Using Near Infrared Reflectance Spectroscopy to Evaluate Phosphorus, Potassium, Calcium, and Magnesium Concentrations in Bermudagrass

Application of nutrients to correct nutrient deficiencies in turfgrasses are often based on tissue analysis. Previous research has indicated that near infrared reflectance spectroscopy (NIRS) may be useful in tissue nutrient concentration determination since it requires minimum sample preparation and has been a reliable predictor of N concentration. The objective of this study was to evaluate the reliability of NIRS in determining P, K, Ca, and Mg concentrations in bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy]. Tissue samples were collected from Florida golf courses, representing different cultivars grown under various conditions and fertilizer regimes. Tissue samples were analyzed using NIRS and traditional wet chemistry (Mehlich-1 extracts analyzed using inductively coupled argon spectrophotometer) before results were statistically compared. Results from wet chemistry analysis averaged 15% lower than those obtained from NIRS. Although results for certain cultivars and elements were positively correlated (‘Tifdwarf Ca, r = 0.72; P < 0.01), precision across all cultivars and nutrients was not sufficient (accounted for only 26% of variability) to indicate that NIRS would be an effective management tool for the elements evaluated in this study. x C. transvaalensis Burtt Davy] (r = 0.92) (Rodriguez and Miller, 2000). Advantages of using NIRS include time savings and simple preparation procedures. Scanning a sample typically takes <3 min. Sample preparation usually only involves drying and pulverizing, and the samples can be tested repeatedly by NIRS or by another procedure, as they are not consumed (Marten et al., 1985). Although P, K, Ca, and Mg are essential nutrients for plant growth, when applied in excessive amounts they may cause deficiencies in other elements. Cations such as K, Ca, and Mg can alter the uptake of other ions. Potassium is a monovalent cation and is absorbed more rapidly by the plant and to a greater degree than divalent cations such as Ca and Mg. High application rates of K have been shown to be associated with decreased soil extractable Ca and Mg, which results in tissue deficiencies of these nutrients (Miller, 1999). Bermudagrass growth can be hindered by excessive P applications due to a decrease in N uptake (Sartain and Dudeck, 1982). Research has also indicated a reduction in plant available K due to over-application of P (Nus et al., 1993). If applied to turfgrass inappropriately, phosphorus can potentially damage surface water. Surface runoff containing P can cause eutrophication. As eutrophication occurs, algae and weeds grow rapidly creating an unhealthy environment for fish and other aquatic organisms and make water unsuitable for drinking (Brady and Weil, 1999). Fertilizers applied to golf courses are believed to be responsible for some P that enters surface water because golf courses are frequently found in areas adjacent to surface water (Christians, 1996). A quick, reliable method of determining P, K, Ca, and Mg concentrations of turfgrass would be a valuable asset, allowing turfgrass managers to apply fertilizers on a per need basis and avoid excessive fertilization. Objectives of this study were to evaluate the reliability of NIRS in determining P, K, Ca, and Mg concentrations in bermudagrass. Materials and Methods Tissue samples were collected from golf courses throughout central and southern Florida. Sixty tissue samples were collected from golf course putting greens, tees, and Near infrared reflectance spectroscopy (NIRS) is a nondestructive method, which can rapidly analyze the chemical composition of materials with little sample preparation. Analysis is based on the principle that each element has its own distinct near infrared absorption properties which can be measured (Marten et al., 1985). NIRS technology has been used for over 30 years in the forage industry measuring forage compositions such as acid detergent fiber, neutral detergent fiber, dry matter, and lignin content (Marten et al., 1985). Research has shown NIRS can accurately predict the response of corn (Zea mays L.) to fertilizer and N-supplying capability of the soil (Fox et al., 1993). NIRS has proven reliable in predicting P, K, and Ca content in forages (r > 0.74) (Clark et al., 1987). Recently NIRS research has been directed towards turfgrass nutrient analysis. Murphy (1993) concluded NIRS has potential as a rapid and none subjective method of predicting N content of perennial ryegrass (Lolium perenne L.) (r = 0.93) and creeping bentgrass (Agrostis palustris L.) (r = 0.89). A study at the Univ. of Florida indicated NIRS could accurately predict N content in ‘FloraDwarf and ‘Tifdwarf bermudagrass [Cynodon dactylon (L.) Pers. Table 1. Mean, standard deviation, and coefficient of determination for wet chemistry and NIRS values for ‘Champion , ‘FloraDwarf , ‘Tifdwarf , and ‘Tifway bermudagrass samples collected from Florida