This project tests the practice of interseeding catch crops into fall planted winter wheat. The goal of interseeded catch crops is to scavenge resources such as light and nutrients that might otherwise be lost during the winter months, before wheat reaches full ground cover. Catch crops such as tillage radish, oats, or phacelia will winterkill and release the scavenged nutrients in the spring to the growing wheat. This project ended up focusing on establishment timing and technique, and expanding the concept to wheat growers in southern Illinois.
- Objective: Determine the effect of interseeded catch crops on grain yield of winter wheat as a factor of species and intercepted Photosynthetically Active Radiation (PAR).
- Monitor % cover and cumulative PAR in situ through fall months with Unmanned Aerial Vehicle (UAV).
- Sample biomass, test for C, N uptake in early winter to estimate impact of catch crop on nutrient uptake.
- Yield samples.
- Objective: Increase grower knowledge and adoption of interseeding catch crops.
- Lead group discussion at Illinois Wheat Association summer meeting, discussing success and setbacks with the catch crop practice. Timing, tilllage, planting, and weather are all important factors for them to be aware of.
2017: Catch crops seeded on 4 farms did not establish well. More participants will be recruited at this year’s Illinois Wheat Growers Conference.
2018: Added a few sites and growers further south, and committed to planting before fly free date. Seeding successful on 6 plots in southern Illinois. Fields were imaged last in early January 2019, and biomass was to be recorded on the next visit but then weather conditions led to not only the sudden death of companions, but also their quick deterioration. Next year biomass will be sampled early and often for repeated measures.
2017: Biomass sampling in December revealed that only 2 of the 4 sites had any growth. Efforts will be redoubled in 2018, to find more southern locations and earlier planting dates.
2018: 6 sites planted, 5 imaged with UAV. Experiment will be repeated in 2019 to increase data points.
Tillage speeds emergence, incorporation further increases emergence rate and biomass accumulation since GDD wane quickly in the fall. With more data points, relationships between the relative value of reduced tillage (resulting in increased stover residue and soil cover) compared to the increased GDD capture of tillage, and relative impact on crop establishment and resulting CC coverage.
Also kale and phacelia probably are not necessary in the future, they germinate slower. Important functional traits to consider include emergence speed, temperature, conditions (seed to soil contact necessary), seed size (a practical downside of oats is the increased mass for comparable seeding rate, ~5x radish). Wintery hardiness also varies as temperatures fall below freezing; the tissues of winter killed CC can rupture, releasing P, nitrates. Field decisions rely on specific goals and interaction with other factors that influence mineralization such as termination and residue quality(Cober, Macrae, & Eerd, 2018).
Research should further investigate the 1. functional traits corresponding to the tradeoff of R:S with soil quality factors such as erosion protection and soil aggregation. Root length or other traits may offer glimpses of different perspectives of soil health. 2. quantification of mgmt. practices on system resource and biomass accumulation.
Forage radish has been shown to suppress winter annuals from fall competition effect (Lawley 2012). Lawley reported no allelopathy, citing that similar weed suppression resulted in all treatments that grew radish, regardless of residue removal or placement. Testing this niche with different cover crops can improve confidence in this hypothesis.
Lawley’s fall competition hypothesis discounts allelopathy, but that does not preclude a species specific effect; nutrient availability has also been linked to germination of some species(Lawley, Teasdale, & Weil, n.d.). Therefore while no direct allelopathy may be present, species specific functions could still factor, or could simply reflect species differences in functional traits.
One relevant functional trait is the root to shoot ratio (R:S). In many species root mass and root length vary inversely, where grasses such as oats would have high root length but lower root mass in contrast to sunflower which has higher root biomass but lower root length. Radish however expresses differently with rooting depth; favoring biomass accumulation in the top 20 cm but root length deeper in the profile (Wendling et al., 2016). This might offer a unique ability to scavenge and aggregate soil services.
We should also consider the root:shoot ratios of the CC since oat and radish vary at .2 and .6 respectively. NDVI correlates linearly to biomass accumulation up to 700 GDD, or canopy closure (Prabhakara, Dean Hively, & McCarty, 2015). Therefore for each linear unit of above ground growth, radish accumulates 3x total biomass as oat. Therefore while oats in this case increased NDVI ~3%, radish plots accumulated more biomass than control, approximately 8-9%.
Educational & Outreach Activities
Outreach and promotion of project planned for Wheat Growers Association meeting, where I spoke in 2018 and will again in 2019
Field studies took place at four locations in 2018
Harold Wilken- Iroquois County- Organic for over a decade 1000+ acres
Gary Hunter- Marion County- Conventional 1000+ acres
Troy Throneburg- Christian County- mixed conventional and organic grains 1000+ acres
Chris Evans- Pope County- Forestry and Extension Research Specialist- maintain a conventional replication
In 2018 Kevin Rose (Salem) and Bob Grote (Centralia), both conventional allowed plots.
catch crop management and in field assessment
Expected outcomes: Assist farmers in developing intercropping practices. Determine the impact of fall inter-seeded catch crops(tillage radish, oats, forage kale, phacelia) on nutrient cycling, yield, in winter wheat.
Q1: Do inter seeded catch crops increase wheat system resource uptake (sunlight, nitrogen), or yield?
Catch crops increased NDVI compared to control; nitrogen and yield not tested.
Q2: Characterize differences among the catch crop species.
Radish and oats were the fastest to germinate and establish biomass. Phacelia and forage kale were slower to establish; while they could still fulfill this niche role, they are slower and therefore not recommended. Oats increased the NDVI more than the radish plots, but more data is needed for statistical significance.
Q3: Practically speaking, what observational recommendations can we give to farmers attempting this practice, such as methods, timing, and economic viability?
Tillage and/or incorporation of cover crop seed generally increases emergence anywhere between 2-7 days depending on conditions. We hypothesize this is a function of 1. increased seed to soil contact 2. warming of exposed soil. Decreasing solar and thermal energy in the fall can delay or inhibit cover crop germination and establishment. Therefore catch crops should be fast to establish and quick growing. Short lived covers should be both cold hardy and in the ground before the local frost free date in an average year to see reliable accumulation of biomass.
Spreading of seed with or without incorporation can be a viable method of catch crop establishment, especially with consideration growing degree days and soil temperatures. We did not test efficacy of this spreading method against direct drilling but anecdotally have seen variable reports depending on weather conditions.
Inspired by the concept, one farmer reported adopting the practice of adding a low rate of radish and turnips into all fall fertilizer applications, which is primarily wheat and cover crop acreage. Another rents most of his land but is considering asking his tenants to do the same.