Volume 9 Issue 7
For some cover crops are an afterthought. They are planted after cash crops are harvested or between perennial row crops and outside of seed bed preparation, are provided with limited inputs. Yes, they are effective at capturing excess nutrients after cash crops are harvested and, in some cases, more importantly should require as little input as possible for sustained use over time.
For others, cover crops are a high priority that provide nutrients, add organic matter, counteract detrimental tillage activities, and can harbor beneficial insects. Cover crops also compete with weeds (whether it is during the summer or overwintering) and can reduce weed seed production as they grow alongside them through competition.
There are some very basic strategies that can improve cover crop establishment and growth and these principles apply regardless of the season they are growing, the production system they are integrated within, or what cover crop(s) are being utilized.
Reducing Weed Competition
If soil is prepared prior to seeding for cover crops you must properly prepare the seedbed to reduce weed emergence and establishment. Weeds directly compete for the same resources that cover crops need. Primary tillage is effective at knocking back established weeds or cash crop residues, but it also provides an environmental cue for certain weed species to germinate. There are several alternative tillage strategies to consider (note these also apply for cash crops).
The following techniques are both based on a few principles (Brown, 2019; Hooks et al., 2014):
- Cover crops (or cash crops) are most susceptible to competition from weeds in the early stage of their life (“critical weed free period),
- Cultivation (light, secondary tillage; “disturbance”) promotes weed germination,
- A small percentage of weed seeds are not dormant and can germinate quickly at any given time, and
- The large portion of weeds emerge from seeds within a shallow portion of the soil profile.
False Seedbed
The first step is to prepare the seedbed to knock bad established weeds and incorporate any crop residue as if you were immediately ready to plant. Then, once a new flush of weeds emerge, weeds are knocked back by several options (shallow cultivation, herbicide, or a flame weeder) but deep (>2”) disturbance of soil is avoided. This avoids the redistribution of weed seeds from deeper in the soil profile to the shallow, active portion of soil. Once these weeds are controlled, seeding of the cover crop proceeds immediately (Peachey, 2020).
Stale Seedbed
Like false seedbed technique, the seedbed is prepared as if you were ready to plant. But what is different here is that cover crop seeding occurs prior to activities used to knock back weeds (shallow cultivation, herbicide, or flame weeder). Ideally there is a slight delay in the weeding so that weeds begin to germinate, but just prior to emergence of the cover crop (Peachey, 2020).
2020 Field Trial
In response to interest from local producers, an on-farm trial was initiated to evaluate these techniques alongside traditional seedbed preparation (day) and in comparison, to traditional seedbed preparation that occurred at night. Tillage at night reduces/eliminates the likelihood that light will be introduced into the soil profile during activities and cue germination in certain species (Scopel et al., 1991); though this has not been found true for all weed species (Juroszek et al., 2017).
Methods
The entire field was prepared similarly prior to treatment initiation and replicated plots were setup in a strip-plot, randomized design. Treatments included: a.) traditional tillage (rototiller)[Day], b.) traditional tillage (rototiller) occurring at night[Night], c.) traditional tillage (rototiller) + false seedbed (tine weeder)[False], d.) traditional tillage (rototiller) + stale seedbed (tine weeder)[Stale]. The cover crop Sorghum-Sudan Grass ‘Viking 100’ was used as a model cover crop and was seeded in the day, stale, and night treatments on 6/24, and the false was seeded on 7/7. Weed counts (1/4m2), cover crop biomass, cover crop stand counts, and weed biomass were all acquired.
Results and Conclusion
- By 7/14/2020, stale and false treatments significantly reduced weed counts as compared to day and night (Table 1). Night was also significantly lower than traditional tillage.
Table 1. Weed counts/biomass and cover crop stand counts and biomass in a trial evaluate pre-plant seedbed strategies.
| 7/14/2020 | 7/24/2020 | ||||||||
| Cover Crop Seeding Date | 20a/7b DAS | 30a/17bDAS | |||||||
| Treatment | Weed Counts | CC Stand Count | CC Biomass (g) | Weed Biomass (g) | |||||
| Day | 6/24/2020 | 74.0 | a | 17.5 | ab | 37.8 | a | 58.4 | a |
| Stale | 6/24/2020 | 16.3 | b | 16.7 | b | 25.1 | b | 25.7 | bc |
| Night | 6/24/2020 | 50.0 | c | 18.2 | ab | 36.4 | a | 40.4 | b |
| False | 7/7/2020 | 9.7 | b | 29.3 | a | 21.9 | b | 20.9 | c |
| <0.0001 | 0.0267 | 0.0006 | <0.0001 | ||||||
aDay, Stale, Night
bFalse
- By 7/24/2020, false seedbed treatments had higher cover crop stand counts than stale seedbed. Both traditional tillage methods (night and day) resulted in greater cover crop biomass, but also higher weed biomass (except stale and night were synonymous). It should be noted that false seedbed treatment’s cover crop was planted almost 13 days later but produced similar cover crop biomass as the stale treatment.
- Both stale and false techniques show great promise but require the right equipment and timing. These techniques should also have similar weed density and biomass results in cash crops, though seasonal logistics of timing will be different. We intend to further evaluate these techniques under various conditions and productions systems so if you have interest in participating please contact Chris Benedict (chrisbenedict@wsu.edu).