有機質肥料之肥效試驗及結果判釋之若干觀點

Abstract

有機質肥料之試驗雖多，卻因試驗處理普遍欠缺系統性，正確的肥效評估並非容易。本文檢討國內外若干有機質肥料長期連用試驗，試從定量觀點分析肥料及有關因素，結果綜合如下。 1.有機質肥料之功能雖多，惟就水旱田之糧食作物而言，其實際肥效係以所含肥料要素，尤以氮素之供給為主，且可由化學氮肥所代替。c/N比低之有機質肥料（豆粕、綠肥等），因礦化率高，肥效與化學氮肥相當；長期施用並不見土壤有機質顯著累積，肥效率自無顯著變化。c/N比高之有機質肥料（堆肥、廢肥）在施用初期則肥效率概低於施肥量相當的化學肥料，乃其礦化率較低所致。但連年施用後，因其分解殘餘之有機質逐漸累積，礦化率漸增，肥效率亦漸接近於施肥量相當之化學氮肥。但此累積之礦化率終究不超過100%，其肥效率在本質上並不超過施肥量相當之化學肥料。實際上，有機質肥料之肥效在連用後或有超越化學肥料區情形，惟差異並非很大；如化肥氮素施用得當，此種差異仍可獲相當之彌補。 2.生產力極高的水田固有較高有機質含量，惟一般言之，二者並無一定之正相關；就台灣水田而言，南部中鹼性土壤第二期作之透水性和北部酸性土壤之有效態矽酸供應能力常為優先於有機質含量的主要肥力限制因素。 3.就蔬菜、花卉等作物而言，有機質肥料之肥效誠較其他水旱田作物為高。此種效果尤以育苗期或移植期為最，係與此等作物苗期之物理性質（通氣性和保水性）需求有關。惟除此之外，在整個生育過程所表現之實際肥效則仍與所含肥料養分之釋出、供應關係最為密切，而養分之礦化率仍為主宰肥效之關鍵。 4.總之，有機質肥料的肥效，就一般作物而言，係以肥料要素，尤以氮素之供應為主。肥料要素以外的特殊效果並非非常顯著。故有機質肥料的評價應以所含肥料要素之量及其礦化速率為基礎。 有機質肥料之肥效既與所含氮素之釋出關係最為密切，施有不同有機質肥料的複雜土壤系統中有關氮素礦化之模擬、預測或一定期間可礦化氮量之化學速測等乃為有效應用有機質肥料，並使環境免於污染的重要手段。 Although many experiments have been conducted to study the effects of organic manures in crop production, most of them were with the treatments unsystematic, consequently the results obtained were often ambiguous, and the interpretations unscientific. Some of the long term experiments on the application of organic manures conducted in Taiwan and other countries were reviewed, and the following conclusions are drawn. Most of the effect of any organic manure can be attributed to the nitrogen it contains, and N fertilizer gives equivalent yields. The effects of nanure-N and fertilizer-N are additive in nature and compen- sational. The estimations of N mineralization from the manure as well as from the soil during a cropping season are, therefore, important for the adjustment of the requirement of fertilizer -N to be applied incom bination with the manure.