Effects of N-fertilizers, straw, and dry fallow on the nitrogen balance of a flooded soil planted with rice

Abstract

Summary Nitrogen balance studies were made on rice (Oryza sativa) grown in flooded soil in pots. A low rate of fertilizer (5.64 mg N. kg-I soil) did not depress the N gain, but a high rate (99.72 mg N .kg -1 soil) elminated the N gain. Soil N loss was negligible since 15N applied as ammonium sulfate and thoroughly mixed with the soil was recovered from the soil-plant system after 3 crops. The observed N gain, therefore, was caused by N2-fixation, not by a reduction of soil N loss.Straw enhanced N gain at the rate of 2-4 mg per g straw. However, this gain was not observed when soil N availability was high. Dry fallow between rice crops decreased the N gain.

Nitrogen Transformations in Submerged Soils

“…Estimates of BNF by free-living heterotrophic bacteria are typically <20 kg N ha −1 crop −1 (Roger and Ladha, 1992). The application of straw enhances heterotrophic and photodependent BNF by an estimated 2 to 4 kg N ha −1 Mg −1 of applied straw (Santiago-Ventura et al, 1986). The straw serves as a C substrate for heterotrophs, and it can create a more favorable environment for BNF by reducing inorganic N through temporary immobilization.…”

Biological N2 Fixation in wetland rice fields: Estimation and contribution to nitrogen balance

“…Recent greenhouse and field experiments show that straw application may significantly increase populations and N 2-fixing activity of photosynthetic bacteria and BGA (Ladha and Boonkerd, 1988). However, pot experiments by Santiago-Ventura et al (1986) showed N gains of 2 -4 m g N g -I straw added with no difference when soil was exposed to light or kept in darkness. Quantitative estimates of BNF in field experiments with straw are not available, but a few semiquantitative data and laboratory data suggest that straw might increase BNF by 2-4 kg N t-1 applied.…”

“…Data are from 14 reports, including both field and pot studies. To allow for comparisons, data from pot experi- (19751;App et al (1980App et al ( , 1984App et al ( , 1986; De and Sulaiman (1950); Firth et al (1973); Greenland and Watanabe (19821;Inatsu and Watanabe (1969); Konishi and Seino (1961); Koyama and App (1979); Santiago-Ventura et al (1986); Singh and Singh (19871;Trolldenier (1987); and Willis and Green (1948). 177 values obtained in pots were extrapolated to kgNha t i crop on an area basis.…”

Managing native and legume-fixed nitrogen in lowland rice-based cropping systems

“…Maintaining flooding between and during rice crops increases the soil N supply (Ponnamperuma, 1985;Santiago-Ventura et al, 1986;Ventura and Watanabe, 1978). Nitrate does not accumulate in the soil since soil drying between rice crops is minimal.…”