Abstract
Irrigated urban agriculture (UA) supports the economy and health of urban inhabitants in low-income countries. This system is often characterized by high nutrient inputs and mostly utilizes wastewater for irrigation. Biochar has been proposed to increase crop yields and improve soil properties. In this study, we assessed the transient effect of rice husk biochar (20 t ha−1) and/or fertilizer (NPK: 15-15-15) on microbial respiration, microbial biomass carbon and enzyme activities of irrigated (wastewater and tap water) soil from an UA field experiment in the Guinea savannah zones of Ghana. Our results showed an increase by up to 123% in soil organic carbon (SOC) after a year of biochar application, while hot water extractable carbon (HWEC) was increased by only 11 to 26% and microbial biomass carbon (MBC) by 34%. Basal respiration was significantly increased in mineral fertilized soil by up to 46% but decreased by 12–45% under wastewater irrigation. Overall, the metabolic quotient (qCO2) indicated less stress for the microbial community and increased carbon use efficiency with biochar application and wastewater irrigation. Total enzymes activity was increased under wastewater irrigation and biochar treated soils exhibit a more diverse composition of C-cycling enzymes and a higher activity of aminopeptidases. Biochar and wastewater showed positive effects on biological soil properties and contributed to soil fertility. Our results suggest beneficial effects of biochar on non-biochar SOC stocks in the long term.
Highlights
Irrigated urban agriculture (UA) is a common phenomenon in African cities that contributes to 60–100% of the fresh vegetable supply [1]
The addition of biochar caused an increase in soil organic carbon (SOC) by up to 123% in the unfertilized treatments and 86% in the normal agricultural practices (NAP) which included NPK addition
Hot water extractable carbon (HWEC), an indicator of microbial based SOC was increased in biochar amended plots by 26% in the unfertilized soils with both irrigation water qualities
Summary
Irrigated urban agriculture (UA) is a common phenomenon in African cities that contributes to 60–100% of the fresh vegetable supply [1] It makes use of free spaces, provides income for farmer households and contributes to more diverse diets [2]. It is often characterized by excessive use of mineral or organic fertilizer, intensive continuous cropping cycles without fallow periods, production of cash crops and irrigation with untreated sewage water [3]. Soil fertility in these systems is often highly weathered and very poor. Little is known about soil biological properties and its contribution to the nutrient cycle in these agroecosystems
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