Isotopic Lysimeter Studies on Effects of Soil pH on the Behavior of Different Forms of N Fertilizer for Maize

Abstract

               A lysimeter experiment, using the ¹⁵N technique, was conducted with a Reddish Brown Lateritic (Oxic Paleustult) soil adjusted to different pH’s to compare the effects of N fertilizer in the forms of ammonium, nitrate and urea on the yields and N uptake of maize (Zea mays, L) and on the balance sheets of the applied N at different pH’s. In strongly acid to neutral soils, ammonium, nitrate and urea were comparable in their fertilizer use efficiencies whereas in moderately alkali soils, nitrate was comparable to urea but superior to ammonium. Leaching losses of the fertilizer N increased with soil pH but was not affected by different forms of fertilizer. Gaseous loss of fertilizer N (3.7-38.2%) was much higher than leaching loss (0.2-3.8%) and was generally highest in alkali soils and lowest in neutral soils. In strongly acid soils, gaseous loss of N from urea was higher than those from ammonium and nitrate. In neutral to moderately alkali soils, the gaseous losses from ammonium and urea were comparable but higher than the loss from nitrate, with the difference being greater at higher pH. After the harvest, the amounts of fertilizer N remaining in neutral soils were not affected by the forms of fertilizer. In strongly acid soils. The amount of fertilizer N remaining in the soil from nitrate was greater than those from ammonium and urea. In moderately alkali soils, the amount of fertilizer N remaining in the soil from nitrate was comparable to that from urea but greater than that from ammonium. The figures obtained from the lysimeters on fertilizer-N recovery by maize were over-estimation whereas those on the amounts of N remaining in the soil were under-estimation compared to those obtained in the field. The total amounts of N loss from fertilizer obtained from the lysimeters were comparable to those obtained in the field.

                Considering the comparative effects on fertilizer recovery by plant and losses of the fertilizer, the three forms of N fertilizer are equally recommended for neutral soils. For strongly acid soils, ammonium and nitrate forms are recommended. For moderately alkali soils, nitrate form is highly recommended.