Increasing nitrogen-use efficiency by wheat in volcanic ash soils

Timing of application and type of N fertilizer, irrigation and interactions with S, genotypes and rotational effects were studied and progress made in selecting conditions for increasing fertilizer-N efficiency with wheat. Results indicated that residue incorporation in the rotation, optimum irrigation (>170 mm), three split applications of N and nutritional problem correction (acidification and sulfur deficiency), promoted wheat yields and fertilizer-N efficiency. Applied-N recoveries were only about 50%. However, grain yields of 6 to 8 t ha-1 were achieved when the soil was managed appropriately. The chlorophyll meter may be useful to define wheat N requirement if used in conjunction with well fertilized reference strips within the same field. (author)