抄襲文章係列－土壤的救星

這篇也是在診所看到的，雜誌名字好像是《Good organic Gardening》作者是Anfelo Eliade。這篇文章很好的講述了土壤的各種改良劑的使用機理，是我現下正需要的。

 

Soil saviours

By Anfelo Eliade

 

Various soil amendments (各種土壤改良劑) can be used in autumn to restore structure and fertility to tired and overworked garden beds. Increasing productivity over the cool season and maintaining optimum soil health.

 

Most summer vegetables are heavy feeders and once they’ve yielded their harvest, they often leave the soil somewhat lacking and depleted (疲乏和耗盡). Before replanting with cool season crops, it’s important to replenish (補充) the soil to maintain productivity over the autumn-winder period.

 

Healthy soil must contain organic matter and a reserve of nutrients for plant growth. It should hold enough water for plant requirements while still draining well. Last , but not least, it must have good structure to allow water, air and plant roots to move freely through it. These three factors are what we seek to maintain for good plant health and maximum productivity.

A good soil care routine can work wonders for a garden and, when it comes to timing, the beginning of spring (September) and autumn (March) are the best times to rejuvenate （複原） the soil.

 

Keeping it simple

 

The primary soil amendments to add at these times are compost to improve soil structure (which improves drainage in heavy clay soils and moisture retention in fast-draining sandy soils) and balanced fertilisers to replace lost nutrients.

 

Here’s how to improve the soil in three easy steps:  

 

·      Dig compost into the soil, mixing one part compost to three parts soil by volume. Any more compost than that and the soil level will sink as it settles.

 

·      Dig manure into the soil, using half as much manure as the volume of compost added (much less for poultry manure). Add any other soil amendments as desired. Water it all in.

 

·      Wait one to two weeks before planting to allow the soil to settle and to prevent (避免) possible fertiliser burn of tender seeding roots (especially when using poultry manure).

 

Repeating this process twice a year is the very least that should be done to keep the soil fertile and friable (鬆散). For maximum productivity, fertilise every 6-8 weeks from September through to March.

 

The no-dig version of the soil preparation process requires one extra step but it’s much quicker and takes far less effort:

·      Add a thin layer of manure or other fertiliser to the soil surface.

·      Add a layer of compost and any other soil amendments.

·      Cover with mulch (to lock nutrients into the soil) and water in.

·      Wait a week or two before planting.

Manures need to be covered or dug in to prevent the loss of nitrogen to the atmosphere.

 

Replacing nutrients

 

Plants require three macronutrients in large quantities: nitrogen (N) for leafy green growth, phosphorus (P) for root development, and potassium (K) for flowering and fruiting.

The secondary macronutrients, which are required in lower quantities, are magnesium (Mg), calcium (Ca) and sulphur (S). Micronutrients are nutrients plants require in trace amounts, such as iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni) and chlorine (Cl), and these are referred to as trace elements in fertilisers.

Manures are a great way to replenish depleted soil nutrients, as are specially formulated balanced fertilisers. These contain all the macronutrients necessary for plant growth.

Green manures are fast-growing annual crops, a combination of legumes to add nitrogen to the soil and grasses to add bulk organic matter. They’re sown as seeds and left to grow. When the plants begin to flower, they’re chopped down and laid flat or dug in, then left to rot down for six weeks before replanting the garden bed. Warm-season green manures typically include plants such as buckwheat (蕎麥), cowpea (豇豆), millet (粟，小米), lablab, mung bean （綠豆） and soybean, while cool-season green manures usually contain broad bean, fenugreek (葫蘆巴)， lupins (羽扇豆，魯冰花), mustard, oats, subclover (子苜蓿)

and vetch （野豌豆） . 

Rock dust is a popular soil amendment that slowly releases phosphorus and important trace elements into the soil. It’s often used in the first stages of no-dig garden bed construction as part of the soil –building process, especially when building soil from scratch.

Seaweed extract as a soil conditioner is a great source of trace elements and also contains various hormones that act as growth stimulants (興奮劑) for plants, such as auxins (生長素), gibbelerins , cytokinins （細胞分裂素） and betaines.

 

Improving soil water issues and everything else in the process

 

Water tends to pool in heavy clay soil, causing waterlogging and root rot. Conversely, sandy soils aren’t very moisture-retentive, allowing water to pass straight through, leaching out water-soluble nutrients from soil.

Compost fixes almost every soil issue! In sandy soils the organic matter increases moisture retention by acting like a sponge, soaking water up through capillary action. Humus, produced by the decomposition of compost, can bind nutrients and slowly release them, improving nutrient retention in sandy soils. Digging compost into clay soil incorporates larger particles of organic matter into the soil, improving soil structure and increasing drainage.

Gypsum (calcium sulphate,石膏 ) is used as a “clay breaker” to improve the structure of sodic clay (鈉黏土) soils only (clays that disperse in water, with more than 5 per cent exchangeable sodium and low salinity). Since gypsum contains calcium and sulphur, it can serve as a source of these nutrients for plants, without changing the soil pH. The way gypsum breaks up sodic clays is by replacing sodium ions (Na+) with calcium ions (Ca+2), which causes clumping of clay particles (flocculation)( 絮凝)and helps aggregate the soil.

Aggregated clay is still clay, but adding compost allows organic matter to work its way between the clay particles to improve the soil significantly.

Wetting agents should only be used when soils are water repellent(憎水性). Safe, natural organic wetting agents are made of humates (腐殖酸) and fulvates （棕黃酸鹽）, which are components of soil humus(土壤腐殖質); saponins(皂苷), natural soap-like glycoside compounds found in plants; or alginates (藻酸鹽), which are gel-like substances derived from seaweed.

Zeolite (沸石) is a naturally occurring mineral with a porous crystalline structure and an incredibly high surface area, allowing it to hold up to 60 percent of its weight in water, and also making it useful for improving soil aeration. Having a very high cation exchange capacity(陽離子交換能力), zeolite reduces nutrient loss by binding nutrients such as ammonium and potassium, later releasing them slowly back into the soil. Unlike most other soil amendments, zeolite doesn’t break down over time, so once it’s applied it keeps working indefinitely.

Biochar (生物炭)is another a highly porous soil amendment material that similarly increases water retention (保水率) and reduces fertiliser leaching (浸出).

 

Adjusting soil pH

Soil pH can be raised to make it more alkaline through the addition of garden lime (calcium carbonateCaCO3) or dolomite lime (calcium magnesium carbonate磷酸鈣鎂). Both add calcium to the soil but dolomite also adds magnesium, making it a better choice.

Sulphur (硫) is used to reduce the soil pH to make it more suitable for acid-loving plants. It takes about six months for this soil amendment to take full effect and reduce the pH by about 0.6 points. The pH scale is logarithmic (對數的), not linear, so lowering the pH one point makes the soil 10 times more acidic. Two points equals 100 times more – that should put things into perspective!

Add these amendments if your plants require them, but don’t mess too much with soil pH, as the complex soil chemistry buffers pH fluctuations to maintain a stable environment, and some nutrients will increase in availability while others may decrease as the soil pH is altered, leading to potential human-caused (人為引起的) plant nutrient deficiencies(營養缺乏) or excessive nutrient toxicity (營養過剩).

How critical is soil pH if government agriculture departments advise that a soil pH of 5.2 to 8.0 provides optimum conditions for most agricultural plants? It’s risky playing with soil pH knowing that the home garden colour indicator pH test kits are quite inaccurate and should only be used as a rough guide. Best to play it safe when amending soil.