Response of upland rice cultivars to nitrogen as affected by water deficiency
DOI:
https://doi.org/10.1590/S1678-3921.pab1979.v14.16706Keywords:
water deficiency, nitrogen, leaf area index, leaf area duration, water consumption, upland riceAbstract
Two field experiments were carried out (in an attempt) to determine the influence of water deficiency on the response of rice cultivars to nigrogen. In the first experiment, the treatments inducing water deficiency were suppression of the irrigation after the seedting emergence from: a. 45 to 60 days, b. 75 to 90 days and e. 45 to 60 and 75 to 90 days. Also, included a control with continuous irrigation. Four levels of nitrogen (0, 30, 60 and 90 kg/ha of N and three cultivars (IAC 1246, IAC 47 and IET 1444) were used. In the second experiment, water deficiency was induced by the suppression of irrigation 90 days after the emergence of the plants. The nitrogen levels and cultivars were the same as those in the first experiment, excepting cultivar IET 1444 which was substituted by CICA 4. In the first experiment, there was no significant influence of the water suppression treatments on grain yield, due to rain occurence. When the soil water content was not a limiting factor, grain yield increased in response to nitrogen fertilization up to 60 kg/ha of N. There was no significant difference among the cultivars with regard to grain yield. The cultivars IAC 1246 and IAC 47 showed a linear and positive correlation between the leaf area index (LAI) at flowering, and grain yield. When the soil water content was low, there was no response to nitrogen fertilization. The grain yield of cultivar CICA 4 was lower than those of IAC 1246 and IAC 47, exhibiting a linear and negative correlation with the leaf area duration (LAD). There was a linear and positive correlation between the LAD and actual evapotranspiration, proving thereby the influence of leaf area on the water consumption. The relationship between LAD and grain yield is better explained by the quadratic equation. It is evident that the application of any input that increases the leaf area over a critical point is responsible for the decrease in grain yield when water is the limiting factor.
