The Rehabilitation of the Fertility of Irragri Gipsic Calcisols in Azerbaijan Arid Zone
At present, in Azerbaijan arid zone, the humus content in the topsoil of Irragri Gipsic Calcisols (0-25 cm) has decreased from 2.15-2.18% (1992) to 1,7-2,09% (2000) and it keeps decreasing. Even in works by Dokuchaev V.V., Kostychov P.A. and Williams V.R, the tremendous significance of perennial and annual herbs in the accumulation of organic matter in soils was mentioned. The research objective is the study of the influence of plant residues of intermediate sowings of fodder crops on the rehabilitation of the fertility of Irragri Gipsic Calcisols in the arid zone of the Absheron peninsula. The article describes the results of the researches carried out on the same plot in order to determine the influence of intermediate sowings of fodder crops on the main indices of fertility of Irragri Gipsic Calcisols. Soil-climatic conditions in the arid zone enable reaping three harvests of the green mass (1250,0 centners) from one hectare and accumulating on the average 185,44 centners of the dry mass of stubble and root residues: winter rye+vetch+rape (harvest I) → corn+soya+sorghum+amaranth (harvest II) → barley+vetch (harvest III) in the soil layer 0-50cm. Together with stubble and root residues, the soil receives 6120 kg of carbon, 287,4 kg of biologically fixed nitrogen, 150,2 kg of phosphorus, 391,3 kg of potassium. Comparing to the previous indices in the soil layer 0-50 cm, there was the increase in humus content from 1,55% to 1,79% and humus supply -from 89,90 t/ha to 121,8 t/ha; humus balance - (+0,38 t/ha); total porosity -from 48% to 60% and water permeability -from 1,15 mm/min to 1,75mm/min; the density of soil (1,15 g/cm<sup>3</sup> ) and the density of the solid phase (2,6 g/cm<sup>3</sup>) are optimal.