Nutrient requirement depends on Target yield and soil nutrient supply Type of fertilizer and recovery Timing (which is dependent on the maturity of variety) To estimate fertilizer requirements we need to know Target yield Crop yield with no fertilizer Fertilizer recovery Example Target yield: 4.5 tonnes per hectare Yield without fertilizer: 1.5 tonnes per hectare Yield to come from the fertilizer: 4.5 – 1.5 = 3 tonnes per hectare Approximate fertilizer needed per tonne of crop N = 15 - 20 kg N/ha, P = 2.5 – 3 kg P/ha , K = 15 – 20 kg K/ha Thus to get additional yield of 3 tonnes grain per/ha the crop require an additional 3 (15 - 20) = 45 – 60 kg N/ha 3 (2.5 – 3.0) = 7.5 – 9 kg P/ha 3 (15 – 20 ) = 45 – 60 kg K/ha Typically N is the primary limitation and the other nutrients may or may not be needed. N recovery is typically of the order of 50% thus to supply 45-60 kg N per ha to the crop, it will be necessary to apply between 90-120 kg N per ha. If slow release of urea, super granules applied by deep placement – increase the recovery of N and thus the quantity of fertilizer can be reduced. If 1/3 N as basal , 1/3 at mid tillering and 1/3 at P.I, the recovery of N is of the order of 35%, 45% and 65% of applied N respectively. Therefore 1/3 x 30% + 1/3 x 45% + 1/3 x 65% = 48% total recovery. If there is no basal, 1/3 delayed, 2/3 at PI, then the recovery in the order of 40% and 60% of applied N respectively. Therefore 1/3 x 40% + 2/3 x 60% = 53% total recovery.

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