Nutrient Deficiencies in Export Tree and Food Crops: Literature Review and Field Observations

This paper reviews nutrient deficiencies in agricultural crops of PNG using the literature of agronomic trials and field observations made throughout the country. Nutrient deficiencies have been investigated systematically since the mid-1950s, but research has mainly focused on export tree crops and relatively little information is available on food crops. Literature analysis and field observations showed consistent trends, with deficiencies of boron and phosphorus in large parts of the PNG highlands. The review has been useful in delineating areas where nutrient deficiencies occur and these findings could be used for planning nutrient management research and extension activities in food crops. T HE availability of soil nutrients to plants depends on many factors. Low levels of available nutrients in the soil may be due to low amounts in the parent material from which the soil is derived, fixation and immobilisation of nutrients, or excess losses under high rainfall conditions when nutrients are leached from the soil. Nutrient imbalances in the soil may also cause limited availability of nutrients. Low nutrient levels may also result from cultivation because of removal of nutrients by agricultural crops without subsequent replenishment, leading to accelerated losses compared to natural ecosystems. In many smallholder agricultural systems in tropical regions, nutrient deficiencies limit food crop production. This effect is enhanced by increasing land pressure. Detailed information on the spatial distribution and seriousness of nutrient deficiencies is needed in order to develop research strategies aimed at alleviating the problems and increasing food production. Such information systems are used for planning research on integrated nutrient management in some tropical countries, but in many countries including PNG, the information is scattered or unavailable at the national or regional level. In PNG, subsistence agriculture is practised by more than three-quarters of the population in a wide range of environmental conditions. Annual rainfall varies from 1000 millimetres around Port Moresby to over 8000 millimetres in the mountains of the far west. The rugged mainland and the surrounding islands form part of a highly mobile zone of the earth’s crust where volcanic activity occurs. Many areas have been covered by volcanic deposits, while weathering and denudation of the steeply sloping mountains have caused the deposition of extensive alluvial plains (Bleeker 1983). Due to the great variety of parent materials, climatic conditions and differences in topography, there are many different * International Soil Reference and Information Centre, PO Box 353, 6700 AJ, Wageningen, The Netherlands. Email: [email protected] † Department of Human Geography, Research School of Pacific and Asian Studies, The Australian National University, Canberra, ACT 0200, Australia. 1 This paper is an abridged and adapted version of Hartemink and Bourke (2000). Proceedings.book Page 316 Monday, September 17, 2001 11:30 AM