Evaluation of Forage Brassica Establishment and Productivity on Grazing Farms

Yield estimates for each trial are summarized in Table 2. Forage quality data are summarized in Tables 3a, 3b, and 3b. Observational notes and data quirks for each individual trial and for individual crop varieties are discussed in the following sub-section.

Mild weather conditions were ideal for brassica crop growth, and yields were good. Broadcast establishment was found to be less than ideal because it was difficult to get uniform seed distribution at the low seeding rates.

Grazing after the first harvest was probably more severe than it should have been, as the plots were small relative to the number of sheep and it was overgrazed within 24 hours. As a result, regrowth seemed to be substantially impaired. This, combined with our inability to collect data for frequent harvests, probably biased the yield results against varieties that depend on multiple harvests to optimize yield.

There was some uncertainty about optimal harvest timing. The harvest dates were based on published suggestions about time to first harvest for different types of crops, but there was (and remains) significant ambiguity in the literature about how to evaluate whether the crops in a specific situation are ready to harvest. For example, it is commonly written that forage rapes should not be harvested until the leaves turn red. However, there is no good explanation for this and based on our observations and conversations with seed company representatives, it is probably incorrect. The late summer harvest was probably later than it ideally should have been. New York Turnip developed a leaf disease and leaves had begun to senesce by the time of the late summer harvest. Bonar and Winfred rapes and Kestrel Kale had also begun to senesce on lower leaves, though the plants were still healthy. As a result of the two different harvest dates, the varieties cannot be compared directly. This was anticipated and seemed unavoidable in the experimental design, but in retrospect they could probably all have been harvested simultaneously at the earlier date or at an intermediate date. Harvest timing remains one of the more confusing aspects of brassica management.

Since sheep broke into the plots and ate everything before the final planned harvest, full season yield data were not obtained.

Planting was delayed due to wet weather. This trial was established with a no-till drill into a sod that had been sprayed with glyphosate 5 days earlier. This establishment method seemed reasonably successful overall, though it appeared that it would have worked better had a longer time elapsed between spraying the sod and planting, as there was still significant green leaf matter in the sod at planting. Sheep broke into the plots and ate everything before any data were collected.

Planting was delayed due to wet weather and wet soil. The plot area chosen by the farm owner was poorly drained and the brassicas grew unevenly. The oat intercrop appeared to be a rational practice in these conditions, as the oats provided good quality forage dry matter more quickly than did the brassicas in these conditions. Due to late planting and cool conditions, brassica plants were smaller at harvest than would have been desirable.

Stand establishment was good for most varieties. However, problems with weed control and poor drainage caused significant yield loss to much of the trial area. The ability of these crops to withstand less than ideal conditions was severely tested. Two varieties had very poor stand establishment, probably due to seed quality issues. The plots included a fodder beet variety, which had poor stand establishment (presumably due in part to non-availability of the correct planting equipment), but which appeared to have significant potential for high yield and high quality nonetheless. Due to the high variability between plots, the analysis of variance indicated no significant differences between varieties. For purposes of suggesting the yield potential of the crops under good conditions, yields are reported from the highest-yielding plot for each variety (since for most varieties at least one plot of the three was situated in a reasonably productive environment).

Stand establishment was good for most varieties, although again two varieties appeared to have seed quality issues. Productivity was very uneven. Several varieties appeared to suffer from excessively high planting densities, and variable soil fertility also appeared to be a factor in uneven productivity. The crop was grazed by dairy cattle in November. Palatability was apparently very high, and milk production increased during the grazing period. Utilization of bulbs was initially low, but after a learning period, cattle returned to graze the bulbs and final utilization was high. This trial was the only opportunity to test the Ethiopian Cabbage and the Barenbrug varieties.

The most consistent and potentially useful observation in the variety trials was noting a distinction between varieties with storage organs (i.e. turnips with bulbs, swedes, and marrowstem kales) and those without significant carbohydrate storage capacity (i.e. the rapes, some kales, and the bulbless “grazing turnips” like Hunter, Pasja, and T-Raptor). Varieties with storage organs had the highest dry matter yields and the most favorable energy to protein ratios for lactating dairy animals or finishing meat animals. Turnip and swede bulbs had energy concentrations comparable to ear corn.

Presumably the biological explanation for the higher yield potential of storage varieties is that these varieties have a “bank” into which they can sequester carbohydrates as they photosynthesize. In contrast, the bulbless varieties can only put carbohydrates to work in making new leaves, but as the new leaves shades the old leaves, the older leaves die and fall off, leading to little net accumulation of biomass past a certain level of growth. These bulbless varieties are commonly sold with a suggestion that they can be grazed multiple times, regrowing well in between. If they are regrazed at an optimal interval and to the appropriate residual level so that there is little “idling” of photosynthetic capacity, it may be possible for the yields of these varieties to compete with those of the bulbing varieties. However, given these crops’ sensitivity to overgrazing and trampling, achieving this would require very careful management and probably good luck.

The disadvantage of the bulbed crops is that the bulb may be difficult to utilize fully. In sandy, unfrozen soils, cattle often seem to be able to pull turnips out of the ground. Sheep are more likely to eat the turnip bulbs in situ, often chewing off all that is accessible, but leaving the bottom portion of the bulb in the soil. Either way there is probably significant ingestion of soil, which is not optimal. In heavier soils or frozen soils, pulling the bulbs out is more difficult and utilization will be limited to what animals can chew off with their teeth. While this is roughly 70% of a typical turnip bulb (depending on the variety), it still represents some utilization loss. Swedes have a larger proportion of of their bulb above ground, while marrowstem kales (e.g. Caledonian) provide almost the best of both worlds by placing the storage organ (a swollen stem) completely above ground. Due to its structural function, however, the kale stem is somewhat higher in indigestible fiber than a turnip or swede bulb.

Advertisements for rapes often claim that they will regrow for multiple grazings (though some vendors are clear that this is not their strong point when compared to the leafy turnips). It was observed that the regrowth potential of most of these crops, but especially rapes, are extremely sensitive to the extent of grazing. When Bonar and WInfred were grazed by sheep in 2009, the sheep left the stems and bit off the leaves. It was noted that grazed plants regrew much better than those that had been hand-harvested (in quadrats) by cutting 3 inches above the ground. In the 2010 ELF study, the first cutting was removed with a Carter Harvester after quadrat harvests, but one strip was left uncut in one of the Winfred plots. This strip was sampled for yield at the fall harvest time, and was found to yield about 3.5 times more than the total (summer + fall) yield in the area that had been cut in the same plot. In the 2010 Zufall trial, hungry cattle mowed down the rapes to a few inches above the ground, so claims that rapes will regrow should be evaluated carefully.

Future researchers on grazing topics should pay special attention to the potential for data loss from grazing animals if fencing is inadequate. It may be common on farms for interior fencing to be imperfect on the assumption that if animals get out it isn’t a big problem, as long as they stay within the perimeter fence. In a research situation with a highly palatable crop, care should be taken that the fence is firmly planted, has a good charge, and preferably has more than one strand. As brassicas are also palatable to deer, fencing should be adequate to deter them if they are in the area.

Appin Turnip is notable in a number of respects. It consistently had among the highest yields in any trial. The seed is relatively easy to source. It has a sizeable bulb and it has multiple shoots on a bulb, giving it a unique capacity for leafy regrowth compared to most other bulb turnips. In order to make use of the regrowth potential, care must be taken not to allow overgrazing.

Barabas Turnip and Barkant Turnip both yielded well in the Zufall 2010 trial but had very different qualities. It is possible that they were inadvertently switched and mislabeled at some point. Barkant is described in Barenbrug literature as being a “tankard” type, which means the bulb is more or less cylindrical, significantly taller than it is wide. Barabas is given a more generic description. In our trials, the crop labeled “Barabas” was a tankard type, while “Barkant” was a more typical turnip shape. “Barabas” had very low germination rates, but the sparse populations allowed it to grow huge bulbs and ultimately lead the trial in estimated yield. Because of its high bulb to leaf ratio, it had among the highest energy to protein ratios in all the trials. The tankard shaped bulb, which sticks up out of the soil, is reputed to improve utilization in situations where the livestock would not be able to pull bulbs out of the ground.

Bonar Rape was the highest yielding rape in some trials (Zufall 2010, ELF 2010, Crowe 2009) and a very close second highest yielding rape in the ELF 2009 trial. In all the 2009 trials it was very similar in size, shape, and yield to Winfred, but it seemed to be somewhat more reliable than Winfred in 2010.

Caledonia Kale is a marrowstem kale, meaning it has a swollen stem which stores carbohydrates. Seed was not available to test in 2009. Based on the ELF 2010 trial (and the anecdotes of Tim Darbishire, who provided the seed), it appears to have very high yield and quality potential, yielding about 4 tons per acre of dry matter in one plot, about 55% of which is the carbohydrate-storing stem. However, it is slower to get started than turnips and rapes, so in the short season Zufall 2010 trial it yielded poorly.

Dominion Swede is the only forage swede variety able to be sourced for these trials. Unfortunately good examples of its yield potential have yet to be measured. It was expected to have a very high yield potential in the 2009 ELF spring trial, based on the very large heavy bulbs it developed. As noted above, it was grazed before a good yield sample could be obtained. However, extrapolation from the aftermath of grazing suggests a potential yield of about 3.4 tons of high energy dry matter per acre. Due to its very high bulb to leaf ratio (about 88% of total biomass is the bulb, by one sample estimate, compared to only about 30-40% for turnips), it probably is the most effective of the brassica crops, perhaps alongside fodder beet, at functioning as a replacement for grain in the ration. Like kale, it is slower to get started than turnips and rapes and needs a full season to develop its potential. Dominion did not distinguish itself in the 2010 ELF trial, probably due to its slow starting, which would make it less competitive with weeds in the early season.
Dwarf Essex Rape has seed that is very easy to find, and is often used for wildlife plots. It is indeed dwarf, and yields were low in the Zufall 2010 trial. The seed was contaminated with about 5% of some kind of turnip.

Graza Radish consistently underperformed in our trials. While it has a (smallish) carbohydrate storing root, the root was very difficult to pull out and did not extend above the ground, so was not generally grazeable. The root penetrates deeply and may have some value in aerating compacted soils. The seed company representative suggests its strength is in its resistance to being pulled out by grazing, resilience to trampling and regrowth after grazing, and thus it may shine in a situation where it would be valued for repeated grazing rounds.

Hunter Leaf Turnip is supposedly a variety selected from Pasja, and they strongly resemble each other. They also seem to have similar yields. In most cases Hunter yields trended higher than Pasja by a small amount.

Maestro (aka Robbos) Fodder Beet had very poor establishment in the ELF 2010 trial. Fodder beets are reputedly somewhat more management intensive than the brassica crops, requiring planting with a row-crop planter and (due to its very slow start) requiring either selective herbicides or mechanical weed control. In regions where they are commonly grown, yields are quite high (about 6 tons dry matter per acre in Britain). Our plots were planted later than ideal and without the correct equipment, but if the yields of individual plants or small groups of plants could be extrapolated to the whole plot (i.e. by throwing out quadrats without any crop plants), the yield potential of this crop seems to be relatively high. The roots are very high in sugars, making it a potentially valuable crop for finishing animals or lactating dairy animals where energy is limiting. According to Tim Darbishire (Limagrain dealer), they are traditionally grazed by cattle in the fall, then pigs are turned in and any roots which remain underground are eaten by the pigs.

Maris Kestrel Kale was not harvested in yield sampling in the ELF 2009 trial due to early sheep grazing. It appeared to yield similarly to Winfred and Bonar in that trial. It did not yield particularly well in the ELF 2010 trial.

New York Bulb Turnip was a strong yielder in most of the trials.

Oasis Chicory is not technically a brassica, but was included in 2009 as a curiosity because it is often on the same page as brassicas in seed catalogs. It is a perennial that can regrow after close grazing. It is reputed to have anthelmintic properties for sheep. Sheep found it highly palatable, grazing it off before starting on other brassicas. The yield at any given cutting was low compared to the brassicas, but it shines when it is grazed repeatedly. Chicory is typically sown with clover and grasses to boost yield and quality of a perennial pasture.

Pasja Leaf Turnip as noted above is very similar to Hunter.

PG 584 Ethiopian Cabbage is a widely unfamiliar addition to the study. There is very little published information available about Ethiopian Cabbage. It has a structure similar to the forage rapes (tall stem with leaves), though the leaves look different from the rapes. The stem seems to be more fibrous than the rape stems.

Winfred Rape had quite variable performance. As noted above, its ability to regrow seems to be especially sensitive to harvest method.

Those crops not mentioned above (Interval , Barnapoli, Barsica, Pinfold, Rangiora, and T-Raptor) did not particularly distinguish themselves in the conditions of the 2010 studies. As those conditions are not necessarily representative of other situations which might be reasonably expected, these varieties are probably all worth further research.

There was no apparent difference between establishment success in conventional tillage with or without a nurse crop of oats, but the oats provided some additional biomass. Vinegar gave a short term impression of complete vegetation control (leaf necrosis), but perennial grasses and clovers quickly grew out of the damage. Establishment was an almost complete failure in the no-till plots, regardless of vinegar applications. Cows broke through the fence a few days before the planned harvest and cleaned up the plots, so no data were collected, but the observational results were clear. The farmer was impressed with the obvious palatability of the brassicas and plans to grow them again.

In the summer trial, vinegar again resulted in almost complete leaf necrosis, but again the grasses recovered, though not as completely as in the spring. Establishment of brassicas was again nearly a complete failure regardless of vinegar application. No yield data were collected due to the obvious absence of brassica plants.

Brassica crops may be appropriate for certain situations, but are not necessarily appropriate for every farm. Based on experience in these trials, as well as literature review and conversations with others who have more experience with brassicas, the following summary recommendations are offered beyond what is commonly found in fact sheets:

• Some brassicas have strong yield potential, but they are very sensitive to environmental conditions and may be somewhat unreliable agronomically. It would be unwise for a farmer to rely too heavily on a certain yield expectation until he or she has significant experience with the agronomic requirements of a particular variety.There are at least three other reasons to avoid brassicas except in cases where they are truly the best option: (a) metabolic issues from inclusion at too high of a rate in the diet, (b) tainting of flavor in milk or meat if not managed correctly, and (c) providing a spacious refuge and breeding ground for pests and diseases of brassica crops which are very difficult and costly to manage for the vegetable farmers in your neighborhood.

  Generally speaking, a farmer would be wise to focus management attention on maximizing yield, quality, and utilization of intensively managed perennial pastures, only diverting attention to annuals when those efforts reach a plateau.

  Generally speaking, it is probably not cost effective to kill a perfectly good perennial pasture in order to plant brassicas. Brassicas and other annuals may, however, have a place in a rotational sequence when a perennial pasture needs to be killed in order to be renovated and replaced with a higher quality forage seeding. Having a break between sod crops can help control diseases, pests, and weeds endemic to sods.

  The most valuable role of brassicas in a rotation should be as a replacement for grain or grain crop silages as an energy supplement to other grass- or clover-based pastures. This may be most likely to be cost effective when either (a) grain prices are unusually high and the farmer does not have equipment for harvesting and storing home-grown grains or silages, or (b)the farmer gets a price premium for a grain-free (aka grass-fed/grass-finished) product. Use of brassicas to replace forage volume on cool-season perennial pastures during the summer slump seems too risky and low-yielding compared to summer annual grasses like sorghum-sudangrass, millets, or grazing corn. Similarly, brassicas should not be used alone in an attempt to increase forage volume in late fall and early winter. However due to their cold hardiness and standability in snow, they may have a useful role as a supplement during that period, to improve the average quality of a ration based on stockpiled perennial grasses or corn aftermath.

  Use of brassicas which do not have a carbohydrate storage organ (either a bulb or a swollen stem) is not advised. The quality parameters of brassica leaves are good, but not sufficiently different from those of high quality clover-grass pastures to justify the expense and risk of sowing brassicas. It is the energy storage organs which are capable of improving the energy to protein ratio in rations for livestock with high energy needs (i.e. lactating dairy or finishing meat animals). In addition, under conditions like those in our trials, or where the farmer doesn’t want to take the risk of attempting multiple grazings, the crops with storage organs had higher yield potential.

  Some fact sheets fail to mention the critical importance of avoiding an excessively high seeding rate. Many farmers will not take the time to calibrate their seeding equipment and will have little experience with such small seeds at such low rates. Brassicas are auto-toxic and total yields are reduced when plants are too crowded. This is doubly critical for varieties where a bulb is anticipated.

  Statements from seed companies which suggest that crops can be grazed multiple times should be treated with caution. While it is not impossible, grazing management must be skillful to make sure that crops are not trampled, pulled up, or overgrazed. A rule of thumb for the leaves is “take half, leave half.”

• Photographs of varieties in 2009 ELF Variety Trial
• Table 3: Summary of Forage Quality Analyses
• Table 2: Summary of Dry Matter Yields and Statistical Analyses
• Photographs of 2009 ELF Variety Trial before, during and after grazing