How much fertilizer N is needed by a rice crop?
• The fertilizer N needed by a rice crop can be estimated as shown in the table below from the expected increase or response in grain yield due to fertilizer N application and the expected agronomic efficiency of fertilizer N use by the crop. Agronomic efficiency (kg grain increase kg−1 applied N) 15 18 20 25 Expected yield response (t ha−1) Fertilizer N rate (kg ha−1) 1 65 55 50 40 2 130 110 100 80 3 195 165 150 120 4 220 200 160 5 250 200 Additional Questions: • How is yield response determined? • The grain yield response with fertilizer N application is the difference between the yield target and yield without fertilizer N (N-limited yield). The yield target is the yield attainable by farmers with good crop and nutrient management and average climatic conditions. The yield without fertilizer N indicates the ability of the soil to supply N to the crop. It can be determined with an N omission plot receiving no fertilizer N but sufficient quantities of other nutrients to ensure that th
