Nitrogen use efficiency, crop productivity and environmental impacts of urea deep placement in lowland rice fields

Yam Kanta Gaihre 1, Upendra Singh1, Azmul Huda2, S.M. Mofijul Islam3, M. Rafiqul Islam2, Jatish Chandra Biswas3, Josh DeWald1

1 International Fertilizer Development Center (IFDC), Muscle Shoals, 35622 USA (

2 Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh

3 Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh


Nitrogen (N) fertilization is critical for cereal production; however, its low use efficiency poses both economic and environmental concerns. Urea deep placement (UDP) in lowland rice fields is one of the best currently applicable management techniques to increase N use efficiency (NUE) and crop productivity. Multi-location experiments conducted in Bangladesh in 2014-2015 have demonstrated several benefits of UDP use including reduced N losses through ammonia volatilization and greenhouse gas nitrous oxide (N2O) and nitric oxide (NO) emissions. Nitrogen loss as N2O and NO emissions were measured continuously throughout rice-growing and fallow seasons using an automated gas sampling and analysis system. Across the years and sites, UDP increased yield on average by 21% as compared to broadcast urea while using at least 25% less fertilizer. UDP reduced floodwater ammonium and ammonia volatilization similar to the control (N0) treatment, while both were significantly higher in broadcast urea treatments.  UDP reduced N2O emissions by up to 80% as compared to broadcast urea under continuous flooded (CF) conditions. The effects of UDP on N2O emissions under alternate wetting and drying (AWD) irrigation practices were site specific: depending on the duration and intensity of soil drying, emissions were reduced under mild soil drying but increased with more intense soil drying. These results confirm that UDP not only increases NUE and grain yields but also reduces negative environmental impacts including N2O emissions.

Nitrogen dynamics in deep ploughed soils of North Germany

Rolf Nieder1, Zaur Jumshudov1, Viridiana Alcántara2, Axel Don2, Reinhard Well2

1Institute of Geoecology, Technische Universität Braunschweig, Langer Kamp 19c, Braunschweig 38106, 


2Thünen Institute of Climate-Smart Agriculture, Bundesallee 50, Braunschweig 38116, Germany


On average 45 years after the deep ploughing operation, deep ploughed soils contained 24±5% more total N compared to conventionally ploughed reference soils. However, the mean N stock in the new topsoils was still 8% lower compared to the reference soils. This indicates a long-term N accumulation potential lasting more than 4-5 decades. The potential N mineralization and nitrification capacities of loamy deep ploughed soils were higher compared to sandy deep ploughed soils. All sites showed very low N mineralization potentials and nitrification capacities in the buried Ap material compared to surface Ap horizons.

Field evaluation of N2O, CO2 and CH4 emissions and enzyme activities under corn-soybean intercropping system

Artemio A. Martin, Jr 1Diane S, Stott2

Isabela State University, Echague, Isabela, Philippines

NRS-USDA, Purdue University, West Lafayette, Indiana, USA


The effect of cover crops (ryegrass, hairy vetch, and oilseed radish) in terms of microbial biomass   carbon   (MBC),  C and N   mineralization,   and   enzymatic   activities   in   a  corn-wheat-soybean cropping systems under a Mollisol was evaluated. The distributions of total organic C (TOC), total Kjeldahl N (TKN), microbial biomass C (MBC), readily mineralizable C and N, and five enzyme activities (β-glucosidase,  β-glucosamidase, acid phosphatase, arylamidase, and fluorescein diacetate hydrolysis) involved in the cycling of C, N, P and S were studied in three soil depths (0-5. 5-10, 10-20 cm) while soil surface fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were estimated.  Rye   grass   showed   higher   activity   in   acid   phosphatase,   β-glucosidase   and   β-glucosaminidase. Rye grass and hairy vetch significantly increased organic C and N, and MBC.  Level of mineralized C and N were the same in rye grass and hairy vetch. There was no clear variation in CO2, N2O and CH4 fluxes from the cover crop treatments. N2O fluxes increased with an   increase   in   soil   moisture.   The   negative   CHfluxes   manifest   the   soil   as   CHsink.   No significant   differences  among   cover   crop   treatments   in   terms   of   CO2-C,   N2O-N   and   CH4C emissions, a reflection that their emissions are highly variable.

Empirical data on carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes are important in management systems to evaluate mitigation strategies, while microbial biomass and enzyme activities can be used as sensitive indicators of ecological stability.

A model of animal manure nitrogen mineralisation in soil

Peter Sørensen1,Ingrid K. Thomsen1, Jaap J. Schröder2

1 Department of Agroecology, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark,,

2 Plant Research International, Wageningen University and Research Centre, P.O. Box 16, 6700 AP Wageningen, The Netherlands


A general model was developed for net mineralisation of pig and cattle slurry N in arable soil under cool moist climate conditions. The model is based on a 3-year field experiment and literature data and describes the cumulative net mineralisation of manure N during the initial 5 years after spring application. The model estimates a faster mineralisation rate for organic N in pig slurry compared to cattle slurry, and the model includes an initial N immobilisation phase for both manure types. The model estimates a cumulated mineralisation of 71% of the organic N in pig slurry and 51% of the organic N in cattle slurry after 5 years. These estimates are in accordance with other mineralisation studies and studies of manure residual N effects.

Should soil nitrogen be mined?

Deli Chen1, Shu Kee Lam1, Arvin R. Mosier1, Richard Eckard1, Peter Vitousek2

1Crop and Soil Science Section, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, VIC 3010, Australia, Email:

2Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA


Misunderstanding of the intricacies of nitrogen (N) cycling in agricultural soils has led to improper fertiliser N use in important global agroecosystems, ranging from excessive use to unsustainable exploitation (mining) of soil organic matter reserves. This must be addressed to avoid excessive N accumulation and to ensure adequate N reserve. Here we develop a framework for answering the question “Should soil organic N be mined, and if so, for how long?” to maintain sustainable agricultural production in major agroecosystems worldwide. Agricultural systems where external N input exceeds the capacity of the soil to form soil organic matter are prone to leak reactive N to the environment. Excessive additions need to be halted, and where excess reactive N remains in these systems it needs to be mined, at least for some time. In other agroecosystems, external N input is low and current use of the land mines N acquired through the mineralization of soil organic matter. Thus the paradox of mining soil organic N, where on the one hand it can be desirable for agroecosystem health and on the other threatens agroecosystem function. Untangling the paradox of mining soil organic N and revealing the residual effect of fertiliser N will contribute to answering the question of whether N use efficiency is as low as perceived. This has major implications for food security and environmental quality.

Two-way nitrogen transfer between Dalbergia odorifera and its hemiparasite Santalum album is enhanced when the N2-fixing host effectively fixes nitrogen

Xinhua He1,2,3, Junkun Lu3, Lihua Kang3, Janet Sprent4, Daping Xu3

1 Centre of Excellence for Soil Biology, College of Resources and Environment, Southwest University, 2 Tiansheng Road, Beibei, Chongqing, China, 400715, and, 2School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA, Australia, 6009;

3 Research Institute of Tropical Forestry, Guangzhou, Guangdong, China, 510520

4 Division of Plant Sciences, University of Dundee at James Hutton Institute, Dundee, UK, DD2 5DA


Understanding plant-parasite interactions between root hemiparasite Santalum album and its host trees has theoretical and practical significance in plantations of precious sandalwood as well as tree nutrition or fertilization management. Nutrient translocation from a host plant is vital to the growth and survival of its root parasitic plant, but few studies have investigated whether a parasitic plant is also able to transfer nutrients to its host. The role of N2-fixation in nitrogen (N) transfer between 7-month-old Dalbergia odorifera T. Chen nodulated with Bradyrhizobium elkanii DG and its hemiparasite Santalum album Linn. was examined by external 15N labelling in a pot study. Four paired treatments were used, with 15N given to either host or hemiparasite and the host either nodulated or grown on combined N. N2-fixation supplied 41–44% of total N in D. odorifera. Biomass, N and 15N contents were significantly greater in both nodulated D. odorifera and S. album grown with paired nodulated D. odorifera. Significantly higher total plant 15N recovery was in N-donor D. odorifera (68–72%) than in N-donor S. album (42–44%), regardless of the nodulation status in D. odorifera. Nitrogen transfer to S. album was significantly greater (27.8–67.8 mg plant−1) than to D. odorifera (2.0–8.9 mg plant−1) and 2.4–4.5 times greater in the nodulated pair than in the non-nodulated pair. Irrespective of the nodulation status, S. album was always the N-sink plant. The amount of two-way N transfer was increased by the presence of effective nodules, resulting in a greater net N transfer (22.6 mg plant−1) from host D. odorifera to hemiparasite S. album. Our results may provide better N management strategies for successfully mixed field plantation of S. album with D. odorifera, both are in great market demanding as preciously fragrant timbers, but have been globally over-exploited in the field.

Could the nitrogenase enzyme be N2 limited in legume symbioses?

Murray Unkovich1 and David Layzell2

School Agriculture, Food and Wine, The University of Adelaide, PMB 1, Glen Osmond SA 5064. Australia.

Department of Biological Sciences, University of Calgary, 2500 University Drive N.W., Calgary AB Canada T2N 1N4


Despite the fact that N2 gas comprises 78% of the earth’s atmosphere, there is some evidence that its concentration in legume nodules may be less than that needed to saturate the activity of nitrogenase, the bacterial enzyme responsible for fixing N2 into NH4+ needed for protein and DNA synthesis in biological systems. This paper reviews that evidence. If this hypothesis were true, to meet their demand for fixed N, legumes would need to produce more nodules, bigger nodules or more nitrogenase enzyme activity per nodule. Given the high energy cost of legume nodules, N2 limited nitrogenase could reduce legume productivity.

We provide an overview of the published literature on 15N isotope enrichment associated with nitrogenase activity and evidence to suggest that in legumes nitrogenase may not be N2 saturated. We then consider the biophysical properties of legume nodules, and the biochemical properties of the nitrogenase enzyme to explore a possible explanation for the isotopic data and the stated hypothesis.

Towards synthetic nitrogen-fixing symbioses in grasses

Michael Udvardi1, Evangelia Kouri1, John Peters2, Amaya Garcia Costas2, Florence Mus2, Jean-Michel Ane3, Kevin Garcia3, Chris Voigt4, Min-Hyung Ryu4, Giles Oldroyd5, Ponraj Paramasivian5, Ramakrishnan Karunakaran5, Barney Geddes6, and Philip Poole6.

1The Samuel Roberts Noble Foundation, USA

2Montana State University, USA

3University of Wisconsin-Madison, USA;

4Massachusetts Institute of Technology, USA;

5John Innes Center, UK;

6University of Oxford, UK. 



Too much nitrogen (N)-fertilizer is used in many agricultural systems, at great environmental cost, while too little is used in the poorest systems, jeopardising food security.  As a step towards solving these contrasting N-related problems, we aim to build synthetic nitrogen-fixing symbioses between bacteria and grasses, based on knowledge gained from decades of research on natural nitrogen-fixing symbioses in legumes.  Key steps in this synthetic biology project include engineering of: signal compound production in bacteria and signal recognition in plants; concomitant biosynthesis of a specialized C-source by the plant for use by the bacteria; catabolism of this specialized C-source for energy production, as well as nitrogen fixation, respiratory protection of nitrogenase, and conditional suppression of ammonia assimilation in bacteria; and, finally, ammonium uptake by plant cells.  Chassis’ for the bacterial synthetic biology are natural endophytes or epiphytes of grasses, while the target model and crop species are barley and maize.  Significant progress has been made in each of these areas. Ultimately, substantial synthetic associative nitrogen-fixation in staple food crops could increase yields of resource-poor farmers and decrease the need for industrial N-fertilizers in resource-rich agricultural systems.