2.1 Development of Soil Standards and Agricultural Land-use Guidelines in Uganda

Early attempts to establish land-use management guidelines were preceded by land inventories to establish the status of the Uganda soil resource base. Resource inventories started in 1933 (Martin, at Kawanda) and the limited results were embodied in the Provisional Soil Map of East Africa"
compiled by Milne (1935). Between 1935-1954 several attempts were made to improve the first soil map so that appropriate land-use management guidelines (especially for agricultural land use) could be put in place. The first
detailed country-wide resource Inventories were carried out during the reconnaissance survey (1955-1960) by the Soil Unit at Kawanda. Geomorphological surfaces on which the soils were formed was a major criterion used in soil survey and classification and the mapping unit employed was the series and soil catenary associations. Most of the present Soil Conservation Bye-Laws and Land Management Laws were based on information gathered during this survey.

The survey recognized 138 soil mapping units which were initially published in black and white soil maps at a scale of 1:500,000. These were later revised to produce more detailed 17 coloured soil maps at a scale of 1:250,000. The findings of the survey were published in six volumes of memoirs.

The memoirs contain a wealth of information which has partly been the basis for the establishment of critical values (thresholds) for soil chemical and physical parameters. Laboratory data on selected pedons are given, outlining
soil texture, exchangeable bases, soil reaction, organic carbon, and available phosphorus. Comments are made on some nutrient values, whether they are very high or too low for normal crop production.

The memoirs grouped the soils of Uganda according to their suitability for major cash crops in 1959; namely, coffee, cotton, tobacco, tea, sugarcane, and cocoa. Additionally there were soil groupings for suitability for plantains. For each crop the soils were arranged in three categories:

 eminently suitable,
 suitable,
 barely suitable.
Unsuitable soils were not mentioned.

2.1.1 Soil Fertility and Productivity Rating

The report rated Ugandan soils in 1959, for their fertility and productivity. It pointed out that the fertility of the red tropical soils in Uganda was confined in the top-soil which is usually 23-36 cm deep. The report pointed out the loss of nutrients in the top layer and structure destruction as the most serious causes of soil degradation in Uganda.

It gave some guidelines on the management of soils by farmers in order to reduce soil degradation. The guidelines and recommendations include:

 grass-rest under elephant grass as a management practice for building up fertility and productivity of the soils;
 contour planting and cultivation, contour paspalum- grass bunding, contour strip cultivation on slopping land;
 application of farm yard manure; and,
 application of some selected chemical fertilizers.

These standard practices are valuable in controlling loss of soil fertility. Their enforcement must be urgently reactivated.

2.1.2 Drainage and Irrigation

The report rated internal drainage of practically all upland soils as being free-draining. It indicated that bottom lands were water-logged all through the year or some months of the year, and pointed out that most of the bottom-lands could be safely drained. The report, however, warned against draining and irrigating the acidic and leached bottom-lands in southern Uganda. The richer soils of the Rift Valley, the Sebei and Karamoja plains were rated as
suitable for irrigation if water were available.

2.1.3 Standards for Plant Nutrients

The report classified soil concentration of individual plant nutrients which comprise soil fertility at three levels:
 very high
 high
 low

For each of the plant nutrients considered, Ugandan soils were grouped on the basis of which level of nutrient they belong to.

Between 1960-1970, considerable effort was put in the establishment of minimum chemical standards for soil fertility and productivity rating. Foster (1971), working at Kawanda, developed routine methods for soil chemical
analyses and these were accompanied by the minimum chemical standards that have formed the basis for the present nutrient management guidelines for the whole country

Magunda (1994), proposed soil physical standards for the intensive banana-coffee-lake-shore farming system. These standards have since been validated in the other agro- ecological zones. These standards are to serve as an early warning signal of reduced productive capacity of soils or
degradation. Specific physical parameters and threshold values were suggested for the surface layer and sub-soil. Standards should be viewed as a range of conditions where balance between exploitation and soil formation have moved away from a desired balance (Leonard et al 1990). Consequently the goal of soil quality standards is to maintain, restore or enhance the inherent long-term soil productivity.

2.2 Development of Soil Standards by Other Countries and Agencies

The demands for the kind of soil map and data vary, from one user to another. Some users are searching for the most suitable soil for growing particular crops. Others are interested in management and improvement inputs that puts their land to the most efficient use. There are yet other soil data users who need the data for locating home sites, waste disposal sites, roads, highways, and legislative land-use controls.

Significant effort has been made to develop soil standards at international level. The following are of particular importance. Those measurable soil properties that are important for assessing the soil plant root environment are reported by Bartelli, (1979) as:

 effective depth of root ramification zone;
 texture;
 organic matter content;
 salt content;
 cation exchange capacity;
 base saturation;
 mineral content;
 permeability;
 saturated and unsaturated conductivity;
 soil wetness (drainage); and
 depth to water table and available water holding capacity.

Soil Survey Manual (Soil Survey Staff, 1951) analyzed land features that influence soil behaviour as:

 slope;
 flooding;
 wetness;
 rockiness; and,
 geomorphological position.

Slope is important in that it influences soil erodibility and water run-off, equipment manipulation, street lay-out, under-ground conduits, harvesting of wood products and land levelling (Bartelli, 1979).