MSU Professor Finds Irrigation Timing Benefits Wheat Yield And Quality

In an agricultural state enduring one of the worst droughts in recent history, a Montana State University crop physiologist may have some good news for state watersheds and farmers' pocketbooks when it comes to irrigating one of Montana's top cash crops.

Jessica Torrion, assistant professor of crop physiology at MSU's Northwestern Agricultural Research Center in Creston, recently published an article that shows specifically timed irrigation practices can affect the harvest quality of hard red spring wheat varieties - if they are applied past the medium milk stage of the wheat plant's development. The article, "Impacts and Limits of Irrigation Water Management on Wheat Yield and Quality," appeared in Crop Science, the official journal of the Crop Science Society of America. Torrion's research was funded by the Montana Wheat and Barley Committee.

Milk stages are phases in a wheat plant's growth cycle when the wheat kernel begins to form and secretes a milky fluid containing starch, protein and other nutrients. The milk eventually solidifies as the wheat kernel ripens and matures enough for adequate baking and milling, in a process called "grain filling." Grain filling generally takes four to six weeks, depending on how much moisture the crop gets. That process can be cut short during times of high temperatures, which stresses the plant, Torrion said.

Irrigating during and after the late milk stage, when the milk fluid decreases and plant starches increase to create thicker milk, does not improve the wheat's overall yield and grain quality, Torrion said. Rather, Torrion found that scheduling the final irrigation during the medium-milk stage produces yield benefits similar to that of applied irrigation after the medium milk stage, but with less water.

"Essentially, we found that a producer can irrigate earlier in the grain-filling process and achieve the same yield benefit as irrigating later," Torrion said. "So, we're looking at potentially significant savings in water, energy and time during a crop's maturation cycle, all of which become critical and expensive factors during a drought year and pins down a very common producer question of "when do I stop irrigating wheat?"

Torrion said that never before in the state has there been an experiment that evaluates yield and grain quality comparing hard red spring wheat varieties, solely based on their response to timed irrigation before the completion of grain fill. Torrion said only about eight percent of hard red spring wheat acreage is irrigated in Montana.

"Most Montana wheat farmers practice dryland agriculture, without irrigation infrastructure, so their yield is completely dependent on rainfall," Torrion said. "Given our recent drought conditions and more variable weather patterns, more Montana producers are thinking about irrigating as grain yields have fallen over time. We're seeing an increased interest in irrigation, and so we wanted to test what effects various irrigation practices might have on spring wheat varieties."

According to the USDA, hard red spring wheat is the highest grossing of all commercial crops in Montana, accounting for 23 percent of the nation's hard red spring wheat supply and more than 50 percent of Montana's total spring wheat acreage.

The article, co-authored with Bob Stougaard, NWARC superintendent and MSU professor of weed science, presents results from a yearlong experiment where eight hard red spring wheat plots were subjected to six different water regimens. Three water treatments replaced varying levels of moisture due to evapotranspiration loss. The additional three water regimes included scheduling a final irrigation at specific stages of the wheat plants' grain filling process -- early milk, medium milk and soft-dough.

Torrion then tested each wheat variety and its respective water regime against standard wheat market characteristics: protein content, test weight (a required 60 pounds per bushel) and falling number -- a test that indicates the amount of pre-harvest sprout damage, or starch degradation, in wheat. Torrion said the optimal time to apply a final irrigation was during the medium milk stage.

Results also showed that when irrigation is terminated before the completion of grain filling, it does not affect the yield and quality of the wheat crop. Additionally, the grain's test weight generally improved with irrigation, whereas falling numbers generally decreased with irrigation, but this varied by variety.

"What we found is that so long as at least one irrigation event is applied during the grain-filling process, the overall yield and quality is not negatively affected," Torrion said. "Applying irrigation towards the late grain-filling process doesn't produce a greater yield or produce better quality, rather, it unnecessarily uses extra water, time, energy and income."

According to the U.S. Geological Survey, an acre-inch is equal to about 27,154 gallons of water, and Torrion said standard wheat farms in Montana have about 140 acres under each center pivot. If a producer terminates irrigation at 1 acre-inch, after the final irrigation applied at medium milk, it may save up to 3.8 million gallons of water on a 140-acre parcel, Torrion said.

"That number climbs when you consider a number of farmers that irrigate after the final recommended irrigation application at medium-milk stage," Torrion said. "We were quite surprised by our findings mostly because of the potential for greater sustainability on community water resources. That is what is really impressive," Torrion said.

Torrion added that too much unnecessary irrigation in wheat late in the season caused a lowering of falling number, a common economic challenge for Montana farmers since the condition leads to poor baking quality and reduced grain prices at local elevators.

"The goal of any irrigation practice is to limit risk and produce economic benefit for the producer," Torrion said. "Too much watering and you may have problems with lowered falling number, too little watering and you're going to see a reduction in yield due to water stress. Our ultimate goal is to provide information on best irrigation practices and enable producers to apply the right amount of water without negatively affecting yield and quality at the elevator."

The study may impact a state facing agricultural challenges with water limitations, Stougaard said.

"Ultimately, we found it improves grain quality and farm income, while better managing agricultural water use," Stougaard said. "As changing weather patterns and increased drought continue, there's a critical need to tailor water management to sustainable food production."

Stougaard added that identifying and breeding wheat varieties adapted to reduced irrigation and changing weather patterns is necessary for improving future grain production and quality.

The NWARC is one of seven remote research centers in the Department of Research Centers in MSU's College of Agriculture and the Montana Agricultural Experiment Station. MAES and the College of Agriculture operate remote agricultural research centers in Montana that address production challenges in the diverse agro-ecosystems of the state in research and outreach programs in: crop and animal production methods, market growth opportunities, pest management and disease management, environmental quality issues and agricultural water management research. The research centers are located in Bozeman, Conrad, Corvallis, Creston, Havre, Huntley, Moccasin and Sidney.