What limits nitrate uptake from soil?
Article first published online: 28 APR 2006
Plant, Cell & Environment
Volume 14, Issue 1, pages 77–85, January 1991
How to Cite
ROBINSON, D., LINEHAN, D. J. and CAUL, S. (1991), What limits nitrate uptake from soil?. Plant, Cell & Environment, 14: 77–85. doi: 10.1111/j.1365-3040.1991.tb01373.x
- Issue published online: 28 APR 2006
- Article first published online: 28 APR 2006
- Received 21 February 1990; received in revised form 4 June 1990; accepted for publication 28 June 1990
- Triticum aestivum L.;
- cv. Wembley;
- spring wheat;
- nitrate uptake;
- effective root length.
Abstract. An accepted view, that unless nitrate concentrations in the soil solution are very low (e.g. below 0.1–0.2 mol m−3) the growth of high-yielding crops is not limited by the availability of nitrogen, is challenged. Conventional analyses of nutrient supply and demand, based on calculations of apparent inflow rates (uptake rates per unit total root length) are invalid. Apparent inflow rates are inversely proportional to root length. The convention of using total root length grossly overestimates the fraction of the root system active in nutrient uptake. Consequently, inflow rates based on total root lengths underestimate the true values, indicating unrealistically low nutrient concentration differentials between bulk soil and root surfaces required to drive uptake. An alternative method of analysis is suggested. This is based on total nutrient uptake rather than on inflow rate. Measurements of the former do not depend on estimates of active root length and can be made directly and reliably. The method was applied to data obtained from a pot experiment using spring wheat (Triticum aestivum L., cv. Wembley) grown in soil without nitrogen fertilizer (N0) or with nitrogen fertilizer equivalent to 200kg N ha−1 (N+). Soil nitrate concentrations calculated using the conventional method based on total root length, suggested that any increases in concentration above those measured in the N0 treatment should not have resulted in increased uptake and growth. However, the N+ plants were always bigger than those in the No treatment, refuting this suggestion. Theoretical uptakes of nitrogen (calculated initially on the basis of a fully active root system) were adjusted, by reducing the effective root length incrementally, until the theoretical uptake matched the measured net uptake of nitrogen. The mean fractions of the root systems likely to have been involved in nitrate uptake were 11% and 3.5% of the total lengths of root in the N0 and N+ treatments, respectively.