短期施用生物固形物對小白菜的產量、養分吸收、土壤及洗出液性質的影響

Abstract

生物固形物 (biosolid) 為「都市廢水處理廠所產生可回收利用之有機固體物質（不論其目前有無回收使用）」。生物固形物施用於農地土壤以往皆是以作物的氮肥需要量為基準，然而，以氮含量為基準施用生物固形物可能會造成過量磷肥的施用，造成地下水磷的污染與水質的優養化，因此，生物固形物的施用和氮的管理便有賴各項的研究與評估。 本研究使用國內污水處理廠的廢水污泥，經乾燥處理成生物固形物後，與盆栽上層0-5 cm壤質土壤混合，於人工氣候室中栽種鳳山小白菜 (Brassica rapa L. Chinensis Group cv. Fengshan pak-choi)。肥料施用量分別以小白菜的氮肥與磷肥的施肥推薦量為基準 (200 kg N ha-1, 25 kg P ha-1)，進行兩次的盆栽試驗研究，分為未施肥處理（對照組）、一倍化學氮（磷）肥、一倍氮（磷）肥生物固形物施用量與兩倍氮（磷）肥生物固形物施用量；並以一倍及兩倍台灣年平均雨量 (2500 mm yr-1) 為基準，進行淋洗試驗。 小白菜於播種後第33天採收，各處理間的生長情形及作物產量在統計上均未達到顯著差異，化學肥料處理組中植體的全氮濃度皆顯著高於其他處理組 (p < 0.05)，由於部分盆栽因淋洗試驗的進行造成排水不良，植體中氮的吸收量並未因生物固形物施用量的不同而有顯著上的差異；植體中全磷濃度與磷的吸收量皆因生物固形物的施用而增加。 生物固形物施用於土壤後，表層0-10 cm土壤的pH值會顯著高於化學肥料施用處理組 (p < 0.05)，約可增加0.3-0.5個pH單位；洗出液的電導度值則於淋洗試驗初期會到達最高值，之後則隨著淋洗時間的增加而下降；洗出液的pH值平均約在6-7之間，高於化學肥料處理組 (pH 4-6)。 生物固形物的施用會造成表層0-10 cm土壤Bray-1磷的累積，由於土壤中Bray-1磷濃度與洗出液中溶解性反應磷的流失量有顯著相關 (p < 0.001)，且兩倍雨量淋洗下洗出液中磷的流失量是正常雨量下的3.6倍，因此，生物固形物的施用仍須考量磷流失的風險。 生物固形物施用後，土壤中的可交換性氮較化學肥料處理組增加，且洗出液中可交換性氮的流失量顯著少於化學肥料處理組 (p < 0.05)，因此，推測施用生物固形物可以顯著減少可交換性氮的流失。然而，過多的雨量淋洗仍會增加氮的流失，必須配合適度的灌溉與良好的排水，才可避免過量氮的流失。 生物固形物的施用提供了較佳的土壤環境，有助於減少土壤中因淋洗所造成的氮的流失，但會造成表層土壤磷的累積，增加地下水磷污染的風險，於本研究中生物固形物的施用並未對小白菜的產量造成影響。未來生物固形物若欲運用於農地土壤，應以堆肥處理後的型態運用較佳。

Biosolid is the primarily organic solid product produced by municipal wastewater treatment processes which can be beneficially recycled. Applying municipal biosolid to agricultural area is an effective way to recycle the nutrients and organic matter from biosolid. In the past, biosolid application rates were usually applied to the soil based on nitrogen (N) requirements of vegetarian growth. In most cases of the world, applying biosolid based on the crop N needs usually supplies excess phosphorus (P) to the soil, which can cause the surface water or ground water pollution by eutrophication and other undesirable environment effect. Accurate predictions of biosolid application rates are one of the key factors for benefit crops without risk of excess N and P leaching from soil system. The studied sewage sludge (biosolid) was collected from Nei-Hu sewage treatment in Taipei, Taiwan. The sludge was dewatered and dried for about one month and grounded by the machine. Biosolid was thoroughly mixed with 3.6 kg of Sankengtzu loam soil for plot experiment. Two greenhouse plot studies were conducted based on pak-choi N and P fertilizer recommendation application rate (200 kg N ha-1 and 25 kg P ha-1) were added into the soil on August and September, 2004. In each experiment, four treatments was conducted, including control treatment, biosolid was applied by normal N (or P) fertilizer rate, biosolid was applied by two times of N (or P) fertilizer rate, and a chemical fertilizer application rate treatment. Pak-choi (Brassica rapa L. Chinensis Group cv. Fengshan pak-choi) was seeded and left 6 plants for each plot. The leaching experiment was started after 10 days based on annual and two-times of average precipitation (2500 mm yr-1). Pak-choi was harvested on 33rd day after it was seeding. Plant yield of all the treatments are not significantly different. Under leaching experiment, some biosolid treatments were flooded and make some influences on plant growth. The concentration of total nitrogen in the vegetable of the chemical fertilizer treatment is significantly higher than other treatments (p < 0.05). Nitrogen uptake was not significantly different to the different biosolid application rates (p < 0.05). The total phosphorus concentration and total uptake of vegetable are increasing by the application of biosolid. After application of biosolid into the soil, surface 10 cm soil pH will be significantly higher than that of chemical fertilizer treatment (p < 0.05). The increasing of pH is about 0.3 to 0.5 pH unit and the pH value of leachate solution is ranged from 6 to 7, which also higher than that of chemical treatment (soil pH ranged from 4 to 6). The electrical conductivity (EC) value of leachate solution increase to the highest value at the initial period, then the EC value decrease with the time. Biosolid application can accumulate the Bray-1 phosphorus on the surface 10 cm soil. The increasing of soil Bray-1 phosphorus was significantly correlated to the dissolved labile phosphorus (p < 0.001), and the phosphorus leaching loss under the precipitation of two-times of normal precipitation is more than 3.6 times than that of normal precipitation. We concluded that biosolid application rate should consider the risk of leaching phosphorus loss from the soil system. After biosolid was applied the soil, the soil exchangeable nitrogen is higher than that of chemical fertilizer treatment and the nitrogen loss in the leachate solution is significantly lower than that of chemical fertilizer treatment (p < 0.05). Biosolid application can decrease the loss of exchangeable nitrogen. Too much of precipitation will increase the nitrogen loss. Appropriate irrigation and good drainage can decrease the excess nitrogen and phosphorus leaching loss. Application biosolid into the soil can provide better soil environment condition and decrease the nitrogen loss from leaching, however, available phosphorus will accumulate on the surface soils and increasing the risk of phosphorus loss to the groundwater. From the result of this study, different biosolid application methods do not affect the vegetable yield. In the future, composting of sewage sludge is required to get a better way to recycle the biosolid for land use.