BUSCADOR RECOLECTA

Background and aims: Sorghum (Sorghum bicolor) is able to exude allelochemicals with biological nitrifcation inhibition (BNI) capacity. Therefore, sorghum might be an option as cover crop since its BNI ability may reduce N pollution in the following crop due to a decreased nitrifcation. However, BNI exudation is related to the physiological state and development of the plant, so abiotic stresses such as drought might modify the rate of BNI exudation. Hence, the objective was to determine the efect of drought stress on sorghum plants’ BNI release. Methods: The residual efects of sorghum crops over ammonia-oxidizing bacteria (AOB) were monitored in a 3-year feld experiment. In a controlled-conditions experiment, sorghum plants were grown under Watered (60% WFPS) or Moderate drought (30% WFPS) conditions, and fertilized with ammonium sulphate (A), ammonium sulphate+DMPP (A+D), or potassium nitrate (KNO3 −). Soil mineral N was determined, and AOB populations were quantifed. Additionally, plant biomass, isotopic discrimination of N and C, and photosynthetic parameters were measured in sorghum plants. Results: In the driest year, sorghum was able to reduce the AOB relative abundance by 50% at feld conditions. In the plant-soil microcosm, drought stress reduced leaf photosynthetic parameters, which had an impact on plant biomass. Under these conditions, sorghum plants exposed to Moderate drought reduced the AOB abundance of A treatment by 25% compared to Watered treatment. Conclusion: The release of BNI by sorghum under limited water conditions might ensure high soil NH4 +-N pool for crop uptake due to a reduction of nitrifying microorganisms., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This project was funded by the Spanish Government (RTI2018-094623-B-C21 and C22 MCIU/AEI/FEDER, UE) and by the Basque Government (IT-932-16; IT-1560-22). Dr Adrián Bozal-Leorri held a grant from the Basque Government (PRE-2020-2-0142). Dr. Fernando Torralbo was supported by the European Union – Next Generation EU program. Authors thank the Jesus de Gangoiti Barrera Foundation for the financial support.

Nitrification inhibitors (NIs) are useful tools to reduce nitrogen (N) losses derived from fertilization in agriculture. However, it remains unclear whether a future climate scenario with elevated CO2 could affect NIs efficiency. Thus, the objective of this work was to study whether the increase of atmospheric CO2 concentration would affect the efficiency of two dimethylpyrazole-based NIs: 3,4-dimethylpyrazol phosphate (DMPP) and 3,4-dimethylpyrazol succinic acid (DMPSA) in a plant-soil microcosm. To do so, Hordeum vulgare var. Henley plants were grown in soil fertilized with ammonium sulphate (AS) with or without NIs under controlled environmental conditions at ambient CO2 (aCO(2)) or elevated CO2 (eCO(2); 700 ppm). In the soil, mineral nitrogen and N2O emission evolution were monitored together with nitrifying and denitrifying population that were quantified by qPCR. In the plant, biomass, total amino acid content and isotopic discrimination of N and C were measured. Both NIs showed greater efficiency to maintain soil NH4+ content under eCO(2) compared to aCO(2), as a consequence of 80% reduction of AOB abundance in eCO(2). Indeed, both inhibitors were able to lessen 53% the N2O emissions in eCO(2) compared to aCO(2). Regarding the plant, DMPP and DMPSA negatively affected plant biomass at aCO(2) but this effect was restored at eCO(2) due to a better ammonium tolerance associated with an increase in total amino acid content. Overall, DMPP and DMPSA NIs were highly efficient under eCO(2), reducing N2O emissions and keeping N in the soil stable for longer while maintaining plant biomass production., This project was funded by the Spanish Government (RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE) and by the Basque Government (IT-932-16). Adrian Bozal-Leorri holds a grant from the Basque Government. Mario Corrochano-Monsalve holds a grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725).

Agriculture has increased the release of reactive nitrogen to the environment due to
crops’ low nitrogen-use efficiency (NUE) after the application of nitrogen-fertilisers. Practices like the use of stabilized-fertilisers with nitrification inhibitors such as DMPP (3,4-
dimethylpyrazole phosphate) have been adopted to reduce nitrogen losses. Otherwise, cover
crops can be used in crop-rotation-strategies to reduce soil nitrogen pollution and benefit
the following culture. Sorghum (Sorghum bicolor) could be a good candidate as it is drought
tolerant and its culture can reduce nitrogen losses derived from nitrification because it exudates biological nitrification inhibitors (BNIs). This work aimed to evaluate the effect of
fallow-wheat and sorghum cover crop-wheat rotations on N2O emissions and the grain
yield of winter wheat crop. In addition, the suitability of DMPP addition was also analyzed.
The use of sorghum as a cover crop might not be a suitable option to mitigate nitrogen
losses in the subsequent crop. Although sorghum–wheat rotation was able to reduce 22%
the abundance of amoA, it presented an increment of 77% in cumulative N2O emissions
compared to fallow–wheat rotation, which was probably related to a greater abundance of
heterotrophic-denitrification genes. On the other hand,the application of DMPP avoided the
growth of ammonia-oxidizing bacteria and maintained the N2O emissions at the levels of
unfertilized-soils in both rotations. As a conclusion, the use of DMPP would be recommendable regardless of the rotation since it maintains NH4
+ in the soil for longer and mitigates
the impact of the crop residues on nitrogen soil dynamics, This work was supported by the Spanish Government (RTI2018-094623-B-C21 and C22 MCIU/AEI/FEDER, UE) and the Basque Government (IT-932-16). Dr. Adrián Bozal-Leorri held a grant from the Basque Government (PRE-2020-2-0142). Dr. Mario Corrochano-Monsalve held a grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725).

Background: Agriculture relies on the intensive use of synthetic nitrogen (N) fertilizers to maximize crop yields,
which has led to the transformation of agricultural soils into high-nitrifying environments. Nevertheless, nitrifcation
inhibitors (NIs) have been developed to suppress soil-nitrifer activity and decrease N losses. The NIs 3,4-dimethyl‑
pyrazole phosphate (DMPP) and 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA) are able to
reduce N2O emissions and maintain soil NH4
+ for a longer time. Although both NIs have been proven to be efective
to inhibit soil nitrifcation, their exact mode of action has not been confrmed. We aimed to provide novel insights to
further understand the mode of action of DMP-based NIs. We evaluated the performance of DMPP and DMPSA in soil
and pure cultures of nitrifying bacteria Nitrosomonas europaea.
Results: DMPSA did not inhibit nitrifcation in pure cultures of N. europaea. In the soil, we evidenced that DMPSA
needs to be broken into DMP to achieve the inhibition of nitrifcation, which is mediated by a soil biological process
that remains to be identifed. Moreover, both DMPP and DMPSA are thought to inhibit nitrifcation due to their ability
to chelate the Cu2+ cations that the ammonia monooxygenase enzyme (AMO) needs to carry on the frst step of
NH4
+ oxidation. However, the efciency of DMPP was not altered regardless the Cu2+ concentration in the medium.
In addition, we also showed that DMPP targets AMO but not hydroxylamine oxidoreductase enzyme (HAO).
Conclusions: The inability of DMPSA to inhibit nitrifcation in pure cultures together with the high efciency of
DMPP to inhibit nitrifcation even in presence of toxic Cu2+ concentration in the medium, suggest that the mode of
action of DMP-based NIs does not rely on their capacity as metal chelators., This project was funded by the Spanish Government (RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE), by the Basque Government (IT-932-16), and by EuroChem Agro Iberia S.L.U. Dr. Adrián Bozal-Leorri held a grant from the Basque Government (PRE-2020-2-0142).