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The proportion of acidic purple soils has increased. Consequently, an effective method for amelioration of acidic purple soils is urgently needed. A 40 day incubation experiment using apple tree biochar, fermented sheep manure and chicken manure was conducted to assess the effects of organic materials on the acidity and fertility of acidic purple soil. The results showed that application of organic materials increased soil pH and decreased soil-exchangeable acidity. All of the treatments increased soil-exchangeable and water-soluble base cations after incubation. Specifically, biochar increased soil pH and reduced exchangeable acidity more than the other two fermented manures, because biochar was rich in carbonates and other alkaline substances. The concentration of soil available K was significantly higher under biochar than manure addition, while the opposite was true for soil available P and N, with a higher increase in soil available P in the manure treatments. By evaluating the soil fertility using a fuzzy comprehensive method, it was found that the fermented livestock manure enhanced soil fertility more strongly than biochar. Considering the effectiveness of soil amendments and production cost, applying a large amount of fermented organic fertilizer is an effective approach to the amelioration of acidified purple soil. [ABSTRACT FROM AUTHOR]

Soil acidity is a crop production problem of increasing concern in acid red soil. The potential of biochar as a soil amendment/for soil acid management in agricultural fields is a recently recognized yet underutilized technology. Related evidence is currently limited to short-term indoor experiments with one-time BC applications and no crop cultivation, yet the degree to which soil acidity may be impacted by the biochar aging process on long-time scale remains unclear. To evaluate the effects of successive seasonal applications of rice straw-derived biochar (BC) on acidity and fertility of soil, a five-year outdoor column trial was conducted using wheat-millet rotated acidic upland soils from the south of China. BC was applied to the top 0–15 cm of soil at the rates of 0 (BC0), 2.25 (BCL), and 22.5 (BCM) Mg ha−1 with an identical dose of NPK fertilizers at the beginning of each crop season. Our results showed that the wheat-millet biomass yield gradually decreased over five rotation cycles in BC0 without BC application. In contrast, after five rotations, BCM led to an increase in the total wheat/millet grain yield by 138%, and the straw yield increased by 253% compared to the control. The cumulative above-ground nutrient uptake of P, K, Ca, Na, and Mg in BCM also increased by 139%, 171%, 129%, 182%, and 71%, respectively, compared to that in the control. This positive effect was attributed to the increase in soil pH (3.29 units), cation exchange capacity (5.66 cmol kg−1), soil available P (241%), K (513%), Ca (245%), Mg (265%), exchange base (3.36 cmol kg−1), base saturation percentage (65.7%), and decrease in the exchangeable acidity, especially exchangeable Al3+ content (<0.1 cmol kg−1). Our results demonstrated that rice straw-derived BC application to soil at 22.5 t ha−1 was found to be highly consistent in decreasing soil acidity and reducing soluble and exchangeable Al3+, indicating its higher ameliorating capacity in the south of China in the long run. [ABSTRACT FROM AUTHOR]

A serious acidification trend currently affects paddy soil and soil phosphorus (P) availability has declined in rice production. This study investigated the effect of rice-straw biochar on P availability and the adaptability of rice roots in acidified soil. Rice was grown in rhizoboxes, allowing for the precise sampling of rhizosphere and bulk soil for the sequential extraction of P fractions. Biochar may provide a liming effect and strong nutrient adsorption, leading to soil improvement. The results confirmed that biochar application significantly improved plant growth and P accumulation in shoots by 29% and 75%, respectively. However, the application of washed biochar and equivalent lime only increased shoot biomass and P accumulation by 13.4% and 11.2%, and by 42% and 38%, respectively. Compared with the control, applying biochar increased the plant-available P component contents in rhizosphere and bulk soil. Biochar affected the chemical balance among the different P fractions, increased aluminum-bound phosphate (Al-P) pool, calcium-bound phosphate (Ca-P) pool and decreased the occluded phosphate pool in acidic paddy soil. Biochar amendment significantly improved root growth of and increased the citrate exudation from roots under low P supply, accompanied by the enhanced expression of the anion-transporter-related OsFRDL4 gene and the OsPT1 phosphate transporter. The results showed that biochar application in degraded acidic soils could improve rice potential for P acquisition to increase available P component and maintain high citrate exudation. [ABSTRACT FROM AUTHOR]

Soil pollution by trace elements is a huge problem around the globe. In addition, heavy metal immobilization and primary productivity are two soil ecosystem services of contemporary importance to society. The goal of this study was to evaluate the effects of using olive pit and rice husk biochars as soil amendments for the immobilization of trace elements and on plant development growing in heavy metals-polluted soils under greenhouse conditions. The application of high doses (5% and 10%) of biochar significantly increased pH, water holding capacity and total C content of the soils. Dehydrogenase activity in the moderately acidic soil was greater than in the acidic soil due to the high concentration of metals and high acidity of the latter. The application of biochar reduced the β–glucosidase activity. Furthermore, the concentrations of CaCl2-extractable heavy metals significantly decreased in biochar amended pots, indicating metal immobilization, which was consistent with the increase in soil pH. Distribution of trace elements in the different fractions was modified after 65 days of incubation, independently of the treatment. The Cu and Zn contents in the oxidizable fraction were reduced with incubation, whereas Cd and Zn in the residual fraction increased. The reduction of bioavailable concentrations and increments in the residual or more stable fractions indicated less risk for the organisms in the environment. All biochars addition significantly increased the root-to-shoot ratio compared to the control soil. Particularly, 10% of amendment increased this ratio in the greatest extent. The application of 10% w/w of rice husk biochar produced at 500 °C was the most effective in restoring soil functionality and reducing the availability of heavy metals in the polluted soils. [ABSTRACT FROM AUTHOR]

Nowadays, biochar is increasingly used widely as an important soil amendment to enhance soil nutrients availability. Therefore, we investigated the effect of C.oleifera shell biochar (CSB) on C.oleifera plantation soils to provide evidence that C. oleifera shell as a raw material in biochar has great potential to be a soil amendment. For this, a short-term incubation experiment was conducted in controlled conditions to evaluate the effects of CSB application on two soil chemical properties, microbial biomass, and enzymatic activity. We compared two acidic soils, mixed with CSB of three pyrolysis temperatures (300, 500, and 700 °C), and two application rates (3% and 5% (w/w)), incubated for 180 days. The results showed that the soil pH, total P (TP), and available P (AP) significantly increased under 5CSB700 in two soils, and indicated CSB application rate and pyrolysis temperature had a significant impact on soil pH, TP, and AP (p < 0.05). CSB application also significantly increased the total inorganic P in two soils and presented a significantly positive correlation with soil pH, TP, and AP under redundancy analysis. The results suggested that CSB application has a variable effect on soil enzymatic activity, microbial biomass C (MBC), and microbial biomass P (MBP) on average, while it increased the soil microbial biomass N (MBN) in both soils. We concluded that CSB could be a soil amendment to increase soil nutrients of C.oleifera plantation soils. Before the application of biochar to C.oleifera plantation forest soils, long-term studies are required to assess the effects of biochar under field conditions and its promoting effect on the growth of C. oleifera. [ABSTRACT FROM AUTHOR]