Manure Legacy: Organic Winter Wheat + Manure Variety Trial

McKenna Volkman^1,2, Patrick Carr^1,2, and Sally Dahlhausen^1,2 (CARC Investigators)

Jennifer Reeve³, Earl Creech³ (Project Directors)

Ian Burke⁵, Patrick Carr^1,2, Kynda Curtis⁴, Astrid Jacobson³, Man-Keun Kim⁴, Ryan Larsen⁴, Urszula Norton⁶, and Matt Yost³ (Co-Project Directors)

Montana State University, Dep. Research Centers¹; Central Ag Research Center, Moccasin, MT²; Utah State University, Dep. Plant, Soils, and Climate³; Utah State University, Dep. Applied Economics⁴; Washington State University, Dep. Crop and Soil Sciences⁵; University of Wyoming, Dep. Plant Sciences⁶

Summary                                    

Demand for organic food products requires specialty mills to source enough high-quality winter wheat to meet that need.  However, farmers can face declines in yield and quality because of persistent drought in the northern Great Plains. The MSU Central Agricultural Research Center (CARC) is participating in a multi-state project that explores several elements of organic winter wheat systems to find methods that alleviate those challenges. There are many choices a farmer has when it comes to wheat variety selection.  This trial compared the agronomic performance of 20 winter wheat varieties under dryland organic field conditions at multiple locations, with and without an application of composted manure. The varieties include two from Utah (‘Promontory’ and ‘Curlew’), two from Wyoming (‘Pronghorn’ and ‘SY Wolf’), two from Montana (‘Decade’ and ‘Bobcat’), and two that were chosen to be checks (‘Yellowstone’ and ‘UI Silver’), with the remaining 12 lines selected individually at each site.  Varieties were planted 8 times, twice in each of 4 replicates. The intention was to apply manure at a rate of 22.3 tons/ac to half the plots in each rep with the other half forgoing a manure application, but limited amounts of manure restricted the application to only 8 of the 20 varieties. This resulted in multiple analyses of the data: one analysis using a split plot design (manure as the main plot and variety as the sub plot), and the other using a randomized complete block design with variety as the fixed factor. Spring plant density counts and heading date data were collected along with grain yield, test weight, and protein. In the split-plot analysis, it was found that plots with manure applied had higher protein (18% versus 16.7% in the un-treated plots) and lower yield (11 bu/ac compared to 21 bu/ac in the un-treated plots).  Some varieties (‘Yellowstone’, ‘Decade’, and ‘SY Wolf’) yielded more than the rest (19, 18, and 21 bu/ac versus an average of 14.5) when evaluating variety selection independent of the manure effect.  In the analysis where manure was not considered, no significant difference in yield were detected.  ‘Pronghorn’ headed earliest (173 julian days), nine lines (‘FourOSix’, ‘Loma’, ‘Northern’, ‘Decade’, ‘SY Wolf’, ‘Pronghorn’, ‘Curlew’, ‘Promontory’, and MT1745) had higher test weight (average = 60.8 lbs/bu) than other entries (average = 59.6 lbs/bu) and nine lines (‘Decade’, ‘Keldin’, ‘Loma’, ‘Northern’, ‘Bobcat’, ‘Curlew’, ‘FourOSix’, MTS1903, and MTS18149) had higher grain protein concentration (average = 17.3%) than other entries (average = 16%).

Introduction

Dryland organic wheat producers sometimes encounter low yields and grain protein. Since high protein organic wheat is in high demand, strategies are needed to maintain or enhance grain protein concentration. This project investigates the effects of both composted manure and variety selection on winter wheat yield, protein, other quality factors at multiple locations in three states (MT, UT, and WY).  Results from this project will allow local organic farmers to make variety selection based on results of variety comparisons under conditions managed organically.

Methods

‘Yellowstone’, ‘Bobcat’, ‘Decade’, ‘SY Wolf’, ‘Pronghorn’, ‘Curlew’, ‘Promontory’, and ‘UI Silver’ winter wheat varieties were planted with and without manure application in a split-plot design with four replications in fall 2021, with manure as the main plot and variety as the subplot.  These lines were chosen with each state contributing two high performing lines from their state along with two check varieties. These eight varieties were embedded in a larger experiment in a randomized complete block design that also included the varieties ‘AAC Wildfire’, ‘Byrd CL Plus’, ‘Flathead’, ‘FourOSix’, ‘Keldin’, ‘Loma’, ‘Northern’, ‘SY Monument’, MT1745, MTS1903, and MTS18149. An experimental white winter wheat line from University of Idaho was also included in this portion of the trial, identified here as “Experimental A”. 

Manure was applied at 22.3 tons/ac (25 Mg/ha) to subplots in the embedded study and then all plots (those with and without manure) were disked prior to seeding on October 19, 2021.  Stand counts were taken from two 0.5 m²-areas using a frame 32.3” long centered over two drill rows with 12” spacing.  Hand weeding was conducted throughout June and early July.  Heading date was recorded when 50% of the primary heads in a plot were 50% emerged from the boot.  Plots were harvested August 15-16 and exact length of harvested area measured so grain yield could be determined.  Test weight was measured using a Grain Analyzing Computer (DICKY-john), and protein was measured on a CropScan 3000B-T.  Both were corrected to 12% standard moisture content.Only three replicates were harvested for grain because of severe weed pressure in the fourth.     

Results and Discussion

In the embedded trial that included the manure treatment, main plot effects of manure were detected for grain yield and protein (Table 1). Results were not as expected: plots where manure was applied were lower in grain yield (11 bu/ac versus 21) though higher in protein (18% versus 16.7%). We speculate that yields were lower in manured subplots because of a non-significant trend for lower wheat plant density, reflecting the dry seedbed conditions when planting plots that were exacerbated by adding a dry soil amendment (e.g., composted manure) prior to disking the seedbed. Also, weed pressure was much greater in manured than non-manured subplots, likely reflecting the failure of composting to kill viable weed seed contained in the manure.

‘SY Wolf’ produced more grain (21 bu/ac) than other varieties except for ‘Decade’ (18 bu/ac) and ‘Yellowstone’ (19 bu/ac) (Table 2). Those three were also amongst the lines with highest seeding density (52 to 56 plants per square meter respectively), along with ‘Pronghorn’ (68) and ‘Curlew’ (57).  The earliest line to head out was ‘Pronghorn’ at 173 Julian days.  Grain produced by ‘Decade’ was higher in protein (18.3%) than other varieties except ‘Curlew’ (18.0%).  ‘Promontory’ had the highest test weight (61.8 lbs/bu), along with ‘Decade’, ‘SY Wolf’, ‘Pronghorn’, and ‘UI Silver’ (average = 60.8 lbs/bu) compared to the other lines (average = 59.8 lbs/bu).  When examining the combined effects of manure and variety together, no statistical differences were detected (Table 3).   

The white wheat Experimental A performed poorly compared with other lines when compared to hard red winter wheat entries (Table 4a and 4b).  As a result, Experimental A was an outlier and the study reanalyzed by including only the 19 hard red winter wheat varieties and experimental lines. No differences were detected across the 19 varieties/lines for grain yield (average = 21 bu/ac) or plant density (average = 58 plants per square meter).   FourOSix’, ‘Loma’, ‘Northern’, ‘Decade’, ‘SY Wolf’, ‘Pronghorn’, ‘Curlew’, ‘Promontory’, and MT1745 had higher test weight (average = 60.8 lbs/bu) than other entries (average = 59.6 lbs/bu).  ‘Pronghorn’ headed earliest among entries (173) while protein concentration of grain produced by ‘Decade’, ‘Keldin’, ‘Loma’, ‘Northern’, ‘Bobcat’, ‘Curlew’, ‘FourOSix’, and two Montana experimental lines (MTS1903 and MTS18149) was comparable or greater than that of other varieties/lines.

Table 1:  Main Plot Effects- 2022 Manure x Variety Trial (Split Plot Portion), Central Ag Research Center, Moccasin, MT

Table 2:  Sub-Plot Effects- 2022 Manure x Variety Trial (Split Plot Portion), Central Ag Research Center, Moccasin, MT

Table 3:  Interaction Effects of Main + Sub Plots- 2022 Manure x Variety Trial (Split Plot Portion), Central Ag Research Center, Moccasin, MT

Table 4a:  2022 Manure x Variety Trial (RCBD Portion), Central Ag Research Center, Moccasin, MT

Table 4b:  2022 Manure x Variety Trial (RCBD Portion), Central Ag Research Center, Moccasin, MT

Statistical analyses were performed using R Statistical Software.  Fisher’s protected LSD (Least Significant Difference) is not significant when P-value is greater than 0.05, or when CV exceeds 15 (for grain yield only).  The top performer in each category is indicated by bold and asterisk, while just bold indicates statistical equivalence to the top performer.  To determine a statistically significant difference between lines, the difference must be equal to or larger than the LSD value.