Estimation of the nitrogen balance for irrigated rice and the contribution of phototrophic nitrogen fixation

Abstract

Estimation of the nitrogen balance for irrigated rice and the contribution of 'phototropic nitrogen fixation. Field Crops Res., 9: 17-27. The total N content of soils from long-term fertility plots in two sites in the Philippines was measured by Kjeldahl analysis. One site had grown 24 and the other 17 crops of irrigated rice (Oryza sativa L.). It appears that the total soil N at each site did not decrease during the cropping period. There was litt? evidence that N, P, o r K fertilization affected the total soil N content. Nitrogen (NH, and NO;) input by rainfall varied between 0.6 and 2.4 kg of N/ha per year. Calculations based on crop yields and known N inputs suggest that the two flooded rice crops grown each year resulted in a positive N balance equivalent to 79 and 103 kg N/ha per year. An attempt was made to measure the accumulation of N that may occur in the oxidized surface layer of the soil in the field as a result of N fixation by phototrophic microorganisms during a rice crop. No acetylene reduction activity or accumulation of N (Kjeldahl analysis) was observed in the surface soil when the light was not allowed t o penetrate to the water and soil surface. Plots open to the light accumulated the equivalent of approximately 6-8 kg N/ha in the surface soil between transplanting and heading.

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

“…With rice grown alternately with an upland crop, the average was 4 4 k g N h a ~year ~ in 3 fields with no N fertilizer and -29 kg N in 2 fields with applied urea. At two Philippine sites, App et al (1984) found no decrease in total soil N after 24 and 17 crops, respectively. Calculations based on yields and -1 known inputs suggested that two crops year resulted in balances of 79 and 103 kg N ha -1 -1…”

“…Biological N 2 fixation in rice fields and its use have been reviewed by Watanabe and Roger (1984) and Roger and Watanabe (1986). Specific reviews deal with BGA (Roger, 1991), heterotrophs (Yoshida and Rinaudo, 1982), BNF associated with straw (Ladha and Boonkerd, 1988), rice genotypic differences in stimulating BNF (Ladha et al, 1988b), Azolla , and leguminous green manures (Ladha et al, 1988c).…”

Nitrogen Transformations in Submerged Soils

“…Nitrogen inputs by BNF help sustain SNSC and maintain SOM, and the input of N by BNF has helped sustain rice yields at low levels without fertilizer N for hundreds of years on submerged soils. Long-term N balances for rice grown on submerged soils without fertilizer N typically indicate the maintenance of total soil N content, as a result of BNF by associative and free-living microorganisms (App et al, 1984).…”

Decline in Fertility of Paddy Soils Induced by Paddy Rice and Upland Soybean Rotation, and Measures against the Decline

“…Annual N budgets in an upland soybean field converted from a paddy rice field on gray lowland soil were negative, ranging from -14.2 to -6.4 g N/m 2 , because a large quantity of N was removed from the field with harvested soybeans (Takakai et al 2010). In contrast, the N budgets in paddy rice fields (rice cultivation) have been shown to be even or positive (App et al 1984, Kyuma 2004. The negative N budget in upland soybean cultivation might be one reason for the decrease in soil N fertility in paddy-upland rotation.…”