Abstract
Replacing chemical fertilizers with human waste for vegetable planting is a traditional, economical, and environmentally friendly waste resource utilization strategy. However, whether the human waste substitute strategy can improve soil fertility and increase crop yield and quality compared to the simple application of chemical fertilizers is still unclear, especially under acidic and alkaline soil conditions. In this study, we studied the effects of different ratios of human waste (urine and feces) to chemical fertilizer on the crop yield, crop quality, soil fertility, and soil chemical parameters in alkaline Cambisols and acidic Alisols cultivated with water spinach (Ipomoea aquatica Forssk.). The application variants of human waste and chemical fertilizer were as follows: (i) Control, no fertilization (CK), (ii) human waste application (HW), (iii) chemical fertilizer application (CF), (iv) 1/3 human waste to chemical fertilizer (P1), and (v) 2/3 human waste to chemical fertilizer (P2). Human waste application increased the total nitrogen, available phosphorus, available potassium, organic matter, NO3−-N, and conductivity in soil, enhanced soil enzyme activity, slowed down soil acidification, and increased the yield, soluble sugar, and vitamin C contents of the water spinach while reducing its nitrate content. Our findings indicate that human waste substitution improved soil fertility while reducing the potential risks of soil acidification, salinization, and human exposure to nitrates. These findings may be applied to increase vegetable production and quality, improve the soil environment, and increase the utilization of human waste as a valuable resource.
Highlights
The types of toilets being promoted in the rural toilet renovation project in China include a three-compartment septic tank, double-vault funnel, double-pit alternate, biogaslinked, urine–feces division, and integrated flushing toilet [1]
Our results show that human waste and chemical fertilizer altered the chemical properties of the soil, pH, electrical conductivity (EC), available phosphorus (AP), and AK
From the two-dimensional sequence diagram (Figure 3A) of soil enzyme activity and chemical properties of Cambisols, we found that the arrow lines of pH, NO3−-N, NH4+-N, total nitrogen (TN), and C/N were the longest, indicating that these chemical properties played a better role in explaining soil enzyme activities than others
Summary
The types of toilets being promoted in the rural toilet renovation project in China include a three-compartment septic tank, double-vault funnel, double-pit alternate, biogaslinked, urine–feces division, and integrated flushing toilet [1]. The threecompartment septic tank toilet has become the most popular In this toilet, human waste (urine and feces) enters a three-compartment septic tank where it is stored in the third tank after anaerobic fermentation and static separation and collected by the feces collection truck for centralized processing [2]. Human waste (urine and feces) enters a three-compartment septic tank where it is stored in the third tank after anaerobic fermentation and static separation and collected by the feces collection truck for centralized processing [2] This type of toilet has been widely promoted in rural areas of China. With the increasing population and the increasing use of threecompartment septic tank toilets, the amount of human waste is increasing [3], as are the costs and demand for centralized disposal. There is an urgent need to develop economical and environmentally sound techniques for human waste disposal
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