How can yield without fertilizer N be approximated?
• 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 N fertilizer but sufficient quantities of other nutrients to ensure that they do not limit yield. As a rule of thumb, experiences with N omission plots across irrigated rice-growing areas in Asia indicate the grain yield of rice without fertilizer N is about 3 t ha-1 at low soil fertility or in very intensively cultivated fields, 4 t ha-1 at medium soil fertility, and 5 t ha-1 at high soil fertility.
