Ash contamination in silage results in more than just energy loss

There are a variety of factors that impact the ensiling process, and one of those is soil contamination. The amount of soil brought into the silage bunker with the forage can be shown by the percentage of ash.

Ash in the silage

The plants’ internal ash provides minerals like magnesium, calcium and potassium that can be utilised by ruminants, although it adds no calories. The average ash content in forages is normally 3 to 5 percent in corn, 6 to 8 percent in grasses and 8 to 10 percent in legumes.

On the other hand, high ash content due to soil contamination is characterised by elevated concentrations of iron, aluminium and silica. There are different manners that soil contaminates the plant: weather (rain, flooding, wind), plant lodging, grazing and mechanical operations during harvest and soil from dirt silage yards.

Lowering the cutting height increases the total yield but will likely increase the content of ash. In addition, it reduces the forage quality due to the high proportion of fibre and will negatively affect the stand life of some grasses. Cutting height should be about 75mm or even 100mm on loose soils that risk increased soil inclusion.

Heavy rain splashing soil onto leaves – and extreme weather conditions and flooding of crop fields – can result in contamination. On the flip side, dry weather and drought conditions may also contribute to soil contamination in terms of dusty winds and dust from dirt roads near the field.

Swath width may have an impact on ash contamination, and one would expect the issue when wide swathing – due to sometimes driving over the mowed swath. However, research has not shown significant differences in ash levels, likely because the bottom portion of a narrow swath remains wet for a longer period of time, sagging to the ground and leading to soil contamination when the windrow is picked up. So, keep your forage on top of the stubble, not in contact with the ground.

The type of knives on disc mowers can also impact soil contamination: Curved knives can retrieve forage from the ground better, but they also tend to pick up more ash; flat horizontal knives create less suction and introduce less soil in the mowed forage.

Mergers can be an option to rakes because the windrow is picked up and moved horizontally by a conveyer rather than being rolled across the ground, resulting in 1 to 2 percent less ash on forage. If rakes or tedders are the option, make sure the tines are adjusted so they won’t touch the ground and move soil into the forage. Scalping the field is more likely in uneven fields or if driving fast, which causes the equipment to jump up and down.

Silage piles and bunkers directly on the ground can incorporate soil into the crop during filling. Under wet, muddy conditions, soil can accumulate onto tyres and tyre treads of tractors and trucks, bringing more dirt into the forage mass conversely dry dusty conditions in the silage yard can bring layers of dust onto the silage with every load that comes past and to the silage pile.

Feeding implications

Ash can be a contaminant of the fibre content. Although pectin is in the plants’ cell walls, the “fibre” portion for ruminant diets relates to the amount and proportion of cellulose, hemicellulose and lignin. Moreover, only the organic matter in fibre will generate energy to the animal. Dirt is not a nutrient. Excess ash from soil contamination replaces real, productive nutrients in the diet.

Soil contamination can become a big issue when formulating a diet, especially for high producing cows on a full TMR diet. As much as 2 kg of dirt could be fed per cow daily. For every 2 points of external ash contamination, there can be a 5-point decrease in relative forage quality (RFQ).

Although soil contamination affects the ensiling process, soil contamination will also bring issues with unwanted spoilage micro-organisms, poor fermentation and impaired quality of silage and compound challenges to the animals.

Furthermore, feeding the compromised silage results in issues for most dairy herds with lower feed intake and milk production, high somatic cell counts, lowered milkfat.

All this makes it extremely important to focus on producing silage that is a nutritious and clean feed for animals.