MICROVARIABILITY IN SOIL TEST, PLANT NUTRIENT, AND YIELD PARAMETERS IN BERMUDAGRASS

The scale or resolution where distinct differences in soil test and yi eld parameters can be detected has not been thoroughly evaluated in cr op production systems. This study was conducted to determine if large differences in soil test-and forage yield parameters were present with in small areas (<1 m(2). a 2.13 by 21.33 m area was selected for inten sive forage and soil sampling from two bermudagrass [Cynodon dactylon (L.) Pers.] pasture sites (Burneyville and Efaw, OK). Each 2.13 by 21. 33 m area was partitioned into 490, 0.30 by 0.30 m (1 by 1 ft) subplot s. Bermudagrass forage was hand harvested at ground level from each 0. 30 by 0.30 m subplot. Prior to forage harvest, spectral radiance readi ngs (red, 671 +/- 6 nm; green, 550 +/- 6 nm; and near infrared, 780 +/ - 6 nm) were recorded from each subplot. Composite samples composed of eight soil cores, 0 to 15 cm deep and 1.9 cm in diameter, were collec ted from each subplot. At both locations, bermudagrass forage yield ha rvested from 0.30 by 030 m subplots ranged from <1300 to >10 000 kg ha (-1) Soil pH ranged from 4.37 to 6.29 within the 2.12 by 21.33 m area at Burneyville and 5.37 to 6.34 at Efaw. No P or K fertilizer would ha ve been recommended at Efaw using mean soil test P and K. The range in recommended fertilizer rates would have been 0 to 31 and 0 to 17 kg P ha(-1) and 0 to 107 and 0 to 108 kg K ha(-1) at Burneyville and Efaw, respectively, if recommendations were based on individual 0.30 by 0.3 0 m grid data. Significant differences in surface soil test analyses w ere Pound when samples were <1 m apart for both mobile and immobile nu trients.