Bill Schillinger1, Ron Jirava2, Tim Paulitz3, Jeremy Hansen3, John Jacobsen1, and Steve Schofstoll1
1Dept. of Crop and Soil Sciences, WSU; 2Farmer Collaborator, Ritzville; 3USDA-ARS, Pullman
We are investigating the effects of canola, winter triticale, and winter wheat on soil fungal and bacterial communities and the grain yield of subsequent spring wheat. The study was initiated in 2016 on the Ron Jirava farm west of Ritzville. These are 3-year rotations with a year of fallow after the spring wheat. Spring canola is substituted for winter canola when adequate winter canola stands are not achieved. There are 36 plots with each phase of the three, 3-year rotations present each year. Individual plots are 500 feet long and 30 feet wide.
This experiment is now in its 6th year, thus all three rotations are truly “in rotation”. We closely monitor soil water dynamics from all phases of all rotations and collect accurate grain yield data. Soil microbial activity is currently being assessed using DNA sequencing of rhizosphere soil (i.e., soil adhering to roots) as well as phospholipid fatty acid analysis (PLFA) of bulk soil. Such data can only be obtained through long-term cropping systems experiments.
During the past five years, significantly less overwinter precipitation has been stored in the soil in canola stubble in three years (Fig. 1). Averaged over the five years, canola stubble has stored significantly less over winter precipitation in the soil than winter triticale or winter wheat stubble. These differences were particularly pronounced during a winter of heavy snow accumulation in 2017. There were no significant differences in water storage among treatments during winters with little snow (such as 2019 and 2021). Average spring wheat grain yields for the first four year after canola, winter triticale, and winter wheat have been 33, 41, and 39 bushels/acre, respectively (Fig. 1).
Every year to date, spring wheat grain yields have been significantly related to soil water content measured in early April (Fig. 2). However, as can be seen from the simple linear regression equations in Figure 2, soil water content is not telling the full story on spring wheat yield. We suspect soil microbial activity may play an important role and we look forward to fully analyzing the soil DNA sequencing and PLFA data during this next year.