Variability of physical attributes in tropical weathered soil cultivated with irrigated beans (Phaseolus vulgaris L.)

Abstract

Soil physical attributes are affected by several events. The ability to identify the variation of those attributes can be used to decide the best crop management. Although it is known that smaller grids are more representative, predicting the least number of points while maintaining accuracy is a tool that might reflect a gain in yield and time. The aims of this study were to evaluate the spatial physical variability and to define the minimum sampling density in a tropical Typic Haplustults soil using a scaled semivariogram in a central pivot area with pinto bean (Phaseolus vulgaris L.) after the eighth bean harvest in Cristalina, Goias State. Soil samples were collected at a regular grid of 10-m intervals, totaling 180 points, and at depths of 0.00–0.10 m, 0.10–0.20 m, and 0.20–0.30 m to determine total sand content (TS), silt (SIL), clay (CL), water-dispersed clay (WDC), mean weight diameter of soil aggregates (MWD), soil penetration resistance (PR), soil macroporosity (Ma), soil microporosity (Mi), and soil bulk density (BD). The results demonstrated that management promoted superficial soil compaction with increasing BD and Mi and decreasing Ma and TP. The scaled semivariogram demonstrated similarity between attributes in the three studied soil layers, evidencing strong spatial dependency. The sample density showed a strong influence of WDC in the irrigated soil properties. Adoption of a scaled semivariogram is a strategy that can be used to determine a minimum number of points that represents the spatial variability of soil physical attributes and to assist the best management in irrigated soils.

Soil sampling optimization using spatial analysis in irrigated mango fields under brazilian semi-arid conditions

“…The high CV values for clay content can be explained by the large range in variation in the area considering the large amplitude (minimum and maximum values, Tables 2 and 3), and in addition, consistent with the results obtained by Ceddia et al (2009), owing to the greater error associated with clay suction during the pipette method. Similar results were obtained by Rodrigues et al (2015) in an Ultisol under guava cultivation, which also presented high variability for the clay content.…”

“…The experiment carried out by Catani et al (1954), where the current recommendation (20 individual samples) was determined, occurred in two areas under Oxisols, one cultivated with intercropped coffee and maize, and the other with a maize monoculture, both areas of up to 6 ha. Those conditions differ greatly from the conditions of the present study in terms of soil texture (mostly sandy), area (up to 10 ha), crop type (fruit crop), and soil management (daily irrigations and fertilization concentrated in the region under the plant canopy).…”

“…Semivariogram models were utilized to estimate the spatial dependence between the samples and to identify whether the variations were systematic or random. The semivariogram is a basic tool that can quantitatively represent the variation in a regionalized phenomenon in space and was estimated by Equation (CATANI et al, 1954),…”

“…After obtaining the parameters of the experimental semivariograms for each variable, the scaled semivariograms were performed by dividing the semivariance by the statistical variance, with the objective of reducing them to the same scale, to make the comparison between results of different variables easier (CASTIONI et al, 2019) and allowing the determination of an ideal number of samples that satisfy all the studied variables simultaneously. Three scaled semivariograms were prepared for each area, related to the three groups of variables: chemistry, physics, and soil texture in the two evaluated layers.…”

“…The condition of the agricultural field should be reproduced as accurately as possible using a minimum number of soil samples to estimate the mean value of the soil properties with some precision (LIMA et al, 2010). In this context, there is a limitation to the use of classical statistics, as suggested in the study by Catani et al (1954) wherein the collection of 20 individual soil samples is recommended to obtain a composite sample in areas of up to 10 ha that are considered homogeneous. This method has been used indiscriminately in Brazilian agricultural fields regardless of the management system (conventional or no-tillage), crops (annual or perennial), and soil variability.…”