有機耕作年期對土壤與蔬菜之影響

Abstract

本論文係探討在長年的有機耕作管理下，對耕地土壤理化性質及作物生育的影響，並探討遙感探測科學所發展出的即時分析技術應用於改善有機農業的維護管理及生產品質的可行性；同時，在節能減碳議題受到關注的今日，也藉此試驗檢測有機耕作對於土壤有機碳庫(soil organic carbon, SOC)的蓄積能力。研究結果簡述如下： （一）農地經過長期的有機耕作之後，其土壤酸鹼度有上升的趨勢（> pH=5.0）；有機質、有機碳、有效性磷、交換性鉀、交換性鎂、交換性鈣皆隨有機耕作時間增長而逐漸增加。在溫室內土壤的電導度及有機質皆高於室外田區；有效性磷、交換性鈣、交換性鎂、鋅的含量在溫室內皆高於溫室外。顯示長年的有機耕作可以改善土壤的環境。 （二）有機耕作年期的增加，可以提高蔬菜的株高、乾物重；土壤有機值的增加，可以使各元素的吸收更趨穩定，除了可以提高蔬菜鉀與鋅元素含量，也降低了鈉的含量。藉此得以有效提升農作物本身之品質及經濟價值。 （三）有機栽培年期的增加，在蔬菜葉片反射光譜上，於可見光與近紅外光區的反射率可呈現特定規律，並與光合色素含量變化之趨勢一致；NDVI、SRVI、NDVIbroad 、SRVIbroad等植生指數及SPAD值可作為有機栽培蔬菜老化及葉綠素含量大幅降低時的指標。利用反射光譜計算植生指數，非破壞性地估算葉片色素含量之變化，進而監測作物生長狀況，於實際田間耕作上為一具應用潛力之可行方法。 （四）在不同有機栽培年期溫室區中，種植一期蔬菜前後，表土20 cm內之土壤有機碳增加約1 ~ 9 Mg ha-1，相當於固定了3.7 ~ 33 Mg CO2 ha-1。不同有機栽培年期(1~7年)溫室區土壤可貯存SOC量約31 ~ 56 Mg ha-1，相當於114 ~ 206 Mg CO2 ha-1。長年施行有機耕作每年平均可固定14 Mg CO2 ha-1，並於持續有機耕作5~7年後，達到最大SOC貯量。明顯地，在未來推廣有機耕作可達到CO2減量、提升農業經濟與農地保育等多重功能，在產量、品質、環境保護和永續農業之間找到平衡點。

The major objects of this study is to find out the effect of long-term organic farming on the soil physic-chemical properties and the crop growth, and to investigate the feasibility of applying the real-time analysis, based on the remote-sensing science, to improve the organic agricultural management and the corp quality control. At the meantime, the issues of global warming and carbon reduction were highly-concerned; we also try to exam the capability of soil organic carbon (SOC) stock of the organic farming. The results of the study are shown as follows： (1) After the long-term organic farming, the soil pH got a rising trend (> pH 5.0). The content of organic matter, organic carbon, bio-available phosphorus, exchangeable potassium, exchangeable magnesium, and exchangeable calcium are increased with the duration of the organic cultivation. These indicate the long-term organic farming can improve the soil condition. (2) The increasing of organic cultivation duration can raise the height and dry weight, in addition, can stabilize the plant absorption of the nutrimental elements. In addition to increase the content of the potassium and zinc in vegetables, it reduces the content of the sodium. (3) The increasing of organic farming duration can been shown by a specific regular pattern of the leaf spectral reflectance at the wavelength of visible light and near infra-red regions, and been coincided with the variation of the photosynthetic pigments content. The vegetation index, such as NDVI, SRVI, NDVIbroad and SRVIbroad, and the value of SPAD can be served as the pointers, when the senescence of the organic cultivated-plants and the reduction of the chloroplast are happened. By utilizing reflectance spectrum to calculate vegetation index and to measure the variation of the pigment content in leaves, and to monitor the whole crop growth condition, finally. (4) In the greenhouses with different duration of organic cultivation, the SOC content within 20 cm-depth from soil surface was increased about 100 to 900 Mg ha-1 (i.e. 370 to 3,300 Mg CO2 ha-1 was got fixed.) throughout a vegetable cultivating cycle. The soil in the greenhouse with different duration of organic farming (from 1 to 7 years) can stock 3,100 to 5,600 Mg ha-1 SOC, which is equivalent to 11,400 ~ 20,600 Mg CO2 ha-1. Under long-term organic cultivation, there is 1400 Mg CO2 ha-1 got fixed each year. The SOC could keep accumulated to the maximum amount while the organic farming was continued more than 5 to 7 years. Evidently, to popularize the organic agricultural management in the future will get benefit from CO2 reduction, promotion of the agricultural crop value, and maintenance of even more healthy cropping fields and products. Eventually, we wish to reach a balance between crop production / quality, environmental protection, and sustainable cultivating environment.