Optimal doses of phosphorous fertilizers (soil biochemical aspects of the problem)

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At present, the problem of supplying soils of Siberia with phosphorus has become much more acute in comparison with the past decades. This is due to virtually complete termination of the use of phosphate fertilizers for grain crops and a sharp increase in the price of these fertilizers compared to the price of grain. There are various approaches to diagnosing the pool of phosphorus available to plants, including methods based on the use of phosphatase preparations allowing to assess the mobility of organic phosphorous compounds in the soil. The content of biologically available soil phosphorus was assessed in the leached chernozem of Priobye, depending on the type of crop rotation and the use of phosphate fertilizers, with the aim of fi nding optimal doses of these fertilizers. After fi ve rotations of three-fi eld grain-fallow crop rotations, the fraction of biologically available soil phosphorus was not detected against the background of no fertilizers or with application of low doses of phosphorus (P15). A certain reserve of phosphorus in the soil was found with the annual use of P60 on the grain-grass crop rotation and long-term application of manure on the farm crop rotation. It was concluded that in the forest-steppe of Priobye, the supply of plants with phosphorus can occur without the formation of biologically available soil phosphorus reserves, whereby the dose of phosphate fertilizer P15 compensates for the annual removal of the element with grain in the average multiyear cycle of years with different climate conditions. Annual application of P60 forms reserves of surplus phosphorus in the form of its biologically available fraction, which makes the economic effi ciency of this doze of the fertilizer questionable.