In-situ Soil Nitrogen Mineralization in response to Nitrogen management for Corn and Soybean in poorly drained Soils with and without Tile-Drainage

Fabián G. Fernández1, Karina Fabrizzi1

1 University of Minnesota, 1991 Upper Buford Circle, St Paul, MN, 55801,,  


Greater understanding of N mineralization is needed to improve N rate guidelines and fertilizer efficiency. Our objective was to quantify N mineralization throughout the growing season when corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are grown under different N and soil drainage management. In-situ N mineralization incubations were conducted in drained and undrained soils with corn and soybean and different N rates over a two-year period. In the first three years of drainage installation 2.4 Mg C ha-1 yr-1 were lost. This factor combined with the effect of drainage on soil water content, N rate, and previous crop substantially influenced net mineralization and mineralization rate. However, substantial yearly differences due to moisture conditions often overshadowed the effects of these variables. Our results highlight the need to continue concerted research efforts to refine our understanding of how different factors influence the mineralization process to improve N management.

An empirical model of wheat baking quality under elevated CO2

Malcolm McCaskill1, Garry O’Leary2, Joe Panozzo2, Cassandra Walker2, Debra Partington1

1 Department of Economic Development, Jobs, Transport and Resources, Hamilton, Victoria, 3300,

2 Department of Economic Development, Jobs, Transport and Resources, Horsham, Victoria, 3400


Elevated CO2 (eCO2) is associated with lower grain protein concentration of wheat, and an inferior baking quality.  To extend the functionality of process-based models of wheat growth and nitrogen uptake, an empirical model for bread making quality (loaf volume and dough extensibility) was developed from five years of data from the free air carbon dioxide enrichment experiment at Horsham, Victoria, for three bread-wheat cultivars – Janz, Silverstar and Yitpi.

Loaf volume was modelled by a relationship derived by linear regression, which accounted for 82% of variation, and had  significant terms for eCO2, grain protein concentration, cultivar and a cultivar-CO2 interaction. A model of dough extensibility accounted for 79% of variation.. At a given protein concentration and CO2 level, Janz and Silverstar both had loaf volumes over 100 cm3 larger than Yitpi. It is suggested that acceptance criteria for grain receival into premium categories be based on cultivar-specific protein levels that produce equivalent loaf volumes. This would incentivise breeding efforts to improve the baking quality of wheat protein as an adaptation strategy for higher CO2 levels.

Temporary immobilisation promotes nitrogen use efficiency of irrigated rice

J.F. Angus1*, P.E. Bacon2, R. F. Reinke3*

1CSIRO Agriculture and Food, GPO Box 1600, Canberra, ACT 2601, Australia *corresponding author

2Woodlots and Wetlands Pty Ltd, 220 Purchase Rd, Cherrybroook NSW 2126, Australia

3International Rice Research Institute, Los Baños, Philippines


Nitrogen use efficiency (NUE) of flooded rice is notoriously low compared to upland crops. An exception is irrigated rice growing in the semi-arid, temperate Riverina region of south-eastern Australia where NUE is high and the time of fertiliser application is unusual by international standards. In this region, N fertiliser applied at the permanent flood (PF) stage leads to larger yield responses than when topdressed at panicle initiation (PI). In many other regions topdressing at PI is more efficient. In the field experiment described here, application of 200 kg N ha-1 as urea immediately before PF increased yield of medium-grain rice from 7.3 to 13.6 t ha-1, representing an apparent recovery of 76% of the applied N, compared with a yield of 11.4 t ha-1 and apparent recovery of 39% for same amount of N topdressed at PI. Sequential sampling showed that soil ammonium fell to low concentrations soon after urea application at both PF and PI and remained at background levels similar to the zero-N control for the rest of the growing season. Meanwhile above-ground N content of the crop increased steadily until maturity, suggesting that 38 kg N ha-1 of the fertiliser N had been temporarily immobilised before re-mineralisation and uptake by the crop. The higher efficiency of the PF application was because urea was washed into the soil with the irrigation water, while the urea topdressed at PI was initially held in the water column and at the soil-water interface before crop uptake, temporary immobilisation and loss, presumably via denitrification or ammonia volatilisation.

Effect of rice husk biochar on nitrous oxide emission from decomposing hairy vetch in two soils under high-soil moisture condition

Yoshitaka Uchida1, Moe Shimotsuma2

1 Research Faculty of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan,,

2 Graduate School of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan


Hairy vetch (Vicia villosa Roth) plants are widely used as green manures. They fix nitrogen (N) and provide a fraction of the fixed N to other crops when they decompose. Thus, green manuring with legumes is considered as an alternative to chemical N fertilizer application. However, N-rich plant residue is also a potential source for nitrous oxide (N2O), a greenhouse gas. On one hand, rice husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to reduce N2O emissions. The interaction between biochar and N rich composting materials on N2O emission has not been studied well. We conducted a soil core incubation experiment under high soil moisture (~100% WFPS) to investigate the N2O emissions from two soils, i.e., an Andosol and a Fluvisol after application (0.8 kg m-2) of 15N labelled (0.49 atom %) hairy vetch. Additionally, the experiment contains a biochar treatment. The N2O emissions and inorganic-N in soils were monitored for 1.5 month. Generally, the use of biochar suppressed soil NH4+-N concentrations in the Andosol whereas the effect of biochar on NH4+-N was not significant in the Fluvisol. Biochar application did not influence the cumulative N2O emissions but increased the contribution of hairy vetch-N to the cumulative N2O emissions, according to the analyses of N2O-15N. Our study suggests that rice husk biochar is not a good option to mitigate N2O emissions during the decomposition of surface applied hairy vetch, although this study was performed under a laboratory condition without plants. However, the trends of the inorganic-N concentration changes following the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.

How does inorganic N fertilizer affect soil nitrogen mineralization?

Navreet K. Mahal*, Fernando E. Miguez, Hanna J. Poffenbarger, John E. Sawyer, William R. Osterholz and Michael J. Castellano

Department of Agronomy, Iowa State University, Ames, Iowa, USA (50011), *


The effect of N fertilizer on soil organic matter mineralization is uncertain. This uncertainty has led to suggestions that inorganic N fertilizer may enhance soil N mineralization, thereby decreasing soil organic matter. This uncertainty has also led to confusion about how to measure crop system fertilizer N use efficiency (FNUE). Two options exist to measure FNUE: The indirect ‘N difference’ method compares N uptake in a zero N control plot compared to N uptake in a fertilized plot (FNUE = (N uptake in fertilized – N uptake in control)/N fertilizer input).  The direct ‘15N tracer’ method uses isotopically labeled N fertilizer to directly measure the uptake of individual N atoms. The ‘N difference’ method always measures higher FNUE and this result has been hypothesized to be due to a ‘priming effect’ or enhancement of added-N on soil N mineralization. The objective of this study was to quantify the effects of inorganic N fertilizer application on soil organic matter mineralization via measurement of gross ammonification. We measured gross ammonification rates in long-term N fertilizer rate experiments at two sites located in central and southern Iowa. In 2015, plots with continuous corn that had received one of three historic N fertilizer rates for the past 15 years: 0, 202 (long-term AONR) and 269 kg N/ha (highest rate) at the central Iowa site and 0, 224 (rate increment just below the AONR) and 269 (long-term AONR, at the highest rate) at southern Iowa site, were split into two subplots that received either the agronomic optimum N rate (AONR) or zero N fertilizer. Gross ammonification was measured at the V5 and V12 maize growth stages. Across all historical N fertilizer rates at the V5 maize growth stage, N fertilizer input at the AONR significantly reduced gross ammonification rates by 15 and 12% as compared to zero N at the central and southern Iowa sites, respectively; whereas there was no effect at the V12 stage. At both sites, the effect of N fertilizer on gross N ammonification rate decreased with an increase in historic N application rate from zero to highest. Because C and N mineralization occur in tandem, our results are inconsistent with the hypothesis that N fertilizer application reduces soil organic matter. Moreover, our results suggest that the ‘N difference’ method is more accurate than the ‘15N tracer’ method for measurement of FNUE, because gross N mineralization is positively associated with soil C mineralization.

Biological factors influence N mineralization from soil organic matter and crop residues in Australian cropping systems

Vadakattu V.S.R. Gupta

CSIRO Agriculture & Food, PMB 2, Glen Osmond, SA 5064, Email:


Nitrogen mineralized from the soil organic matter (SOM) and crop residues makes a substantial contribution to crop N uptake. Soil N supply comes from soil organic matter and recent crop residues and the rate of supply is influenced by the soil biological capacity, i.e. microbial biomass (MB) and microbial turnover, and modulated by management and environmental factors. Soil type, crop rotation and management practices associated with tillage, stubble retention and fertilizer application can influence the diversity of microbial populations and the size of MB, and along with the environment they affect biological processes involved in N2 fixation, mineralization and availability and losses. The rate and timing of the availability of N from stubble to the following crops is determined by the rate of decomposition and immobilization by soil microorganisms (N in MB). The amount of MB-C & N vary with soil type, crop rotation, tillage and other management practices that can influence microbial populations. In southern Australian cropping regions, the effect of loss of N from stubble removal may not be greater than its temporary tie-up during decomposition.

Building critical SOC concentration as a major pathway for improving nutrient use efficiency in sub-Saharan Africa

Patrick Musinguzi; Peter Ebanyat; John Stephen Tenywa; Twaha Ali Basamba, Moses Makooma Tenywa

Department of Agricultural Production, Makerere University, Kampala, Uganda

Corresponding email:


Building and maintenance critical Soil Organic Carbon (SOC) concentrations in tropical soils could be the greatest soil fertility challenge in sub-Saharan Africa (SSA). Measures that can boost SOC restoration to critical levels remain less understood. A study was conducted on a Ferralsol in sub-humid Uganda to explore the critical range of SOC concentrations for optimal response of maize to added N fertilizer. Computations were made to estimate the amount of carbon required for SOC restoration using the available organic C materials. Maize grain yield response to N rates was assessed with 0, 25, 50, and 100 kg N ha-1 in 30 fields of low fertility (SOC<1.2%), medium fertility (SOC=1.2-1.7%) and high fertility (SOC>1.7%). Non-linear regression models predicted 1.9-2.2% SOC as the critical concentration range for high yields. Theoretical projections suggest that high quantities of organic materials (19-65 t ha-1) are needed every year to build SOC to critical levels. Some organic materials can be potentially applied continuously 10 to 12 times in a year such as compost, bean-trash and mucuna pruriens, and as low as 2 times for biochar.  The projections demonstrated the difficulty in restoring SOC to optimal levels due to scarcity of materials especially among the resource constrained farmers in SSA.

Soil microbial community structures and activities in relation to nitrogen cycling in two contrasting soils in Malawi – community responses to added carbon

Akane Chiba¹, Yoshitaka Uchida¹, Satoshi Ishii2, Patson Nalivata3, Keston Njira3

1 Graduate School of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan,,

2University of Minnesota, USA

3Lilongwe University of Agriculture and Natural Resources, Malawi


Fallowing is known as one of the conservative farm management techniques, which results in high crop yields and quality, potentially due to some changes in soil microbial structures and activities. However, few studies have investigated these changes in sub-Saharan Africa, where decreasing soil fertility is a serious issue. In this study, we examined the effects of different farm managements on the soil microbial community structures using soils sampled in Malawi, sub-Saharan Africa. Two sites located next to each other, within 100 m, were selected. One was the conservatively managed soil (maize after bean, followed by 1 year fallow) and another was the intensively farmed soil (maize after maize, continuous). Meanwhile, the addition of crop residues, including rice straw, is known as a technique to prevent the decrease of soil fertility. Thus, we performed incubation studies to investigate soil microbial responses of these soils to rice straw application. Changes in the bacterial diversities in these soils following the addition of rice straw were investigated with 16S rRNA gene approach on Miseq. Similar trends of nitrogen activities, such as the rapid decrease in soil NO3-N after rice straw application, were observed in the two soils. Bacterial community structural analyses suggested that the rapid increases in the ratios of Firmicutes and Betaproteobacteria to added carbon were different in the two soils. Future studies should focus more on functional genes to understand the gap between soil microbial activities and community.

Organic nitrogen drives shifts in carbon allocation at multiple levels along the plant – soil continuum

Marta Gallart1, Camila Cambui5, Peter Clinton2, Jiangming Xue2, Dean Meason3, Matthew Turnbull1, Karen Adair1,4, Jonathan Love1,5, Torgny Näsholm5

1 Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.

2 ScionResearch, P.O. Box 2923, Christchurch, New Zealand

3 ScionResearch, Private Bag 3020, Rotorua, New Zealand

4 Department of Entomology, Cornell University, Ithaca, NY 14853 United States

5 Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden


Is nitrogen just nitrogen from a plant´s perspective or does the form of nitrogen, inorganic or organic, matter? In this paper we combine data from several experiments in which the form of nitrogen (N) supplied to plant, but not the amount, was varied. We present data from a breadth of systems spanning the model plant Arabidopsis where intrinsic responses in carbon (C) allocation patterns could be observed in the absence of microbial interactions on sterile agar to pot-grown conifer trees where a DNA metabarcoding approach was used to describe the root associated microbiome. Taken together, these studies point to a fundamental difference between organic and inorganic N as nutritional sources for plants and microbes. Our results provide evidence that organic N, in contrast to inorganic N, promotes growth of roots, root hairs and mycorrhizal fungi. Biochemical shifts in C contents of shoots and roots suggest a C-bonus from organic compared to inorganic N, possibly explained by a smaller fraction of C partitioned to N assimilation.

Changes in N cycling in the rhizosphere of canola lead to decreased N requirements in a following wheat crop.

Cathryn A O’Sullivan1, Elliott G Duncan2, Kelley Whisson1, Karen Treble1, Margaret M Roper1, Mark B Peoples3.

1 CSIRO Agriculture, Private Bag 5, Wembley, WA 6913, Australia.

2 Future Industries Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095, Australia.

3 CSIRO Agriculture, Clunies Ross St, Black Mountain, ACT 2601, Australia.


Growing canola in rotations is known to increase the yield of following cereal crops. In addition to providing a disease break and better weed management, it has been suggested that following crops have lower N fertiliser requirements. The aim of this study was to confirm the lower N requirement of wheat following canola and to postulate possible mechanisms to explain this effect.

In a field study, wheat was grown under several N fertiliser levels in paddocks where either canola or wheat/pasture were grown in the previous year. In parallel, laboratory and glasshouse studies were used to examine the impact of canola  on nitrification, N mineralisation and N immobilisation rates.

Two seasons of field data in Wongan Hills, WA, and one season in Merredin, WA, showed that wheat had a lower N fertiliser requirement following canola than a wheat or pasture rotation.  In the laboratory, nitrification rates were significantly lower in the rhizosphere of canola cv. Hyola 404RR than wheat cv. Janz, while N immobilisation and remobilisation rates were significantly higher.

To explain this we hypothesise that decreased nitrification rates conserve N as NH4+ during the canola season leading to increased N immobilisation rates and an elevated organic N pool that is likely to be stored over hot and dry summers in the WA region.  this organic N pool can be remobilised providing an alternative N source for the following crop. Further study is needed to fully explore this concept.