Plant Nutrition from the Root Environment

The need to feed We have already made the point that what is taken out of the soil must be put back, and therefore part of the soil management is the use of compost, manure or fertilisers to maintain soil fertility.

Sources of added Nutrients Organic matter is usually some form of compost or manure. Its primary benefit is to improve the quality and structure of the soil, although it also provides some nutrients. Fertilisers are concentrated forms of nutrients that have been produced by some form of processing. Note that these are not really alternatives. Organic matter is a soil conditioner that improves the quality of the soil, and soils that are only fertilised will deteriorate over a period of time.

Organic matter Of all the nutrients, nitrogen is the one most likely to be needed, as plants require a significant amount, and it is easily leached from the soil. The others likely to be needed are phosphorus and potassium, and many proprietary fertilisers contain all three. Remember that an excess of fertilisers can harm the plants and the environment.

Organic matter The nutrient content of compost and manure is low compared to fertilisers but because they are applied in bulk the effect can be similar They can be incorporated into the soil when it is cultivated or they can be applied as a surface mulch,(gradually incorporated by earthworms). Amount: One barrowload per 4 sq m. The best time to apply it: – to clay soils is in the autumn so that it can be broken down over the winter, – but in sandy soils leave it to late winter or early spring to avoid it being leached out.

Green manures These are different to other manures as they are plants that-are grown on the soil to be manured, and are incorporated directly into that soil a few weeks before a crop is to be planted. The plants are grown and used in one season and should be incorporated into the soil before they start to turn woody. Ones that can be sown in late summer and dug in the following spring are probably the most useful as they cover the bare soil in winter and protect the soil structure.

Advantages of Green Manuers 1. Provides organic matter and nutrients to the soil particularly when nitrogen fixing plants are used. 2. Protects the surface of the soil and prevents erosion or the leaching of nutrients 3. Prevents- the proliferation of weeds.

Plants Suitable as Green Manures 1. Clover (Trifolium pratense) Clover has the advantage of fixing nitrogen and can be left to overwinter. Sow from April to July. 2. Mustard (Sinapis alba) A fast growing summer crop. Sow between March and August and dig in before flowering. 3. Winter rye (Secale cereale) Sow from August to October to overwinter.

Fertilisers Fertilisers can be organic or inorganic. Organic fertilisers, such as bonemeal, are derived from material which was once living. Inorganic fertilisers, such as sulphate of ammonia, are manufactured or- derived from minerals. Inorganic fertilisers are probably more precise in their nutrient content, and may be quicker acting. Also, since the BSE crisis are considered safer to handle.

Fertilisers Fertilisers can also be straight, which means they- contain one nutrient, usually nitrogen, phosphorus or potassium, Or compound; which means they contain more than one. 'Growmore' and 'Fish, blood and bone' -are examples of compound fertilisers. Fertilisers can come as a powder to be used directly on the soil, or in a solution, or as granules.

Controlled Release Fertilisers Most fertilisers are quick acting but a comparatively recent development is the use of controlled release fertilisers which allow the nutrients to be released over a period of time. This is particularly useful for nutrients which are easily leached from the soil such as nitrogen. Originally aimed at crop production such fertilisers are now available for a wide variety of environments including pot plants and lawns.

Application of fertilisers Base dressing The fertiliser is incorporated in the soil. In a domestic garden situation it would be dug in, but in a commercial situation more sophisticated methods are used: – distributing it with the seed directly into the drill, – or applying it as a band alongside the drill. Top dressing The fertiliser is applied to the surface of the soil and relies on rain or irrigation to carry it down to the roots. For this reason the fertiliser must be soluble.

Application of fertilisers Liquid The fertiliser is dissolved in water and applied to the soil surface. This will give a faster reaction than a top dressing. Foliar feed The fertiliser is dissolved in water and applied as a spray to the leaves of the plant. Foliar feeds are quick acting and are particularly useful where the soil conditions prevent the uptake of some nutrients.

Timing of Fertilisers Nitrogen fertilisers are best applied 2-4 weeks before planting because of the possibility of them being leached out. Also, since they encourage vegetative growth, they are not applied in late summer or autumn when new growth may be damaged by winter weather. The application of other fertilisers is not so critical, but as a general rule apply in spring before new growth begins. Some crops may also require additional applications during the growing season. Whatever the method or time of application it is important to follow the manufacturer's instructions.

Comparison of bulky organic matter with fertilisers

Nutrient content of organic matter and fertilisers