use of 300 kg ha-1 of N did not alter the leaf appearance rate (0.0124 leaf degree-days-1). The use of up to 300 kg ha-1 of N increases the Alexandergrass nitrogen content. The leaf appearance rate in Alexandergrass is modified using N while the morphogenic characteristics leaf expansion, stem expansion, phyllochron, leaf lifespan, leaf elongation duration and tiller structure are not altered by N utilization.