Radiation use efficiency in corn crop in Alagoas/Eficiencia do uso da radiacao em cultivos de milho em Alagoas

Maize was cultivated under three management systems: i) mulching (grass cover); ii) plastic cover in the inter rows and iii) traditional cultivation (bare soil). The components of the incident and transmitted solar radiation in a maize canopy were measured in order to determine the radiation use efficiency (RUE). The photosynthetic irradiation (HF) was considered as 44% of the solar global irradiation. The transmitted HF ([HF.sub.T]) was estimated using Beer's law applied to a plant canopy ([HF.sub.T] = HF exp (-k LAI)), with the light extinction coefficient (k) by fitting an exponential function, which related the fraction of [HF.sub.T] ([HF.sub.T]/HF) and leaf area index (LAI). The intercepted HF (HF:) was calculated by the difference (HF: = HF--[HF.sub.T]). The RUE was estimated using a linear regression (forced to pass through the origin) between the dry matter accumulation (DM) and [HF.sub.I]. The k was 0.628 with the determination coefficient of 0.88. The plants RUE in plots covered with plastic was 3.85 g DM [MJ.sup.-1] of [HF.sub.I], showing a higher efficiency compared to other treatments (bare soil 3.31 g [MJ.sup.-1] and grass 3.58 g [MJ.sub.-1]). However, this promoted lower LAI and therefore had less accumulated [HF.sub.I], resulting in lower production of DM. Key words: plant growth photosynthetic radiation leaf area index O milho foi cultivado em tres sistemas de manejo: i) cobertura de capim; ii) plastico na entrelinha e iii) cultivo tradicional (solo nu). Com o objetivo de determinar a eficiencia do uso da radiacao (EUR) mediram-se componentes da radiacao solar (incidente e transmitida) em dossel de milho. A irradiacao fotossintetica (HF) incidente foi considerada equivalente a 44% da irradiacao solar global. A HF transmitida ([HF.sub.T]) foi estimada utilizando-se a lei de Beer para radiacao aplicada a um dossel vegetal ([HF.sub.T] = HF exp(-k IAF)), com coeficiente de extincao da luz (k) ajustado de uma funcao exponencial, que relacionou a fracao da [HF.sub.T] ([HF.sub.T]/HF) e o indice de area foliar (IAF). A HF interceptada (HF:) foi calculada por diferenca (HF: = HF--[HF.sub.T]). Estimou-se a EUR por meio de regressao linear, forcada a passar pela origem, entre o acumulo de materia seca (MS) e a HFr O k foi de 0,628 com coeficiente de determinacao de 0,88. A EUR das plantas da parcela coberta com plastico foi de 3,85 g de MS [MJ.sup.-1] de [HF.sub.I], que mostrou eficiencia superior a dos demais tratamentos (solo nu 3,31 g [MJ.sup.-1]