SOIL NUTRIENTS IN AGRO-ECOLOGICAL ZONES OF SWAZILAND

摘要

Per capita food production in Swaziland and other parts of sub-Saharan Africa will continue to decline unless soil fertility depletion is assessed. In light of this, total N, exchangeable bases, P fractions, available P, Cu, Zn, Mn and Fe contents wer e assessed in the 0-30 cm layer s of soils in the highveld (> 1500 m above sea level), middleveld (950-1500 m above sea level) and lowveld (<950 m above sea level) agro-ecological zones of Swaziland Soils in the lowveld had significantly (P<0.10) higher Ca and Mg than other soils; and soils in the middleveld had significantly (P<0.05) lower N contents than other soils. Compared with critical levels, the soils were generally deficient in N, but had adequate Ca and Mg, especially in the lowveld Potassium deficiency could also be expected in some low-CEC soils in the highveld Highveld soils contained significantly more occluded P but less Al-P than other soils Lowveld soils contained significantly more Ca-P but less Fe-P than other soils. Highveld soils c ontained less water-extractable P, resin-desorbed P and P fixation power than the other soils. Available P determined by nine different methods with their respective critical levels, showed that most of the soils were P-deficient according to four method s and P-sufficient according to the other five Soils in the highveld contained significantly more Fe (both Fe-DTPA and Fe-HCl) than othefsoils, and soils in the middleveld had significantly more Zn-HCl than the other soils Copper and Zn contents were gen erally highest in the lowveld, but the differences were not significantly different Compared with critical levels, Cu and Fe contents seemed adequate, but Zn and Mn were deficient at some sites.