Global Movements and Fate of Plant Nutrients in Fertilizers and Agricultural Products

The objective of this paper is to trace, and where possible to quantify, the movements of the three plant macronutrients – nitrogen, phosphate and potash – from their origin at the production site or mine to their final destination. There are nutrient losses at each stage of the cycle, low while the products are under the control of the industrial sector, increasing progressively as the nutrients reach their final destination. Most of the phosphate and potash not taken up by the crops is fixed in the soil and becomes available to subsequent crops. In the case of the nitrogen, about half of the applied nutrient is lost to the atmosphere or through leaching. Management practices that minimize the losses of fertilizer nutrients applied in agriculture exist and are constantly being improved. Nonetheless it is an immense task to transmit this knowledge to the hundreds of millions of farmers and to help them adapt it to local conditions. The nutrients in crop and animal products that are not assimilated by the human population end up in organic wastes. At the global level, these wastes contain roughly as many nutrients as are provided annually through mineral fertilizers. A review covering seventeen non-OECD countries shows generally very low rates of recycling of organic wastes. The demand for animal products by the population of Asian and other countries is increasing rapidly as the standard of living improves. Correspondingly so to are the problems of waste disposal. A sharp fall of nutrient recycling in China is causing concern. The situation may be partly alleviated by continuing improvements in the feed conversion rates of nutrients by animals. There is a clear imperative to increase nutrient use efficiency and to enhance nutrient recycling.