Land potential assessment

The agricultural land potential of an area is determined by the climatic, slope and soil conditions. Informed decisions about land use can therefore only be made if the classification of land potential and knowledge of the geographical distribution within an area are known. The climate capability classes in the table below are based on broad recommendations.

Climate capability classes

Climate capability class	Limitation	Description
C 1	None to slight	The local climate is favourable for good yields for a wide range of crops throughout the year
C 2	Slight	The local climate is favourable for a wide range of adapted crops and a year-round growing season. Moisture stress and lower temperatures increase risk and decrease yields relative to C1.
C 3	Slight to moderate	Slightly restricted growing season due to the occurrence of low temperatures and frost. Good yield potential for a moderate range of adapted crops.
C 4	Moderate	Moderately restricted growing season due to low temperatures and severe frost. Good yield potential for a moderate range of adapted crops but planting date options are more limited than C3.
C 5	Moderate to severe	Moderately restricted growing season due to low temperatures, frost and/or moisture stress. Suitable crops at risk of some yield loss.
C 6	Severe	Moderately restricted growing season due to low temperatures, frost and/or moisture stress. Limited suitable crops frequently experience yield loss.
C 7	Severe to very severe	Severely restricted choice of crops due to heat, cold and/or moisture stress.
C 8	Very severely restricted crop choice	Very severely restricted choice of crops due to heat and moisture stress. Suitable crops at high risk of yield loss.

Criteria for climatic capability classes are as follow:

The ratio of mean annual precipitation (MAP) to annual Class A pan:

0.30 – 0.34 = C8
0.34 – 0.38 = C7
0.38 – 0.41 = C6
0.41 – 0.44 = C5
0.44 – 0.47 = C4
0.47 – 0.50 = C3
0.50 – 0.75 = C2
0.75 – 1.00 = C1

Mean September temperatures for C6-C1, where temperature data are available:

< 10 ^oC = C6
10 – 11 ^oC = C5
11 – 12 ^oC = C4
12 – 13 ^oC = C3
>13 ^oC = C1

Mean June temperatures:

< 9 ^oC = C5
9 – 10 ^oC = C4
10 – 11 ^oC = 3
11 – 12 ^oC = C2

Mean annual temperatures:

> 20 ^oC = C1, C7, C8
18 – 12 ^oC = C2, C5, C6, C7, C8
16 – 18 ^oC = C3, C5, C6, C7
12 – 16 ^oC = C4, C5, C6
< 12 ^oC = C7

To determine the climate capability class from the information above, the following steps should be followed:

Step 1: Obtain the mean annual precipitation (MAP) and annual Class A pan evaporation figures for the area in question.

Step 2: Determine the ratio of MAP to Class A pan by dividing the MAP by the Class A pan. The ratio will determine climate capability classes.

Step 3: If monthly temperature data are available, using the mean September and June temperatures will narrow the selection to individual classes. This step is, however, only applicable if the MAP: Class A pan ratio is greater than 0.5.

Example:

a) MAP = 750

Class A pan = 1250

MAP:Class A pan = 750:1250

MAP:Class A pan = 0.6

0.6 falls into category C2.

b) But September temperature = 16 ^oC

Therefore category = C1

c)June temperature = 14 ^oC

Therefore, the climate class stays as C1. If the June temperature were 12 ^C, it would be downgraded to a C2.

Land potential classes have been developed to guide crop production practices and avoid the risk of yield loss. The criteria to identify land for suitable usage are described in the table below.

Land potential and land potential class

Land potential	Description of land potential class
L 1	Very high potential: No limitations. Appropriate contour protection must be implemented and inspected.
L 2	High potential: Very infrequent and/or minor limitations due to the soil, slope, temperatures pr rainfall. Appropriate contour protection must be implemented and inspected.
L 3	Good potential: Infrequent and/or moderate limitations due to the soil, slope, temperatures and rainfall. Appropriate contour protection must be implemented and inspected.
L 4	Moderate potential: Moderately regular and/or severe to moderate limitations due to soil, slope, temperatures and rainfall. Appropriate permission is required before ploughing virgin land.
L 5	Restricted potential: Regular and/or moderate to severe limitations due to soil, slope, temperatures and rainfall.
L 6	Very restricted potential: Regular and/or severe limitations due to soil, slope, temperatures and rainfall. Non-arable.
L 7	Low potential: Severe limitations due to soil, slope, temperatures and rainfall. Non-arable.
L 8	Very low potential: Very severe limitations due to soil, slope, temperatures and rainfall. Non-arable.

Land in a low rainfall area that is categorised as land capability class 1 does not have the same agricultural potential as land in a high rainfall area in the same category. If a climate capability assessment were conducted in both areas, the land potential would be very different. The land capability class 1 in the high rainfall area could have a climate capability rating of C1, resulting in a land potential of L1, which could produce 5 tons of maize/ha. However, the same land capability class in the low rainfall area could have a climate capability rating of C8, resulting in a land potential of L4, which could produce an uneconomical 1 ton of maize/ha. This land is therefore more suited for livestock production.

For farm planning purposes, a land capability survey must be carried out to ensure that land-use hazards can be identified and in managed accord