Colorado and North China, although on opposite sides of the globe, have one thing in common: They are areas of increasingly limited and erratic rainfall and irrigation water. Building on the commonality, field tests of wheat-corn double-cropping systems in China and cornfields in Colorado were created. Researchers in both locations teamed up to see how far they could stretch water resources, as well as nitrogen, without cutting yields.
Stateside, the research team included USDA Agricultural Research Service engineers Laj Ahuja, Walter Bausch, and Gerald Buchleiter based at Colorado State University. At Fort Collins, they tried four irrigation levels and found that in limited irrigation, it was best to skip the traditional preplanting irrigation for wheat. “We also found it best to use 80% of the water for the two critical wheat growth stages and only 20% at corn planting,” Ahuja says. “This promises the highest yields, the best water-use efficiency, and the least water drainage overall.”
The team completed two years of experiments with four irrigation levels in China. “While the combination of models has been used in other experiments to test alternative water- and nitrogen-management practices, this is the first time the models have been used to evaluate crop responses to lack of water across critical crop-growth stages and the first to use long-term weather data,” Ahuja explains.
93 Years Of Data, Eight Years Of Field Tests
The long-term simulation with 38 years of weather data shows that North China plain farmers should apply no more than 180 pounds of nitrogen fertilizer per acre to get the best yields for winter wheat followed by corn. Those farmers usually use about 270 pounds per acre. The model results indicate that cutting back nitrogen fertilizer use by one third would reduce nitrate leaching by 60% without affecting crop yields.
In Colorado, ARS researchers used the Decision Support System for Agrotechnology Transfer (DSSAT) model to look at corn produced either with or without irrigation. They used local historical weather records from 1912 through 2005. Field data came from eight years of experiments.
The results are similar to those in China in terms of favoring crop-growth stages with irrigation water. When simulated irrigation water supplies are limited, it is best for yields, water-use efficiency, and minimization of nitrogen losses when 20% of the water is used during the vegetative stage of development and 80% is used for the critical flowering and grain-filling stage.