Sampling soil with the auger hole is simpler and faster than with the cutting shovel. The last is frequently used in no till systems to obtain soil samples for fertility analyses. This study had the following objectives: comparison of two different localized soil sampling systems concerning the horizontal variability of chemical soil characteristics; determination of the necessary unit number to compose a representative sample of the area, and the demonstration that mean fertility values obtained from the composite sample are the same as the obtained from the arithmetic mean of single samplings. The study was carried out in an area under no till system since 15 years. The localized sampling systems were: cutting shovel (24 single samples collected perpendicularly to the furrow and in the middle of the space between two furrows) and auger hole (20 single samples collected in the planting furrow (Ts), 20 single samples collected 10 cm beside the furrow (T10), and 20 single samples collected 40 cm beside the furrow (T40).Representative sub-samples of both methods were randomly chosen from the single ones, and mixed to make up respective composite samples. P, K, Ca2+, Mg2+, and Al3+, and the values of pH, H + Al, and P-rem were determined in the single and composite samples, and their means, standard deviation, and variation coefficient calculated. Data means were compared by the Student test. Only K, Mg2+, and H + Al values differed according to the employed sampling system. When the auger hole was used, the variability of all studied characteristics and the necessary number of single samples to compose a representative sample were higher than for sampling with the cutting shovel. The variability was low for pH, P-rem, and H + Al, and high for P, Al3+, Mg2+, K, and Ca2+. Ten single samples collected with the cutting shovel or 27 single samples collected by the auger hole (five samples collected in the furrow, nine collected 10 cm beside the furrow, and 13 collected in the space between two furrows) were necessary to compose representative samples. Analyses of the composite sample for both pieces of equipment presented values near the medium values obtained with single samples, thus characterizing the medium fertility of sampling units adequately.
cutting shovel; auger hole; single sample number and composed sample
