Diagnosis and Optimization of Phosphorus Nutrition Conditions of Grain Crops in Northern Kazakhstan

The phosphorus fertilization of crops is a most important issue because of the limited resources of phosphate rock on the one hand and the possible negative impacts on aquatic and terrestrial ecosystems on the other hand. This chapter deals with the results of long-term field experiments to diagnose and optimize the phosphorus nutrition of cereal crops in Northern Kazakhstan. The efficiency of the phosphorus fertilization was most dependent on the plant-available P content in the soil as analyzed using Machigin’s extraction method. We present an approach to evaluate the phosphate status in the soil and to determine the particular requirements of grain crops. The inputs used to calculate fertilizer demand are the optimum content of plant-available phosphorus, its current concentration in the topsoil and the quantity of phosphorus to be fertilized in order to raise the plant-available P₂O₅ by 1 mg kg⁻¹ soil. The approach is based on the Machigin method and is currently not transferrable to other regions, where other analytical methods are common. In order to compare this approach with other methods worldwide, methodical comparisons of different analytical methods for assessing the plant available P content in soils are necessary in future. We also require a better understanding and quantification of phosphorus cycling in ecosystems, based on internationally acknowledged analytical methods, models and long-term experiments.