Effects of Crop Residues, Rice Husk Biochar, and Urea Application on Growth, Chemical Composition, and Nitrogen Use Efficiency of Spinach in a Calcareous Soil

Application of N fertilizer to soil is known as an effective practice for crop yield improvement, but its inappropriate use could result in N loss, which is important from both environmental pollution and economic feasibility standpoints. Therefore, one of the great concerns lies in finding suitable methods for effective use of N fertilizers. Research on the effects of simultaneous application of biochar, resides, and nitrogen fertilizer on plants growth and chemical composition, especially N use efficiency (NUE), is very limited. In this study, an experiment was designed according to a completely randomized factorial design, in which the treatments consisted of three levels of urea (0, 100 and 200 mg N kg-1) and four levels of biochar/residue (0, 2% biochar, 2% crop residue, and 2% biochar+crop residue) with three replication. Biochar increased the uptake and concentration of N and P in spinach shoots as compared to the control, but had not effects on the uptake of Fe, Mn, Cu and Zn. Results indicated that biochar and crop residue had a positive effect on N use efficiency, especially at 100 mg kg-1 level of urea. Results also showed that co-application of biochar and residues with urea significantly improved plant wet and dry matter yield. Due to the desirable effects of biochar and residues application on plant responses and improving nitrogen use efficiency, more attention should be paid to the use of such materials in fertilizer recommendation programs. Before making recommendations, further investigations under field conditions are crucial to verify the results of the present study.