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何謂nitrogen cycle?


何謂nitrogen cycle?為何它對養耕共生如此重要? 

If you want to be successful with your aquaponics system, you will need to understand how the nitrogen cycle works. I will explain what the nitrogen cycle is, why it's important, how it progresses and how to ensure it works efficiently in your established system. Armed with this important information, you'll be well on your way to growing fish and plants just like the pros do.


What is the Nitrogen Cycle?

The nitrogen cycle is what powers aquaponics. There are several key players in the overall nitrogen cycle, but the ones who tie it all together are nitrifying bacteria. If these nitrifying bacteria are present in sufficient numbers to efficiently process toxic ammonia and nitrite into relatively benign nitrate, we consider the system to be "cycled". However, this doesn't simply happen overnight. It takes some time for the bacterial population to establish, usually between several weeks and several months, depending on various factors. When a system is just embarking on this process, and until it has completed, we say the system is "cycling". The words "cycling" and "cycled" are really just words used to describe the state a system is in, with regard to the overall process of nitrification.

The Cycling Process Begins
For all practical purposes, the nitrogen cycle starts when fish food (rich in nitrogen), or some other nitrogen source (like ammonia), is first added to the system. Fish food is the primary source of nitrogen input in an aquaponic system. Fish consume the fish food, utilizing about 25% of the nitrogen in the food for growth, and then excrete the rest as ammonia. This ammonia takes on two different forms in water, un-ionized ammonia (NH3) and ionized ammonia, called ammonium (NH4+). As previously mentioned, ammonia (NH3) is highly toxic to fish, but ammonium (NH4+) is not. Typically, only about 10% of the total ammonia nitrogen (TAN) in a system consists of this toxic ammonia form, but it doesn't take much to kill fish, so it has to be dealt with quickly. The system's pH plays a significant role in determining the ratio of ammonia to ammonium. Temperature plays a role as well, but to a much lesser extent. Without getting too terribly technical, the higher the pH and temperature, the higher the percentage of toxic ammonia you'll have as part of the overall TAN mix.

The Nitrification Process
Once there is sufficient ammonia in the system, the first group of nitrifying bacteria (primarily Nitrosomonas and some others) begin converting it by way of oxidation into nitrite (chemical compound NO2-), and the population increases rapidly as a result. We call this group of bacteria "ammonia oxidizing bacteria" (AOB). During this phase of the cycling process, the system will typically experience a considerable spike in nitrite levels and a reduction in TAN (ammonia/ammonium). However, just like ammonia, nitrite is also quite toxic to fish, so we rely on another group of bacteria to continue the cycle. Now that nitrite is present, a new group of bacteria (primarily Nitrobacter and some others) begin to populate the system. They convert the nitrite by way of oxidation into nitrate (chemical compound NO3-). We call this group of bacteria "nitrite oxidizing bacteria" (NOB).

Nitrogen Uptake by Plants
The vast majority of terrestrial (land dwelling) plants prefer their nitrogen (N) source to be in the nitrate form. Secondarily, they'll also take up ammonium, but in the presence of readily available nitrates, they'll take up ammonium in much lower amounts. Many aquatic (water dwelling) plants on the other hand tend to have a higher preference for ammonium over nitrate. These differences of N uptake preference between terrestrial and aquatic plants has frequently caused confusion for those just entering the world of aquaponics. Since aquaponics is primarily focused on terrestrial plant production, we're going to keep it simple and restrict this discussion to terrestrial plants and nitrates. Think of nitrates as "plant food".

As long as you continue to add fish food, and the nitrification process is not hindered or interrupted, your system will continue to produce nitrates. These nitrates will then be "consumed" by your plants. If there are not enough plants growing in the system, nitrate levels will climb higher and higher. If you have an overabundance of plants in relation to the amount of fish food you are adding, the nitrate levels will fall, and your plants will compete for them immediately as the become available. Plant growth will then suffer.

Maintaining the Nitrogen Balance
There is no such thing as a self-balanced aquaponics system. Maintaining a healthy, productive aquaponics system requires some monitoring, and making adjustments when necessary. We strongly recommend routinely checking your system's water temperature, pH, ammonia, nitrite and nitrate levels. There are numerous electronic meters available for this, but they tend to be quite expensive, and are really only suitable for very large systems due to the high cost. There are also chemical test kits available, which are extremely affordable and provide very accurate results for our needs. We routinely recommend the API Freshwater Master Test Kit. It costs around $25 or less in the US, will last for about 800 total tests, and is available at many pet stores, garden pond stores and online suppliers. Armed with a test kit, you will be able to determine what adjustments you need to make and when you need to make them.

Here are the most common scenarios you will encounter that require adjustments:




Declining pH - Generally speaking, you will want to maintain your cycled system pH around 6.8-7.2. If it falls below this range, the nitrifying bacteria will be adversely impacted. You need to add a base. There are commercially available products for this, but you can also use relatively common chemical salts like sodium bicarbonate, calcium bicarbonate, potassium bicarbonate, calcium hydroxide, calcium chloride and many others. Specific recommendations are beyond the scope of this article, but will be featured in a later article related to maintaining pH levels.


Rising ammonia levels in an established system - In a properly performing aquaponics system, ammonia levels should barely be traceable. The AOB's should be "processing" them almost as quickly as they become available in the system. There are numerous causes of elevated ammonia levels, but here are several of the most common: Overfeeding, inadequate biofiltration, interruption to the AOB population


Rising nitrite levels in an established system - In a properly performing aquaponics system, just like ammonia levels, nitrite levels should barely be traceable. The NOB's should be "processing" them almost as quickly as they become available in the system. Some of the more common causes include: Inadequate biofiltration, interruption to the NOB population or nitrate to nitrite "reversion" or denitrification caused by Anoxic/anaerobic (low/no oxygen) areas in the system where heterotrophic bacteria "convert" existing nitrates and accumulated solids into nitrite which the NOB's are unable to keep up with.


Extremely elevated nitrate levels in an established system - It is usually ideal to have some stockpiled nitrate exist in the system, but if it begins to climb to extremely elevated levels, you could potentially risk a resulting nitrite spike due to denitrification. Either you need to decrease your fish food input, or even better, add additional plants to take up the excess production.


Inadaquate or trace levels of nitrate in an established system - Either you need to increase your fish food input or reduce your plant mass by culling or harvesting.

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蔬菜對溫度日照條件的要求

蔬菜對溫度日照條件的要求
全日照  8個小時日照 瓜類、茄果類、豆類、山藥、豆薯(地瓜)。番茄、黃瓜、茄子、辣椒等喜溫中、強光性
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其次是根莖類,如:馬鈴薯、甜菜、胡蘿蔔、白蘿蔔、甘藷、山藥等等。至少需半日照,才能生長,芋頭雖喜歡全日照,但比其他蔬菜耐蔭。 
需要中等光照大白菜、甘藍、芥菜、蒜、洋蔥。 

長日性蔬菜白菜、甘藍、芥菜、蘿蔔、胡蘿蔔、芹菜、菠菜、萵苣、蠶豆、豌豆、大蔥、洋蔥。

短日性蔬菜豇豆、扁豆、莧菜、空心菜。         

中光性蔬菜黃瓜、番茄、茄子、辣椒、菜豆

菜豆

菜豆喜溫暖,不耐高溫和霜凍。菜豆種子發芽的適溫為20-30℃;在40℃以上的高溫和10℃以下的低溫,種子不易發芽。幼苗生長適宜氣溫為18-25℃。花芽分化的適宜氣溫為20-25℃,過高或過低溫度易出現發育不完全的花蕾、落花。

菜豆對光照強度的要求較高。在適宜溫度條件下,光照充足則植株生長健壯,莖的節間短而分枝多,開花結莢比較多,而且有利於根部對磷肥的吸收。當光照強度減弱時,植株易徒長,莖的節間長,分枝少,葉質薄,而且開花結莢數少,易落花落莢。

菜豆根系強大,能耐一定程度乾旱,但喜中度濕潤土壤條件,要求水分供應適中,不耐澇。生長期適宜土壤濕度為田間最大持水量的60%-70%,空氣相對濕度以80%為宜。開花結莢期對水分最敏感,此期土壤乾旱對開花結莢有不良影響,開花數、結莢數及莢內種子數減少。土壤水分過大時,下部葉片黃化,早脫落。空氣濕度過大會引起徒長、結莢不良。

菜豆具有深根性和根瘤菌,對土壤的要求不甚嚴格,但仍以土層深厚肥沃、排水良好的輕砂壤土或粘質壤土為好。土壤過於粘重、低溫、排水和通氣不良則生長不良,炭疽病重。菜豆喜中性至微酸性土壤,適宜的土壤pH為5-7.0,其中以州6.2-6.8最適宜。菜豆最忌連作,生產中應實行2-3年輪作。

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黑檸檬

黑檸檬
Dried lemons are actually limes and are used heavily in Persian Gulf and also Iranian cuisine where they add a strong bitter flavor in addition to sourness. They are made by boiling ripe limes in salt water, and then sun drying until the insides turn black. The outside color varies from tan to black. They are sold whole or ground.

Black Lime is a spice used in Middle Eastern dishes. It is made by boiling fresh lime in salt water and sun drying until the insides turn black. The outside color varies from tan to black. It is sold whole or ground.

黑檸檬實際上是使用萊姆,並且在波斯灣和伊朗料理中被大量使用,除了酸味外,它們還添加了強烈的苦味。它們是利用鹽水煮成熟萊姆,然後曬乾,直到內部變黑。外部顏色從棕褐色變化到黑色。他們可以整顆或切片販售。
黑檸檬是用於中東菜餚的香料。它是通過在鹽水中煮沸新鮮的檸檬並經天然乾燥,直到內部變黑。外觀從棕褐色變成黑色。
USE Black limes are usually used in legume, seafood or meat dishes. They are pierced, peeled or crushed before adding them to the dish. After cooking they become softer and edible. They can also be powdered and added to rice dishes. Powdered black lime is also used as an ingredient in Gulf-…

為何冰箱冷凍室非得是零下18度?

為何冰箱冷凍室非得是零下18度? 不少家庭的冰箱有led面板,可顯示冷藏室和冷凍室溫度。每次看到那個零下18℃,不少人,包括筆者在內就會禁不住提出一個小疑問:為什麼冷凍室溫度非得是零下18℃?最多零下1℃不就結冰了嗎?搞這麼低溫度實在是浪費電呢。

聰明如很多人是這樣推測的

百思不得其解,於是很多人,包括筆者在內就開始推測後面的機制了。冷凍室的零下18℃其實不費電,相反,它是節約電力的一個好措施。為何?

冰箱隔一段時間,內部溫度升高後,它就要啟動壓縮機,嗡嗡嗡的。頻繁啟動壓縮機不僅耗電,冰箱的壽命也會降低,還有就是很吵人。怎麼辦?簡單,先把冷凍室的溫度搞得低低的,比如零下18℃左右。


然後,冷凍室的冷氣往上走,來到冷藏室,如此,就能長時間保持冷藏室的溫度處於0到8℃以內了。

待冷凍室的冷氣散失過多,溫度升高到零下幾度時,再啟動冰箱的壓縮機把溫度再次降到零下18℃,如此,冰箱的啟動次數就變少了。

實際是這樣嗎?很遺憾,不是。

原因之一:不一樣的水

水到零度以下就結冰了,這是絕大多數人的認識。然而仔細一想,這不適用於冰箱的冷凍室。因為冷凍室存放的不是上百升礦泉水,而是各種各樣的食物。

食物中含有大量水這沒錯,但這些水同時含有大量的鹽、糖等物質。就像每1升海水中大約含有35克鹽,所以平均起來,要到零下1.33℃時海水才會結冰。

因此,要想把食物凍結,並不是溫度只要達到水的冰點就可以,得保證足夠低的溫度,食物中的水才能凍結,這很重要,因為食物中只要有液態水存在,這就等於是為各種細菌的繁殖提供了必備條件。

圖為牛肉薄片在不同溫度和不同時間內測得的牛肉中凍結水量的曲線。

當牛肉薄片的溫度為零下4℃時,只有70%的水分被凍結;溫度下降到零下9℃左右時,也還有3%的水分未凍結;即使牛肉薄片的溫度降低到零下18℃時,也不是100%的水分都被凍結住。

原因之二:嗜冷微生物

根據微生物對不同溫度的適應範圍,可將微生物分為三大類,嗜熱菌、嗜溫菌和嗜冷菌。在食物的冷藏和冷凍過程中,我們面對的「敵人」是嗜溫菌和嗜冷菌。

一般來說,能引起食物腐敗和食物致毒的嗜溫菌,在低於3 ℃情況下不產生毒素,當然,個別菌種例外。

而對於嗜冷菌,一般得在零下10 ℃到零下12 ℃時才會停止生長。

有的黴菌甚至要到零下15~零下18 ℃時才會停止生長。

瞧,我們以為,零下幾攝氏度後微生物就被殺死或停止繁殖了,但…