Pedological Characteristics and Heavy Metals Contamination of the Paddy Soils in Taiwan

Extensive rice production on numerous alluviums and terraces in Taiwan has been done by the complete irrigation systems since the early and mid stages of the 20th century. Irrigation water and the fluctuation of groundwater play important roles in controlling the soil hydrology and redoximorphology. Redoximorphic features are consequently formed by the alternative wet and dry cycles, such as Fe soft masses, Fe and clay depletions and Fe-Mn nodules through the profiles of paddy soils. The saturated and reducing durations were specified associated with the definite redoximorphic features in the soils under a landscape unit. In the case studies of rice-growing Ultisols on red earth terrace in northwestern Taiwan, the optimum durations of saturation and reduction were about 50% of the year in the formation of redoxi-morphic features. This anthraquic condition could promote the formation of diverse redoximorphic features associated with plinthites. In the paddy soils of Taiwan, Entisols, Inceptisols, Alfisols, Ultisols, Mollisols and Oxisols are main Soil Orders based on Soil Taxonomy. On one hand considering by soil quality and food security of rice, heavy metal contamination is the main issue in rice production of Taiwan. On the other hand by rice market liberalization, changing the land use from paddy soils into non-waterlogged cropping has some problems in initial soil properties such as poor drainage and impeded root growth by the subsurface compacted layers for upland crops. Irrigation water for rice production in Taiwan has been contaminated by illegal discharges of industrial and livestock wastewater affecting the paddy soil qualities by heavy metals. According to the regulation for pollutants in Soil and Groundwater Pollution Remediation Act of Taiwan, the total seriously contaminated area by heavy metals is more than 300ha, especially by Cd, Cr, Cu, Ni and Pb contamination of rice in Taiwan. Due to the special profile morphology and hydrology of paddy soils, dilution by deep plowing and mixing, acid washing, chemical stabilization, and phytoremediation are major remediation technologies applied on the contaminated sites with pilot or field scales. However, the recovery of soil fertilities and ecological functions is needed to be evaluated after remediation.Special Revie

Impacts of Biochar on Physical Properties and Erosion Potential of a Mudstone Slopeland Soil

Food demand and soil sustainability have become urgent issues recently because of the global climate changes. This study aims to evaluate the application of a biochar produced by rice hull, on changes of physiochemical characteristics and erosion potential of a degraded slopeland soil. Rice hull biochar pyrolized at 400°C was incorporated into the soil at rates of 2.5%, 5%, and 10% (w/w) and was incubated for 168 d in this study. The results indicated that biochar application reduced the Bd by 12% to 25% and the PR by 57% to 92% after incubation, compared with the control. Besides, porosity and aggregate size increased by 16% to 22% and by 0.59 to 0.94 mm, respectively. The results presented that available water contents significantly increased in the amended soils by 18% to 89% because of the obvious increase of micropores. The water conductivity of the biochar-amended soils was only found in 10% biochar treatment, which might result from significant increase of macropores and reduction of soil strength (Bd and PR). During a simulated rainfall event, soil loss contents significantly decreased by 35% to 90% in the biochar-amended soils. In conclusion, biochar application could availably raise soil quality and physical properties for tilth increasing in the degraded mudstone soil

Sequestration of P fractions in the soils of an incipient ferralisation chronosequence on a humid tropical volcanic island

Background: Phosphorus (P) is the limiting nutrient in many mature tropical forests. The ecological significance of declining P stocks as soils age is exacerbated by much of the remaining P being progressively sequestered. However, the details of how and where P is sequestered during the ageing in tropical forest soils remains unclear. Results: We examined the relationships between various forms of the Fe and Al sesquioxides and the Hedley fractions of P in soils of an incipient ferralitic chronosequence on an altitudinal series of gently sloping benches on Green Island, off the southeastern coast of Taiwan. These soils contain limited amounts of easily exchangeable P. Of the sesquioxide variables, only Fe and Al crystallinities increased significantly with bench altitude/soil age, indicating that the ferralisation trend is weak. The bulk of the soil P was in the NaOH and residual extractable fractions, and of low lability. The P fractions that correlated best with the sesquioxides were the organic components of the NaHCO3 and NaOH extracts. Conclusions: The amorphous sesquioxides, Feo and Alo, were the forms that correlated best with the P fractions. A substantial proportion of the labile P appears to be organic and to be associated with Alo in organic-aluminium complexes. The progression of P sequestration appears to be slightly slower than the chemical and mineralogical indicators of ferralisation

Molecular signature of clinical severity in recovering patients with severe acute respiratory syndrome coronavirus (SARS-CoV)

BACKGROUND: Severe acute respiratory syndrome (SARS), a recent epidemic human disease, is caused by a novel coronavirus (SARS-CoV). First reported in Asia, SARS quickly spread worldwide through international travelling. As of July 2003, the World Health Organization reported a total of 8,437 people afflicted with SARS with a 9.6% mortality rate. Although immunopathological damages may account for the severity of respiratory distress, little is known about how the genome-wide gene expression of the host changes under the attack of SARS-CoV. RESULTS: Based on changes in gene expression of peripheral blood, we identified 52 signature genes that accurately discriminated acute SARS patients from non-SARS controls. While a general suppression of gene expression predominated in SARS-infected blood, several genes including those involved in innate immunity, such as defensins and eosinophil-derived neurotoxin, were upregulated. Instead of employing clustering methods, we ranked the severity of recovering SARS patients by generalized associate plots (GAP) according to the expression profiles of 52 signature genes. Through this method, we discovered a smooth transition pattern of severity from normal controls to acute SARS patients. The rank of SARS severity was significantly correlated with the recovery period (in days) and with the clinical pulmonary infection score. CONCLUSION: The use of the GAP approach has proved useful in analyzing the complexity and continuity of biological systems. The severity rank derived from the global expression profile of significantly regulated genes in patients may be useful for further elucidating the pathophysiology of their disease

Identification of the Redoximorphic Features and Formation Mechanism of Fe-Mn Nodules in Ultisols with Plinthite under Different Moisture Regime in Chungli Terrace

鐵錳聚積物 (例如鐵錳軟團塊、鐵錳結核)於含鐵網紋 (plinthite)極育土中為一明顯的形態特徵。鐵錳聚積物的生成與水文狀況關係密切，諸如季節性地下水位的變動或表面灌溉水的灌排都將影響土壤中元素的重新分佈或氧化還原形態特徵上的變化。本研究在桃園中壢臺地上，針對不同水分境況且不同形態特徵之土壤，探討其氧化還原形態特徵之鑑定方法及鐵錳結核生成與當地水文狀況之關係並且推論鐵錳結核生成機制。 本研究選定桃園中壢臺地上之三種不同水分境況土壤，分別為湖口土系 (Plithic Paleaquults)，竹圍土系 (Typic Plinthaquults)和蘆竹土系 (Typic Plinthaquults)。分別於三種土壤之表面下25、50、100及200公分處於2004年1月至2005年12月每兩星期土壤水分基質勢能、土壤氧化還原電位，及另設置一200公分監測井以觀察地下水位變化。將10×10公分之鋁製方盒於每土層中收集土樣，攜回實驗室後以濕篩方式收集不同粒徑大小之鐵錳結核，收集之粒徑分別為2-5, 5-10, 10-20和>20 mm。 研究結果發現處於地勢較低的湖口土系，常年季節性地下水位為三土系中最高，長年於Bt1層(20-40 cm)處變動。此深度附近由於乾濕交替頻繁，導致整個剖面中之鐵錳結核含量於Bt1和Bt2 (20-60 cm)處最多 (9-33 kg/55cm/m2) (20公分至75公分間)。湖口土系為三土系中還原時間最久之土系，表土50公分以下之平均還原時間為一年之74%，總結核含量為約9 kg/150cm/m2 (50-200公分)，為三剖面中之最少量。原因為土壤長期處於還原狀況下，導致鐵錳結核不易生成。竹圍土系為三種土壤中總鐵錳結核含量最多之剖面 (表土50至200公分總量約740 kg/150cm/m2)。由於此剖面地下水位變動頻繁，長年於50-180公分間變動，且表土50公分下之平均還原時間為一年之40-50%，總鐵錳結核含量為740 kg/150cm/m2 ((50-200公分))。由此結果推測中等還原狀況和頻繁地下水位變動乃是造成鐵錳結核形成的主要因子。蘆竹土系排水等級較其餘兩土系較佳，但受暫棲水和地下水位變動的雙重影響，在Btv1 (20-50 cm)層內，氧化還原作用盛行，鐵錳結核含量稍多 (22-53 g/kg)且粒徑較大，以10-20mm的結核為主。剖面愈往下層部分，雖長期浸水飽和但卻未達還原狀況，應該為地下水含氧的關係，使得還原狀態不盛行，導致鐵錳分凝作用不佳，鐵錳結核不易生成。此土系表土50公分下鐵錳結核總量只達 220 kg/150cm/m2 (50-200公分)。 由無定形、游離態和全量鐵和錳分析可判定鐵錳結核之結晶化程度及鐵活性指標。結晶程度可由結晶化指數 ((Fed-Feo)/Fed)比較得知，研究結果發現，三剖面中各不同粒徑下之鐵錳結核結晶化程度與土壤一年中還原時間具有顯著之負相關 (r=-0.30*, p<0.05)，顯示當土層處於還原狀況愈久時，現地所形成之結核結晶程度越差。另一方面，鐵活度指標 (Feo/Fed)與土壤還原時間具顯著正相關 (r=0.43**, p<0.01)，結果表示，當鐵錳結核粒徑越大時，Feo/Fed有較大的趨勢。此現象可解釋鐵錳結核為現地生成，由小粒徑之鐵錳結核為核心並逐漸而增大。由微形態方面之觀察，結果可證實大部分結核確實為現地生成 (邊界漸往外擴散)，且大部分之結核皆為以錳為核心。由此現象，可推測當土層處還原狀態一段時間後，錳還原而往下淋洗至孔洞或石英等不易風化之礦物上，待氧化而後沉澱，接續還原的鐵或錳再逐漸洗入原先沉澱的錳核裂隙中或沉澱並包覆於表面上逐漸增大。 本研究推論在含鐵網紋之極育土中的鐵錳結核生成機制有三個步驟：(1) 受還原的錳先移動至土壤微孔隙中或不易風化之礦物表面上沉澱形成結晶性不佳之錳核；(2) 接續由於地下水位變動或表面灌溉水之淋洗，導致還原的鐵隨黏粒或獨自洗入移動至一開始之錳核表面或裂隙中再氧化而沉澱；(3) 長久乾溼交替的水文變動，鐵錳結核逐漸氧化累積增大。Iron and manganese nodules are dominant redoximorphic features in most of rice growing soils of Taiwan that are characterized by the effects of variability in anthraquic and seasonally fluctuating of shallow ground water tables. A field experiment was conducted in Chungli terrace from January of 2004 to December of 2005 to characterize the chemical and physical properties of Fe-Mn nodules and to examine the possible mechanisms for nodule formation under different moisture regimes. It was found that the quantities and characteristics of these nodules were to a greater extent influenced by fluctuating soil moisture regime. The objectives of this study are(1) to characterize the chemical and physical properties of Fe-Mn nodules, and (2) to propose possible mechanisms for nodule formation under different regimes of soil water conditions Three Ultisols with Fe-Mn rich nodules and different moisture regime were selected in Chungli rice growing terrace located in the northern Taiwan. The selected soils were Typic Plinthaquult (Luchu soil), Typic Plinthaquult (Chuwei soil) and Plinthic Paleaquult (Houko soil) within an elevation of 20 to 30m above sea level. Routine soil sampling and analyses included variables such as the measurements of ground water table, soil matric potential and soil redox potential (Eh) which were than combined with the measurements of physical and chemical characteristics of whole soils and Fe-Mn nodules with different sizes to understand the formation mechanism of the redoximorphic features in these anthraquic soils with plinthite. It was observed that the soil pedon (below 50 cm depth in the profile) in Plinthic Paleaquult (Houko soil) located at the bottom of the hydrosequence was most reduced (70% of the year) compared with other soils in the hydrosequence. The highest reduction at 50 cm depth in Houko soil was found to be associated with the slightly development of Fe-Mn nodules (9 kg/150 cm/m2). The Chuwei soil had moderately reduced pedon (40% of the year) but was found to be associated with the highest development of Fe-Mn nodules (740 kg/150 cm/m2). Based on these observations, it was assumed that moderately reduced duration was the most suitable condition for the formation of Fe-Mn nodules along this toposequence. Iron and manganese nodules of four sizes (2-5, 5-10, 10-20, and >20mm radius) were also determined to study their formation under different water regime conditions. These nodule samples were analyzed for amorphous material (Feo, Mno, and Alo), crystalline material (Fed, Mnd, and Ald), and total content (Fet and Mnt) of Fe, Mn and Al. The results indicated that Fed and Fet decreased with increasing sizes of the nodules. No trend was found in any fraction of Mn of three pedons for Mno, Mnd and Mnt. The crystalline index ((Fed-Feo)/Fed) of different size nodules ranged from 0.5 to 1. A significantly negative correlation was observed between the crystalline index and the duration of reduced time in a year (r=0.30*, p<0.05). It indicated that the degree of crystalline of nodules decreased with length of reduced duration. Nodules of different sizes had similar Fe activity index (Feo/Fed). It showed a trend such that Feo/Fed ratio slightly increased with the nodule sizes, and the largest nodule (> 20 mm) had significantly lower bulk density compared with other nodule sizes. These evidences implied that the poor crystalline iron nodules are still accruing which could be explained by the occurrences of nodules of varying sizes as a nucleus. The micromorphological features of Fe-Mn nodules with different sizes and water regimes were also studied. These features indicated that the most nodules are formed in-situ with diffuse boundary. The Ap horizon of Luchu soil, as well as soils in Ap and AB horizons of Chuwei soils that were mostly in reduced condition had maximum amount of Mn nodules of different sizes . In these horizons, it appears that reduced Mn would have been moved and precipitated on the surface of the coarse minerals such as quartz, and then reduced Fe and Mn continuously precipitated on their surface or over time infilled into the minerals and grew to the larger ones. On the other hand, concentric nodules (always smaller than 0.5 mm) presenting only in the Luchu soil could be attributed to the dominant role of the finer soil texture (i.e., clay loam). Relatively fewer, smaller and poorer structures of nodules observed in Houko pedon might be because of long-term reduced condition and higher content of organic matter. Based on the results of this study as above, it appears that Fe and Mn nodules formation in these Ultisols with plinthite of Chungli of northern Taiwan have undergone changes through three stages of development: (1) in the initial stage of nodule formation, reduced Mn moved to mineral surfaces and then re-oxidized to poor crystalline Mn oxide form; (2) Fe or Mn continued depositing on or infilling into the Mn nodules and these deposits or infillings of Fe were developed to a recognizable crystalline Fe forms; and (3) depending on the redox condition of the profile over time, these particles continued growing, more of the small nodules were added and poorly crystalline Fe formed into the bigger volumes of Fe-Mn nodules.目 錄 頁碼 中文摘要----------------------------------------------------------------------------------- I 英文摘要----------------------------------------------------------------------------------- IV 目錄----------------------------------------------------------------------------------------- VII 圖目錄-------------------------------------------------------------------------------------- IX 表目錄-------------------------------------------------------------------------------------- X 第一章、前言----------------------------------------------------------------------------- 1 第二章、文獻回顧----------------------------------------------------------------------- 5 第一節、不同水文狀況下氧化還原特徵之生成----------------------------- 5 1. 浸水狀況------------------------------------------------------------------------ 5 1.1 內浸水狀況--------------------------------------------------------------- 6 1.2 表面浸水狀況------------------------------------------------------------ 6 1.3 人為浸水狀況------------------------------------------------------------ 8 2. 濕潤境況------------------------------------------------------------------------ 9 3. 暫乾境況------------------------------------------------------------------------ 15 4. 土壤形態特徵之量化與水分境況之關係--------------------------------- 16 5. 水成土壤指標之判定--------------------------------------------------------- 20 6. 影像分析技術對氧化還原形態特徵的衝擊------------------------------ 22 第二節、鐵錳元素在週期性浸水土壤環境中之動向----------------------- 23 第三節、鐵錳結核在週期性浸水土壤環境中之生成----------------------- 24 第四節、浸水土壤中鐵錳結核的微形態特徵與生成作用----------------- 26 第三章、材料與方法-------------------------------------------------------------------- 30 1. 研究區域之選定---------------------------------------------------------- 30 2. 研究區域之地質與地理概況------------------------------------------- 30 3. 研究區域之水文條件及氣候概況------------------------------------- 31 4. 代表性土系之選擇------------------------------------------------------- 35 5. 研究區域之土地利用---------------------------------------------------- 36 6. 田間監測項目------------------------------------------------------------- 36 7. 形態特徵描述------------------------------------------------------------- 40 8. 氧化還原形態特徵量化------------------------------------------------- 41 9. 顏色指標模式選定------------------------------------------------------- 44 10. 土壤基本性質分析------------------------------------------------------ 44 11. 土壤微形態觀察--------------------------------------------------------- 46 12. 鐵錳結核物理化學分析------------------------------------------------ 47 第四章、結果----------------------------------------------------------------------------- 50 第一節、土壤剖面形態特徵----------------------------------------------------- 50 1. 野外形態特徵-------------------------------------------------------------- 50 (1)湖口土系--------------------------------------------------------------- 50 (2)竹圍土系--------------------------------------------------------------- 55 (3)蘆竹土系--------------------------------------------------------------- 57 第二節、土壤基本物理性質分析----------------------------------------------- 58 1. 湖口土系-------------------------------------------------------------------- 58 2. 竹圍土系--------------------------------------------------------------------- 58 3. 蘆竹土系-------------------------------------------------------------------- 60 第三節、土壤基本化學性質分析----------------------------------------------- 60 1. 湖口土系-------------------------------------------------------------------- 60 2. 竹圍土系-------------------------------------------------------------------- 64 3. 蘆竹土系-------------------------------------------------------------------- 66 第四節、土壤水文狀況---------------------------------------------------------- 67 1. 湖口土系-------------------------------------------------------------------- 67 2. 竹圍土系-------------------------------------------------------------------- 70 3. 蘆竹土系-------------------------------------------------------------------- 72 第五節、土壤氧化還原狀況----------------------------------------------------- 74 1. 湖口土系-------------------------------------------------------------------- 76 2. 竹圍土系-------------------------------------------------------------------- 76 3. 蘆竹土系-------------------------------------------------------------------- 78 第六節、鐵錳結核在週期性浸水土壤中之性質與分佈-------------------- 81 1. 鐵錳結核物理性質-------------------------------------------------------- 81 2. 鐵錳結核化學性質-------------------------------------------------------- 83 3. 鐵錳結核含量與水文狀況之關係-------------------------------------- 88 4. 鐵錳結核之微形態特徵之觀察----------------------------------------- 94 第七節、半影像分析與目視法對氧化還原形態特徵的比較------------- 101 1. 湖口土系-------------------------------------------------------------------- 101 2. 竹圍土系-------------------------------------------------------------------- 102 3. 蘆竹土系-------------------------------------------------------------------- 102 第五章、討論------------------------------------------------------------------------------ 107 第一節、氧化還原形特徵與水文狀況之關係-------------------------------- 107 1. 利用色度指標預測水田化土壤之水文狀況--------------------------- 107 2. 形態特徵指標與水分境況之關係--------------------------------------- 113 第二節、影像分析對土壤中氧化還原形態特徵之改善------------------ 119 1. 影像分析與目示法在鑑定形態特徵上的差異----------------------- 119 2. 影像分析對水文預測指標的影響--------------------------------------- 124 第三節、土壤不同水文狀況對鐵錳結核生成機制之探討--------------- 128 第四節、不同還原狀況下含鐵網紋浸水極育土分類標準之建立------- 139 第五節、未來研究方向----------------------------------------------------------- 141 第六章、結論------------------------------------------------------------------------------ 143 第七章、參考文獻------------------------------------------------------------------------ 145 附錄------------------------------------------------------------------------------------------ 156 圖 目 錄 圖2-1土壤剖面浸水飽和之三種型式------------------------------------------------ 7 圖2-2第一型式氧化斑紋的形成機制------------------------------------------------ 13 圖2-3第二型式氧化斑紋的形成機制------------------------------------------------ 14 圖3-1中壢台地之地理位置圖--------------------------------------------------------- 32 圖3-2 1985-2005年研究區域之平均月降雨量和蒸發散量---------------------- 33 圖3-3研究區域及研究土系地形位置圖--------------------------------------------- 34 圖3-4監測裝置位置深度及位置分配圖--------------------------------------------- 39 圖3-5面積連續加總法之示意圖------------------------------------------------------ 43 圖3-6無定形態鐵、鋁、錳之萃取與測定步驟------------------------------------ 48 圖3-7游離態鐵、鋁、錳之萃取與測定步驟--------------------------------------- 49 圖4-1湖口土系之剖面形態特徵------------------------------------------------------ 51 圖4-2竹圍土系之剖面形態特徵------------------------------------------------------ 56 圖4-3蘆竹土系之剖面形態特徵------------------------------------------------------ 59 圖4-4湖口、竹圍與蘆竹土系於2004及2005中之地下水位變化------------ 68 圖4-5湖口土系2004和2005年中25、50、100及200公分深度水勢能變化 69 圖4-6竹圍土系2004和2005年中25、50、100及200公分深度水勢能變化 71 圖4-7蘆竹土系2004和2005年中25、50、100及200公分深度水勢能變化 73 圖4-8湖口土系2004和2005年中25、50、100及200公分深度之氧化 還原電位變化-------------------------------------------------------------------- 75 圖4-9竹圍土系2004和2005年中25、50、100及200公分深度之氧化 還原電位變化-------------------------------------------------------------------- 77 圖4-10蘆竹土系2004和2005年中25、50、100及200公分深度之氧化 還原電位變化-------------------------------------------------------------------- 80 圖4-11湖口土系不同粒徑鐵錳含量剖面分佈------------------------------------- 90 圖4-12竹圍土系不同粒徑鐵錳含量剖面分佈------------------------------------- 91 圖4-13蘆竹土系不同粒徑鐵錳含量剖面分佈------------------------------------- 93 圖4-14湖口土系不同土層下氧化還原微形態特徵照片------------------------- 99 圖4-15湖口土系不同土層下氧化還原微形態特徵照片------------------------- 97 圖4-16竹圍土系不同土層下氧化還原微形態特徵照片------------------------- 98 圖4-17蘆竹土系不同土層下氧化還原微形態特徵照片------------------------- 99 圖4-18蘆竹土系不同土層下氧化還原微形態特徵照片------------------------- 100 圖5-1台灣北部桃園地區中不同海拔高度之土系的地理位置分佈----------- 109 圖5-2背坡位置1996至1997年之(a)地下水位、(b) 25, 50, 100及200公分 深度的水勢能，及(c) 25, 50, 100及200公分之平均氧化還原電位- 112 圖5-3麓坡位置1996至1997年之(a)地下水位、(b) 25, 50, 100及200公分 深度的水勢能，及(c) 25, 50, 100及200公分之平均氧化還原電位- 114 圖5-4趾坡位置1996至1997年之(a)地下水位、(b) 25, 50, 100及200公分 深度的水勢能，及(c) 25, 50, 100及200公分之平均氧化還原電位- 115 圖5-5色度指標與還原時間之迴歸(a)<50公分，實線代表迴歸線，虛線 代表信賴區間(99%) (b)50-100公分(c)>100公分------------------------ 116 圖5-6色度指標與飽和時間之迴歸(a)<50公分，實線代表迴歸線，虛線 代表信賴區間(99%) (b)50-100公分(c)>100公分------------------------ 117 圖5-7目視法與影像分析法鑑定湖口土系氧化還原形態特徵之比較-------- 121 圖5-8目視法與影像分析法鑑定竹圍土系氧化還原形態特徵之比較-------- 122 圖5-9 目視法與影像分析法鑑定蘆竹土系氧化還原形態特徵之比較-------- 123 圖5-10 色度指標與土壤還原時間之迴歸分析------------------------------------- 127 圖5-11 鐵結晶化指標與活度指標與土壤還原時間之迴歸分析---------------- 135 圖5-12 本研究之鐵錳結核生成機制圖---------------------------------------------- 136 圖5-13 鐵錳結核形成過程機制推論圖---------------------------------------------- 137 圖5-14 鐵錳結核增大過程機制推論圖---------------------------------------------- 13

Reduction of Nutrient Leaching Potential in Coarse-Textured Soil by Using Biochar

Background: Loss of nutrients and organic carbon (OC) through leaching or erosion may degrade soil and water quality, which in turn could lead to food insecurity. Adding biochar to soil can effectively improve soil stability, therefore, evaluating the effects of biochar on OC and nutrient retention and leaching is critical. Methods: We conducted a 42-day column leaching experiment by using sandy loam soil samples mixed with 2% of biochar pyrolyzed from Honduran mahogany (Swietenia macrophylla) wood sawdust at 300 °C (WB300) and 600 °C (WB600) and a control sample. Leaching was achieved by flushing the soil column on day 4 and every week during the 42-day experiment and adding a water volume for each flushing equivalent to the field water capacity. Results: Biochar application increased the final soil pH and OC, NH4+-N, NO3−-N, available P concentrations but not exchangeable K concentrations. In particular, WB600 exhibited superior performance in alleviating soil acidification; WB300 engendered high NO3−-N concentrations. Biochar application effectively retained water in soil and inhibited the leaching of the aforementioned nutrients and dissolved OC. WB300 reduced NH4+-N and K leaching by 30%, and WB600 reduced P leaching by 68%. Conclusions: Biochar application can improve nutrient retention and reduce the leaching potential of soils and connected water bodies

Retention and loss pathways of soluble nutrients in biochar-treated slope land soil based on a rainfall simulator

Global food crisis makes intense agricultural activity necessary, which accelerates soil degradation and increases pollution risk to nearby catchments. Application of biochar can effectively retain plant-required nutrients in soils. However, the linkage between retention and loss pathways of nutrients is still unclear, particularly at slope lands. Therefore, a simulated rainfall experiment (rainfall intensity ​= ​50 ​mm ​h−1) was conducted in a sandy soil with 10° gradient slope (indoor experiment) to clarify loss pathways of soluble C, N, P and K in biochar-amended soils. Wood biochar pyrolized at 300 ​°C (LWB) or 600 ​°C (HWB) was applied at 1% (LWB1; HWB1) or 2% (LWB2; HWB2). Our results show that the pathways for C, N, P and K loss was percolation ​> ​surface runoff ​> ​soil erosion. Compared to control, HWB2 treatment had a 2–4 times higher infiltration amount but 5–6 times lower surface runoff and soil loss, indicating that this treatment alleviated nutrient loss via erosion and runoff in the sloped soil. Among all treatments, HWB2 treatment was the most effective for retaining organic C, dissolved organic C, total N, and exchangeable K through various pathways. However, a substantial amount of soluble P was lost through percolation. Therefore, the potential pollution of groundwater by P through percolation pathway should be considered during biochar application