Evaluation of the phosphorus available for plants from various types of fertilizers (manures, liquid manures, dung and muds) and their fertilizing value with isotopic marking of the soil phosphorus

This work was carried out for the research program entitled 'green Pigsty' relating to the evaluation of the phytodisponibility of the phosphorus of 13 organic materials (TSP, Phytate, fresh Manure, young and ripe compost litter of pig, litter of chips composted, Litter of ripe fine layer, stored biological muds S1 and S4, green waste mixture and fermentable fraction of household garbage). These various fertilizing products whose P content is known are added in pots (50 Mg of P) by carefully mixing them with ground which was already marked with a solution containing the radioactive phosphate ions without trainer (carrier-free). This work which permitted to obtain many results in particular on the fertilizing value of the various contributions of manure were completed. We used as plants, Italian ryegrass which have many advantages such as the fast regeneration of the leaves after different harvests and the exploitation of a population of individuals allowing to avoid some artefacts like genetic nature. The tillage consisted in making a mixing radioactive soil-solution and transferring the mixture in pots for culture after addition of the various fertilizing products. Sowings of ryegrass were added on the pots of culture and different cuts were realized each 20 days. Finally, 4 cuts were done and for each harvest, the samples were dried, weighed, crushed and calcined. The quantity of phosphorus was determined on one hand by measurement of radioactivity in the samples of plants and by using a scintillation counter and on the other hand by measuring their phosphorus content after mineralisation by using a colorimetric technique with green malachite. The data collected were: the dry weight biomass of the leaves for all the harvests; phosphorus content of this biomass for all the processing and for each harvest; r/R isotopic ratio of dilution (R is the total radioactivity introduced into the pots of culture and r is radioactivity taken by the plants). From these data, we deduce a direct and precise characterization of the phytodisponibility of phosphorus brought from fertilizer and from the soil; the isotopic composition, ratio of the radioactivity taken from fertilizer to the quantity of phosphorus taken by the culture; the value L which represents the available phosphorus pool for the plants during the culture; the phosphorus taken from the soil, calculated by considering that the P taken from the soil has the same isotopic composition with the P taken in the control which is not fertilized; quantity of phosphorus taken from the fertilizer; the real coefficient of use (CRU) which expressed as a percentage indicates the proportion of P taken from the fertilizer by the culture in the quantity introduced; the phosphorus derived from fertilizer (pdff) which determines the participation of the contribution in the phosphatic plant nutrition. From these different data, it is then possible to determine the fertilizing value of the various products studied by expressing the value of a variable compared to that from a form of reference (TSP). The degree of stability of the organic matter is relatively low. The various products studied during this test were thus classified for their efficiency and the results obtained were discussed