Evolution of organic matter added to soils under cultivation conditions

The development of an organic matter (OM) based on mixed sheep manure and peat, when it was incorporated into soils as fertilizer, was studied. The experiment was carried out in soils under almond tree culture, with drip irrigation and non irrigation regimes. Two doses, 10 and 4.5 kg tree(-1), were assayed. Changes in the humic acid fraction one year after incorporation into soils showed oxidation and enrichment in condensed structures, as observed by an increase of the O*:H* ratio and a decrease of the H*:C* ratio, and also by FTIR spectra. The oxidative process was more significant in the coarser textured and also in the non-irrigated soil. The evolution of the ratios C-ext:C-ox and C-HA:C-FA throughout the culture cycle was followed by sampling and chemical analysis of different forms of organic carbon. Evolution of C-ext:C-ox showed a uniform humification state in the irrigated soil, and a significant decrease in the non-irrigated soil, at the beginning of the experiment. Curves of C-HA:C-FA evolution showed changes attributed to mineralization or drainage of the fulvic acids fraction, giving a maximum in spring in both soils and a final increase at the end of the cycle by drainage only in the irrigated soil.