Spring 2012 On-Farm Cover Crop Plots: Spring Pre-Burndown Biomass Yields
Posted: September 4, 2012
Beginning during the second week of September 2011, and continuing until Oct 7th, replicated small plots of various cover crop mixtures were no-till drilled on nine farms in eight counties. Some of the mid and late September field work was delayed due to abnormally wet conditions. This On-Farm Research project is partially funded by a USDA-NRCS Conservation Innovation Grant that will continue for one more year. Sites were selected on small to mid-sized dairy farms where corn had recently been harvested for silage. Field days were held at these locations last November, and again during April 2012. The overarching goal of this project is to encourage more widespread adoption of cover crops on our Pennsylvania farms, especially where corn silage harvest often leaves fields with little or no cover through the late fall, winter, and early spring months. Additional environmental problems can arise when these barren fields also receive a fall application of manure on farms where some manure must be spread onto fields to increase capacity for at-barn winter manure storage.
Some sites had a history of regular applications of moderate quantities of dairy slurry, while other fields had received much less manure in recent years. Aboveground biomass was clipped from all plots beginning in mid April and continuing through early May. Samples were dried and weighed, and yields were determined. A subsample of each sample was saved, ground to a fine powder, and sent to a laboratory for fertility nutrient analyses. From select treatments, another sample was clipped leaving a two-inch stubble, dried, and also ground for forage quality analyses. The species and seeding rates included in each mixture are listed in Table 1.
|2||Crimson clover||15||"815" triticale
|3||Crimson clover||15||"Everleaf" oat||70|
|5||"Everleaf" oat||70||"Aroostook" rye||84|
Fall growth vigor was directly correlated to both length of time between establishment of the plots and winter freeze-up and the nitrogen available to the young plants as they began to grow. Where nitrogen was plentiful, and moisture was adequate, fall growth was vigorous and the herbage was a dark green color. In the spring, those same sites continued to exhibit rapid growth. Had the early spring experienced in much of PA enjoyed near-normal spring rainfall, biomass growth could have much greater at most locations.
Spring biomass data were analyzed by location (averaged across species) and by species (averaged across locations). In figure 1, average yields across all eight treatments, along with minimum and maximum values for a location are shown. The amount of nitrogen available to these crops was average; all sites had seen at least 2 applications of manure during the previous 2 years, some received 3 or more applications as manure was applied near the time these plots were no-till drilled during the fall of 2011 as well as during the previous spring before corn was planted. While numbers of manure applications were similar across sites, rates of application were not. Most applications ranged from 4000 to 7000 gallons per acre, with a few farmers applying more than this. Factors other than available N that also contributed to the amount of biomass accumulated at a given location include:
- Earliness of fall planting: earlier planted sites will produce more biomass before freeze-up than those planted later, and this additional fall biomass often is carried into the spring and measured during spring biomass harvest.
- Time of spring thaw: sites further south and east will warm sooner than northern locations, giving a longer spring growth period and greater potential for more spring biomass production.
- Time of cover crop control prior to planting the next grain crop: this factor may be the single greatest determinant of how much biomass can be accumulated prior to burn-down or other means of terminating the cover crop. We made all attempts to delay our biomass harvests until just prior to when the host farmer wanted to terminate the plots. During late April and early May, with ample soil moisture and fertility, many of these species can often double their biomass every 7 to 10 days!
- Crop available moisture: the dry conditions at many locations during April undoubtedly slowed the growth of many of the species included in this trial. How much more biomass could have been produced had these sited enjoyed near normal spring precipitation?
Figure 1. Spring growth of aboveground biomass from replicated cover crop plots at nine locations in Pennsylvania. Colored bars indicate the average across eight treatments at a location and the “I – bar” indicates the maximum and minimum values observed within each of the respective sites.
Figure 2. Spring growth of aboveground biomass from replicated cover crop plots that included eight species or mixtures of species. Each colored bar represents the average across the nine locations included in the study and the “I – bar” indicates the maximum and minimum values observed for a given specie or mixture.
Spring oats were included in several treatments, primarily to investigate the potential for producing late summer/early fall forage that might be harvested as oatlage. A vigorous fall oat crop will compete with other species seeded with oats, reducing the growth potential for those other species, both in the fall and especially in the spring. The exception to this observation is cereal rye. Cereal rye is probably the most competitive species included in this trial. Cereal rye’s fall, and especially, spring growth was not reduced very much, if at all, when grown with oats or other species of cover crops.
Analysis of aboveground biomass for N content (data not shown) reveals that most cover crops will take up considerable available nitrogen. The same can be shown for P uptake. Typical N concentrations in the aboveground biomass for these treatments will range between 2 and 3 percent, with some able to soak up so much N that levels will exceed 3.5 % of their dry matter. This represents a potential for fall planted cover crops to conservatively take up and hold 40 to 60 lbs/ton of biomass produced. Per the data above, we’ve documented that some plots have captured, to make available at a later date to the following crop, in excess of 200 lbs N per acre, where PSU and other studies have estimated that at least half of that captured N can be released to the following crop. What is the value of 100 lbs/ac N to next year’s crop? What is the value to the environment when keeping as much of 200 lbs/ac of N locked into/onto your fields?
Now that corn silage harvest has commenced on your farms, perhaps a little earlier than during an average year, do you have a plan to include a cover crop on those acres after corn has been harvested? If not, why not? Many farmers ask: “what should I plant?” What they are really asking is “What is the best species or mixture to drill after removing my corn or bean crop?” I often answer the question with another question: “what are your cover crop goals?” Do you want forage to harvest in the fall? Oats need to be considered. Do you want spring forage to harvest? Crimson clover and ryegrass are tough to beat. Is there a lot of N to soak up? One should include a cereal grain and/or annual ryegrass. Concerned about cereal rye “getting away from you” during a wet spring? Perhaps triticale or even wheat or barley would be a better winter cereal for you. The choice of cover crops to use should be made in the context of your whole farm cropping system. On those fields that you anticipate getting onto early, or into which you plan to rotate to soybeans, perhaps cereal rye alone is the best fit. The farmers I encounter who are cover crop veterans often have 3 to 5 mixtures they use, depending upon the circumstances. Even on a given farm, “one size does NOT fit all.”
To those who are new to cover crops: try something! Then learn from what you’ve done, and what others are doing around you, attend meetings and workshops and field days. Stay abreast of information published in our many farm press outlets. All this information will help you to fine-tune your cover cropping practices for future years.