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Title: DELINEATING SITE-SPECIFIC MANAGEMENT UNITS ON AN IRRIGATED, ARID-ZONE SOIL

Author
item Corwin, Dennis
item LESCH, SCOTT - UC RIVERSIDE, CA

Submitted to: Proceedings of the International Salinity Forum
Publication Type: Proceedings
Publication Acceptance Date: 4/11/2005
Publication Date: 4/25/2005
Citation: Corwin, D.L., Lesch, S.M. 2005. Delineating site-specific management units on an irrigated, arid-zone soil. In: Proceedings of the International Salinity Forum, Managing Saline Soils and Water: Science, Technology, and Soil Issues. April 25-27, 2005. Riverside, CA pp:39-42.

Interpretive Summary: Conventional farming applies inputs within a field; as a results, it is inefficient due to the spatial variability of soil properties influenceing crop yield. Site-specific management units (SSMUs) have been proposed as a means of managing the spatial variation in properties influencig crop yield. This paper presents an approach for preparing maps of SSMUs and their associated recommendations to increase cotton yield on an irrigated, arid zone field in California's San Joaquin Valley. Within-field spatial variation of soil properties influencing cotton yield are characterized using spatial measurements of apparent soil electrical conductivity (ECa) to direct soil sampling. Classical and spatial statistics are then used in conjunction with a geographic information system to develop a cotton yield response model and to develop a map of SSMUa with associated recommendations for increasing cotton yield. This approach is only applicable when crop yield monitoring measurements are correlated with corresponding spatial ECa measurements.

Technical Abstract: Site-specific crop management has been proposed as a means of managing the spatial variability of factors that influence crop yield. It is hypothesized that in instances where ECa correlates with crop yield, spatial ECa information can be used to direct a soil sampling plan, which spatially characterizes soil properties influencing crop yield. The objectives of this study were (i) to utilize a geo-referenced ECa survey to direct soil sampling, (ii) to identify soil-related properties that influence cotton yield, and (iii) to use this spatial information to delineate site-specific management units (SSMUs). A 32.4-ha irrigated cotton field in California’s San Joaquin Valley was monitored for yield in August 1999 followed by an intensive ECa survey. Sixty soil sample sites were selected based upon a response-surface sampling design utilizing the spatial ECa measurements. Scatter plots were obtained and correlation and regression analyses were performed to assess the relationship between cotton yield and the properties of pH, boron, nitrate-nitrogen, chloride, salinity (i.e., electrical conductivity of the saturation extract; ECa), leaching fraction (LF), water content (WC), bulk density, % clay, and saturation percentage. Correlation coefficients of -0.01, 0.50, -0.03, 0.25, 0.53, -0.49, 0.42, -0.29, 0.36, and 0.38, respectively, were found. The correlation coefficient between yield and ECa was 0.51. A site-specific response model of cotton yield adjusted for spatial autocorrelation using restricted maximum likelihood was developed. The response model indicated that LF, ECe, WC, and pH were the most significant soil properties influencing cotton yield: cotton yield (Mg ha) = 19.28 + 0.22 ECe – 0.02 ECa2 – 4.42 LF2 – 1.99 pH + 6.93 WC. The spatial information and response model provided sufficient information to delineate SSMUs with associated recommendations to increase cotton yield.