Micro-spatial variability of soil nitrate following nitrogen fertilization and drip irrigation

• Published in: Water, air, and soil pollution air, and soil pollution, 1999-12, Vol.116 (3/4), p.605-619
• Main Authors: Sharmasarkar, F.C, Sharmasarkar, S, Zhang, R, Vance, G.F, Miller, S.D
• Format: Article
• Language: English
• Subjects: Acidic soils; Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; cokriging; Contaminants; Drip irrigation; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental monitoring; Exact sciences and technology; Fertilization; Fertilizers; Fundamental and applied biological sciences. Psychology; irrigated conditions; irrigated soils; kriging; microirrigation; nitrates; Nitrification; Nitrogen; pH effects; Pollution; Pollution sources. Measurement results; Pollution, environment geology; sandy loam soils; Soil and sediments pollution; Soil and water pollution; soil fertility; soil pH; Soil pollution; Soil science; Soils; Spatial analysis; Spatial distribution; spatial variation; statistical analysis; Studies; variance
• ISSN: 0049-6979; 1573-2932
• DOI: 10.1023/A:1005188827642

Micro-spatial analysis of nitrate (NO^sub 3^), an environmental contaminant partially attributed to nitrogen fertilization, can be useful for estimating its distribution in soils. A study was conducted to determine the micro-spatial distribution of soil NO^sub 3^ using kriging and cokriging in a drip-irrigated and nitrogen-fertilized field. One hundred soil samples were collected in a regular grid pattern from a 10 m × 20 m plot, and analyzed for soil NO^sub 3^ and pH. The effect of reduced sample size on NO^sub 3^ estimation was also evaluated. The pH data indicated the soils were slightly acidic to neutral with log[NO^sub 3^] values ranging from 1.66 to 2.95. These parameters were inversely related; which was probably an attribute of soil nitrification process. Sample variograms and cross-variograms suggested that the spatial distribution of pH and log[NO^sub 3^] could be described by linear models in the area studied, as indicated by small MSE (mean sum error), and RKV (reduced kriging variance) values close to 1. Contour maps based on kriging and cokriging estimates indicated greater homogeneity of the variables in the south-north direction than the east-west, except for zones of high NO^sub 3^ and low pH in the north-central edge and north-east corner of the grid area. Cokriging of log[NO^sub 3^] estimation, using pH data, improved MSE, MSSE (mean sum square error), MKV (mean kriging variance), RKV, CEE (correlation between estimated data and error), CEM (correlation between estimated and measured data) by 46, 31, 30, 22, 96, and 98%, respectively, as compared to kriging. Lower cokriging variance for any estimated log[NO^sub 3^] value, as compared to the kriging analysis, indicated that cokriging provided more accurate estimates. With reduced sample observations (n) for NO^sub 3^ similar conclusions were obtained; and the estimation accuracy was maintained up to n >70. Cokriging analysis with reduced n also curtailed the analytical cost, and facilitated NO^sub 3^ estimation by means of pH, which was measured at a cheaper cost.[PUBLICATION ABSTRACT]