Short-Term Uptake Rates and Partitioning of Nitrogen in a Potato Crop

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Abstract
Robinson, D. and Millard, P. 1987. Short-term uptake rates and partitioning of nitrogen in a potato crop.-J. exp. Bot. 38: 551–557. A method is described for isolating an intact portion of the root system of a field-grown potato plant. Soon after emergence, soil from half of the ridge adjacent to a plant was removed and replaced by a polyacrylamide gel/sand mixture containing slow-release fertilizer. Roots grew into this medium and were later isolated by washing away the gel/sand mixture. Isolated roots were immersed in 15NH415NO3 solution for 24 h and the subsequent distribution of 15N throughout the plant monitored over 8 d. Two experiments, one in July and the other in August 1985, tested the method. N-inflow rates were some of the highest that have been reported, and were related inversely to the length of root exposed to 15N. Leaves at the top of the canopy were the strongest sinks for 15N in both July and August In the oldest leaves, the sink strength for total N declined, but that for 15N did not. Tuber growth was related to an increase in the allocation of the plant's existing N capital, the increase in allocation of' 3N to the tubers being significantly smaller. Possible applications of the technique are suggested.

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