Management cell size determination for site-specific crop management

Abstract

The prevention of groundwater and surface water contamination by pesticides, herbicides, and nitrogen fertilizers is complicated by the spatial variability of agricultural soils. Variations in soil properties can cause different loss potentials for crop inputs across any given field. Changes in production input levels (nitrogen, phosphorous, soil moisture, etc.) also cause variability of profitability across a field by causing variations in yield. Areas of low yield may require a higher input level, or may not have the same production potential, and a reduction in input level is justified. Site-specific crop management (SSCM) is a set of tools that addresses these situations. The goal of SSCM is to meet the specific needs of field areas, reducing input loss potential and maximizing input efficiency and profitability. One approach using this management technique is to divide a field into management units or cells, and treat each of them as uniform application units. Application can be tailored to meet specific input requirements in each area, rather than treating the entire field with the same application rate. A major problem using this method of SSCM is determining the appropriate management cell size. Implement size, location accuracy, applicator response rate, the spatial resolution of soil property measurements, and the variability of the crop input across a field affect cell size. Implement size and applicator response rate will depend on the user's specific equipment. Location error is determined by the type and quality of the equipment used. A methodology has been developed to suggest an acceptable range for management cell size based upon a user's specific situation. Another problem with SSCM is developing an applicator that can quickly and accurately respond to the changes in application rates of the crop input. A variable rate planter and fertilizer application device was built and tested. The positioning error, application accuracy, and response rate of the system were measured. Positioning system errors were less than I m (6.6 ft). Application errors were typically less than 7%. The system's response to an application rate change took less than one second.