CANDI: Environmental Protection Software for
Irrigation and Pesticide Management

CANDI (Chemicals AND Irrigation) software is designed to aid in managing agricultural pesticides and irrigation systems by considering the potential for groundwater contamination (Aly & Peralta, 1993). CANDI facilitates estimating the relative reduction of potential pesticide contamination of groundwater achievable by improved water/pesticide management. By comparing the potential contamination results of different water management schemes, best management systems (BMSs) can be selected. When BMSs are implemented, the likelihood of groundwater contamination is reduced. CANDI uses the concept of relative amount of pesticide, which is the fraction of the applied chemical that exists in the soil profile by the time the pesticide reaches groundwater.

CANDI can do the following:

1. For a particular irrigation system design, predict which pesticide will yield an acceptable relative amount of pesticide at a specific depth. In this case, the user must provide CANDI with the irrigation system efficiency, soil and crop data, weather information, and pesticide application dates.

2. For a selected range of possible irrigation system designs, show the irrigation system design that will result in the least relative amount of pesticide reaching a specific depth. For this option, the user provides CANDI with the pesticide physical and chemical properties, application date, cultivated crop data, soil data, and weather information. For the surface irrigation system, the final result is curves showing relative amount as a function of furrow inflow rate for selected furrow lengths. For sprinkler irrigation systems, relative amount is a function of two design parameters, uniformity coefficient, and fraction of area adequately irrigated.

3. Demonstrate the zones of contributing groundwater to specified wells during prescribed travel times. This permits the user to know where using pesticides is more hazardous to groundwater consumers. For this optional output, the user must provide CANDI with pumping wells data and aquifer parameters (storativity and transmissivity or hydraulic conductivity).

Predicting the amount of pesticide that will leach to the groundwater is not trivial. It can require using multiple computer simulation modules in series. CANDI helps the user to perform this task easily and is designed for use by persons only slightly familiar with groundwater hydraulics or chemical leaching processes.

CANDI contains several simulation modules. The modules are efficiently coded and integrated to achieve rapid processing for all applications.

The first module used simulates the irrigation system, either furrow or sprinkler. In any irrigation system, reduction in potential pesticide contamination can be achieved by efficient water application. Efficiency, in turn, is a function of several factors.

In surface irrigation, efficiency is a function of the furrow length, inflow rate, topography, and soil characteristics. These variables are used as inputs for the surface irrigation simulation module (SIRMOD) (Walker & Humpherys, 1983). SIRMOD predicts the water storage efficiency for a specified surface irrigation system at the site of interest and for a specific irrigation schedule. CANDI provides a database of much needed information for Utah conditions. SIRMOD will predict the total infiltrated depth of water for the prescribed combination of parameters.

In sprinkler irrigation, efficiency is a function of the uniformity coefficient, the fraction of area adequately irrigated, and soil characteristics. These variables are required as inputs. The sprinkler irrigation module estimates the soil storage efficiency, and uses the approach of Hart and Reynolds to predict the total infiltrated depth of water for the prescribed combination of parameters (Hart & Reynolds (1965).

Total infiltrated depth, soil data, crop data, and pesticide data are subsequently used as inputs for a module that emulates the simulation abilities of the widely-used Chemical Movement in Layered Soil (CMLS) (Nofziger & Hornsby, 1988). The relative amount of pesticide that reaches a prescribed depth after a period of time has elapsed is calculated by this module.

CANDI also delineates the capture zones for all wells within a study area by incorporating the Multiple Well Capture Zone module (MWCAP) (Office of Groundwater Protection, 1990). MWCAP provides efficient delineation of steady-state, time-related, and hybrid capture zones for wells in homogeneous aquifers. Knowing the capture zone of his/her well, the user might select different water/pesticide management schemes for inside the capture zone than for outside it.

CANDI can be used in humid or arid regions, while the pesticide leaching module can be used anywhere. The irrigation modules should be used only at irrigated sites. The well-head capture zone module is applicable for locations having fairly homogenous underlying aquifers.

The user's manual contains instructions and examples to guide CANDI's use. CANDI will run on 286 or more powerful PC systems with math coprocessors. It requires at least 512K of RAM, a hard disk, and an EGA (or better) monitor. CANDI can be obtained for $150 from the Dept. of Biological and Irrigation Engineering, Utah State University, Logan, UT 84322-4105, phone (801)797-2785, FAX (801)797-1248.

Aly, A. H., & Peralta, R. C. (1993). CANDI: Chemicals and irrigation management software, version 2.0, user's manual. Logan: Utah State University.

Hart, W. E., & Reynolds, W. N. (1965). Analytical design of sprinkler systems. Transactions of the ASAE, 8(2), 83-89.

Nofziger, D. L., & Hornsby, A. G. (1988). Chemical movement in layered soils: User's manual. Stillwater: Oklahoma State University, Agricultural Experiment Station, Division of Agriculture.

Office of Groundwater Protection. (1990). WHPA: A modular semi-analytical model for the delineation of wellhead protection areas (Version 1). Washington, DC: U.S. Environmental Protection Agency.

Walker, W. R., & Humpherys, A. S. (1983). Kinematic-wave furrow irrigation model. Journal of Irrigation and Drainage Division, ASCE, 109(IR4), 377-392.

This article is online at http://www.joe.org/joe/1995february/tt3.html.

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