Quadratic equation, maximum and optimum dose of N, maximum yield in research on response to N fertilization in lowland and irrigated rice fields

The relationship between N doses and rice yields was linear quadratic, with an R2 value ranging from 0.61 to 0.97. The highest doses of N fertilizer for rice in lowlands ranged from 110 to 303 kg N ha-1, resulting in maximum yields between 7.28 and 7.93 t ha-1. The optimum N dose for rainfed rice fields ranged from 90 to 140 kg N ha-1, corresponding to the dose of urea fertilization based on productivity per sub-district.

The dose of urea fertilizer on rice fields with productivity levels of ˂ 5, 5 to 6, and ˃ 6 t ha-1 was 200, 250, and 300 kg Urea ha-1, respectively.Rice plants in technically irrigated fields were very responsive to N fertilizer, and average yields in unfertilized fields ranged from 1.90 to 5.65 t ha-1. The lowest rice yields occurred in unfertilised fields in Kediri Sub District, East Java Province, where the hybrid variety H6444 was cultivated.