生物炭材料與熱解溫度對其農藝性能的影響

Abstract

生物炭的農業應用是目前熱門的環境議題，將生物炭與土壤混合後，不僅能夠改善土壤的物理及化學性質，提昇土壤的生產力，並能吸附土壤重金屬離子與有機污染物，且生物炭的穩定結構能長期將有機物儲存在土壤中，達到增加土壤固碳的效果。不過，生物炭的性質受到原料與熱解溫度的影響，因而影響生物炭的農業應用效果，若能了解材料與製作方法的差異，將可使生物炭的應用效果發揮到最大。本研究選用三種台灣常見的農林廢棄物為材料，包含稻殼 (RH)、柳杉木材 (CJ) 與田菁植體 (SR)，分別以300℃(300)與500℃(500)加熱製作成生物炭，除了利用傅立葉轉換紅外線光譜與碳-13核磁共振等技術，分析生物炭的各項性質與探討原料種類與熱解溫度的影響外，並以大肚山高風化酸性紅壤為對象，進行管柱淋洗與盆栽試驗，由作物生產、養分保持能力與殺草劑效果等方面，評估生物炭農業施用的效果。研究結果顯示，生物炭受到原料種類與熱解溫度影響甚大，隨熱解溫度增加，不僅碳含量增加，芳香族構造也相對增高，植物有效性無機養分元素 (e.g., P、Ca、K) 也愈高，但CEC則隨溫度上升而下降。三種材料間，以田菁生物炭的養分含量與陽離子交換容量最高，而柳杉生物炭最低。管柱淋洗試驗的結果顯示，生物炭對無機態氮、磷與K、Ca、Mg等金屬元素的淋洗沒有顯著的影響，但SR-300與SR-500由於交換性金屬含量較高的關係，反而會使金屬離子淋洗量增加。在作物生產方面，未炭化植體在土壤中引起固定化作用，消耗土壤中的無機養分含量，因此使作物乾重顯著下降，生物炭添加則無法顯著提昇作物乾重。經過施肥處理後，除SR-500有較高產量外，其餘處理 (控制組、未炭化植體添加、300℃生物炭添加與500℃生物炭添加) 並無顯著差異。SR-500較高的作物生物量可能是顯著提高土壤pH值，使施肥處理效果增加所造成的。此外，添加生物炭會顯著降低達有龍施用效果，且300℃生物炭較500℃生物炭的影響效果更為顯著。三種材料間以田菁生物炭的影響效果最大，甚至在6.0 mg kg-1的施用量下，黑麥草仍有高達超過80%以上的存活率。綜合各項結果，熱解溫度與生質材料的差異，其製成生物炭的性質也不同。本實驗發現以SR-300與SR-500具有較高的pH值、養分含量與陽離子交換容量，並在土壤中可能提高土壤pH值與養分有效性，使作物乾重生長上升，但卻顯著降低了殺草劑的使用效果。綜合各項結果，田菁生物炭具有提昇土壤酸鹼度的能力，且在土壤中能夠提供K+、Ca2+、Mg2+等金屬離子，但在土壤中會明顯的降低殺草劑的有效性。SR-500殺草劑施用效果下降的幅度低於SR-300，若使用SR-500則可能在提高作物乾重生產的同時，保持殺草劑的施用效果。

Amending biochar in soils has been proposed as a mean to sequestrate carbon and to mitigate the increasing atmospheric CO2 concentration and global warming. In addition, biochar can improve soil fertility, chemo-physical properties, and crop yield. Thus, using biochar in soils has recently been implemented in many experiments worldwide. However, the properties of biochar would change with different feedstock and pyrolytical processes. It is important to understand how feedsotck and pyrolytical processes influence the properties of biochar in order to have its suitable agricultural application. I selected three common agricultural wastes in Taiwan, including rice husk (RH), Cryptomeria japonica woods (CJ) and Sesbania roxburghii (SR), as the feedstock for making biochar. The feedstock was pyrolyzied at 300℃and 500℃, respectively. Firstly, the chemical and spectral (e.g., FTIR and solid-state 13C NMR) analyses were applied to determine the properties and structure of biochars. And then, the column leaching and pot experiments were applied to understand the nutrients release and uptake of biochars. Finally, a bioassay of herbicide efficacy experiment was conducted to evaluate the effect of amending biochar on inactivating herbicide effectiveness. The results showed that biochar properties were different under different feedstock and pyrolytical temperature. The biochar derived from CJ had the highest carbon content, while SR biochar had the higher nutrient content. Higher pyrolytical temperature resulted in higher carbon and nutrients (e.g., P, Ca, Mg, K) content, and also altered the structure from O-alkyl C of raw feedstock to aromatic-C for biochars. Most of biochar application did not increase the dry mass of corn significantly even with ferilizer treatment except the biochar made from SR. In the soil column leaching experiment, biochar had no significant effects on nitrate-N, ammonium-N and phospahte-P . The biochar application could not change the leaching of K+, Ca2+ and Mg2+ except SR biochar. SR biochar increase the leaching of K+ and Ca2+due to the high content of extractable ion. In the bioassay of herbicide efficacy experiment, 300℃ biochar could decrease the bioavailability of diuron more efficient than 500℃ biochar because of the combination of partition and adsorption. SR-300 and SR-500 biochar could reduce the bioavailability of diuron at 1.5 and 6.0 mg kg-1. To summerize, the SR biochar had higher pH and extractable ion and it could reduce the bioavailability of diuron efficiently. However, SR-500 could retain more bioavailability of diuron efficiently then SR-300. Using SR-500 as soil amendment might increase the soil productivity and retain bioavailability of diuron efficiently.