Effect of Agricultural Intervention on the Spatial Variability of some Soils Chemical Properties in the Eastern Plains of Colombia

Abstract

A B S T R A C TGrowing demand for food exerts pressure on natural resources and may lead to the expansion of agricultural frontiers in developing countries. Most of this pressure appears in tropical zones, in native savannahs, with naturally infertile soils prone to degradation. Crop management in these regions is based on generalized estimates, leaving aside the inherent soil variability, leading to low production efficiency and high risk of environmental damage. This study aims at determining the spatial variability of some chemical properties, including organic carbon, pH, exchangeable acidity, exchangeable aluminum, P, Ca, Mg, K and Na for two Oxisols with different levels of agricultural intervention, in Puerto Lopez, Colombia, in order to identify guidelines for site-specific management. A forty-two point grid (25 × 25 m) was established for samplings at two depths: 0-100 and 100-200 mm. Descriptive statistics and geostatistics were used to analyze soil properties spatial dependence. Variogram models were obtained and from them maps of properties were drawn using ordinary punctual kriging. The results showed that spatial variability of the soil chemical properties depends upon the use of amendments, fertilizing methods, tillage and the inherent characteristics of each variable analyzed. A greater influence of the agricultural intervention on spatial variability was evident in the upper 100 mm of soil. Spatial dependence was found for most of the studied soil properties. However, K and Na presented variograms with pure nugget effects and/or very short ranges. The information generated is a base to derive guidelines for site-specific agriculture.

Spatial variability of an Alfisol cultivated with sugarcane

“…The other attributes presented mean variability, where the highest value of the Cv of the P outstands. This variability observed in the attributes has been reported by different authors (Silva and Chaves, 2001;Yemefack et al, 2005;Camacho-Tamayo et al, 2008), who also emphasized the behavior of P, element that is distributed superficially or incorporated in the first centimeters of soil.…”

“…The fit for normality for these attributes, in different soil types, is reported by various authors (Silva et al, 2001;Yemefack et al, 2005;Camacho-Tamayo et al, 2008).…”

“…According to Camacho-Tamayo et al (2008), this behavior with higher values than the natural soil contents and high variability shown by maximum and minimum values, is due to the distribution of this agricultural input through the years, modifying soil contents, especially on the surface, because of the scarce mobility and solubility of this element. According to Cressie (1993), it is convenient to verify that not very long tails are present in the normal distribution, more than in normality, in order to avoid a result compromise, especially when kriging is performed using estimations based on mean values (Warrick and Nielsen, 1980).…”

“…These R 2 values, along the cross validation for all the attributes, indicate adequate data reliability. Studies developed by different authors obtained theoretical semivariograms models fitting for chemical attributes (Silva and Chaves, 2001;Gallardo andParamá, 2007 andCamacho-Tamayo et al, 2008). Loading factors higher than 0.7 (absolute value) are shown in italic.…”

“…However, crop establishment also modifies soil variability (Burgos et al, 2006), especially by farming work and implementation of agricultural inputs, especially on the surface (Camacho-Tamayo et al, 2008). Mello et al (2006) found heterogeneous attributes in different soil types and indicated that spatial dependence is conditioned by relief, which causes to determine different management areas from each evaluated attribute of the soil, evidencing the need of carrying out researches in different soil classes.…”