Analysis of Foliage Phosphorus Requirements of Radiata Pine Plantations

Monitoring of foliage nutrients in forest plantations is used as a method to identify nutritional problems and recommend ameliorations. A requirement is the development of nutrient bench marks and these are usually a single concentration based on the level at which symptoms appear. The critical level is defined as 90% of optimum growth below which it is expected that growth responses to applied nutrients would be obtained. The phosphorus critical level at different ages in radiata pine has been developed showing a decline with age from 0.18% P at 2 years to 0.12% after 15 years. A typical standard level applied is 0.14% P which would underestimate young stands and overestimate older stands. Routine assessments in plantations show patterns of decline in P over time, on some soils they generally remain above the critical levels, others below, and some move into deficiency with time.