Nitrogen budget and barley response to organic amendments in a sandy soil under simulated arid climate

Besides their potential for carbon sequestration, compost and biochar application in agriculture may constitute an alternative to mineral fertilizers by improving soil fertility and productivity in carbon-poor soils. This study focused on the impact of biochar and compost produced from date palm residues on nitrogen (N) leaching and plant uptake in a sandy soil cultivated with barley under arid climatic conditions. In addition to the unamended control soil (S), treatments with biochar (BC), urea (U), biochar + urea (BCU), compost (C) and biochar + compost (BCC) were tested. We followed soil fertility parameters, N leaching losses, N uptake and plant growth. Results showed a significant increase of barley yields with compost compared to urea (+66%) treatment (U), biochar amended (BC) and unamended soil (S). Biochar alone or co-applied with a nutrient source seems to reduce barley shoot biomass and grain yields at short term. Leachate N recovery and soil extractable inorganic N at the end of barley cultivation indicated that compost did not provide N in excess at barley maturation stage. Compost amended soils led to the highest N losses through leaching and thus environmental risk of N vertical transfer. However, compost had positive effects on soil nutrient status and barley yields. No synergistic effect was observed between biochar and compost. In conclusion, this paper highlights that date palm compost improved barley productivity in a coarse-textured soil, but with very short-term effects concerning available soil N.