The analysis and interpretation of the spatial variability of soil properties are keystones in site-specific management. Soil sampling interval is typically used in establishing management zones for site-specific application of nutrients. Sampling intensity is an important factor that can potentially limit the accuracy of the management zone. The objectives of this study were (i) to quantify the spatial variability of soil properties across tobacco plantation fields, (ii) to select the reasonable sampling interval for eight soil variables to minimize cost and maximize evaluation accuracy, and (iii) to provide a theoretical basis for setting a reasonable sampling interval in precision agriculture. Soil samples were collected at approximately 20 m at 0- to 20-cm depth. The coordinates of each of the 111 points were recorded using global positioning system. Using a geographic information system software platform, the soil sampling points from the primary scheme were regularly deleted to create comparative schemes. The geostatistical method was used to produce distribution maps of the soil nutrients. Seven sampling points were randomly selected. The interpolation of the values of the seven soil points was compared under three sampling intervals with their actual measurements. The interpolation errors of soil organic matter and available copper were lowest in the 60-m sampling interval. In the 20-m sampling interval, alkaline hydrolyzable N, available phosphorus, available potassium, available iron, and available zinc had the least errors of interpolation. Available manganese had the least interpolation error at the 40-m sampling interval. Overall, the sampling efficiency could be further improved. The method can be applied in a practical and cost-effective manner to facilitate soil sampling.
1Tobacco College Agronomy Department of Henan Agricultural University, National Tobacco Cultivation, and Physiology and Biochemistry Research Center, Zhengzhou, China. Mr. Liu Guo-Shun is corresponding author. E-mail: firstname.lastname@example.org
2Nanyang Tobacco Company of Henan Province, Nanyang, China.
3Technology Center of Tobacco Leaf, Dali Tobacco Company, Dali, Yunnan, China.
4Pingdingshan Tobacco Company, Pingdingshan, China.
5Jia County Branch of Henan Tobacco Company, Jia County, China.
Received February 28, 2010.
Accepted for publication June 21, 2010.