Biochar and sewage sludge phosphorus fertilizer effects on phosphorus bioavailability and spinach ( Spinacia oleracea L.) yields under no-till system in semi-arid soils

Purpose This field study evaluated the interactive effects of biochar (BC) and sewage sludge (SS) on P bioavailability and spinach yields for two seasons.Method Treatments were combinations of biochar (۰, ۲.۵ and ۵ Mg ha-۱) and sewage sludge (۰, ۶ and ۱۲ Mg ha-۱), or mineral fertilizer (۲۰۰, ۲۸, and ۱۸.۹ kg ha-۱), amended in a randomized complete block design to Luvisol and Cambisol.Results Significant (p < ۰.۰۵) yield increase of ۵۳ and ۶۵%, respectively occurred with increasing sole biochar doses on the Luvisol. Both applied alone and in combination with BC, the high rate of SS increased (p < ۰.۰۵) yields on the Luvisol over two seasons. Complimentary effects of ۶SS+۵BC on the Luvisol showed the highest yield increase for the study period. Co-application of amendments on the Cambisol decreased (p > ۰.۰۵) yields compared to sole amendments. Mehlich – ۳ extractable P (M۳-P) in control plots (CONT) increased between seasons, presumably due to P inputs from the irrigation water. Co-amendments on the Cambisol resulted in higher M۳-P increase over mineral fertilizer than on the Luvisol in both seasons. Accumulation of M۳-P in control plots confounded correlations between crop yields and available P. Higher P under BC compared to SS amended soils emphasize biochar capacity to capture P from irrigation water.Conclusion The results suggest that combined low rates of SS and BC can have significant effects on P availability and crop yields. Biochar enhanced plant P uptake, but decrease in yields with simultaneous increase in M۳-P between seasons warrants further research.

Keywords:

Co-Application , bioavailability , phosphorus , spinach , Yield