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). 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.
Highlights
Soil fertilization with sewage sludge is an effective way to recycle nutrients and combat nutrient deficiency in agricultural systems (Sharma et al, 2017)
Except for application of low rate of sole sewage sludge (6SS), organic amendments significantly (p < 0.05) increased NO3- on the Luvisol while the effects were insignificant on the Cambisol during the first season
The highest NO3levels during this season were caused by co-application of 6 Mg ha-1 sewage sludge and 5 Mg ha-1 biochar on the Luvisol (19.6 mg kg-1) while on the Cambisol, sole sewage sludge application at 12 Mg ha-1 gave the highest NO3- level (15.1 mg kg-1), which coincided with the highest spinach yields for the respective soils
Summary
Soil fertilization with sewage sludge is an effective way to recycle nutrients and combat nutrient deficiency in agricultural systems (Sharma et al, 2017). Many studies have reported high spinach yield response to mineral fertilizers and sewage sludge applications Et al, 1996; Wang and Li, 2004; Lefsrud et al, 2007; Stagnari et al, 2007; Rodríguez‐Hidalgo et al, 2010; Türkmen* et al, 2004). These studies showed that adequate N availability from sewage sludge is critical for high quality and yields of spinach. When contents of heavy metals, pathogens, and toxic organic compounds in sludge are within the WHO limits, such as the case for the Glen Valley sludge (Ngole, 2010; Mosekiemang and Dikinya, 2012), application rates of sludge to agricultural soils is based on the crop nitrogen (N) demand (Gilmour and Skinner, 1999; Correa et al, 2006)
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