In the absence of accurate and rapid N testing methods, many growers currently apply N fertilizer in excess rather than risk of yield reduction through N deficiency. Crop growth and crop need for supplemental N can be strongly influenced by crop-growing conditions, crop and soil management, and climate, which can vary greatly among fields, villages, seasons and years. The current recommendation of fixed-time split N application at specified growth stages is not adequate to synchronize N supply with actual crop N demand because of poorly designed N splitting and variations in crop N demand and...