Abstract
BackgroundThe increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution. Nowadays, agricultural soils have been turned into high-nitrifying environments that increase N pollution. To decrease N losses, synthetic nitrification inhibitors (SNIs) such as 3,4-dimethylpyrazole phosphate (DMPP) have been developed. However, SNIs are not widely adopted by farmers due to their biologically limited stability and soil mobility. On the other hand, allelopathic substances from root exudates from crops such as sorghum are known for their activity as biological nitrification inhibitors (BNIs). These substances are released directly into the rhizosphere. Nevertheless, BNI exudation could be modified or even suppressed if crop development is affected. In this work, we compare the performance of biological (sorghum crop) and synthetic (DMPP) nitrification inhibitors in field conditions.ResultsSorghum crop BNIs and DMPP prevented an increase in the abundance of ammonia-oxidizing bacteria (AOB) without affecting the total bacterial abundance. Both nitrification inhibitors maintained similar soil NH4+ content, but at 30 days post-fertilization (DPF), the sorghum BNIs resulted in higher soil NO3− content than DMPP. Even so, these inhibitors managed to reduce 64% and 96%, respectively, of the NO3−-N/NH4+-N ratio compared to the control treatment. Similar to soil mineral N, there were no differences in leaf δ15N values between the two nitrification inhibitors, yet at 30 DPF, δ15N values from sorghum BNI were more positive than those of DMPP. N2O emissions from DMPP-treated soil were low throughout the experiment. Nevertheless, while sorghum BNIs also maintained low N2O emissions, they were associated with a substantial N2O emission peak at 3 DPF that lasted until 7 DPF.ConclusionsOur results indicate that while sorghum root exudates can reduce nitrification in field soil, even at the same efficiency as DMPP for a certain amount of time, they are not able to prevent the N pollution derived from N fertilization as DMPP does during the entire experiment.Graphic
Highlights
The increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution
biological nitrification inhibitor (BNI) from sorghum were able to prevent an increase in amoA after N fertilization with the same efficiency as dimethylpyrazole phosphate (DMPP)
Sorghum root exudates could not prevent the appearance of soil NO3− after 20 days post-fertilization (DPF), which might indicate that the BNI effect decreases in efficiency after a certain amount of time
Summary
The increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution. Allelopathic substances from root exudates from crops such as sorghum are known for their activity as biological nitrification inhibitors (BNIs). These substances are released directly into the rhizosphere. More than 80% of the hydrophobic component of sorghum-exuded BNIs is sorgoleone [11], while MHPP comprises the hydrophilic component Both molecules can reduce nitrification in soil [12, 13]. Subbarao et al [14] characterize the BNI activity from MHPP and sorgoleone in the soil Once these molecules are released from sorghum roots, their nitrification inhibitory action seems to be relatively stable over a pH range of 3.0 to 9.0. The inhibitory effect on soil nitrification of MHPP and sorgoleone appears to be stable in the temperature range of 20 to 30 °C
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