Seasonal Changes in N2 Fixation Activity and N Enrichment in Paddy Soils as Affected by Soil Management in the Northern Area of Japan

Abstract

Enhancing the indigenous ability of biological N 2 fixation (BNF) in paddy soils to increase N fertility is important to develop sustainable rice cultivation systems. This study aimed at evaluating the effect of light conditions and long-term soil management on the seasonal changes in the BNF activity of paddy soils associated with the decomposition of rice straw and cellulose, by determining the acetylene reduction activity (ARA) and N enrichment in the Tohoku region of Japan under cool temperate conditions. ARA of the straw applied on the soil surface showed a peak in the mid-cropping season in the summer. The ARA of the straw applied in autumn was 30% of that in spring application. Carbon use efficiency for N enrichment with cellulose was about 3 times higher under light than dark conditions. Among the long-term soil management practices, continuous application of fresh organic materials such as rice straw and manure considerably enhanced N enrichment and ARA. In the soil without P, the inhibition of N enrichment by the low P availability appeared in the early cropping season. Soils from paddy fields converted to upland fields (hereafter referred to as "converted upland soils") showed the highest level of N enrichment when the soils were amended with cellulose. The highest level of N enrichment with and without cellulose amendment was estimated to be 1.6-2.0 g m -2in one cropping season. The results indicated the important contribution of BNF even under cool temperate conditions and the significant effect of soil management related to organic matter application and the water regime on the magnitude of BNF and, therefore, possibly on the N cycling of the paddy soil systems.

Effects of Temperature, Water Regime, Light, and Soil Properties on 15N2 Fixation Associated with Decomposition of Organic Matter in Paddy Soils

“…The positive relation of 15 N 2 fixation with the total-C and mineralizable-N contents under the light conditions indicated the importance of the role of decomposable organic matter in the increase of the populations of phototrophic N 2 fixers. Among the organic materials, fresh organic materials such as manure and rice straw were found to be more effective in enhancing 15 N 2 fixation than the compost, which is in agreement with the trends in N enrichment in field evaluation 9 . On the other hand, soils with lower total-C and mineralizable-N contents tended to depend more on heterotrophic BNF, presumably due to the alleviation of the adverse effect of NH 4 on heterotrophic N 2 fixation in part 11 .…”

“…The details of soil management of the field trials were reported elsewhere 9 . The properties of the soils are presented in Table 1.…”

“…Our previous observations in fields 9,18 suggested the importance of BNF for the enrichment of soil N along with the decomposition of rice straw and cellulose in the Tohoku region, which is one of the major rice-producing areas of Japan under cool temperate conditions. Many soil factors are known to affect the BNF activity in paddy soils such as the contents of available-P, NH 4 , pH, and redox potential 2,10,12,17 .…”

“…Many soil factors are known to affect the BNF activity in paddy soils such as the contents of available-P, NH 4 , pH, and redox potential 2,10,12,17 . Soil management related to the application of N, P and organic matter considerably affected N enrichment in fields 9,18 . However, the effects of soil management and properties on BNF by various heterotrophic and photodependent N 2 fixers have not been fully documented.…”

Towards an understanding of the high productivity of rice with System of Rice Intensification (SRI) management from the perspectives of soil and plant physiological processes

“…In addition, the effect of returning the soil surface to its initial condition might be beneficial for biological nitrogen fixation by algae which proliferate on the puddled soil surface (Roger and Kulasooriya 1980). Kondo and Yasuda (2003) reported that the amount of biologically fixed nitrogen would be 1.6-2.0 g m À2 in one cropping season for paddy fields in Japan under conventional management. Moreover, total N in the soil surface layer significantly increased compared with conventional water treatment when an early drained condition was introduced to a clayey paddy field, and algae proliferation was suggested on such a drained moist soil surface (Kobayashi et al 2000).…”