Predicting Response of Southeast Texas Loblolly Pine to Fertilization

The Diagnosis and Recommendation Integrated System (DRIS), vector analysis, and critical level approaches are diagnostic tools commonly used for assessing nutrient status of trees by foliar analysis. This study evaluated the relative merits of the three approaches for identifying N and P deficiencies in stands of loblolly pine (Pinus taeda L.) in southeast Texas. Only 25% of the time did all three approaches select the same stands as N deficient, and only once did they agree that a stand was N sufficient. The three approaches agreed 25% of the time that stands were P deficient and 13% of the time that stands were P sufficient. No method was universally accurate in predicting response across soil groups. The critical level approach proved best for identifying all responsive sites, and it would be useful if the cost of fertilization was deemed low in comparison with the cost of lost growth when responsive sites are not fertilized. The DRIS approach failed to identify some responsive sites, but a high proportion of the sites it predicted would respond, did respond. It would be useful if the cost of fertilization were deemed high in comparison with the cost of lost growth when responsive sites are not fertilized. The vector analysis approach proved most useful because of its ability to predict response to N and P when added together. Soil group alone was a reasonable predictor of response to fertilization. South. J. Appl. For. 25(2):84–87.