No abstract

No abstract

Distribution characteristics of salinity and sodicity in furrow‐irrigated fields have not been adequately evaluated. This study examined the pattern of salt accumulation within crop beds and its spatial variation along or across crop rows, mainly for developing sampling guides for routine salinity appraisal. Soil samples were collected at spacings ranging from 1.5 to 6 m in four furrow‐irrigated fields of the middle Rio Grande Basin and were analyzed for salinity of the saturation extract and in selected cases for the sodium adsorption ratio (SAR). Salinity varied two to sixfold within the row lengths of 110 to 190 m, and its variation generally increased with increasing sampling depth and numbers of irrigation. The analyses of autocorrelation showed that salinity readings were spatially dependent at one of the four tested fields, and the distance of dependence reached 46 m. This field showed a gradual change in soil texture (from silty clay loam to silty clay), and provided a semivariogram conforming to a generalized linear model. When samples were collected from an area consisting of a single soil type or when salinity values were stratified by soil type, the distance of dependence decreased to <15 m. The frequency distribution of both salinity and sodicity within the same soil type followed a normal distribution with the standard error of estimates of mostly <8%. The sampling sites required to obtain a mean value within 15% of the true mean ranged from 3 to 11 per test row when sampled at 0‐ to 0.20‐m depth prior to preplant irrigation, and the required number increased with increasing sampling depth and numbers of irrigation. For routine appraisal of salinity in the fields similar to examined here, soil samples can be collected on the basis of soil type, and salinity data can be analyzed by conventional statistics with a reasonable assurance that salinity values are spatially independent.

No 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.