How is the need for fertilizer N affected by cropping season?
• The estimated need for fertilizer N based on yield target and yield without fertilizer N can be adjusted for contrasting cropping seasons with different achievable AEN as shown in the table below. Season Yield target 5 t ha−1 6 t ha−1 7 t ha−1 8 t ha−1 9 t ha−1 Approximate yield without fertilizer N (t ha−1) Fertilizer N rate (kg N ha−1) Low-yielding (AEN = 18) 3 110 – – – – 4 55 110 – – – 5 0 55 – – – High-yielding (AEN = 25) 3 80 120 160 200 – 4 – 80 120 160 200 5 – – 80 120 160 Yield targets are lower in the low-yielding season (i.e., rainy season with relatively low solar radiation) than the high-yielding season (i.e., dry season with higher solar radiation). An AEN of 25 kg kg−1 can often be achieved with high yield and good fertilizer N management in high-yielding seasons in the tropics. This is equivalent to 40 kg fertilizer N for every one ton increase in grain yield. An AEN of about 18 kg kg−1 can often be attained with high yield and good fertilizer N management in low-yiel
