SPATIAL VARIABILITY OF SELECTED CARBON, NITROGEN, AND PHOSPHORUS PARAMETERS ON ACID AND CALCAREOUS RANGELAND SOILS

The magnitude of C, N, and P seasonal or long-term variability in rangelands is difficult to assess because of intrinsic soil heterogeneity even in seemingly uniform areas. A need exists, therefore, to determine the minimum number of samples necessary so significant changes in C, N and P can be assessed where minimal confounding from soil types and vegetation exist. To achieve this end, laboratory and field studies of selected C, N, and P parameters were conducted to compare variability among six transect lines, radiating from a central point. Samples were taken along each transect line every 3 m to a distance of 15 m. Parameters measured were: total organic C (OC), total Kjeldahl N (TKN), NH-4-N, NO3-N, NaHCO3-extractable inorganic P (NaHP), and total organic P (TPo). Two rangeland soils, a moderately acid Ascalon sandy loam, and a calcareous Haverson loam, were sampled at two depths to assess spatial differences. Results indicated that under the experimental conditions, OC, TKN and TPo would require at least 9, 6, and 10 replications, respectively, for 95% confidence limit for an allowable error of 10%. The smaller available mineral pools were much more variable than the total pools, and could require as many as 20 to 30 samples.