Biophysical Conditions

The biophysical conditions are qualities of the land. Water, soil, and air are the components of the biophysical surroundings of any farm system. The nature and extension of natural biotopes is determined by biophysical conditions [29]. Agriculture is heavily dependent on natural biotopes because they form the main production factor of farming. Throughout the years, the components of the biophysical surroundings are changed by various land uses, resulting sometimes in near-perfect production conditions.

The quality of these components is an important factor for growing any crop or keeping most animals. Some sorts of farming can function without their natural environment (such as greenhouse systems), but they are not reviewed here because they are hardly affected by land-use planning.

The FAO has defined a land quality as "a complex attribute of land which acts in a distinct manner in its influence on the suitability of land for a specific kind of use" [30]. If the suitability of land for farming has to be increased with land-use planning, the qualities of the land have to be altered through land-use planning. The land qualities that apply to rainfed agriculture are listed in Table 2.7.

Some of these land qualities cannot be influenced by land-use planning. For example, the radiation regime is a factor that is unchangeable. The same goes for temperature regime and climatic hazards. Other land qualities are influenced by normal farming procedures. Rooting conditions are improved by plowing, moisture availability is improved

Table 2.7. Land qualities for rainfed agriculture

No.

Quality

1

Radiation regime

2

Temperature regime

3

Moisture availability

4

Oxygen availability to roots (drainage)

5

Nutrient availability

6

Nutrient retention capacity

7

Rooting conditions

8

Conditions affecting germination and establishment

9

Air humidity as affecting growth

10

Conditions for ripening

11

Flood hazard

12

Climatic hazards

13

Excess of salts

14

Soil toxicities

15

Pests and diseases

16

Soil workability

17

Potential for mechanization

18

Land preparation and clearance requirements

19

Conditions for storage and processing

20

Conditions affecting timing of production

21

Access within the production unit

22

Size of potential management units

23

Location: accessibility

24

Erosion hazard

25

Soil degradation hazard

Source:

■ [32].

by sprinklers, and nutrient availability is improved by application of manure. The improvement of these qualities is not land-use planning.

Typical land qualities that can be ranked under land-use planning are access (Nos. 21 and 23 in Table 2.7), size (No. 22), location, and shape of the farms and fields. These land qualities are reviewed in Section 2.2.2, "Spatial Conditions." Other land qualities that can be improved through land-use planning are structural soil improvements (Nos. 4,7,16, and 17), erosion control (Nos. 24 and 25), and flood hazard (l.q. 11). The nature of these qualities and the way to improve them are dealt with in other sections of this Handbook. In this chapter, the way land-use planning affects these qualities is reviewed.

Structural soil improvements can be achieved outside land-use planning but nearly all land development plans contain measures to improve the soils. The conditions of the soil are important for crops and for mechanization.

The rooting conditions, that is, the conditions for the development of an effective root system [31], refer to the ability to keep the plant in place and the plant's ability to extract moisture and nutrients. If the volume of the root system is limited, the parts of the plant that are aboveground will suffer [32]. The characteristic by which the rooting conditions are measured is the effective soil depth. Additional characteristics include soil structure, consistency, and texture. Land-use planning involves measures to improve rooting conditions, such as deep ploughing, adding chalk or sand to clay or peat, removing of the topsoil, or applying drainage. If the land-use plan contains uses of land that require perfect rooting conditions, the measures should be part of the land-use plan.

Almost all crops need to take up oxygen through their roots, although plants vary in their tolerance of short periods of waterlogging. Oxygen availability to roots is therefore very important. Because oxygen is available above the water table and not below it, the depth of the water table is the key factor for this land quality. Drainage is a way to improve oxygen availability. Most land-use plans involve interventions in the water management system. Ditches, dikes, pumps, and field drainage, are ways to influence the amount of water in an area. Because water management is of a regional nature, land-use planning is a preeminent way to achieve the right level of availability of water.

Water management is also very important for soil workability and mechanization. The moisture content of the soil is particularly important for the workability. Some soils are always easy to work, whereas other soils have strict limitations with regard to the water content. Generally, sandy soils are easier to work than clayey soils and well-textured soils are easier to work than massive soils [32]. The measures in a land-use plan that can be applied to improve soil workability are the same as with land quality 7, rooting conditions.

Apart from soil workability, the texture of soil is also important for mechanization. This land quality applies only to agricultural systems that are highly mechanized. Characteristics of land that define potential for mechanization are slope angle, rock hindrances, stoniness or extreme shallowness of the soil, and the presence of heavy clays [32]. The potential for mechanization can be improved by lessening the slope angle and by improving the soil characteristics. The slope angle can be lessened by terracing the lots (Fig. 2.11). These improvements, like soil improvements, can very well take place in connection with land-use planning schemes.

Erosion is one of the main problems for agriculture across the world. It causes fertile soils to be washed or blown away, leaving poor, nonproductive land. The many aspects of erosion are discussed in other parts of this book. The ways in which land-use planning can reduce erosion are reviewed here.

Land-use planning can prevent erosion by assigning uses of the land that protect sensitive soils (such as dense woods). Less sensitive soils can be used for agriculture. Where this is not possible, a small-scale mix of certain land uses provides a way to prevent erosion: For example, when agriculture is combined with forestry or nature reserves, the forest or the reserve functions as a buffer, preventing the water or the wind from eroding the nearby fields. Other ways to prevent erosion include terracing fields, building dikes, planting grass strips for water flows and to trap sediments, and planting before terracing after terracing

Figure 2.11. Terracing of fields.

before terracing after terracing

Figure 2.11. Terracing of fields.

zone suitable for:

nature meadow crop field level high-water level low-water level

Figure 2.12. Damage resulting from flooding can be reduced by planning the use of the land.

trees as a protection against wind. These measures can also be taken outside land-use plans and they are discussed elsewhere in this volume (see Chapter 4).

Flood hazard is a problem that requires more than just land-use planning. However, planning can mitigate the effects of flooding by making sure that land threatened by flooding is used appropriately (see Fig. 2.12). Some uses of land even benefit from incidental or permanent inundation.

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