Nitrogen Cycling in Rice Paddy Environments: Past Achievements and Future Challenges

Abstract

Nitrogen is generally the most limiting nutrient for rice production. In rice paddy soils, various biochemical processes can occur regarding N cycling, including nitrification, denitrification, and nitrogen fixation. Since its discovery in the 1930s, the nitrification-denitrification process has been extensively studied in Japan. It may cause N loss from rice paddy soils, while it can also reduce environmental pollutions such as nitrate leaching and emission of nitrous oxide (N 2 O). In this review article, we first summarize the early and important findings regarding nitrification-denitrification in rice paddy soils, and then update recent findings regarding key players in denitrification and N 2 O reduction. In addition, we also discuss the potential occurrence of other newly found reactions in the N cycle, such as archaeal ammonia oxidization, fungal denitrification, anaerobic methane oxidation coupled with denitrification, and anaerobic ammonium oxidation.

Evaluation of nitrogen balance in a direct-seeded-rice field experiment using Hydrus-1D

“…Paddy soils are dynamic environments, and the transport of N and its transformations in the soil profile are very complex and vary in time depending on alternate wetting and drying conditions (Lüdemann et al, 2000;Ishii et al, 2011). Additionally, the crop roots and microorganisms, variably distributed in the soil, significantly affect the N transformations and thus further complicate N distribution in the soil.…”

“…The risk of groundwater contamination by N depends largely on the N input to agricultural fields in the form of inorganic fertilizers and on its effective use by agricultural crops (Becker et al, 2007). Paddy fields represent a special environment for the transport and transformations of N species due to their semi-artificial, alternate drying, and wetting conditions (Lüdemann et al, 2000;Ishii et al, 2011). Furthermore, diverse rice cultivation approaches may produce different types of N losses from paddy fields (Brar and Bhullar, 2013).…”

“…In particular, the rhizosphere dynamics of N uptake is very complicated, since it may involve both passive and active uptake (Šimůnek and Hopmans, 2009), as well as other processes such as N mineralization, nitrification-denitrification, and rhizosphere acidity (Singh et al, 2011;Li and Wang, 2013;Najafi, 2013). Meanwhile, rice prefers ammonium (NH 4 + -N) to nitrate (NO 3 − -N) as a source of N (Ishii et al, 2011), and in the presence of both N species, rice seedlings take up NH 4 + -N faster than NO 3 − -N (Sasakawa and Yamamoto, 1978). However, in order to simplify the model and to limit the number of required parameters, many studies made the common assumption that the root uptake of NH 4 + -N and NO 3 − -N is strictly passive and other uptake mechanisms may be neglected (Hanson et al, 2006;Ravikumar et al, 2011;Ramos et al, 2012).…”

Robust optimal model for sustainable joint production of green tea and paddy rice in Japanese agricultural watersheds

“…In the NRS, most PFs observed recorded nil amounts of NO 3 -N despite that it was just after the end of RS. This all may point to effective NO 3 -N reduction processes of PFs as reviewed by Ishii et al (2011).…”

“…Paddy rice and green tea crops pose a potential partnership that can generate greatest benefits in both sectors, in terms of profitability and environment sustainability. The positive technological interdependence and topo-sequence nature common between these two crops can facilitate potential joint production through indivisible sharing of water and N. N is the most limiting nutrient for rice production (Ishii et al, 2011). Therefore, N concentrated drainage water from tea plantations if diverted to paddy fields has potential direct benefit to contributing towards viable production of rice through freely availing most important inputs for rice production, that is, N nutrients and water.…”