Nitrous oxide emission in response to N application in irrigated sugarcane/ Emissao de oxido nitroso em resposta a aplicacao de N em cana-de-acucar irrigada

The objective of this study was to compare the emissions of nitrous oxide ([N.sub.2]O) resulting from the application of nitrogen (N) and potassium (K) doses in fertigated sugarcane, in comparison to emissions from conventional fertilizer application. The study was conducted in the experimental area of Embrapa Mid-North, Teresina, Piaui state, Brazil, from August 2014 to January 2015. The experimental design was in randomized blocks, analyzed in a (2 x 2) +1 factorial scheme, with four replicates. The treatments consisted of the combination of two doses of N and [K.sub.2]O (60-120 and 120-180 kg [ha.sup.-1], respectively) and two methods of application (in soil and fertigation), and a control. The use of fertigation reduced the emissions of [N.sub.2]O in sugarcane compared with the crop under conventional fertilization. Increase in N dose from 60 to 120 kg [ha.sup.-1] applied through fertigation did not affect [N.sub.2]O emissions, while 60 and 120 kg [ha.sup.-1] applied in the soil led to 40.6 and 50.2% increases in [N.sub.2]O emissions, respectively. The application of 60 and 120 kg [ha.sup.-1] of N in the soil led to higher [N.sub.2]O emission factor, being 1.39 and 2.08% higher than in the crop fertigated with 60 and 120 kg [ha.sup.-1] of N, respectively. Key words: Saccharum officinarum nitrogen GHG Objetivou-se neste estudo comparar as emissoes de oxido nitroso ([N.sub.2]O) decorrentes da aplicacao de doses de nitrogenio (N) e potassio (K) em cana-de-acucar fertirrigada, comparando-as as emissoes provenientes da adubacao convencional. O estudo foi conduzido na area experimental da Embrapa Meio Norte, Teresina, PI, de agosto de 2014 a janeiro de 2015. O delineamento utilizado foi o de blocos ao acaso, analisado em esquema fatorial (2 x 2) +1, com quatro repeticoes. Os tratamentos consistiram na combinacao de duas doses de N e [K.sub.2]O (60-120 e 120-180 kg [ha.sup.-1], respectivamente) e duas formas de aplicacao (via solo e fertirrigacao) e uma testemunha. O uso da fertirrigacao reduziu as emissoes de [N.sub.2]O em cana-de-acucar em comparacao ao cultivo fertilizado de forma convencional. O aumento da dose de N de 60 para 120 kg [ha.sup.-1] aplicado via fertirrigacao nao afetou as emissoes de [N.sub.2]O, enquanto que a aplicacao de 60 e 120 kg [ha.sup.-1] via solo proporcionou aumento de 40,6 e 50,2% nas emissoes de [N.sub.2]O, respectivamente. A aplicacao de 60 e 120 kg [ha.sup.-1] de N via solo obtiveram maior fator de emissao de [N.sub.2]O, sendo