Source: landwirt.com
Good forage quality is important for every farmer. Soil contamination reduces forage quality, animal performance and health, and ultimately economic success. Therefore, it is important for farmers to reduce feed contamination.
Farm animals have an increasing genetic performance potential. This can only be optimally exploited if fresh and canned feed provide a sufficient density of valuable ingredients and are hygienically safe.
Soil is responsible for many negative effects in feed, such as butyric acid fermentation.
In Austria, approximately 50% of farms are likely to regularly encounter soil in forage. 10–15% of farmers struggle with significant to severe problems (crude ash over 120 g/kg DM, sand content over 25 g/kg DM, iron over 1,000 mg/kg DM). This section of the special supplement addresses the causes of soil contamination in forage. It also discusses preventive measures to prevent or at least reduce contamination.
Influence of the weather
In regions with low rainfall or on dry soils, the topsoil can dry out, especially in the summer months. Wind erosion of soil particles can subsequently lead to soil contamination of plants. A field study on 21 permanent meadows with dry soils found that the forage in these areas had a crude ash content of 127 g/kg DM. Comparable forage from approximately 1,500 areas with more favorable water supply contained only 98 g crude ash/kg DM.
Exact experiments have shown that grasses are contaminated with slightly less soil (6 g soil/kg forage DM) as a result of weather events than dicotyledonous plants such as legumes and herbs (10 g soil/kg forage DM). In herbaceous plants, almost 70% of the contamination was caused by rainfall, while in grasses, 53% of the soil contamination was caused by wind erosion. A grazing experiment also showed that soil contamination reached higher levels in clover than in ryegrass (35% and 25% respectively). It can therefore be assumed that plant stands rich in clover and herbs are at greater risk of pollution than grass stands.
Prolonged drought dries out the grass roots in the upper soil layers and opens the turf. This allows the soil to be exposed over large areas. Such gaps in the plant cover can have a particularly critical impact on forage contamination when it rains again. The more gaps in the turf and the more precipitation falls, the higher the soil coverage on the plants becomes due to thrown-up and adhering soil particles.
In Austria, in recent years, small-scale extreme events (floods, mudslides, hailstorms, droughts, etc.) have increasingly led to catastrophic damage to forage crops. Water-related damage can destroy harvests through massive contamination with soil, mud, sand, stones, flotsam (wood, garbage, etc.), and other problematic agents (mineral oil, toxins, harmful germs, etc.). Contaminated feed batches must not be given to animals because they can make them sick. Only through composting can this feed be returned to the agricultural cycle as fertilizer. The rehabilitation of silted grassland areas is usually extremely complex and it can often take years until a comparable yield and quality situation is restored.
Optimal turf density reduces soil contamination
An optimal sward density of the grassland and field forage reduces the soil input into the forage. The measure of the sward density of a grassland stand is the so-called projected cover expressed in percent. The study of 1,884 Austrian grassland areas revealed an average gap density (open ground) of 2.5%, or 97.5% projected cover.
The highest gap percentage was 50% open soil. Especially on dry to semi-arid sites, the gap density was significantly higher, averaging approximately 7% open soil, than under fresh, moist, or even wet conditions. Promoting sward-densifying stands such as smooth meadow grass, English ryegrass, and white clover through needs-based fertilization and utilization, as well as overseeding/overseeding, is effective in achieving a high projected cover ratio. Pasture trials in New Zealand showed that rich stands with intensive plant growth resulted in less than 2% soil uptake of the DM uptake, while lean, gappy stands caused up to 14% soil uptake.
Closing gaps through targeted vegetation
Permanent grassland stands with late cutting use often have loosened turf and, if fertilizer is applied in excess of the required amount, also have increased weed pressure. Field forage mixtures, as well as over-fertilization with nitrogen, also lead to lower sward density in the herds, which increases the risk of contamination. Intensive grazing with too many animals per unit area also creates gaps and thus more soil contamination near the ground. In gappy stands, soil infestation is mostly found on the plants up to 10 cm above the ground. Reducing the animal density on the pasture from 16 to 8 ewes/ha reduced soil ingestion from 8% to 2% in an exact experiment.
Gaps in the plant population should be closed quickly through regeneration without tillage, before inferior gap-fillers such as common meadow grass (Poa trivialis) colonize these open spaces. For the restoration of gaps in the population, regardless of the circumstances causing them, the Austrian Working Group for Grassland and Forage Production (ÖAG) recommends site- and use-adapted quality seed mixtures to ensure the turf can heal sustainably (see Info 6/2011 "ÖAG Seed Mixtures – Top Quality Prevails").
Dr. Bernhard Krautzer from the LFZ Raumberg-Gumpenstein takes the following view on grassland regeneration: "A strategic goal of reseeding is to improve sward density in order to reduce forage contamination and improve the load-bearing capacity of the sward for animals and equipment."
Problems caused by animal pests
In Austria, approximately 300,000 hectares of grassland are damaged or destroyed annually by burrowing and digging vertebrates (voles, moles, field mice, wild boars, etc.) and approximately 5,000 hectares by insect larvae (grubs of cockchafers, garden chafers, etc.) and ants.. Voles and moles in particular cause major problems for food conservators in terms of food contamination due to their excretion of soil.
Voles prefer hay meadows, especially when herbs such as dandelion (Taraxacum officinale), cow parsley (Anthriscus sylvestris), hogweed (Heracleum sphondylium), and meadow grass (Poatrivialis) are in high populations. Voles also damage grassland plants because they can consume their own body weight in roots every day. According to precise surveys, with heavy pest infestations, up to 20,000 mounds of soil can occur per hectare. This corresponds to over 80 tons of excavated soil per hectare.
Measures against animal damage
One measure that levels the mounds of earth, at least in the short term, is towing them in spring using a meadow drag. In precise observations on "mouse-infested" areas, the proportion of open soil before towing ranged from 2–32%. After towing, the gaps ranged from 16–95%. With so much open soil, the mown forage has intensive soil contact and is almost impossible to harvest without soil. The LK silage project demonstrated a strong correlation between the number of soil mounds and the crude ash content in the forage.
The problem shows that towing cannot be the only measure, because the tow does not drive away the pests or only slightly. Due to the sometimes extremely high population densities of voles, chambers of agriculture, machinery associations, and individual farmers have focused on mouse control. Regional trapping courses are offered (information from regional associations, agricultural machinery associations, etc.) to show affected farmers how to trap voles professionally. In some federal states, it should be noted that moles are protected and therefore may not be killed.
The grubs of the cockchafer and the garden chafer (commonly known as the June beetle) are causing major regional problems. Root-feeding causes the turf to loosen, making a clean forage harvest virtually impossible. Mushroom barley is used as an effective control measure in the most severely affected areas. Wild boars are increasingly causing massive damage to grassland and even alpine pastures. Herds of several animals usually roam at night and, in some cases, severely tear the turf with their snouts, so that entire pieces of turf and soil can end up in the forage harvest. In this case, hunters are called upon to increase hunting pressure on wild boar.
Pasture management plays an important role
Pasture management plays a very important role in forage contamination. For example, soil contamination on pastures increases when forage availability is limited. This situation can occur in spring or during the fall grazing season, as well as with short-term pastures or excessive stocking density.
In a trial conducted on twelve farms in southwest England, soil coverage was 5.6% at the start of grazing in April, and only 1.5% in June with sufficient forage. Shortening the grazing rotation from 28 to seven days (padded pasture) led to an increase in soil coverage from 10% to 37%. Shortly grazed pastures with open patches and abundant earthworm casts can lead to severe soil contamination in the grazing system. Turning out heavy animals on sloping terrain should be avoided during wet weather and soil conditions.
Pay attention to driving style
The cause of feed contamination with soil is in many cases related to the way farmers work. Driving on wet ground, especially on sloping terrain or with heavy equipment, easily leads to turf damage. These damages are caused by slippage of the drive wheels or drift on slopes. When driving through wet meadows, even 15% slippage will tear the turf from the subsoil and shift it in the direction of travel. This can lead to the introduction of roots and soil during forage harvesting. The same effect of turf damage can occur if the headland is too narrow. Optimal tire selection and low tire pressure reduce turf damage.
Use harvesting technology correctly
The mechanical technology of forage harvesting can also lead to noticeable soil contamination in the forage. The LK Hay Project, an Austria-wide field study, showed that crop moisture at the time of mowing was strongly correlated with crude ash content. The wetter the meadow forage, the higher the crude ash content. Therefore, mowing should only take place when the crop has dried out and the soil is no longer too moist. The higher crop moisture during later growth (from mid-August) and during post-grazing is also the main reason for the greater risk of contamination in these forage lots.
The cutting height adjustment of the mower must also be considered critically. Forage mown at a cutting height of less than 5 cm had significantly higher soil content than that mown at a cutting height of more than 5 cm. Soil contamination of forage can be further exacerbated during mowing when high-speed rotating equipment is used.
These exert a suction effect towards the ground (e.g., mower conditioners). "Vacuum-sucking" mowing techniques are particularly relevant for soiling in patchy forage crops (e.g., field forage), areas infested with voles, and also in severely dry soils. Mower conditioners are critical because intensively processed forage releases sugary cell sap from the damaged plant parts, to which soil particles adhere very well. Modern mowing technology with ground-hugging properties can perform even better in terms of soiling if, in addition to optimal equipment settings and driving speed, the field conditions (dense turf, no mounds of soil) are suitable, and the mowing modules are no wider than 3 m on uneven surfaces.
For field forage crops, a minimum cutting height of 7–8 cm is recommended in order to reduce the soil content accordingly.. Piles of earth quickly reduce the blade edge and increase the effort and diesel consumption during mowing.
Pre-adjustment of the fertilizing equipment should always be carried out on firm ground on the farm. Equipment (tedders, rakes, pick-ups) that are set too low will scratch the ground, increasing the risk of forage contamination.
The final device setting must be checked in the field and adjusted depending on the field conditions.
The spring tines should be spaced 2–3 cm from the ground. In sparse crops where forage lies directly on the ground, an "optimal" setting leads to poor raking results because a significant amount of forage mass remains. Reducing the distance from the ground in this case improves the swathing results, but the risk of soil contamination increases significantly.
During swath merging, it was proven that side-loading rakes resulted in greater soil contamination than center-loading rakes. New swathing technologies with cross conveyor belts loosely form all crops into swaths without stones, soil, or other contaminants, but without a precise placement edge. Ground tracking via feeler wheels and correctly preselected driving speeds (depending on the forage mass: rotors max. 5 km/h, swaths max. 8–10 km/h) reduce the risk of soil contamination.
Less contamination in dry feed
The highest concentrations of soil are found in fresh green fodder. In wilted silage, fermented hay, and hay, soil contamination decreases, meaning that drying generally has a positive effect on soil content. An increase in dry matter by 25 g reduces the crude ash content by an average of 1 g/kg DM. However, wilting alone is no guarantee of low-soil forage, as shown by analyses of crude ash data from more than 3,000 grass silages from the LK silage project.
Unpaved areas directly in front of flat silos or field piles are a potential source of soil being transferred to the feed via tire treads, causing contamination. This contamination can subsequently lead to fermentation in the feed.. Entrances and exits to flat silos should therefore be paved to exclude this source of entry.
Conclusion
The feed value of grassland fodder is significantly negatively affected by soil infestation. Quality-conscious farmers are well advised to implement crop management measures that promote optimal turf density. These include site-adapted use and fertilization, as well as grassland management and reseeding/overseeding.
Furthermore, consistent pest control is highly recommended. Low-soil forage harvesting can be achieved if the crop is dry at the time of mowing, the cutting height is over 5 cm, and the harvesting equipment is optimally adjusted. Pasture management should consider forage availability, slope gradient, and weather conditions, as well as stocking density and grazing system, to keep soil accumulation on the crops low.