How to use fertiliser to restore degraded soil

It has long been known that the soils of Sub-Saharan Africa are degraded. Poor soils mean poor crops and poor yields.

Take action now and restore fertility to the soils on your farms, fields and in your food gardens. Degraded soils are over-used and exhausted, they have little topsoil, poor structure, low organic matter and poor fertility. They may be saline, too acid or too alkaline to support reasonable crop yields.

No matter how carefully you till, plant or irrigate, you will never get a good harvest from degraded soils. Spend the time and resources fertilising and improving your soils – it’s an investment guaranteed to give you good returns.


A farmer can take various routes when he, or she, decides on his, or her, fertiliser protocol. Some farmers use purely inorganic or synthetic fertiliser, which is water soluble and fast acting.

The organic fertiliser method has gained traction recently. Although it is more of a slow release fertiliser, and not water-soluble, it helps improve soil structure and repopulate micro-fauna and flora in the soils. So there are long-term benefits associated with the use of organic fertiliser. Processed sea weed and its extracts, bone-meal, composted manure, chicken litter and organic waste are all organic fertilisers.

The third approach is to combine both organic and inorganic methods. The grower then invests in the long-term health of the soil with organic fertiliser, but keeps yields as good as possible with synthetic fertiliser.


If you are a newcomer to agriculture and the fertiliser jargon (farmer speak) often doesn’t make sense to you – don’t be intimidated. Ask, ask and ask again – it’s the only way to learn. Don’t miss the opportunity because you don’t feel confident enough to ask. Better to make a fool of yourself than to stay ignorant.

Farmers talking about fertilisers rattle off ratios, 2:3:3; 2:3:1; 5:3:2, interspersed with words like macro-nutrients, micro-nutrients and trace elements, and the letters N, P and K.

It sounds like gobbledegook and gives one the glazed eye look. But understanding the basics of soil fertility is essential to progress.

On the outside of the fertiliser bag, the primary plant nutrients (the macro-nutrients), Nitrogen (N), Phosphorus (P) and Potassium (K) are clearly marked, in that order, in the specific ratios in which they occur in that fertiliser.

For example 2:3:1 indicates 2 parts of N; 3 parts of P and 1 part of K. The total number of parts in this case is 9.


Knowing your soil is a clear priority. One can’t get away from it – the soil test is important and absolutely worth the money. How can you improve the soil, and thus the yields, if you don’t know what your soils lack? And applying fertiliser that is wrong for your soils is just a waste of money.

An augur takes a core of soil out of the land which the farmer wants to test.


Nitrogen (N) is a growth fertiliser that especially boosts leafy growth. Pasture farmers will use N on their pastures to improve and speed up grass growth. N is also involved in fruit and seed production. N is often used as the starter fertiliser.

Phosphorus (P) is important for the plant’s energy and is a key nutrient in promoting root growth and flowering. P supports resilience and the ability of a plant to withstand stress.

Potassium (K) stimulates rooting, blooming and fruit production and helps with disease control.

While N can be broadcast over a land, P and K must be placed deeper into the soil where roots can use them. (For small-scale farmers, South African implement designer, Michris Janse van Rensburg, has designed a superb piece of hand-held equipment that cuts a slot and dispenses the correct amount of P and K deeper into the soil where roots can access the fertiliser)

The fertiliser is said to be complete if all three of the major (macro) nutrients are present.

Incomplete fertilisers have a nutrient missing, which is shown by a zero in the ratio; eg 12:5:0 means there is no K in that fertiliser.


What do the ratios on the fertiliser bags mean to you the farmer, and how do you make sense of them and apply these ratios to your soil? Of course one would not know what the soil needed unless there was a soil test.

The easiest way to explain this is to look at some of the fertilisers.

Example 1: 2:3:4 (30) Always in the order N:P:K

The fertiliser bag shows the ratio 2:3:4 and in brackets 30, a percentage by mass of nutrients in the fertiliser.
Add the numbers 2 (parts N) +3 (parts P) +4 (parts K) to get a total of 9 parts out of a mass percentage of 30%.
The remaining 70% of the fertiliser is made up of fillers, usually lime.

  • The N concentration is 2 (parts) out of 9 (total parts) X 30 (%) = 6,7% or 67g of N in 1kg of fertiliser.
  • The P concentration is 3 (parts) out of 9 (total parts) X 30 (%) = 10% or 100g of P in 1 kg of fertiliser.
  • The K concentration is 4 (parts) out of 9 (total parts) X 30 (%) = 13,3% or 133g of K in 1kg of fertiliser.

The three nutrients add up to 300g of active fertiliser per kilogram. The remaining 700g is the filler.

A good yield comes from fertile soil.

Example 2: 3:1:5 (38)

The fertiliser bag shows the ratio 3:1:5 and the percentage by mass in the fertiliser is 38.
Add the numbers 3 (parts N) + 1 (part P) + 5 (parts K) to get a total of 9 parts.

  • N concentration is 3 (parts) out of 9 (total parts) X 38 (%) = 12,7% or 127g of N in 1kg of fertiliser.
  • P concentration is 1 (part) out of 9 (total parts) X 38 (%) = 4,2% or 42g of P in 1kg of fertiliser.
  • K concentration is 5 (parts) out of 9 (total parts) X 38% = 21,1% or 211g of K in 1kg of fertiliser.

Applied or added in much smaller doses are the micro-nutrients: silicon, calcium, sulphur and magnesium.

Needed in minute quantities (measured in parts per million (ppm)) are the trace elements chlorine, iron, boron, zinc, copper, manganese, molybdenum, sodium and cobalt. The trace elements are often added into the fertiliser.


Check the length of your step. In my own case I must add some spring to my step if I want to calibrate my pace to 1m per step. A reasonably tall man has a fairly easy pace of 1m per step.

If your pace is 1m and you toss a handful of fertiliser in a curved motion into the air at every step you should apply about 60g/m2 (600kg/ha). Halve the amount per square metre by dispersing the fertiliser every second step and it should be 30g/m2 (300kg/ha).

These manual methods can be laborious and time consuming.

Michris Janse van Rensburg’s range of hand-held implements specifically designed for small-scale farmers is certainly worth looking at for any smallholder interested in improving his fertility.

share this