African Journal of
Biotechnology

  • Abbreviation: Afr. J. Biotechnol.
  • Language: English
  • ISSN: 1684-5315
  • DOI: 10.5897/AJB
  • Start Year: 2002
  • Published Articles: 12294

Full Length Research Paper

Effects of biochar and sewage sludge on spinach (Spinacia oleracea L.) yield and soil NO3- content in texturally different soils in Glen Valley, Botswana

Ugele Majaule
  • Ugele Majaule
  • Department of Environmental Science, University of Botswana, Private Bag UB 0704, Gaborone, Botswana.
  • Google Scholar
Oagile Dikinya
  • Oagile Dikinya
  • Department of Environmental Science, University of Botswana, Private Bag UB 0704, Gaborone, Botswana.
  • Google Scholar
Baleseng Moseki
  • Baleseng Moseki
  • Department of Biological Sciences, University of Botswana, Private Bag UB 0704, Gaborone, Botswana.
  • Google Scholar
Bruno Glaser
  • Bruno Glaser
  • Martin Luther University Halle-Wittenberg, Institute of Agronomy and Nutritional Sciences, Soil Biogeochemistry, von-Seckendorff-Platz 3, 06120, Halle/Saale, Germany.
  • Google Scholar


  •  Received: 30 April 2020
  •  Accepted: 22 May 2020
  •  Published: 31 May 2020

Abstract

The effects of biochar and sewage sludge application on spinach (Spinacia oleracea L.) yield and soil NO3- content were investigated in typical soils of Botswana (Luvisol, Cambisol) under field conditions. Ten treatments with 3 levels of biochar (0, 2.5, 5 tons ha-1) and sewage sludge (0, 6, 12 ton ha-1) were applied in 2 subsequent seasons. Significant (p < 0.05) yield increase on the Luvisol occurred if sewage sludge was added at 12 Mg ha-1 with or without biochar. A combination of 6 Mg ha-1 sludge and 5 Mg ha-1 biochar application resulted in the highest crop yield over 2 seasons. On the Cambisol, only marginal yield increase occurred upon high rates of sole organic amendments and chemical fertilizer, while co-applications decreased yields. Decrease in soil NO3- content caused yield declines in the second season, while P uptake increased significantly (p < 0.05). Correlations between yields, soil NO3- and leaf N contents were insignificant (p > 0.05). On the Cambisol, a significant regression model for sludge and soil NO3- was determined. Therefore, one – time combined application of 6 Mg ha-1 sewage sludge and 5 Mg ha-1 on the Luvisol, and 12 Mg ha-1 sewage sludge are recommended for spinach production on the Luvisol and Cambisol, respectively. In subsequent seasons, crop productivity could be maintained by application of mineral N in order to mitigate over-application of P.
 
Key words: Biochar, sewage sludge, soil NO3-, luvisol, cambisol.