Nitrogen mineralization in tropical wetland rice soils: II. Application of exponential models

Abstract

Soil N mineralization during flooded incubation at 25 and 30°C in 30 tropical wetland rice soils from the Philippines, Indonesia, Malaysia, and Thailand, reported earlier, were analyzed by applying first-order kinetic (exponential) equations. The amount of net mineralized N (N) was measured every 2 weeks until 16 weeks (t = d). Linear, N=At, single term equation, N=N 1[l — exp(—k 1 t)], or two-term exponential equation, N=N 1[t—exp(— k 1 t)] +N2[1 — exp(— k 2 t)] was applied separately at both temperature levels. In 17 cases (11 at 25°C, 6 at 30°C) the linear equation gave the best fit, in 19 cases (7 at 25°C, 12 at 30°C) the single term equation gave the best fit, and in 24 cases (12 at 25°C, 12 at 30°C) the two-term equation gave the best fit. When the two-term equation gave the best fit, the second term indicated negative mineralization potentials except for 3 cases, showing net initial N immobilization. When the curves were almost linear, highly negative correlation was found between N 1 and k 1. The slowdown in N mineralization rate in the latter period of incubation was observed in one third of cases at 25°C, and in two thirds of cases at 30°C. Alternatively, exponential equations were applied for mineralization potentials independently of temperature. In 17 cases, single term equation gave the best fit, and in 13 cases, the two-term exponential equation gave the best fit. The second term expressed net initial immobilization fraction except for one soil. Single term equation gave a better fit when the soil clay content was less than 30% and sand content more than 20%, and the kinetic constants were negatively correlated with the clay content. Average ratio of k 1 at 30°C to that at 25°C was 1.7 in the single term equation, and 1.4 in the two-term equation. Comparison of these data with the reported data from Japanese soils was presented. © 1996, Taylor and Francis Group, LLC.

Source or Periodical Title

Soil Science and Plant Nutrition

ISSN

380768

Page

239-249

Document Type

Article

Subject

Effect of temperature, Exponential equation, Nitrogen immobilization, Soil nitrogen mineralization, Wetland rice soi

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