SSSAJ Journal of Natural Resources and Life Sciences Education
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Published in Soil Sci Soc Am J 50:1020-1026 (1986)
© 1986 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Spatial Variability and Soil Sampling for Salinity and Sodicity Appraisal in Surface-irrigated Orchards1

S. Miyamoto and I. Cruz2

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.

NOTES

1 Contributions from Texas Agric. Exp. Stn. Texas A&M Univ. System. This project was supported in part by a grant from the Binational Agricultural Research and Development (BARD) Fund and the Expanded Research Area Fund of the Texas Agric. Exp. Stn.

2 Associate Professor and Assistant Programmer, respectively. Texas A&M Univ. Agric. Res. Ctr. at El Paso, 1380 A&M Circle, El Paso TX 79927.

Received for publication October 15, 1985.




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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
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Environmental Quality		 The Plant Genome
Copyright © 1986 by the Soil Science Society of America.