Disentangling the effects of rice husk ash on increased plant growth and nitrogen recovery

Abstract

Rice production generates large quantities of residues, whose disposal can pose environmental and health risks when not managed properly. The residue after rice husk combustion for energy production, rice husk ash (RHA), is currently underutilized despite its great potential as a soil conditioner. We aim to test the impact of RHA application on wheat growth, functional characteristics of the soil nitrifiers community and on N recovery using a 15N tracing greenhouse experiment. To distinguish between the effects caused by its liming capacity and P content, liming and P application treatments were included in the experiment. The amelioration of soil acidity (by both lime and RHA) lead to reduced losses of applied N fertilizer, but only RHA improved plant growth and plant N uptake. On the other hand, unlike RHA, lime application had strong effect on nitrification, increasing the potential maximal nitrification capacity (NEA) and reducing the affinity for N-NH4+ of soil nitrifiers (NHScom). The application of P reduced losses of applied 15N fertilizer particularly in the control pots, where additional P supply was likely critical to enhance N utilization by soil microorganisms. We therefore conclude that RHA effects on studied parameters are not only caused by soil pH amelioration nor by the P supply, but are likely driven by other inherent RHA properties (such as for instance its high content of macro- and micronutrients). The lack of observed effects on nitrification parameters and enhanced plant growth after RHA application can lead to considerably lower N losses and higher C sequestration in comparison to liming, while helping to solve the problems linked with RHA disposal.