The effect of an intermittent water-table gradient on soil and xylem nitrate in cotton

Abstract

Summary Cotton (Gossypium hirsutum cv Deltapine 61) was grown in a sloping plot of soil in the field to examine the effect of a gradient of water-table depth on soil nitrate availability and plant uptake during two periods of the growing season. Before the water-table was imposed NO 3 was less concentrated at the lower end of the sloping plot. This was attributed to slow denitrification at microsites within the soil at the lower end which was wetter than further up the plot. At flooding NO 3 disappeared only slowly due to a carbon substrate limitation to denitriflcation in the soil. This loss occurred primarily in areas where the water-table was high and oxygen concentration in the soil solution was low. Plant NO 3 uptake, assessed by measuring the concentration in the xylem, parallelled the distribution of NO3 in the soil solution. Under high water-tables xylem NO3 levels fell but it was not possible to say whether this was due to impaired root function or to the reduced concentration of NO3 observed in the soil solution. At intermediate water-table depths where soil NO3 availability remained high xylem NO 3 concentration fell relative to the well drained control plants, suggesting that flooding had damaged the root system.