Evaluation of the mixing of sands into soils on nitrification potential from different land-use systems

- Quartz sand addition reduced the net production of NO3−-N in the three agricultural soils.
- However, the mechanisms involved in the reduction among the three agricultural soils were different.
- Quartz sand addition did not affect all gross N transformation rates in the coniferous forest soil.
- Quartz sand addition may change N transformation rates, and thus possibly alter soil nitrate leaching characteristics.

Quartz sand is often mixed with soil to enable leaching in studies where nitrate leaching is simulated. However, the addition of sand may also have an effect on the N transformations dynamics but this aspect has never been studied so far. A15N tracer experiment was conducted to investigate this effect on coniferous forest soil (CF), rice-rice rotation soil (RR), rice-wheat rotation soil (RW) and maize-wheat rotation soil (MW). Results showed that the addition of quartz sand into the three agricultural soils (RR, RW and MW) reduced the net production of NO3−-N, but the mechanisms involved in the reduction among the three soils were different. In the RR soil, the addition of quartz sand had no effect on gross NO3−-N production (autotrophic nitrification + heterotrophic nitrification), but enhanced gross NO3−-N consumption (NO3−-N immobilization + dissimilatory NO3− reduction to NH4+), resulting in reduced NO3−-N built-up. In the RW soil, the addition of quartz sand significantly inhibited gross autotrophic nitrification rates and stimulated gross NO3−-N immobilization rate. In the MW soil, only dissimilatory NO3− reduction to NH4+ (DNRA) rate was stimulated by the addition of quartz sand. In contrast, in the CF soil sand addition did not have an effect on the gross N transformation rates. Our results show that sand additions will alter N transformations dynamics in an unforeseeable manner and should be considered with the utmost caution.