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

Authors

• Ugele Majaule * ¹
• Oagile Dikinya ²
• Bruno Glaser ³

1. Department of Agricultural Research, Ministry of Agriculture Development and Food Security, Gaborone, Botswana
2. Department of Environmental Science, University of Botswana, Gaborone, Botswana
3. Soil Biogeochemistry, Institute of Agronomy and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle/Saale, Germany

Abstract

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 (0, 2.5 and 5 Mg ha^-1) and sewage sludge (0, 6 and 12 Mg ha^-1), or mineral fertilizer (200, 28, and 18.9 kg ha^-1), amended in a randomized complete block design to Luvisol and Cambisol.
Results Significant (p < 0.05) yield increase of 53 and 65%, 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 < 0.05) yields on the Luvisol over two seasons. Complimentary effects of 6SS+5BC on the Luvisol showed the highest yield increase for the study period. Co-application of amendments on the Cambisol decreased (p > 0.05) yields compared to sole amendments. Mehlich – 3 extractable P (M3-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 M3-P increase over mineral fertilizer than on the Luvisol in both seasons. Accumulation of M3-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 M3-P between seasons warrants further research.

Highlights

• Plant available P increased across treatments in the second season suggestive of P enrichment from the irrigation wastewater.
• Plant leaf P increased between seasons, while organic amendments had similar or greater effects on P uptake relative to mineral fertilizer.
• Increasing dosage of sole biochar markedly increased plant available P than sewage sludge.
• Amendments improved CEC, Ca and Mg bioavailability.
• Co-application had greater effects on improving P bioavailability and crop yields on the Luvisol compared to the Cambisol.

Keywords

• Co-Application
• Phosphorus
• Spinach
• Yield
• Bioavailability