利用水庫淤泥做為水稻育秧替代介質

Abstract

水稻秧苗的培育與移植作業能提高水稻產量與品質，然而，為了培育水稻秧 苗，每一年約需使用 35 萬立方公尺的育苗介質，而現行的水稻育秧用土多開採自山區，近年來，由於山區水土保持意識的提升，伴隨著各縣市政府的限制採土政策，自山區取得育秧用土越趨受到限制，過去育苗場也曾出現無土可用的狀況。另一方面，台灣水庫平均每年約清出 400 萬立方公尺的淤泥，在淤泥產生量上足以供應在水稻育秧產業上所需的育苗土總量，若能以水庫淤泥做為育秧替代介質，除了能解決育秧缺土的問題，也可以提供堆置淤泥另一個去化管道。本論文研究之目的(一)探討使用水庫淤泥做為水稻育秧介質的可行性(二)探討以水庫淤泥種植水稻秧苗下，影響秧苗生長的關鍵因子(三)探討關鍵因子之相關影響機制。本研究首先對淤泥基本物化性質與一般育苗土進行物化性質的分析與比較，找出做為替代育秧介質的限制因子，次以盆栽試驗探討影響水稻秧苗的限制因子及相關機制，参以苗盤試驗與田間試驗檢視以水庫淤泥做為育秧介質在應用上的可行性。由研究結果已知，淤泥的被破壞性的結構與其質地分佈會影響到介質的保水性與水分滲透能力，造成灑水後的苗盤龜裂現象，進而影響到育苗作業，因此水庫淤泥並不適合直接應用於育秧替代介質，然而在添加有機質後，能顯著改善淤泥的物理性質並減少苗盤龜裂的現象。由盆栽試驗可知，在水分供給無虞的狀況下，營養供給是影響水稻秧苗生長的關鍵因子，另外，淤泥的介質、稻殼添加種類與添加比例均會顯著影響到養分供給，進而影響秧苗生長。各處理組中，以細質地淤泥添加 5~10%的稻殼有較佳的秧苗生長勢，其中的關鍵因子有二：1.細質地淤泥因黏粒含量高因此有較高的保肥力 2.在有機質種類的選擇上與添加比例的調配上，氮有效性是影響秧苗生長的關鍵，添加 20%稻殼或稻殼炭會因 C/N 比過高造成微生物搶氮現象，而在有機質種類的選擇上，若使用炭化資材做為改良資材(本研究使用稻殼炭)，所施用的尿素可能會因被炭化資材吸附，進而使氮肥礦化速率下降，降低有效氮含量並造成秧苗生長品質下降，若使用硫酸銨做為氮肥來源則可以改善這個狀況，因此在添加有機改良資材上，有機資材的選擇以及其適用性也是另一需要考量的重要因子。由苗盤試驗證實添加稻殼後的淤泥，無論粗細質地，均有良好的苗盤品質，其中又以細質地淤泥添加 10 %稻殼最佳，而以田間插秧實驗證實，以淤泥做為育秧介質下，秧苗於插秧後的生長表現可與育苗土相當。由本研究結果證實，添加有機質後的水庫淤泥是一可行的水稻育秧替代介質，其中，以添加 10 %稻殼的細質地淤泥能生產出最佳的秧苗品質，此替代介質能解決水稻育苗產業的缺土問題，同時也能為水庫提供另一項清淤管道。

In Taiwan, about 350,000 m3 of nursery substrates are needed to grow rice seedlings. At present, most of the nursery substrates in Taiwan are soil collected from mountain areas. With the growing concern of soil conservation, it is increasingly difficult to obtain soil from mountain areas. Therefore, alternative substrates are in urgent need. On the other hand, in Taiwan, about 4,000,000 m3 sediments are deposited in reservoirs every year. The amount of deposited sediments fits the need of rice nursery substrate in quantity. If the quality of reservoir sediments were suitable for nursing rice seedlings, utilizing reservoir sediments as the alternative substrates could benefit the nursery industry as well as the cleaning of the dredged sediments. The aims of this research are (i) to evaluate the feasibility of utilizing reservoir sediment as an alternative substrate of rice seedlings (ii) to investigate the key factors in growing rice seedlings based on reservoir sediments (iii) to study the related mechanisms of the key factors. In this study, the physical and chemical properties of the sediments were first analyzed. Then, several pot experiments were carried out to study the key factors in the growth of rice seedlings. Finally, the quality of rice mat nursery based on reservoir sediments were evaluated by a tray experiment and a transplanting experiment. The results showed that the poor physical properties of the sediments would adversely influence the water permeability and water retention of nursery substrates and would lead to cracks on the surface of sediment-based mat nursery after water sprinkling. Therefore, reservoir sediments were not suitable for being readily used as nursery substrates. However, after the amendment of organic matters, the surface cracks of sediment-based mat nursery were reduced. According to the pot experiments, under the submerged condition, the key factor in the growth of rice seedlings was substrate nutrients. The texture of sediment, the type of organic matters and the addition amount of organic matters would mutually influence the nutrient availability in substrates hence the growth of rice seedlings. The fine sediment was better than the coarse sediment as a rice nursery substrate since it had high content of clay hence higher nutrient retention ability. In OM types and OM addition amounts, the N availability in substrates after adding OM is the key factor that should be carefully considered. Adding 20 % of rice husk (RH) or rice husk biochar (RHB) would raise the C/N of a substrate up to the level that microbial immobilization of nitrogen easily occurred at. On the other hand, adding pyrolyzed organic matters, RHB in this study, might reduce the nitrogen availability due to the adsorption effect of biochar on urea. Using (NH4)2SO4 as the N source might reduce the loss of available nitrogen in RHB-amended substrates. Overall, according to the pot experiments, the rice seedlings grew best in the fine sediment amended with 10% RH. Based on the tray experiment and the transplanting experiment, the 10% RH-amended sediments could produce mat nursery with the quality as high as that of the nursery soil. In summary, it is feasible to utilize reservoir sediments as the alternative rice nursery substrates. Among the sediment-based substrate mixtures, the fine sediment amended with 10% RH is recommended. Utilizing reservoir sediment as the alternative mat nursery substrate of rice can ease the shortage of nursery soil as well as benefiting the cleaning of deposited reservoir sediments.