The role of rock phosphates in sustainable agriculture: the Hungarian experience with Algerian rock phosphate

From the early 60's till the late 80's, in many countries - among them also in Hungary - agricultural production went through a tremendous development. In Hungary there was a 2-3-fold increase in the average yields of winter wheat, and maize - the two main crops - in comparison to those of the 50's. One of the main factors determining these developments was the increasing use of mineral fertilizers. From the turn of the century till the late 50's, nutrient balances in Hungary were strongly negative: 20 - 30 kg/ha/year less N and K₂O, and 10 kg/ha/year less P₂O₅ was given to the fields in the different forms (farmyard manure, mineral fertilizer and by-products, etc.), than was removed by the harvested yields. Nutrient balances of P became positive in the early 60's, while balances of N and K in the early 70's, resp. Then, for 20 years, N balances were positive by 10 - 20 kg/ha/year, while both P₂O₅ and K₂O balances by 30 - 50 kg/ha/year, resp. These long-term positive nutrient balances resulted in the NPK enrichment of our soils, which was also proven by the national soil test series. During the 80's, for example, the amount of yearly applied mineral fertilizer was 230 - 280 kg/ha N + P₂O₅ + K₂O/arable land. In certain regions N leaching could cause environmental damage, while, as a result of the P-Zn antagonism, on the fields poorly supplied with Zn, overfertilization with P resulted in 1 - 2 t/ha/year maize yield losses. From the early 90's, however, when political and ecological changes took place in the country, the free market was introduced, and state subsidies on mineral fertilizer were withdrawn, there was a sharp decrease in mineral fertilizer use: applied N dropped to 1/5th, P and K to 1/20th of the amount used in the 80's. This dramatic decrease resulted in the change of nutrient balances: in 1991 the balance for N was -60, for P₂O₅ -30, and for K₂O -40 kg/ha for the whole country, resp. In 1992 and 1993 the situation was similar, while in 1994 a slight increase in mineral fertilizer use was observed. According to our estimation, mineral fertilization of 150 kg/ha/year N + P₂O₅ + K₂O is sufficient for long-term sustainable plant nutrition in Hungary, if farmyard manure application and the incorporation of byproducts remains on the recent level. During intensive fertilization practice, emphasis was on the quantity, while crop and soil demands for specific or more economic fertilizers were not taken into consideration. For N, lime ammonium nitrate, for P superphosphate, and for K, potash chloride was used on almost the whole area. As a new attempt to find more economic P sources, Algerian rock phosphate was checked in field trials, set up on characteristic acidic soils in different regions of Hungary, as well as other Central European countries. The first two-year results are discussed in the presentation

Release of trace metals to the soil solution from a phosphate rock containing soil at different acid loads

In agricultural practice basic phosphate rocks (PRs) may be efficient P sources if applied on acidic soils. However, due to their potentially toxic elements content environmental hazards may arise. In a laboratory bulk experiment the appearance and accumulation of such elements (As, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr and Zn) in the soil solution of an acidic sandy soil was studied after various PR and acid treatments. The degree of pH elevating effect of PR treatments was also tested. In the liquid phase of the PR-enriched soil, metal concentrations were generally lower than in the control sample because their release to the soil solution was influenced less by the amount of the pollutants carried into the soil with PR doses than by the pH increasing and/or solubility altering effect of PR. Acid loads, as expected, considerably increased the concentrations of cation forming elements in the soil solution, but their concentrations – due to the immobilizing effect of PR – decreased in the acid treated soil, as well. Extreme strong acid treatment was necessary to compensate for this effect and, while Ba, Co, Cu and Mn concentrations practically did not change with the increasing PR doses, Cd, Sr and Zn concentrations were eleveated. In contrast, the immobilizing effect of PR in case of Pb dominated even under the extreme acid treatment, its concentration decreased with increasing PR doses. Concentration of the anion forming elements (As, Mo) in the acidic soil solution was negligible even at the highest P dose