Nitrogen Use on Irrigated Rice.

Suitable nitrogen dose that provides maximum economic yield and highest doses cause no effects on plants that warrants the increase in the nutrient amount. The aim of this study was to evaluate and discuss N doses in morphological characteristics and yield on I-464 rice developed by EMBRAPA in partnership with University of Tocantins (UNITINS). The experiment was carried in Palmas, Tocantins State, Brazil. Data were collected from May to June of 2016. The experimental design was completely randomized block with five treatments and  four replications, using an Oxisol in pots with six liters of capacity each, in greenhouse conditions. Treatments were five nitrogen doses: 0, 15, 30, 45 and 60 mg dm^-3, using ureia as N source, divided into two equal parcels with 34 and 55 days after germination. Characteristics evaluated were: Plant height, tillers number, panicle number, spike number, leaves dry matter and grain dry matter. Data were estimated and compared by F test at 5%, and when significant, regression was adjusted. N doses did not affect (P>0.05) plant height, tillers number, panicle number, spike number and grain dry matter, probably due to N doses in this experiment were lower than reported in others researches. On the other hand, leaves dry matter was affected (P<0.05) and it was adjusted to a linear regression model according to equation: y = 12.22 + 0.1589x; R² = 0.45; CV%=29.99. In other words, when the N doses increased 1 mg N dm^-3 the leaves dry matter increased 0.1589 g. Thus, the I-464 rice have positive results with nitrogen supply and high doses need to be tested to find the most economical dose.