[ Home ] Introduction ] The Crop ] The Problems ] Glossary ] Credits ] Contact Us ]


Soils contain a complex mixture of chemicals including all the essential nutrients. However, the abundance or availability of any nutrient may not be sufficient to meet the crop’s needs. Fertilizers, manures and composts are used to supplement the soil’s nutrient supplies. Chemical fertilizers contain only one or a few nutrients, in high concentration. Manures and composts, which are derived from plant and animal wastes, generally contain all essential nutrients, but in lower concentrations and not necessarily in appropriate ratios.

The most commonly deficient nutrients are N, P and K. These elements are taken up in sufficient quantities that the soil becomes depleted after a number of crops have been removed. In addition, N is readily lost to the atmosphere, and P is often tightly bound by soils, making it only sparingly available to plants. This is why these nutrients are often routinely applied.

However, in many situations other nutrients are also deficient but the deficiency may not be easily recognized by the farmer. When this is the case, fertilization with NPK fertilizers will not greatly increase yields unless the deficient nutrient is also applied.

It is also important to recognize that supplying a nutrient in excess of the crop’s requirement is of no benefit to the crop. It is an unnecessary expense, and may cause environmental pollution when excess nutrients leach into streams and groundwater supplies.

The following table summarizes the uptake and fertilization method for each nutrient. Fertilizers should only be applied when they are known to be deficient, and in the minimum quantity required to correct the deficiency. This depends not only by the crop’s uptake, but also by losses due to leaching and conversion to unavailable forms in the soil or air. 



(per tonne of storage root yield)

Fertilizer quantity

(kg/ha of nutrient)

Common Sources

Fertilizer Strategy



3-5 kg

30 – 100

Urea (45% N),

Ammonium nitrate (35% N),

Animal manures (0.4 – 6 % N)

Manure buried in top of ridge before planting;

Urea as split application, part at planting plus one or two side-dressings.



0.5-1 kg

20 – 200

Triple Superphosphate (TSP) (24% P),

Single Superphosphate (10% P)

In a furrow on top of ridge (mixed with manure if used) and covered with soil before planting.



5-8 kg

50 – 200

Potassium Chloride (= muriate of potash) (50% K),

Plant mulches and composts (0.1 – 4% K)

Composts incorporated in soil; KCl half in basal application and half as side dressing (once or twice, 30 – 60 days after planting).



1-2 kg

100 - 2000

Lime (40% Ca) –only on acid soils,

Gypsum (22% Ca),

Superphosphate (23% Ca)

Broadcast and incorporated in soil before forming ridges.



0.5-1 kg

10 – 50

Magnesium Sulfate or Kieserite on neutral soils,

Magnesium Oxide or Dolomitic Lime – on acid soils

Broadcast and incorporated in soil before forming ridges. Magnesium sulfate can be sprayed on foliage.



0.2-0.5 kg

10 – 50

Gypsum (17% S),

Ammonium Sulfate (24% S),

Superphosphate (11% S)

Gypsum broadcast and incorporated in soil; other fertilizers banded.



10-20 g

2 – 10

Chelated iron, ammonium ferric sulfate,

pieces of rusted scrap iron

Soluble iron may be sprayed on foliage or banded. Scrap iron buried under hills.



5-10 g

1 – 4

Borax, Solubor (13% B)

Solution may be sprayed on foliage or banded.



10-30 g

10 - 20

Manganese Sulfate or Oxide

Solution may be sprayed on foliage or banded.



5-10 g

3 - 10

Zinc Sulfate (hydrated) (23% Zn)

Solution may be sprayed on foliage or banded.



1-5 g

1 – 7

Copper Sulfate

Solution may be sprayed on foliage or banded.



0.2-1 g

0.2 – 0.3

Sodium- or Ammonium molybdate (8% Mo),

Lime (to raise pH and availability of Mo)

Solution may be sprayed on foliage or banded.

Lime broadcast and incorporated.

Contributed by: Jane O'Sullivan

Further topics on Soil Management:

Soil management

Soil structure

Soil organic matter

Plant nutrients


Causes of nutritional disorders

Diagnosing nutritional disorders

Correcting nutritional disorders

Other topics on Crop Management:

Land preparation

Planting material preparation


Water management

Vine lifting

Integrated pest management


Postharvest practices