Silicon recycling through rice residue management does not prevent silicon depletion in paddy rice cultivation

Abstract

Silicon (Si) is known to help plants mitigate environmental stresses and nutrient deficits. In some regions, the limited plant-available Si in soils can have detrimental effects on yields. Crop residue recycling is used to maintain the amount of plant-available Si in soils. However, the effect of crop residue management practices on Si availability to plants remains largely understudied. Here, we study the effects of three different rice residue management practices on Si-depleted rice fields in northern Vietnam. These management practices were (1) the direct incorporation of rice residues into soils, (2) burning in the field, and (3) use as fodder for animals, followed by composting of the obtained manure, and subsequent application to the field. We analyzed different Si reservoirs in soils and the content of plant-Si under these different practices. Our results show correlations between plant Si content and the different soil Si reservoirs, in particular with Si trapped in soil organic material (SiOrg; R2 = 0.68, n = 18, p < 10–4). However, we found no significant difference between the three residue management practices with respect to plant-available Si in soils and to the content of plant-Si. Moreover, our data suggest that strongly Si-depleted rice-cultivation systems proportionally lose Si through grain harvesting twice as fast as less Si-depleted systems because of the enhanced relative Si accumulation in grain. This loss cannot be mitigated by the recycling of rice residues, which suggests that the recycling of rice residues has only a limited effect in extremely Si-depleted rice-cultivation systems.