Introduction
The Decision Support System for Agrotechnology Transfer (DSSAT) Version 4.5 is a software application program that includes crop simulation models for more than 25 crops, data base management programs for soil, weather, and crop management and experimental data, and utilities and application programs. The crop simulation models simulate growth, development and yield, and the soil and plant water, nitrogen and carbon balances. DSSAT and its crop simulation models have been used for a wide range of applications, including on-farm and precision management to regional impact assessments of the impact of climate change and variability. 
The Decision Support System for Agrotechnology Transfer (DSSAT) has been in use for more than 15 years by researchers in over 100 countries worldwide. DSSAT is a microcomputer software program combining crop soil and weather data bases and programs to manage them, with crop models and application programs, to simulate multi-year outcomes of crop management strategies. As a software package integrating the effects of soil, crop phenotype, weather and management options, DSSAT allows users to ask "what if" questions and simulate results by conducting, in minutes on a desktop computer, experiments which would consume a significant part of an agronomist's career.
DSSAT also provides for validation of crop model outputs; thus allowing users to compare simulated outcomes with observed results. Crop model validation is accomplished by inputting the user's minimum data, running the model, and comparing outputs. By simulating probable outcomes of crop management strategies, DSSAT offers users information with which to rapidly appraise new crops, products, and practices for adoption.
The release of DSSAT Version 4 incorporates changes to both the structure of the crop models and the interface to the models and associated analysis and utility programs. The DSSAT package incorporates models of 27 different crops with new tools that facilitate the creation and management of experimental, soil, and weather data files. DSSAT v4 includes improved application programs for seasonal and sequence analyses that assess the economic risks and environmental impacts associated with irrigation, fertilizer and nutrient management, climate change, soil carbon sequestration, climate variability and precision management.
DSSAT was developed through collaboration between scientists at the University of Florida, the University of Georgia, University of Guelph, University of Hawaii, the International Center for Soil Fertility and Agricultural Development, Iowa State University and other scientists associated with ICASA.
Minimum Data
The minimum data set (MDS) refers to a minimum set of data required to run the crop models and validate the outputs. Validation requires: 
1.	Site weather data for the duration of the growing season, 
2.	Site soil data, and 
3.	management and experimental data for the experiment. 

1. MDS Weather Data
The minimum required weather data includes: 
•	latitude and longitude of the weather station, 
•	daily values of incoming solar radiation (MJ/m²-day), 
•	maximum and minimum air temperature (ºC), and 
•	rainfall (mm). 
You may also include dry and wet bulb temperatures and wind speed as optional data.
The length of weather records for validation must, at minimum, cover the duration of the experiment and preferably should begin a few weeks before planting and continue a few weeks after harvest so that "what-if" type analyses may be performed.

2. MDS Soil Data
Desired soil data includes soil classification (SCS), surface slope, color, permeability, and drainage class. Soil profile data by soil horizons include: 
•	upper and lower horizon depths (cm), 
•	percentage sand, silt, and clay centent, 
•	1/3 bar bulk density, 
•	organic carbon, 
•	pH in water, 
•	aluminum saturation, and 
•	root abundance information. 

3. Management and Experiment Data
Management data includes information on planting date, dates when soil conditions were measured prior to planting, planting density, row spacing, planting depth, crop variety, irrigation, and fertilizer practices. This data are needed for both model validation and strategy evaluation.
In addition to site soil and weather data, experimental data includes crop growth data, soil water and fertility measurements. This data are needed for model validation.
Product Information
Components: 

The Cropping System Model (CSM) released with DSSAT Version 4 represents a major departure from previously released DSSAT crop models, not in function, but in design. The computer source code for the model has been restructured into a modular format in which components separate along scientific discipline lines and are structured to allow easy replacement or addition of modules. CSM now incorporates all crops as modules using a single soil model and a single weather module. The new cropping system model now contains models of 17 crops derived from the old DSSAT CROPGRO and CERES models. The major modules are: 
•	Land Module
•	Management Module
•	Soil module - A soil water balance sub-module and two soil nitrogen / organic matter modules.
•	Weather module - Reads or generates daily weather data
•	Soil-Plant-Atmosphere module - Deals with competition for light and water among the soil, plants, and atmosphere
•	CROPGRO plant growth module 
o	Grain Legumes - Soybean, peanut, drybean, chickpea, cowpea, velvetbean, and faba bean 
o	Vegetables - Pepper, cabbage, tomato 
o	Grasses – Bahia, brachiaria 
•	CERES Plant Growth Module 
o	Grain Cereals -Rice, maize, millet, sorghum, wheat, and barley 
•	SUBSTOR Plant Growth Module 
o	Potato