Crop growth is limited by the nitrogen availability in the soil, one of the primary elements of plants, the deficiency of which leads to a fall in agricultural yield. So nitrogen needs to be added to the soil in the form of nitrogen fertilizers. Yet this nitrogen that is applied may not be efficiently used by the crop. This fact not only leads to significant economic losses for the farming sector, it causes environmental problems, such as water eutrophication due to nitrate leaching, ammonia volatilization, and production of nitrogen oxide (nitric oxide and nitrous oxide) produced by the micro-organisms in the soil. The emission of nitrous oxide (N2O) is hugely significant, as it is a greenhouse gas with a global warming potential 265 times higher than that of CO2.

In order to mitigate these nitrogen losses in agriculture, “agronomic research has to focus on optimizing the use of nitrogen fertilizers by developing better farming practices that will not only help to prevent leaching and gaseous losses but also to obtain maximum crop yield and quality”, explained the PhD student and one of the researchers in the NUMAPS (NUtrition MAnagement in Plant and Soil) group of the UPV/EHU. In this respect, the researchers have conducted a study “focussing on the use of nitrification inhibitors”. Inhibitors of this type slow down the activity of certain bacteria that inhabit agricultural soils and which use the ammoniacal nitrogen provided by the fertilizers for their own growth, thus competing with the plant crop for it. “The use of inhibitors enables the plant to have more time to absorb nitrogen from the soil and assimilate it in the form of amino acids and proteins, thus reducing its loss in the form of nitrates or nitrogen gases,” explained the researcher.

Towards efficient agriculture

The group conducted a field experiment “to see the effect of using an ammoniacal fertilizer combined with a type of nitrification inhibitor (3,4-dimethylpyrazole-succinic acid DMPSA) on two crop management systems:  conventional tillage (deep furrows with mouldboard) and minimum tillage (minimum ploughing, the seeds being sown in small holes)”, as Corrochano-Monsalve described.  The plots were exhaustively monitored, since, as the researcher specified, “on each plot we measured the wheat yield, its quality as bread flour, the evolution in soil nitrogen content and greenhouse gas emissions (GHG) (CO2, N2O and CH4) of the cultivated soil; the genetic indicators of the variation of bacteria populations in the soil responsible for nitrogen oxidation/reduction and therefore its emission as GHG were also analysed”.

The main conclusion of the study is that “the use of the nitrification inhibitor in combination with minimum tillage improved crop efficiency, and reduced the GHG emission without affecting yield,” explained Corrochano-Monsalve. “The most novel aspect of the work is the confirmation that the use of nitrification inhibitors on crops with a minimum tillage system encourages the growth of certain bacteria populations that reduce the N2O to molecular nitrogen (N2), the most abundant form and which does not react with the nitrogen in the atmosphere. That way the loss of nitrogen in the form of gas would be harmless”. In humid Mediterranean climate conditions, like that of Álava, where the study was conducted, “in many phases of the crop cycle we find high levels of soil humidity that may increase nitrogen losses through leaching. Yet the high degree of humidity also generates a highly anaerobic environment that encourages the reduction of N oxides to N2”, he added. The use of nitrification inhibitors can be expected to enable a smaller amount of fertilizer to be applied, which besides a reducing the environmental impact, would lead to economic savings for farmers.”

“Agriculture, just like many other sectors, has to be more and more efficient. It is about achieving sustainable agriculture that combines food security (food for everyone) with the minimum environmental impact,” he concluded. Until now, general recommendations have tended to be made for each geographical area (amount of fertilizer, chemical formulation, when and how to apply it, type of plant protection products, etc.). However, the ideal thing and which is a growing trend is to customise the recommendations much more.  In other words, even each plot within a single geographical area has its unique features, and the ideal thing would be before the start of a growing season for each plot to be analysed beforehand to determine exactly what its needs are and thus prevent the wasting of resources”.

Additional information

This research comes within the framework of the PhD thesis by Mario Corrochano-Monsalve, researcher in the NUMAPS research group of the UPV/EHU’s Department of Plant Biology and Ecology. The nitrification inhibitor used for the study is a blend of isomers of 2-(3,4-dimethyl-1H-pyrazole-1-YL) succinic acid (DMPSA), produced by the company Eurochem Agro Iberia SL. The experimental farms used in this study are located in Arkaute (Álava) (collaboration with Neiker-Tecnalia).