Protein and small grain bi-crops
Many countries have adopted the practice of cultivating spring-sown legume crops and spring-sown grain crops in combination — commonly known as bi-crops — with peas and spring barley being most popular option.
Barley has a higher digestibility than other cereal crops, and peas have a similar harvest date to barley. The cereal crop provides energy in the form of starch while the legume crop provides protein. Improvements in harvesting technology now allows these bi-crops to be harvested at their optimal stage, resulting in higher levels of protein and starch. This increases the benefit of this cropping system beyond the basic ‘eased legume fermentation and reduced lodging’ with pea-cereal crops being especially beneficial to organic farmers.
Soil and Sowing – Optimal yield nutrient availability from the soil must be considered. Soil fertility must ensure availability of phosphorous, potassium, sulphur as well as trace amounts of calcium and magnesium. Bi-crop peas and barley can be grown on various soil types across a pH range of 6 to 7.5, though well drained soil is preferred. Seed bed preparation should not be too fine as this leads to increased water stress during times of drought. Seeds should be planted at a depth of 3-4 cm deep either as a combined seed in the same row or as separate seeds depending on the seeder. If the farm is blending their own seeds, they should be combined in a ratio of 80% peas and 40% of barley (relating to the standard sowing rates of the individual varieties) with rows 10 to 12 cm apart. Selected varieties should have similar maturity times. An initial application of nitrogen at 40 units of nitrogen / Ha at sowing is advisable, which may be followed with a further 40 units of nitrogen / Ha at emergence in low nitrogen soils (peas will utilize atmospheric nitrogen, but barley requires soil nitrogen).
As with permanent grassland, the majority of preparation with peas and barley is focused on reaching the optimal pH and nutrient levels for the growth of grass and herbs. Different soils have a different base pH levels, which, in turn, impacts the availability of macro and micronutrients. Adjusting the pH (liming) of the ground makes nutrients more available, increases fertility and productivity of the land. Ideally, the liming will be done at the end of the previous growing season (at least once every 5 years to every field, usually in a rotational manner across all fields).
Key Point – Allow time for liming to have adjusted the pH prior to sowing, which can take several weeks dependent on liming material.
Growth and Harvesting for silage
Emergence of the bi crop typically takes 10 to 14 days, with peas and barley showing ‘hypogeal emergence’ (the cotyledons remain below the surface). Emergence can be delayed by up to 1 week if soil germination temperature is between 5 to 10°C. Growth of the barley physically supports the growth of the peas and reduces the risk of the peas from lodging (falling). Vegetative pea growth is quickly followed by flowering (flowers may be white, pink or purple) from axilliary buds on the main stem and branches, from lower to higher nodes on the stem, and then by flat pod formation at the lower nodes. Once pods have formed, and the barley grain has some starch and has necked (bent over) with the stem taking on a green gold appearance, the crop can be harvested. This can be done either directly if the dry matter (DM) is high enough (in excess of 30% DM) or mown with a roller conditioner and allowed to wilt for a 24-hour period. If the harvest is delayed, then the use of a conditioner will lead to loss of some grain, and, if the harvest is delayed until semi-hard peas have formed in the pods, the peas themselves will be undigestible to the animal and will pass straight through the animal. The conditioner should be set at its most gentle setting.
Legume and small seed bi crops offer a distinct challenge to the fermentation in that the buffering capacity of the silage is quite high because of the high protein content of the combined forage, and the aerobic stability challenge of the forage is also high during feedout because of the starch availability from the barley, the high DM and the hollow nature of the cereal stem. Depending on varieties, soil and climate conditions the bi-crop will likely be ready to harvest in +/- 100 days post planting.
The headland of the fields are often wetter than the body of the field, and the farm may consider ‘opening up’ the field and baling the headlands. Use a homofermentative forage inoculant product on bales. For added protection, use 6 layers of wrap due to the abrasive nature of the forage and store on a flat, stone free surface. Place baiting around the bales as vermin are highly attracted to bi-crop silage. Clearing the headlands first also reduces the traffic across the cut forage and reduces soil contamination. Bales should not be stacked and a space should be left between the bales to allow cats and foxes to manage the rats.
Mowing height of the combined legume – cereal should be a minimum of 10 cm from the ground, and great care must be taken when mowing to minimize soil contamination. The cut forage should be left narrow swathed and raking should be avoided due to grain loss and soil contamination (swaths can be merged if desired). Cut height is to minimize soil contamination but also allow air circulation underneath the cut forage to aid wilting. Maintenance of the skids on the mower are crucial to ensure little soil contamination.
Mowed bi-crop should be collected with a self-propelled forage harvester fitted with a combine reel header or a specialist wholecrop header, with a chop length of between 2.5 to 3 cm.
Ensiling – ensiling management of bi-crops is important due to the risk of incorporating soil, which can challenge the fermentation. Soil contamination at collection and ensiling must be minimized, and the bunker should be filled in thin layers approximately 20 cm thick with appropriate compaction for the DM.
Compaction of the ensiled bi-crop should be adjusted to the DM of the forage so as to minimize potential effluent production. When effluent is produced, it forms a saturated layer within the ensiled forage (the depth of the layer being dependent on the volume of the effluent produced), which displaces all the built-up carbon dioxide and stops the desirable fermentation bacteria from working.
Key point – compaction of the ensiled bi-crop should be adjusted based on the DM of the forage as it is being ensiled.
The bi-crop needs to be treated with a forage inoculant to ensure silage quality. The selection of inoculant will depend on the DM of the forage as ensiled, the feed-out rate of the silage and the general management of the silage. Using a proven homolactic only forage inoculant rapidly drives the pH fall (fermentation) to maintain the maximum amount of DM, ME, D and protein in the ensiled forage. If the product used also contains enzymes, it can enhance the digestibility of the ensiled forage. The faster the pH falls, the sooner the Enterobacteria are inhibited, and the more milk potential is maintained in the final silage. The sole end-product when using homolactic forage inoculants, is lactic acid, which — although exceptionally good at lowering pH — has no beneficial impact on the stability of the forage at feedout. Stability is defined as the length of time that it takes for the silage to heat when it is exposed to air. This means the silage can be prone to heating if the face is not crossed rapidly enough. Most bi-crops produced will be prone to aerobic instability (heating) when opened to feed, and this can lead to significant losses through moldy silage.
Forage inoculants that contain both homolactic and heterolactic bacteria such as L.buchneri 40788 and L. hilgardii 4785 also rapidly drive the fermentation, but also have the added benefit of producing multiple end products including acetic acid, which is inhibitory to yeast and molds (the normal cause of aerobic instability). This increases the length of time that it takes for the silage to heat and spoil when it is exposed to air. This ensures the quality of the silage is maintained through the feedout period, meaning more silage is available to feed due to less wastage.
Feeding – Feed out management of all silages is important, but with bi-crop silage — because of the variable component of the ensiled swath throughout the field(s) and the impact of location within the bunker on fermentation — it is important to try and feed the bunker in columns or to remove the entire face at each feeding. Plastic should only be cut back sufficiently for 1 or 2 days feeding and whenever possible a frazer / defacer should be used to maintain the integrity of the bunker face.
|DM||Chop Length||Density Kg DM m³||Inoculant|
|<30 **||3 - 4cm||200||Challenge specific homolactic inoculant|
|30 – 35||2.5 - 3cm||220||Challenge specific containing heterolactic and homolactic bacteria|
|35 +||2.5cm||240||Challenge specific containing heterolactic and homolactic bacteria|
** Ensiling below 30% DM is not recommended, and train wheel compactors should not be used.