Keywords: Nutrient balance, Sustainable agriculture, Sub-Saharan Africa.

The majority of agricultural systems in sub-Saharan Africa can be labelled “non-sustainable”. An important, quantifiable indicator of sustainability is the nutrient balance of such systems. The sum of nutrient inputs can either exceed, equal or be lower than the sum of the nutrient outputs. Sub-Saharan Africa falls largely into the latter category. Macronutrient balances were calculated at supra-national level (sub-Saharan Africa) and at district level in Kenya and reveal that nutrient mining has indeed become a serious problem in sub-Saharan African agriculture. Several options are discussed to alleviate nutrient mining. A number of recent interventions in the Kenyan district are elaborated, including zero-grazing, agro-forestry and soil conservation measures. Finally, particular attention is given to the possible role of mineral fertilizers in safeguarding both(short term) productivity and (long term) sustainability.

E M A Smaling, DLO Winard Staring Center for Integrated Land, Soil and Water Research, Wageningen, Netherlands.

18 pages, 6 figures, 1 table, 11 references.


Keywords: Nutrient balance, Sustainable agriculture, Asia.

Asia has to feed approximately 60% of the World’s population on less than 25% of the global land area available for food production. In comparison with Africa and South America, Asia has the biggest population but the lowest population growth, a decreasing number of poor people, the smallest potential for expansion of arable land area but the largest area under irrigation, the highest levels of total fertilizer use but the most unbalanced NPK ratio. In order to suit these characteristics Asia had to experience recently the fastest growth rates in both food production and fertilizer use on this globe.

Where during centuries rice culture on a low input/output level had guaranteed sustainability in Asia, the increasing population pressure since 1950 has demanded for rapid intensification of decreasing land resources which in combination with high yielding varieties of food crops and the unbalanced use of N-fertilizers leads to the exploitation of soil fertility. Thus a highly intensified rice base culture can cause a severe deterioration of soil nutrient reserves e.g. for potassium in China while at the same time on poor nutrient status acid upland soils balanced fertilisation can establish and maintain highly productive and sustainable cropping systems like the oil palm in SE Asia.

H R von Uexküll and E W Mutert, Potash and Phosphate Institute, East & South-East Asia Program, 126 Watten Road, Singapore 1128.

18 pages, 7 figures, 11 tables.