Abstract
Reduced fertilization technology is an eco-friendly strategy to minimize nitrogen (N) and phosphorus (P) surpluses and losses in vegetable production. However, little is known about the performance of chemical fertilizer reduction when supplemented with palm silk biochar (PSB) in subtropical acid soils. A short-term (60 d) field investigation under conditions of in situ incubation was conducted in vegetable farmland in southern China. The treatments included no fertilization (Control), 100% conventional fertilization (CF100), 90% conventional fertilization plus 10% PSB-based fertilization (CF90B10), 85% conventional fertilization plus 15% PSB-based fertilization (CF85B15), and 80% conventional fertilization plus 20% PSB-based fertilization (CF80B20). The CF90B10, CF85B15, and CF80B20 treatments had the same inputs of total N and P as the CF100 treatment. Reduced chemical fertilization generally decreased the soil NH4+-N regardless of the PSB substitution rate (10%, 15%, or 20%), incubation condition (top-covered or top-open: preventing or allowing the leaching process, respectively), and sampling time (1 day or 60 days). Conversely, compared with the CF100 treatment, both the CF85B15 and CF80B20 treatments did not lead to a significant decrease in the NO3−-N concentration in soil under top-open incubation conditions, but significantly (p < 0.05) increased soil NO3−-N under top-covered incubation conditions. The CF80B20 treatment significantly (p < 0.05) decreased soil Olsen-P in comparison with the CF100 treatment, regardless of the incubation condition and sampling time. After applying chemical fertilizer in combination with PSB, soil net ammonification and N mineralization tended to be reduced considerably, with substantial reductions of 39–76% and 24–45%, respectively; reversely, soil net nitrification was stimulated by an increased PSB substitution rate. As the rate of chemical fertilization decreased, the trends in NH4+-N and NO3−-N losses from the soil were similar to the trends observed in soil net ammonification and net nitrification, respectively. Additionally, there were no significant differences in the soil net P mineralization and Olsen-P loss between chemical fertilization alone and in combination with PSB application. Generally, the partial substitution of chemical fertilizer with PSB at a low application rate may not substantially reduce plant-available NO3−-N and Olsen-P. It can also contribute to the sustainable availability of N and P in vegetable farmland soil via a variety of transformation processes, such as mineralization, immobilization, and loss.
Highlights
As the mainstay industry of agriculture in China, vegetable farming has become one major source of household income for many farmers [1]
Different to the above studies, our study showed that, during short-term in situ incubation, reduced chemical fertilization combined with palm silk biochar (PSB) application did not increase the P availability in the vegetable farmland soil compared with chemical fertilization alone, regardless of the incubation condition and sampling time (Table 4)
After 60 days of in situ incubation, the NH4+-N:Olsen-extractable phosphorus (Olsen-P) ratio significantly (p < 0.05) decreased in the PSB-based fertilization in comparison with 100% conventional fertilization (CF100) treatments under topopen and top-covered incubation conditions (O-tube and covered tube (C-tube), respectively), whereas the opposite result was obtained for the NO3−-N:Olsen-P ratio under top-covered incubation conditions (C-tube); interestingly, both of these effects were not observed for the ratios of NH4+-N:Olsen-P, NO3−-N:Olsen-P, and mineral N:Olsen-P after 1 day of in situ incubation (S-tube), largely because of no statistically significant difference in the initial soil N:P ratio between the PSB-based fertilization and CF100 treatments, and regardless of changes in the soil available N and P concentrations (Figure 5c–f, Table 4)
Summary
As the mainstay industry of agriculture in China, vegetable farming has become one major source of household income for many farmers [1]. With increasing amounts of chemical fertilizer input, the average annual input intensity of chemical fertilizer (chemical fertilizer use per unit area of planted land) has shown an increase of 12% during the past 10 years [4,5]. It has far exceeded the maximum safe ceiling of 225 kg hm−2, which was determined by developed countries to prevent chemical fertilizer from polluting water bodies
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