Nutrient Management Research Database

http://research.ipni.net/research/nap.nsf/0/643050167e9c478d85257bce00586e59/$FILE/ID-06F.Hopkins.WNMC2005.pdf

Phosphorus (P) is an essential nutrient required by plants for normal growth and development. The availability of P to plants for uptake and utilization is impaired in alkaline and calcareous soil due to the formation of poorly soluble calcium phosphate minerals. Adding fertilizer P at “normal” rates and with conventional methods may not result in optimal yield and crop quality in these soils 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. Research results show that relatively high P fertilizer rates are required for crops grown in alkaline soil, with increasing rates needed as lime content in these soils increases. Concentrated P fertilizer bands improve P solubility with resulting yield increases, even when applied to crops grown in soil with relatively high soil test P concentrations. Applying organically complexed P in the form of biosolids or as a mixture of liquid P and humic substances can also enhance P nutrition and result in yield increases. Application of slow release and cation complexing specialty fertilizer P materials has also been shown to effectively increase yields in calcareous soil. In-season applied P through the irrigation water can deliver P to plant roots when deficiencies are observed, but the effectiveness and results are less than with P incorporated into the soil. Finally, it is important to maintain a proper balance of P with other nutrients for general plant health and to avoid excess nutrient induced deficiencies of other nutrients. In some cases, these methods are relatively new and need further refinement with regard to rates, timing, and technique; but all are potential methods for improving P supply to plants grown in alkaline and calcareous soil.

• Alkaline soils (those with pH above 7) and calcareous soils (those with significant quantities of excess lime) make managing P nutrition difficult.
• Adjustments to P nutrient management plans must be made when working with alkaline and calcareous soils.
• Strategies covered in this paper include:

1)      Increased P application rates

2)      Concentrated P bands

3)      Complexed P fertilizers

4)      Slow release fertilizers

5)      Cation complexing fertilizers

6)      In-season P fertilizer application

7)      Balancing P with other nutrient to ensure efficient plant uptake