Spatial Variability and Soil Sampling for Salinity and Sodicity Appraisal in Surface‐irrigated Orchards

Abstract

Localized salt accumulation and associated crop damage are common in surface‐irrigated orchards. This study examined salinity and sodicity variation at five pecan (Carya illinoensis K.) orchards in the El Paso Valley, Texas mainly to develop soil smapling schemes for salinity appraisal. The first orchard (13.6 ha) contained three mapping units, and the other orchard blocks (0.5‐3.3 ha), single mapping units or soil types. These fields had been irrigated by border or basin methods mostly with water of 1.1 dS m−1. Soil samples were collected in a systematic grid at 68 sites to a depth of 60 cm in the 13.6‐ha field, and 15 to 28 sites at three depths in the other orchard blocks. Salinity and sodicity of the saturation extract in the 13.6‐ha field ranged from 0.7 to 6.3 dS m−1 and 2.3 to 12.5 (mmol L−1)1/2, respectively. Even in the orchard blocks of <1 ha, salinity and sodicity readings varied two‐ to threefold. The semivariogram of soil salinity and sodicity along transects or within mapping units did not reveal spatial structure. Instead, salinity readings were closely related to the saturation water contents of the soils (r = 0.79), and their variation decreased several fold when stratified by mapping unit. The frequency distribution of soil salinity along transects followed a skew distribution, but when grouped by mapping unit and averaged over a depth, both salinity and sodicity readings followed a normal distribution. For routine salinity appraisal in comparatively small surface‐irrigated orchards, soil map‐based samplings may be more efficient than those based on arbitrary transects or grid. The number of samples required to obtain a mean value in an area consisting of a single mapping unit within 15% of the true mean at the 5% level ranged from 7 to 26 ha−1 for salinity, and 3 to 14 ha−1 for sodicity at a depth of 0 to 60 cm in these alluvial soils.

Zinc Variability in Pecan Orchards: Implications for Leaf Sampling and Nutrient Recommendations

“…Variability in relation to the mean, reflected in the CV, is the primary factor affecting calculation of the sample size needed to obtain results that approach the true population mean of the orchard within an acceptable relative margin of error. This relationship can be seen in the study by Miyamoto and Cruz (1986) who found that as the CV increased for mapping units of an orchard in the El Paso Valley, the sample size required to obtain a soil salinity mean within 15% of the true mean increased. They used a modified version of Eq.…”

“…Carvalho et al (2020) established a minimum sample size for estimation of citrus shoot flush patterns by defining an acceptable relative sampling error from the true population mean and determining a sample size based on the relationship between relative sampling error and known mean and standard deviation. Miyamoto and Cruz (1986) used the same approach to determine the sample size needed to obtain a soil salinity mean within 15% of the true orchard block mean when soil sampling pecan orchards in the El Paso Valley of Texas.…”

Effectiveness of Soil Salinity Management Practices in Basin-irrigated Pecan Orchards

“…Soil samples from three depths (0-1, 1-2, and 2-3 ft) were collected at five to six holes per soil type per treated and untreated zones. According to a previous study (Miyamoto and Cruz, 1986), salinity of soil samples collected in this manner is expected to yield the mean value with a deviate range of 15% from the true mean. Soil samples collected were airdried, passed through a 2-mm screen, and the saturated paste was prepared as described in Rhoades and Miyamoto (1990).…”

“…In the El Paso Valley, reclaimed municipal effluent (Table 1), returnflow, and/or salty groundwater are blended into the river water, especially during drought years, thus raising salinity of the irrigation water and irrigated soils. Salts often accumulate in clayey soils, which have low permeability (Miyamoto and Cruz, 1986). Figure 2 illustrates the typical profile of soil types in the study area, which are prone to soil salinization.…”

Estimating generalized of global impacts to water quality on soil characteristics in basin of the Great Sebkha of Oran

“…However, more recent works uses it for the duration of a single campaign (Bresler and Hoffman 1986). Similarly, the spatial variations in salinity, related to the heterogeneity of water inputs on the plot (Miyamoto and Cruz 1986), cannot be taken into account by the notion of leaching fraction (LF). The concept of leaching fraction thus defined in this way poses as a condition that the water drained out of the profile is in balance with the ground: it is only once this condition has been realized that the formulas which involve electrical conductivities can be developed.…”