Phosphorus (P) is essential for normal plant growth and development. The availability of P to plants is impaired in alkaline and calcareous soil due to the formation of poorly soluble calcium phosphate minerals. Adding fertilizer P with conventional methods at “normal” rates may not result in optimal crop yield and quality in these soils, which are common in arid and semi-arid regions. Several fertilizer P management strategies have been found to improve P nutrition for plants grown in alkaline and calcareous soil, including relatively high P fertilizer rates, concentrated P fertilizer bands, applying organically complexed P, and/or application of slow release and cation complexing specialty fertilizer P materials. For most other nutrients, application through the irrigation water (fertigation) is another means of fertilization that can be used effectively. However, this method is not generally recommended for P due to the very limited mobility of P in soil under most circumstances. Applying P directly in the root zone with one or a combination of the previously listed methods is best for optimum P efficiency and crop growth. Furthermore, certain additives can complex P, making it more mobile in soil and, as a result, more likely to be taken up by roots. Nevertheless, even when these P management strategies are utilized, it is not uncommon to discover in-season P deficiencies. Research shows that, while not as effective as soil applied P, fertigation can result in P uptake by plants and, in many cases, yield increases as well. While not a substitute for a good soil applied P fertilization strategy, fertigated P can be used as a “rescue” when in-season P deficiencies occur due to inadequate early season fertilization, adverse growth conditions, or unanticipated high yield potential.
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