Suppose roots, straw, and grains of a wheat crop produce dry matter of 2.5 t/ha, 6 t/ha, and 4 t/ha containing 0.2%, 0.5%, and 1.5% N, respectively. How much total N uptake by the above-ground portion ?
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Always read the system boundaries in calculation questions carefully. Keywords like 'above-ground' or 'vegetative' specify which plant parts should be included or excluded from the final sum.