The Success of Organic and Other Sustainable Dual-Purpose Wheat Systems Depend on Access to Adapted Varieties

Reported are results from the 2020-2021 and 2021-2022 winter wheat production seasons. Results from the 2019-2020 season are not included, because the study was destroyed prematurely by a hailstorm in that year.  Location, management, treatments, varieties were the same in final two years.  Planting occurred on October 2, 2020 and October 8, 2021.

Precipitation (August-May) was markedly different between the 2020-2021 and 2021-2022 wheat production cycles. The 20-year mean precipitation from August to May for the study site is 491 mm. During the 2020-2021 wheat production year, precipitation was 538 mm (110% of normal). In contrast, the 2021-2022 production year total precipitation was 291 mm (59% normal), resulting in a pronounced year effect on most measured variables. A historic, record-breaking winter weather outbreak in February 2021 resulted in 11 consecutive days of below-freezing temperatures.

Forage standing biomass results from the dual-purpose systems for 2020-2021 and 2021-2022 are shown in Figure 1 and 2, respectively. These results are sums of total standing biomass harvested 3 times in 2020-2021 production season and 2 times in the 2021-2022 production season. Severe drought in 2021-2022 limited forage biomass production. Supplemental irrigation was applied on 1/14/2022 (25.9 mm) to prevent stand loss and again on 4/18/2022 (40.8 mm) to assure grain production. No supplemental irrigation was applied in the 2020-2021 production cycle. Forage samples were collected when sufficient standing biomass was present between December and early March, prior to the first hollow stem growth stage which normally occurs in early March in this region of the Southern Greta Plains. This represents the typical grazing period for dual-purpose winter wheat systems.  In 2020-2021 (Figure 1) total forage biomass prior to development of the first-hollow stem, across wheat varieties, averaged 1392 kg ha^-1 with conventional fertilizer and 942 kg ha^-1 with organic fertilizer. On average, there was a 32% decline in forage yield with organic fertilizer management, though the best performing wheat varieties with organic management produced more forage than the worst performing varieties with conventional management. Forage production values in the 2020-2021 season were lower than typically observed in dual-purpose wheat in this region due to challenging weather conditions. This included wet planting conditions in September (104 mm) that was 152% of average precipitation and a historic freeze from February 8 to 19, 2021.

Total forage biomass before first- hollow stem in 2021-2022 across all varieties receiving conventional fertilization was 848 kg ha^-1 and 775 kg ha^-1 with organic fertilization (Figure 2). Forage biomass production was 9% lower using organic fertilizer under severe drought conditions. Forage biomass production in 2021-2022 with conventional fertilizer was 39% less than during the 2020-2021 season, compared to a 17% decrease observed under organic fertilization. There were relatively minor treatment and variety differences in forage nutritive values in the dual-purpose systems (data not shown). Overall average forage nutritive value between organic and conventional systems were quite similar. Forage nutritive value was sufficient to support 1 kg average daily gains for stocker cattle in this region. Animal gains in both systems and across all varieties would not be constrained by nutrient concentration of the forage, but by overall forage available for grazing under the conditions of this study.

Weed control options are limited in organic wheat management systems and crop productivity is often limited by nitrogen availability. Providing more rapid and complete ground cover is an important character trait for wheat to better compete with weeds. Figures 3 and 4 show changes over time in percent ground cover for all 15 wheat varieties in the grain-only plots in both conventional and organic conditions for 2020-2021 and 2021-2022, respectively. Overall, average wheat percent ground cover exhibited bimodal patterns of increasing ground cover until December, then increasing again in February as wheat begins rapid spring growth. The maximum percent cover attained in both study years were impacted by adverse weather conditions. Historic low temperature freeze for 12 consecutive days in February 2021 left wheat leaves severely burned and limited growth rate  in early spring.  The exceptional drought during the 2021-2022 dramatically reduced above ground biomass production.  Overall percent ground cover across varieties was higher under conventional than organic fertilization throughout the 2020-2021 season.  Ground cover percentage where similar between fertilization practices in 2021-2022 season.  Between seasons, under conventional fertilization 2021-2022 ground cover was 8 to 13 percentage units lower than at comparable time points in 2020-2021. There is sufficient variation among varieties within and between fertilization type to warrant  further wheat variety investigation for germplasm suited for organic hard red wheat production systems in the Southern Great Plains.

Phenological development stage data presented as day of the year (DOY) are summarized for 2020-2021 in Table 1 and 2021-2022 in Table 2.  Average DOY to first hollow stem was 4 days later under organic than conventional fertilization in 2020-2021.  Six varieties FHS stage increased 6 or more days in the organic treatment.  In contrast, average DOY at anthesis and physiologic maturity differed by 1 day.  In the 2021-2022 wheat production year extreme drought increased time to FHS by 5 days and 1 day under conventional and organic fertilization, respectively.  While average day of anthesis was also delayed 5 days and days to physiologic maturity was shortened by 7 to 8 days under prevailing drought conditions.  There appear to be variety effects on the phenological development rate displayed all varieties tested based on genotype by fertility management by environment interactions that will be statistically analyzed to determine which of the tested varieties hold promise for use in organic hard red winter wheat dual-purpose and gain only systems.

Grain yield and quality are the primary drivers of gross sales receipts in wheat production systems.  Grain yield was markedly different between wheat production years in this study (Tables 3 and 4).   Variety, management, and fertilizer source all contributed to a yield range of 59.8 to 23.2 bu ac^-1 in 2020-2021 production year and 27.4 to 8.8 bu ac^-1in 2021-2022 (Table 3).  There are clear environmental effects on the yield differences between years as noted earlier.  Across all varieties in 2020-2021 conventional fertilizer practice averaged 45.8 bu ac^-1 versus 34 bu ac^-1 with organic fertilizer and a 25.8% yield differential.  Dual-purpose wheat management led to 7.5 (-16.4%) conventional and 5.8 (-15.1%) organic bushel yield decreases compared to grain-only management.  The 2021-2022 drought year yields (Table 4)  ranged from 17.2 to 13.5  bu ac^-1 and were from 28 to 14.7 bu ac^-1lower than 2020-2021 yields across fertilizer and management treatments.  Individual varieties experienced up to 70% yield difference between years.

Grain protein analysis for 2021-2022 have not been completed yet.  Some preliminary results suggest grain protein were much greater ( up to 40%)  across varieties and treatments than found in 2020-2021 (Table5).  Considering the severity and duration of drought increased grain protein content was expected.  Grain-only management and conventional fertilizer treatment grain protein content averaged 11.6% versus 9.28% for organic fertilizer.  Interestingly, differential response in grain protein among varieties to fertilizer type and management type were observed.  Further statistical analyses will determine are significant and biologically relevant for inclusion in wheat variety selection for organic production.

We submit that genotype by fertilizer type by management by environment interactions and differences among varieties we are observing suggest some varieties are better adapted for different systems and applications than others. These analyses are underway and will be included our upcoming extension and research publication in 2023.  Findings from research funded by this Graduate Student Grant will form a basis for future research initiatives to determine economic and environmental suitability and sustainability of producing organic hard red winter wheat in the Southern Great Plains dual-purpose and grain only production systems.

Figure 1 SSARE Final Report

Figure 2 SSARE 2022 Final Report

Figure 3 SSARE 2022 Final Report

Figure 4 SSARE 2022 Final Report

Table 1: Phenological data (day of the year) for 2020/2021 wheat varieties in grain-only and dual-purpose systems.

Table 2: Phenological data (day of the year) for 2021/2022 wheat varieties in grain-only and dual-purpose systems

Table 3: Grain yield (bu/ac) for 2020/2021 wheat varieties in grain-only and dual-purpose systems.

Table 4: Grain yield (bu/ac) for 2021/2022 wheat varieties in grain-only and dual-purpose systems.

Table 5: Grain protein concentration (%) for 2020/2021 wheat varieties in grain-only and dual-purpose systems.