The soil fertility means the amount of plant nutrient present in a soil that is available for plant uptake. The following is a list of the macro and micro soil nutrients:
Table 1: Shows the macro and micro nutrients required for optimum plant growth.
|Macro Soil Nutrients||Micro Soil Nutrients|
DETERMINING SOIL NUTRIENT STATUS
|Insolable: incapable of being dissolved. |
Leachable: drain away from soil, ash, or similar material by the action of percolating liquid, especially rainwater.
Soil Analysis: The technique of soil sampling is discussed fully in the Soil Science Lectures, but samples of a soil can be analysed for the major nutrients above routinely. Analysis of minor elements could be done as a special request, but normally the evidence becomes visible in the crop before anything is done to it. Fertiliser recommendations can be made on the basis of a soil analysis.
- Leaf Analysis: In certain crops especially plantation crops such as citrus; an analysis of a sample of leaves indicates the fertility of the soil on which the crop is growing.
- Leaf analysis show exactly what the plant has absorbed and can detect deficiencies (yield and health) before they are noticeable. Analysis is the most precise method of observing nutrient levels in plants.
- Deficiency Symptoms: Minor elements as mentioned above can be discovered in this way. There is literature available which shows pictures of deficiency symptoms in most common crops.
APPLICATION OF FERTILISERS
- Basal Dressing: This is the fertiliser applied before or at planting time. It is normally a crops’ phosphate requirement as this element is very insoluble and needs to be incorporated into the soil. It normally includes all a crops potassium requirement. Potassium is more soluble and could be applied later but is convenient to supply as a basal application. This includes a portion of nitrogen which is approximately 1/3 of a crop’s requirements. Nitrogen is very soluble and hence leachable and needs to be applied when required.
- Top Dressing: is an application of fertiliser to a crop once it has been planted and is normally nitrogen, being the balance of the crops’ requirements that was not applied as an initial application (Basal Dressing). The balance can also be split into 2 applications if there is a large amount of nitrogen needs to be applied or if the growing season is long.
Figure 1: Shows fertiliser spreader topdressing a field which is also known as broadcasting.
- Maintenance Dressing: A maintenance dressing is a level of fertiliser necessary to maintain the level of that nutrient in a soil once the crop has been removed. This normally refers only to the relatively insoluble elements, calcium and phosphorous.
Calcium levels can be maintained by dressing every 4 – 5 years and the phosphorous levels by annual dressings.
- Broadcast: Fertiliser can be broadcasted onto a land by hand, machine (distributor) or aircraft. This gives an even coverage and needs to be incorporated by harrowing which should be done before planting commences. Fertiliser can also be broadcast during the topdressing process.
- Banding: Fertiliser is trickled onto a land usually by machine (50mm below and to the side of the seed) and incorporated at the same time. The plants and seed are planted simultaneously by a planter machine. Tobacco ridging or maize planting are examples.
FORMS OF FERTILISERS
Pure elements (straights) often come in powder form but are difficult to apply as they do not ‘flow’ easily and get blown by the wind. The most common form is granular particles approximately 2 – 3mm in diameter and ‘flow’ more easily.
All our fertilisers, which are mixtures of major elements (Nitrogen, Phosphorus, and Potash) comes in this form and are easy to apply. Fertilisers also come in many different ratios and percentages available to plants and have different micro elements attached to them. All fertilisers should only be applied according to soil analysis recommendations.
Soils may be acid or alkaline (see Soil Science Course), depending on the concentration of Hydrogen in that soil. This is measured on a scale called a pH scale and individual crops have their own specific optimum pH at which they will grow best. Soils become acid through cropping (an exception may occur in the case of an irrigated crop), and the soil needs lime to alter the pH to a more favorable level.
Figure 2: Shows a powered form of fertiliser
Figure 3: Shows a granular form of fertiliser
- 2. CROP ESTABLISHMENT
This covers the planting of the crop, the germination of the seeds and the establishment of young plants. It is dealt with under the following headings:
Materials: These can be seeds, seedlings or propagation material such as runners, stolon’s, tubers, etc. Try to make a collection of seeds of different farm crops for identification purposes. Remember that most seeds which are bought are coated with a pesticide of some sort and should not be eaten because, when coated they are poisonous. Seed should be stored in a dry, rat-proof store room until ready to be planted.
METHODS OF PLANTING
- Hand: This method is used for broadcasting seed, planting seedlings and propagation material such as potato tubers. This is a laborious time-consuming method and needs careful supervision.
Figures 4 and 5: Shows the hand broadcasting method of planting and how the seeds are scattered.
Source: rabbitrunfarm.blogspot Source: modernvictorygarden
- Machine: Seed drills are used for sowing seed in a steady trickle. Seed planters will drop individual seeds and can space them more accurately than a drill. A seed drill can be set to sow so many kilograms of seed per hectare, whereas a planter is set to plant one seed so many centimetres down the row.
Figures 6 and 7: Show the difference between a seed drill and a seed planter. The seed drill has a much closer spacing and is used mainly for finer seed. The seed planter has a large spacing and can plant individual seeds.
Source: jordanatveng Source: philmech
DEPTH OF PLANTING
A general rule is that the larger the seed, the deeper it is planted. Small seeds are planted near the soil surface. Maize seeds are planted at a depth of 50 – 100mm and potato tubers at a depth of 150mm. The nearer the seed is planted to the soil surface, the greater the risk of the soil and germinating seedlings drying out. Small seeds are planted near the soil surface and should have a mulch of organic matter applied to cover the surface to preserve the soil moisture.
POPULATION AND SPACING
There are an optimum number of plants per hectare for each crop which has been determined by research. Crops are planted where possible in rows to reduce the trampling on the crop, for inspection, pest control, weed control and harvesting, etc. Wheat is an exception and can withstand trampling for about the first 8 weeks.
The distance between rows is called the row spacing or inter-row spacing. The distance between plants within a row is called the in-row spacing or intra-row spacing.
When drilling a crop it is important to know how many seeds there are in a certain mass of seed, e.g. 100 seeds/1kg to determine the desired population in terms of kg of seeds per hectare.
TIME OF PLANTING
The time of planting is important in several ways:
- To gain the greatest benefits from the available rainfall;
- To coincide with the optimum day length pattern (photoperiod) and;
- To avoid subjecting the newly planted seeds to excessive heat or cold (frost).
The date of planting is a very important in obtaining maximum yields, and will be discussed specifically in relation to each crop.
FIRST PLANTING RAIN
The First Planting Rain (F.P.R.) is defined as the first effective shower of rain for the season and has to be sufficient to wet the soil to a depth of 100mm. This needs 25mm of rain on a clay soil and 15mm of rain on a sandy soil. As you know from your Soil Science Lectures, rain penetrates a sandy soil more easily and more deeply than i a clay soil.
Rainfall records have been analysed for all the farming areas of the country and information is available which will inform of the start of the rainy season in different parts of the country.
DRY PLANTING, WATER PLANTING AND WET PLANTING
Dry planting means the planting of a crop before the First Planting Rain has fallen. This has to be planned carefully to avoid the partial germination of the seed followed by a dry spell which will kill the seedlings’. This is when the information about the 80% probability of the First Planting Rain falling in an area can be used but it still a risky procedure. The advantage of the crop being planted in dry conditions makes both hand and machine planting easier. In addition the seed is in the ground when the First Planting Rain falls which will germinate and start growing.
Water planting means planting the seed or plant, adding water at the same time to establish the seedlings or germinate the seed. This is done before the First Planting Rains so that the crop will be established when the first rain falls. Water planting is often used with tobacco seedlings and sometimes with maize seed.
Wet planting means planting the seed or plants after the First Planting Rain has fallen and the ground is wet. This normally makes the actual planting operation difficult because of the wet conditions, but does mean that the seed will germinate immediately. This method is less risky than dry planting because the rains have arrived.