Effects of preflood nitrogen rate and midseason nitrogen timing on flooded rice

A field study was conducted to investigate the agronomic performance, nitrogen (N) efficiencies, yield components and yield of rice in Spain for different nitrogen treatments. The experimental variants were six preflood N rates (0, 50, 75, 100, 125 and 150 kg/ha) and three topdressing patterns: (i) non-topdressed, (ii) topdressed with 50 kg N/ha at mid-tillering stage (MT) and (iii) topdressed at panicle initiation stage (PI). The N status of the plant was measured at different growing stages to determine whether a chlorophyll meter would be useful in making N sidedress recommendations. The results showed that grain yield increased with increasing amounts of preflooding N fertilizers up to 100 kg N/ha. The main effect was on panicle number per unit ground area. The effect of additional N supply on yield components and grain yield depended on application timing. Split applications of N did not improve the agronomic efficiency but reduced days to maturity and lodging and increased the harvest index value. Split applications increased grain yield when the total N rate was 150 kg/ha with the second supply at PI. There was a significant but not very good relationship between N content and chlorophyll content (SPAD) values. The regression equation differed significantly depending on growth stage. The SPAD value may determine the need for N topdressing at MT stage, but not at PI. However, the relationship between SPAD value and the rice yield increase from N topdressing application was not very good.