Soils and land capability in Swaziland

Abstract

Swaziland soils are mapped and defined. Soil-slope combinations are the basis for establishing Land Classes which relate to irrigability and to the capability to produce raingrown crops. The pattern of Land Classes suggests ways of channelling agricultural advances to gain most advantage per unit area of fields, orchards and forests. Concentration of effort in Intensive Farming Blocks is advocated.SUMMARY BY CHAPTERS:1 - The location, physiography, geology, climate, landforms, hydrology and vegetation of Swaziland are briefly described. The people of the kingdom, its economy, produce from its soil, and water consumption by irrigators are discussed. Sugarcane is the principal irrigated crop, followed in order of acreage by cotton, rice and citrus. Rainfed agroforestal plantings comprise maize, pine trees, cotton, sorghum, beans etc. Irrigation, afforestation and the more intensive dryland cropping are features of the four Cores, the main zones of economic activity and urbanisation. Elsewhere, in the much larger Periphery, subsistence maize farming and cattle-keeping predominate.2 - The basic soil classification unit is the series. Agriculturally significant combinations of 107 soil series into soil sets for mapping purposes during the National Soil Reconnaissance (NSR) 1963-1967 have proved useful. The sets are portrayed at 1:125,000 scale. Series are also apportioned among broad Service Pedologique Interafricain mapping units, the commonest in terms of area being Raw Mineral Soils 30% then Weakly Developed Soils 26% then Ferralitic Soils 15°/°' An analytical key to series is succeeded by morphological descriptions of sets and series, with supporting laboratory data from the records pertaining to 3,900 soil samples. Comparison is afforded with series and other narrow soil groupings of seven countries in Eastern and Southern Africa. There are shorter notes on fertiliser needs, the internal variability of series and colour aerial photographs as aids in recognising soil boundaries.3 - Agroforestal land capability is defined as the longterm profitability of an area, without soil abuse. Soil sets and series are accorded ratings for specified farming systems. The ratings are divided into slope categories to give Land Classes. Ten Classes relevant to an irrigated rotation of crops are mapped at 1:125,000. The potential for irrigation and dryland cropping, for afforestation and for stock-rearing is discussed. The originally theoretical soil ratings have been monitored from yields of irrigated sugarcane and rainfed maize, cotton and pine trees commercially grown since 1957 on nearly 1,800 plots where management was relatively constant, at rather above average standards. Quantitatively, benefits derivable from farming the better soils are striking. Revision of ratings is foreseen as more advanced techniques and new crop varieties are introduced. Yield prediction will thus be further refined.4 - Trends in the rural economy since the 18th century indicate that the convergence of farmers on choice tracts of high potential has been an almost continuous process. The history of land use and lessons learned which have a bearing upon plans for future agroforestal development are reviewed. Present day debates (e.g. on holding size, land tenure) concerning the next era in farming are summarised. New agroforestal patterns will result from recognising and vigorously promoting Intensive Farming Blocks (IFB) of good soil on suitable slopes inside existing Cores, round their fringes, and along linking routeways. About 6% of the country (240,000 acres) might fall within IFB, whereof two thirds could be irrigated, one third intensively cropped but rainfed. These figures are simply guidelines. Land capability should continue to be a prime consideration on less intensively farmed and forested land.