DRIS (Diagnosis and Recommendation Integrated System) analysis was applied to fast-growing sweetgum (Liquidambar styraciflua L.) plantations in the southeast United States as a tool for nutrient diagnosis and fertilizer recommendations. First, standard foliar nutrient ratios for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were established using high-yield stands from a region-wide sweetgum
DE-AI09-00SR22188JOURNAL ARTICLE 2003 03-22-P fertilization study. DRIS indices were then calculated for the low-yield stands in the same study and stands from four other studies to evaluate foliar nutritional characteristics. Low-yield stands showed strong negative K imbalance, indicating insufficient K, but also showed strong positive Mg imbalance. Potassium imbalance was also observed in the other four data sets tested. DRIS analysis successfully identified the tendency for K insufficiency to increase from early to late in the growing season, probably due to K foliar leaching and low soil K supply. While insufficient N was common in all the stands tested, the DRIS analysis failed to identify any P imbalance. We recommend that K be applied in N:K ratios less than one to correct K imbalance problems in the studied sweetgum plantations. Supraoptimal Ca and Mg levels are expected to decline once insufficient N and K are corrected. DRIS analysis provides the means for diagnosing nutrient imbalance and a potential basis for prescribing corrective amendments in sweetgum plantations.