Influence of Flooding Levels on Changes in C, N and Weight of Rice Straw in a Paddy Soil

Abstract

It is imperative to have a better understanding of the effects of different flooding levels in paddy soils on changes in soil chemical properties, especially information on the N recovery and N mineralization when the rice straw is incorporated into soil as a source of soil organic matter under tropic conditions, such as in Metro, Lampung. A glasshouse study was carried out to determine the effects of different flooding levels (2.5, 5.0, 7.5, and 10.0 cm) on changes in carbon (C), nitrogen (N) contents and weight of rice straw incorporated into paddy soil. The treatments were arranged in a completely randomized block design with six replications. The results showed that C content of the rice straw at the beginning of the trial was 33–40%. These values decreased 2 weeks after flooding except for the flooding level of 10 cm the C content still decreased until 4 weeks after flooding. And then for all flooding levels the values tended to return to the initial values 8 weeks after flooding. Meanwhile, the N content at the beginning of the trial was 0.56-0.60%. The N contents for all flooding levels increased with increasing time of observation (1.34-1.48%). The C:N ratios for all flooding levels at the beginning of the trial greatly decreased until 2 weeks after flooding. Thereafter, the ratios decreased slightly until 8 weeks after flooding. Furthermore, flooding level of 2.5 cm gave the lowest weight of rice straw 8 weeks after flooding, whereas, flooding level of 10.0 cm gave the highest weight of rice straw, suggesting that the lesser the flooding level, the faster the litter decomposition rate. This confirms other findings that at the depth of 1-2 cm below water surface of a paddy field are an aerobic zone, where the litter decomposed most rapidly.

Keywords: Flooding levels, decomposition, C, N, rice straw