Concepts for a more efficient use of phosphorus based on experimental observations

I. The fertiliser industry predicts a sinking rock phosphate production all over the world after the peak production point had been hit in the 1980/1990's. The global Preserves with the currently applicable evaluations (physical, chemical characteristics) and accepted costs for exploitation and processing are expected to last for only approx. 120 more years, reserves of lower quality and higher costs about three times longer. An acute lack of phosphate fertiliser does therefore not yet exist. But phosphate prices have increased by 300% over the last two years. This is a clear signal, for phosphate consumers in particular, to exploit the unused potential in agricultural soil and handle this limited resource in a more efficient way. II. More recent results of long-term P field experiments in different German regions show that approx. 4 mg P/100 g lactate soluble phosphorus are fully sufficient for high yields, in Bavaria content class B (2-4 mg CAL-P/100 g soil) with fertilisation equalling crop removal. In the light of these results, we must very critically examine the system of five content classes dating back to 1997, and the margin of content class C (4-9 mg P/100 g soil) in particular, as with an initial content of 4 mg P/100 g soil (content class B/C) it would need approx. 500 kg P/ha (i.e. an amount of P equivalent to the removal of about 20 harvests) to reach 9 mg P. With prices up by 300% (compared to 2005), this cannot be recommended. III. In Germany, 2.4 million tonnes of dry matter sewage sludge (approx. 2% P) with approx. 48,000 tones of P, 400,000 tonnes of animal meal (approx. 12,000 tones of P) and 160,000 tonnes of meat-and-bone meal (approx. 9,600 tonnes of P) are disposed of as waste every year. Current P consumption in the form of phosphate fertiliser amounts to 108,000 tonnes of P per year. With a P recycling rate of 90%, more than 50% of the currently imported mineral fertiliser P could thus be replaced. In 2004, the Federal Ministry of Education and Research (BMBF) and the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) began to support research and innovation in P recycling. First methods for the production of new P fertilisers are currently being developed and P fertilisers are being tested. First agronomical tests of potential new P fertilisers have already been carried out. IV. P dynamics in the soil are very complicated as phosphate is subject to specific anion adsorption and precipitation by calcium ions in particular. Whereas grain crops handle the low P concentrations in the soil solution with their extensive root system (rye e. g. 3 8 km/m(2)), dicotyledons excrete a series of organic acids (citrate, malate, oxalate) which mobilise phosphate in the rhizosphere through ligand exchange to make it absorbable. The latter principle is, for example, used by eucalypt plants in Japan (5 1). Gene transfer is regarded as a way to indirectly increase the P absorption efficiency of plants. An important method without gene transfer lies in the breeding with a view to high P absorption efficiency by way of marker-assisted breeding with QTLs for P absorption. This method had already been successfully adopted within the scope of a rice project in Japan/India (58; 59). V. The internal P utilisation of arable crops (kg dry-matter production/g absorbed P) obviously has a considerable range of variation. It can therefore also be said in this respect that the P absorption efficiency of the plants can still be increased considerably. VI. The possibilities to apply fertilisers according to the actual needs should be fully exhausted and the use of P fertilisers should be adjusted to the specific site conditions and cropping ratios.