Soil Nitrification Rate is Affected by Plant Species and Nitrogen Levels

The soil nitrification rate is significantly affected by plant species, and it is also modulated by different nitrogen levels in the soil. There are a wide range of plant species with the capacity to produce biological nitrification inhibitors (hereafter referred to as BNI species). The preliminary results of this study report the influence of three different plant species on the nitrification rates under soil supply with three (0 mM, 3.5 mM, and 7.0 mM) nitrogen levels. The aim was to evaluate the potential of hemp, ryegrass, and sorghum in mitigating nitrification, in order to define a sustainable strategy for improving the nitrogen use efficiency by crops and to limit the nitrogen loss from agroecosystems. Leaf gas exchange measurements were also carried out in this study. Photosynthesis was only affected by nitrogen supply in hemp, resulting in a reduction in CO2 assimilation at nitrogen doses higher than the plant’s requirements. Ryegrass devotes more reductive power towards leaf nitrogen assimilation than sorghum and hemp do. The greatest variation in nitrification rate in response to N was observed in soil cultivated with hemp (which also showed the highest potential nitrification rate), followed by sorghum and ryegrass. We speculate that this occurred because the greater seed sowing density for ryegrass ensured a greater quantity in the soil of molecules acting on nitrification compared to sorghum and hemp, with these latter being sown at lower densities. Our results suggest that sorghum and ryegrass might directly affect nitrification by BNI molecules, whereas hemp might indirectly mitigate nitrification through the nitrogen uptake. However, further research is needed to evaluate the effects exerted by the studied plant species on nitrification rates.