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Statistical Parameters and Reproducibility of the Neutron Method of Measuring Soil Moisture¹

ABSTRACT

The neutron device used in the study was essentially that of Stone et al., Soil Sci. Sco. Am. Proc. 19:419-423. 1955. Reproducibility (that is, repeat performance at a given location) of the neutron device was evaluated in the laboratory and in the field. Observed coefficients of variation for laboratory and field were about 1.5% to 2.5%. Random counting error component accounted for most of this percentage.

In comparing gravimetric sampling with neutron measurements at the same locations, a rather poor agreement was observed within locations, but overall average difference in indicated moisture was < 0.1 inch of water per 6-inch soil depth. Poor individual agreement is believed to be due to limitations of bulk density determination and not to the neutron device.

A comparison of the relative abilities of the aravimetric and neutron methods to evaluate moisture in a set of plots where sampling locations were randomized indicates that use of seven gravimetric sites for each neutron site gives a comparable standard error of the mean.

¹ Joint Publication: Journal Paper No. J-3795 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Projects No. 998 and No. 1276, Department of Agronomy; and contribution No. 881 of the Institute for Atomic Research, Ames, Iowa. Acknowledgment is made to Prof. H. O. hartley, Statistics Dept. for assistance in the statistical analyses presented.

² Graduate Research Associate in Agronomy and Institute for Atomic Research, Professor of Agronomy (Agricultural Climatology), and Professor of Soils and Physics, Iowa State University, Ames, Iowa. The senior author is now Associate Professor of Agronomy at Oklahoma State University, Stillwater.

Received for publication February 17, 1960. Accepted for publication April 4, 1960.