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Soil fertility under shifting and semi‐continuous cultivation in the Southern Highlands of Papua New Guinea
Author(s) -
Sillitoe P.,
Shiel R. S.
Publication year - 1999
Publication title -
soil use and management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.709
H-Index - 81
eISSN - 1475-2743
pISSN - 0266-0032
DOI - 10.1111/j.1475-2743.1999.tb00063.x
Subject(s) - agronomy , monoculture , soil fertility , nutrient , ipomoea , imperata , phosphorus , crop , tropics , subsistence agriculture , monocropping , shifting cultivation , biology , environmental science , soil water , nutrient cycle , agroforestry , agriculture , ecology , horticulture , cropping , chemistry , organic chemistry
Abstract. People in the Southern Highlands of Papua New Guinea cultivate some land semi‐continuously within a regime of shifting cultivation; the staple crop is sweet potato ( Ipomoea batatas ). The fertility of Tropepts, variably affected by falls of volcanic ash, was investigated to give further understanding of how subsistence farmers avoid the soil constraints that commonly prompt abandonment. While organic matter, N and K all decrease significantly with time under cultivation, they do not reach critical levels. Phosphorus also decreases significantly over time, although contents are small throughout. Other nutrients show no significant variation with period of use or abandonment. These findings comply with the diversity of crops cultivated early in the life of ‘gardens’, followed by sweet potato, cultivated as a virtual monocrop in long established ‘gardens’. It continues yielding adequately regardless of decrease in nutrient availabilities, notably because nutrient ratios remain favourable for tuberisation and because of sweet potato's tolerance of small phosphorus concentrations. It appears that burning of vegetation significantly increases available minerals and helps maintain a supply which is adequate for longterm sweet potato monoculture. Similar situations are postulated for other areas of less‐weathered soils within the tropics.