Abstract
Greenhouse production can contribute to the accumulation of salt and heavy metals and nutrient imbalance, thus, increasingly degrading greenhouse soils. The potential of rice husk biochar to increase carbon sequestration, neutralize soil pH, increase nutrient retention, and change nutrient/heavy metal sorption/desorption in greenhouse soils is promising. Therefore, we investigated three greenhouse soils (red soil) with 3, 14, and 24 cultivation years (3S, 14S, and 24S) in northern Taiwan to test the effects of rice husk biochar (RHB) on carbon dynamics and nutrient availability. A 100-day incubation study was conducted in which poultry-livestock manure compost (2% by wt.) and six rice-husk-based, slow-pyrolysis biochars pyrolyzed at different temperatures were applied (0%, 0.5%, 1.0%, 4.0%, 10%, and 20% by wt.) to three red soils. The study results indicated that the RHB pyrolyzed at high temperatures, with relatively high pH and Ca content, could lead to a higher neutralizing effect when applied to the soil. In addition, the high temperatures pyrolyzed RHB had a higher capacity to reduce the concentration of Cu, Pb, and Zn in the three soils, especially for the younger cultivation soil, which contributed to the higher pH and relatively high surface area of these RHB, and the relative lower soil pH of the younger soil. Furthermore, only adding 0.5% RHB could result in an evident change in soil characteristics for 3S and 24S soil, including cumulative C release, pH, EC, TC, and available K increase, but 4% RHB addition was needed for 14S soil. In the condition of co-application with 2% compost (by wt.), 4% RHB addition was necessary for carbon sequestration, at least 10% RHB addition was needed for 3S and 14S soil, but 1.0 to 4.0% would be sufficient for 24S. In conclusion, the RHB and compost co-application in greenhouse soil resulted in improved chemical properties, and the effect of the pyrolysis temperature, application rate, and cultivation age had varying improvements.
Highlights
Greenhouse vegetable production, an intensive form of agriculture and the best structure for growing winter horticultural crops [1] and for producing fresh vegetables in the off-seasons [2], has rapidly expanded around the world in response to market demands and economic incentives [3,4].The climate in Taiwan, with >2500 mm of precipitation per year, warm (23~25 ◦ C) air temperature, and frequent disturbance by typhoons and northeastern monsoons, usually leads to the rapid decomposition of soil organic matter and organic fertilizers, extensive soil erosion, and significant nutrient loss in open-field cultivation
The study results indicated that the rice husk biochar (RHB) pyrolyzed at high temperatures, with relatively high pH and Ca content, could lead to a higher neutralizing effect when applied to the soil
We suggest that the soil buffering capacity may have prevented major changes in soil pH, and the acidification of 2% compost decomposition and nitrification may offset the neutralizing effect of RHB
Summary
September to year April), usually leads to the rapid decomposition of soil organic matter and organic fertilizers, extensive soil erosion, and significant nutrient loss in open-field cultivation. The greenhouse environment has high temperature and humidity that leads to the rapid decomposition of organic matter and release of base ions; frequent irrigation that adds salts to the greenhouse soils; a lack of leaching by natural precipitation; and upward movement of soil water. These conditions can lead to the degradation of soil quality through acidification, secondary salinization, nutrition enrichment, and nutrient imbalance [3]. Cultivation age is an important factor that affects soil physicochemical properties (organic matter and inorganic nutrients) as well as HM contamination [3,7,8,9,10]
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